Microbiomes for the Management of Agricultural Sustainability 303132966X, 9783031329661

Table of contents :
Foreword
Preface
Acknowledgments
About the Book
Key Features
Contents
About the Editors
Chapter 1: Integrated Approaches to Agri-nanotechnology: Applications, Challenges, and Future Perspectives
1 Introduction
2 Overview of Multifarious Applications of Nanotechnology in Agricultural and Food Sector
2.1 Precision Agriculture
2.2 Nanobiosensors
2.3 Nano-agrochemicals
2.3.1 Nano-fertilizer
2.3.2 Nano-pesticides
2.3.3 Nano-herbicide
2.4 Crop Improvement
2.5 Postharvest Processing
2.6 Food Industry
2.6.1 Food Processing
2.6.2 Food Processing
2.6.3 Identification, Tracking, and Tracing of Agri-foods
2.7 Water Quality Management
2.7.1 Water Filtration/Purification
2.7.2 Desalination
2.8 Soil Remediation
3 Key Challenges
3.1 Toxicity
3.2 Risk Assessment
3.3 Public Awareness and Acceptance
3.4 Regulatory Policies
4 Future Perspectives
5 Concluding Remarks
References
Chapter 2: Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry
1 Introduction
2 Organic Waste Generation and Its Sources
3 Mechanisms of Microbial Degradation of Organic Wastes
4 Types of Biodegradations
4.1 Aerobic Biodegradation of Organic Wastes
4.1.1 Phases of Aerobic Composting
4.2 Anaerobic Biodegradation of Organic Wastes
4.2.1 Steps Involved in the Anaerobic Process
5 Microbial Intervention in the Breakdown of Organic Wastes
5.1 Aerobic Degradation
5.2 Anaerobic Degradation
6 Utilisation of Value-Added Products from Sustainable Microbial Degradation in Agriculture
7 Innovative Application of Microbial Organic Waste Degradation
8 Advances in Recycling of Agricultural Wastes
9 Challenges and Future Perspective
10 Conclusion
References
Chapter 3: Microbial Degradation of Toxic Agri-wastes
1 Introduction
2 Biotechnology for Agriculture Waste Management
2.1 Bioconversion of Agriculture Waste for Energy
2.1.1 Anaerobic Digestion for Biogas
2.2 Factors Affecting Production of Biogas Using Anaerobic Digestion
2.2.1 Temperature
2.2.2 pH
2.2.3 C/N Ratio
2.2.4 OLR
3 Utilization of Waste for Soil Productivity
4 Conclusions
References
Chapter 4: Introduction of Biofertilizers in Agriculture with Emphasis on Nitrogen Fixers and Phosphate Solubilizers
1 Introduction
2 Biofertilizers in Alleviating Environmental Stress Tolerance in Plants
3 Biofertilizers in Nitrogen Fixation and Nitrogen-Fixing Microbes
4 Biofertilizers in Phosphate Solubilization and Phosphate-Solubilizing Microbes
5 Application of Biofertilizers
5.1 Seed Treatment
5.2 Root Dipping of Seedlings
5.3 Soil Application
6 Conclusion
References
Chapter 5: Biofertilisers and Biopesticides: Approaches Towards Sustainable Development
1 Introduction
2 Strategies for Sustainable Agriculture Development
3 Pests and Their Associated Diseases
4 Biopesticides
4.1 Biopesticides’ Categories and Their Modes of Action
4.1.1 Microbial Biopesticides
4.1.2 Biochemical Biopesticide
4.1.3 Plant-Incorporated Protectants
4.2 Advantages of Biopesticide
4.3 Biopesticide Prospects and Limitations
4.4 Present Status
4.5 Recent Advances
5 Biofertilisers
5.1 Types of Biofertilisers
5.2 Advantages of Biofertilisers
5.3 Current Status of Biofertiliser Development
5.4 Future Perspective of Biofertilisers
6 Conclusion
References
Chapter 6: Credibility of Biofertilizers Towards Restoration of Fertility Phenomenon in Degraded Soil Environs
1 Introduction
2 Soil-Agricultural Production Nexus
3 Biofertilizers and Soil Health
3.1 History of Biofertilizers
3.2 Application of Biofertilizers to Soil
3.3 Beneficial Microorganisms for Biofertilizers
3.3.1 Symbiotic Beneficial PGPR
3.3.1.1 Rhizobium
3.3.1.2 AMF
3.3.2 Free-Living Beneficial PGPR
3.3.3 Other PGPR
4 Types of Biofertilizers
4.1 Nitrogen-Fixing Biofertilizers
4.2 Phosphorus Biofertilizers
4.3 Potassium Biofertilizers
4.4 Sulphur Biofertilizers
4.5 Zinc Biofertilizers
4.6 Compost Biofertilizers
5 Net Advantages of Biofertilizers Over Chemical Fertilizers
6 Roles of Biofertilizers in Protecting the Soil Environment
7 Limitations of Using Biofertilizers for Restoration of Soil Fertility in Degraded Lands
8 Conclusion
References
Chapter 7: Macrophytes as Biofertilizer for Agriculture: Concept and Applications
1 Introduction
2 Microbiota for Biofertilizers
3 Aquatic Plants as Biofertilizers
4 Cyanobacteria as a Potential Biofertilizer
5 Steps in Developing a Macrophytic Biofertilizer
6 Biotechnological Interventions for Preparation of Macrophytic Biofertilizer
6.1 Solid-State Fermentation
6.2 Immobilization and Co-immobilization
6.3 Elicitation and Biostimulants
6.4 Benefits
6.5 Application of Macrophytic Biofertilizers
6.5.1 Soil Fertility
6.5.2 Nitrogen Fixation
6.5.3 Production of Plant Growth Biostimulants
6.5.4 Biopesticidal Substances
6.5.5 Pollution Control
7 Conclusion and Recommendations
References
Chapter 8: Potential Role of Biofertilizers in Fruit Crops
1 Introduction
2 Biofertilizer Types Related to Nitrogen and Phosphorous Nutrition
2.1 Free Living: Nitrogen-Fixing Biofertilizers
2.2 Symbiotic: Nitrogen-Fixing Biofertilizers
2.3 Associative: Nitrogen-Fixing Biofertilizers
2.4 Phosphorus-Solubilizing Microbes
2.5 Phosphorous-Mobilizing Fungi
3 Effect of Biofertilizers on Fruit Plant Growth
4 Effect of Biofertilizers on Fruit Quality
5 Effect of Biofertilizers on Fruit Yield
6 Effect of Biofertilizers on Nutrient Uptake in Fruit Plants
7 Effect of Biofertilizers on Soil Health–Holding Fruit Plants
8 Limitations of Biofertilizer Use in Fruit Crops
9 Biofertilizer Application Methods
10 Conclusion
References
Chapter 9: Microbial Biofertilizers: An Environmentally-friendly Approach to Sustainable Agriculture
1 Introduction
2 Mycorrhiza as Biofertilizers
2.1 Ectomycorrhizal Fungi
2.2 Endomycorrhizal Fungi
2.2.1 Arbuscular Mycorrhizal Fungi
3 Other Beneficial Fungi as Biofertilizers
4 Algae as Biofertilizers
4.1 Blue-Green Algae
4.2 Red Algae
4.3 Brown Algae
5 Conclusion
References
Chapter 10: Actinomycetes as Biofertilisers for Sustainable Agriculture
1 Introduction
2 Biofertilisers
3 Microorganisms Used as Biofertilisers
4 Actinomycetes: Nature & Habitat
5 Actinomycetes as Potential Candidates for Nitrogen Fixation
6 Role of Actinomycetes in the Decomposition of Organic Matter
7 Actinomycetes as Plant Growth-Promoting Bacteria
8 Actinomycetes: An Excellent Candidate for Growing Healthy Crops
9 Enzymes Produced by Actinomycetes
10 Bioremediation by Actinomycetes
11 Conclusion
References
Chapter 11: Innovations in Biotechnology: Boons for Agriculture and Soil Fertility
1 Introduction
2 Biofertilizers
2.1 Plant Growth–Promoting Rhizobacteria (PGPR)
2.2 Algal Biofertilizers
3 Vermicomposting Biotechnology
3.1 Procedure for Vermicomposting SOW by Using Earthworms
4 Biochar
4.1 Production of Biochar
4.2 Effect of Biochar on Soil Microflora and Microfauna
5 Nanotechnology in Soil Development
5.1 Using Nanotechnology in Soil Pollution Control
6 Conclusion
References
Chapter 12: Microbiomes in Climate Smart Agriculture and Sustainability
1 Introduction
2 Plant Microbiome and Tolerance to Climate Change
2.1 Extreme Temperature Stress
2.2 Drought Stress
2.3 Salt Stress
2.4 Heavy Metal Stress
2.5 Water Lodging
2.6 Greenhouse Gases
3 Integration of Target Traits into the Crop Plants Through Adaptive Symbiotic Technology
3.1 Development and Characteristics of Formulation
4 Inoculating Microbial Formulation into Plant to Form Meta-organism
5 Conclusion
References
Chapter 13: Genetic Engineering Aiming to Improve the Use of Phosphorus in Agriculture
1 Introduction
1.1 Phosphorus’ Bioaccessibility and Use Efficiency in Plants
2 Genetic Engineering Strategies as Tools to Optimize Agricultural Use of Phosphorus
3 Conclusions
4 Future Perspectives
References
Chapter 14: Pseudomonas as Backbone for Environmental Health
1 Introduction
2 Terrestrial Environmental Degradation and Corrective Potentials of Pseudomonas
2.1 Deleterious Mining Activities
2.2 Heavy Metal Concentration in Agricultural Lands
2.3 Bioremoval of Heavy Metal Concentration from Landfills
2.4 Removal of Pesticides
2.5 Drought-Induced Abiotic Stresses
2.6 Restoration of Degraded Soils
2.7 Cleansing Effect of Pseudomonas on Pathogen-Laden Soils for Plant Growth
2.8 Waste Management and Contributions of Pseudomonas
3 Aquatic Environment Degradation and Corrective Potentials of Pseudomonas
4 Conclusion
References
Chapter 15: Cyanobacteria as Sustainable Microbe for Agricultural Industries
1 Introduction
2 Biofertilizers
3 Classification of Biofertilizers
3.1 Nitrogen-Fixing Biofertilizers
3.2 Phosphate Biofertilizers
3.3 Plant Growth-Promoting Biofertilizers
4 Types of Biofertilizers
5 Components of Biofertilizers
5.1 Bio Compost
5.2 Tricho-Card
5.3 Azotobacter
5.4 Phosphorus
6 Role of Cyanobacteria and Sustainable Agriculture
6.1 Cyanobacteria as Biofertilizer
6.2 Role in Bioremediation
6.3 Role in Wastewater Treatment
6.4 Role in Bioenergy
6.5 Role in Nutrition and Health
7 Mass Cultivation of Cyanobacteria
8 Cultivation Using Sunlight in Open Systems
8.1 Closed System Cultivation Using Sunlight
8.2 Cultivation Using Artificial Light in Closed System
9 Advantages of Biofertilizers
10 Conclusion
References
Chapter 16: Functional Diversity of Endophytic Microbiota in Crop Management of Cucumis sativus L.
1 Introduction
2 Cucumber Plant Growth Promotion by Endophytes as Biofertilizers
2.1 Direct Enhancing of Plant Growth
2.1.1 Nitrogen Fixation
2.1.2 Phosphate Solubilization
2.1.3 Phytohormone Production
2.1.4 Endophytes Promoted Siderophore Production
2.2 Indirect Plant Growth Promotion
2.2.1 Biological Control
3 Endophyte-Assisted Phytoremediation
4 Endophyte-Conferred Abiotic Stress Tolerance
5 Conclusions
References
Chapter 17: Nanoscience in Agricultural Steadiness
1 Introduction
2 Applications of Nanotechnology in Agriculture
2.1 Nanofertilizers
2.2 Nanopesticides
2.3 Systems for Delivering Nutrients and Plant Hormones Using Nanotechnology
2.4 Nanotechnology for Organic Farming
2.5 Nanoherbicides
3 Future Advantages of Using Nanotechnology in Agriculture
4 Conclusion
References
Chapter 18: Carbon and Silver Nanoparticles for Applications in Agriculture
1 Introduction
2 Applications of Carbon-Based Nanomaterials in Agriculture
2.1 Carbon Nanotubes
2.2 Carbon Dots
2.3 Graphene And Derivatives
2.4 Fullerenes
2.5 Negative Effects of Carbon-Based Nanomaterials in Agriculture
3 Applications of Silver Nanoparticles in Agriculture
3.1 Negative Effects of Silver Nanomaterials in Agriculture
4 Conclusion and Future Prospects
References
Correction to: Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry
Index

Citation preview

Gowhar Hamid Dar Rouf Ahmad Bhat Mohammad Aneesul Mehmood   Editors

Microbiomes for the Management of Agricultural Sustainability

Microbiomes for the Management of Agricultural Sustainability

Gowhar Hamid Dar  •  Rouf Ahmad Bhat Mohammad Aneesul Mehmood Editors

Microbiomes for the Management of Agricultural Sustainability

Editors Gowhar Hamid Dar Post Graduate Department of Environmental Science Sri Pratap College Cluster University Srinagar Srinagar, Jammu and Kashmir, India

Rouf Ahmad Bhat Department of School Education Government of Jammu and Kashmir Srinagar, Jammu and Kashmir, India

Mohammad Aneesul Mehmood Department of Environmental Science Government Degree College Pulwama, Jammu and Kashmir, India

ISBN 978-3-031-32966-1    ISBN 978-3-031-32967-8 (eBook) https://doi.org/10.1007/978-3-031-32967-8 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023, Corrected Publication 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

This book is dedicated to Rachel Louise Carson (1907–1964) for her remarkable and outstanding contribution for the conservation of environment. She is very well known for being a biologist, writer, environmentalist and conservationist. Among her writings, the most influential book was Silent Spring (1962) which imparted the pioneering ideas and strategies for need of environmental protection and significance of optimum environment for all of us.

Foreword

The agriculture industry has to play a strong role in dealing with the mounting demand for food production. The indiscriminate use of agrochemicals has completely changed and altered the soil health which may have disastrous consequences on food production in near future. Microbiomes could be a promising eco-friendly, cost-effective, and sustainable substitute for synthetic agrochemicals. Microbiomes can play a very crucial role in nutrient mobilization and crop yield and have been found cost-­effective and promising alternatives to bridge the gap between conventional and organic agriculture. The present book volume has incorporated the fundamental ideas and methods from the soil and crop microbiomes to integrate recent trends like recombinant DNA technology and nanotechnology to provide a strong sustainable foundation to agricultural sector. The book Microbiomes for the Management of Agricultural Sustainability constitutes 18 chapters with comprehensive coverage of all aspects of book theme. The first chapter, entitled “Integrated Approaches to Agri-nanotechnology: Applications, Challenges, and Future Perspectives,” has been contributed by authors from India. This chapter has attempted to provide an insight into the role of nanotechnology to overcome the flaws in conventional farming practices. In this book chapter, the authors also provided an overview of several stupendous applications of nanotechnology in the food and agriculture sector, while also highlighting its unresolved issues and prospective merits. The second chapter, entitled “Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry,” deals with the biological approach for the treatment and degradation of organic waste. This chapter discusses in detail the various available microbial technologies in the use of microorganisms for organic waste degradation and utilization in the agricultural business. The third chapter, entitled “Microbial Degradation of Toxic Agri-wastes,” focuses on the role of biotechnology in utilizing the waste as valuable products. This chapter highlights the strategies to remove and convert the waste into less toxic or beneficial products such as manure production, energy production and some value-added products. vii

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Foreword

The fourth chapter, entitled “Introduction of Biofertilizers in Agriculture with Emphasis on Nitrogen Fixers and Phosphate Solubilizers,” illustrates the significance of biofertilizers in agriculture systems by improving plant nutrition uptake, soil quality and crop production. This chapter also describes some important classes of carbon-based nanomaterial and their derivatives for remediation of environmental pollutants and addresses main strategies using carbon-based nanomaterial to remediate soil, water and air pollution. The fifth chapter, entitled “Biofertilisers and Biopesticides: Approaches Towards Sustainable Development,” contributed by Indian scientists, highlights the application of synthetic fertilizers and pesticides in Indian agriculture and its impact on soil health. This chapter highlights the potential of integrated farming system (IFM) and limitations of biopesticides for sustainable agriculture. This chapter also provides insight into the connection of sustainable development and sustainable agriculture. The sixth chapter, entitled “Credibility of Biofertilizers Towards Restoration of Fertility Phenomenon in Degraded Soil Environs,” has been contributed by the researchers from Uganda and Sudan. The authors highlighted the appraisal of biofertilizer use for restoration of fertility in degraded soil environments. They have presented an inside-out analysis using staircase argumentation and the way forward. The seventh chapter, entitled “Macrophytes as Biofertilizer for Agriculture: Concept and Applications,” has been contributed by Indian researchers wherein they have meticulously presented the use of different microbial consortia in the management of soil fertility, nitrogen fixation and pollution control. The eighth chapter, entitled “Potential Role of Biofertilizers in Fruit Crops,” highlights the role of ecofriendly approach to boost the fruit industry. The authors have beautifully presented the sustainable fruit production systems and minimizing chemical fertilizers input through biofertilizers technology. The ninth chapter, entitled “Microbial Biofertilizers: An Approach to Sustainable Agriculture,” highlights the role of biofertilizers like PGPR, fungi, algae, etc. in modern agronomic practices. This chapter focuses on the importance of microbial fertilizers and their advantageous effects on plants in promoting sustainable agriculture. The tenth chapter, entitled “Actinomycetes as Biofertilisers for Sustainable Agriculture,” beautifully presents the sustainable integrated farming system by using actinomycetes. The authors have highlighted the role of these microbes in nitrogen fixation, breakdown of organic matter, plant growth promoting activity, production of various enzymes and bioremediation of different pollutants. The eleventh chapter, entitled “Innovations in Biotechnology: Boon for Agriculture and Soil Fertility,” by researchers from Saudi Arabia highlights the impact of agrochemicals on soil and agriculture. It also attempts to provide insight into the biotechnological and innovative approach to maintain the soil health. The twelfth chapter, entitled “Microbiomes in Climate Smart Agriculture and Sustainability,” beautifully highlights the importance of microbiome to achieve the

Foreword

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global agriculture which will be resilient to climate change. The authors have encouraged to adopt symbiotic technology that provides a well-designed solution to this problem by inoculating the microbial inoculant into crop plants that can sustainably improve production and abiotic resistance with the goal of achieving food security. The thirteenth chapter, entitled “Genetic Engineering Towards Improvement of Phosphorus Agricultural Utilization,” by the researchers from Morocco, presents a beautiful perspective of the significance of phosphorus (P) for bumper crop production. This chapter aims to provide a review of some important strategies of genetically modifying vegetal species to achieve a better phosphorus use efficiency in agronomic environments. The fourteenth chapter, entitled “Pseudomonas as Backbone for Environmental Health,” contributed by the authors from Sudan and Tanzania, highlights the significance and importance of Pseudomonas in maintaining the optimum quality of environment. It presents the extant analysis of genus Pseudomonas to the different components of the environment and clearly justifies the bioremediation potential of several strains of Pseudomonas in environmental bioengineering technology. The fifteenth chapter, entitled “Cyanobacteria as Sustainable Microbe for Agricultural Industries,” by Indian authors, has given special illustration of using Cyanobacteria in sustainable agricultural practices. The authors have highlighted the potential of cyanobacteria to remove pesticides, insecticides and excess nutrients from contaminated soils and wastewater. Moreover, the authors have also described the role of cyanobacteria in producing biofuels like hydrogen, ethanol and biodiesel. The sixteenth chapter, entitled “Functional Diversity of Endophytic Microbiota in Crop Management of Cucumis sativus L.,” has been contributed by the authors of Germany wherein they have highlighted the most effective and sustainable strategy for the management of cucumber crop by using endophytic microbiota to get sustainable agricultural outputs. The seventeenth chapter, entitled “Nanoscience in Agricultural Steadiness,” summarizes all the aspects of nanoscience to deal with all the ongoing and emerging problems faced by the agricultural industry and environment. With the help of advanced technology and research in the field of nanoscience, the authors have given some strong recommendations for sustainable management of agronomic crops. In the eighteenth chapter, entitled “Carbon and Silver Nanoparticles for Applications in Agriculture,” the authors have described carbon and silver as miraculous nanomaterials. With the help of research evidence, the authors have focused on the various aspects and applications of silver and carbon-based nanomaterials in agriculture for precise and sustainable farming to meet the world’s food demand. The book presents the chapters from authors worldwide to offer an interdisciplinary approach to get a detailed account of the role of microbiomes in the management

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Foreword

and sustainability of agricultural industry. This masterpiece of information in the form of book shall be a wonderful source of scientific dimensions about microbiome and sustainable development to the researchers, faculty, students, academicians at global level. Kristina Toderich Specially Appointed Professor International Platform for Dryland Research and Education, Tottori University, Tottori, Japan

Preface

Agricultural production has a profound role to play in the economic development of a country. With amounting increase in the population, the pressure has increased on the agricultural land which led to the indiscriminate use of agrochemicals in the agriculture industry. Huge challenge is faced by the agricultural industry to produce the crops which pass the biosafety standards. Innovative strategies and approaches are very much needed to produce ecofriendly, cost-effective and healthy crops. In order to achieve the standard of sustainable development, microbiomes can play a very crucial role to encourage the agriculturists to go for biofertilizers. By virtue of some characteristic features like regulation of soil bio-health, enhancement of plant growth, maintenance of soil fertility and decrease in disease incidence, microbiomes can be promising tools for sustainable organic agriculture. Researchers have successfully found the efficient role of microbiomes in agricultural sector and can be promising in revolutionizing the agricultural and horticultural crop sectors. Scientific studies have also shown a promising role of microbiomes in the management of soil biology and soil microecology and intern optimum crop yield in in vitro studies. Some scientific evidences are also available wherein the microbiomes have also destroyed the pathogenic microbes in soil and in turn can act as biopesticides. Indiscriminate use of agrochemicals has badly damaged the soil biology and biochemistry and have also shown some sharp decline in the crop yield due to change in soil chemistry. Microbiomes offer a very innovative and sustainable solution to connect the existing agricultural practices to sustainable agriculture market. This book is an attempt to offer academicians, students, readers, researchers and scientists very informative and updated knowledge base on the significance and importance of microbiomes and their application in the agriculture industry. The book is comprised of 18 chapters on all relevant aspects of the book theme contributed by authors from around the globe to provide a detailed account of all the essential aspects of microbiomes in agriculture, horticulture and agronomy. Furthermore, the book also highlights the various challenges to fully transfer the microbiomes from laboratory to land by adopting various scientific and advanced approaches. xi

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Preface

We feel extremely grateful to all the contributing authors and publishing staff for their unconditional cooperation and support for making this endeavor successful. Srinagar, Jammu and Kashmir, India Srinagar, Jammu and Kashmir, India  Pulwama, Jammu and Kashmir, India

Gowhar Hamid Dar Rouf Ahmad Bhat Mohammad Aneesul Mehmood

Acknowledgments

The editors would like to acknowledge the efforts of the following in one way or other for rendering tremendous support while drafting this book and making it possible to happen. 1. Mrs. Rafia Rasool Gowhar 2. Master Mohammad Zaeem Gowhar 3. Dr. Hummara Sultan 4. All the Authors of different Chapters 5. Supporting staff of Springer Nature 6. Mr. Asif Ahmad Bhat 7. Mr. Shahid Bashir Haji 8. Mr. Mohd Shafi Guchoo

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About the Book

Microbiomes for the Management of Agricultural Sustainability presents all significant aspects of microbiomes to be promising catalysts in integrated agricultural system. The book beautifully describes the importance of blending microbiomes in agriculture industry to maintain the reliable soil health and optimum productivity. This research masterpiece elaborates all the advanced tools and techniques like nanotechnology to successfully adapt the microbiomes in modern agriculture and horticulture. The book comprehensively highlights the innovative research foundations to encourage the application of microbiomes in the sustainable management of agronomic and agricultural produce. This book is a promising reference material in the direction to achieve the goal of sustainable development.

Key Features • Provides detailed account on the importance of microbiomes in soil and plant interface for optimum productivity • Provides in  vitro and in  vivo experimental findings for microbiomes to be transferred from laboratory to land for soil ecosystem restoration • Provides a detailed account of advanced technologies and techniques, particularly the nanoscience in agricultural revolution • Addresses the current agricultural crisis and provides insight into the sustainable and innovative options in the form of microbiomes for future agricultural economy

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Contents

1

Integrated Approaches to Agri-­nanotechnology: Applications, Challenges, and Future Perspectives������������������������������������������������������    1 Mir Zahoor Gul and Sashidhar Rao Beedu

2

Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry������������������������������������������   29 Murugaiyan Sinduja, Joseph Ezra John, R. Suganthi, S. Ragul, B. Balaganesh, K. Mathiyarasi, P. Kalpana, and V. Sathya

3

Microbial Degradation of Toxic Agri-wastes ����������������������������������������   59 Archit Mohapatra, Davood Ahmad Dar, and Priti Raj Pandit

4

Introduction of Biofertilizers in Agriculture with Emphasis on Nitrogen Fixers and Phosphate Solubilizers������������������������������������   71 Mir Sajad Rabani, Insha Hameed, Mahendra K. Gupta, Bilal Ahmad Wani, Mudasir Fayaz, Humaira Hussain, Anjali Pathak, Shivani Tripathi, Charu Gupta, Meenakshi Srivastav, and Moniem Benti Ahad

5

Biofertilisers and Biopesticides: Approaches Towards Sustainable Development������������������������������������������������������������������������   95 Toyeeba Hassan and Gowhar Rashid

6

 Credibility of Biofertilizers Towards Restoration of Fertility Phenomenon in Degraded Soil Environs������������������������������������������������  113 J. A. Ruley, J. O. Galla, T. A. Basamba, and J. B. Tumuhairwe

7

 Macrophytes as Biofertilizer for Agriculture: Concept and Applications����������������������������������������������������������������������������������������������  133 Shabeena Farooq, Shah Ishfaq, Syeed Mudasir, and Baba Uqab

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Contents

 8 Potential  Role of Biofertilizers in Fruit Crops��������������������������������������  145 Mohammed Tauseef Ali, Umar Iqbal, Sheikh Mehraj, Zahoor Ahmad Shah, Sharbat Hussain, M. A. Kuchay, and Owais Ali Wani  9 M  icrobial Biofertilizers: An Environmentally-friendly Approach to Sustainable Agriculture����������������������������������������������������  167 Lukman Ahamad, Mohammad Shahid, and Mohammad Danish 10 Actinomycetes as Biofertilisers for Sustainable Agriculture����������������  183 Jeelani Gousia, Shah Ishfaq, Baba Uqab, and Syeed Mudasir 11 Innovations  in Biotechnology: Boons for Agriculture and Soil Fertility��������������������������������������������������������������������������������������  193 Johra Khan 12 Microbiomes  in Climate Smart Agriculture and Sustainability����������  209 Aadil Farooq War, Iqra Bashir, Rezwana Assad, Iflah Rafiq, Zafar Ahmad Reshi, and Irfan Rashid 13 Genetic  Engineering Aiming to Improve the Use of Phosphorus in Agriculture�������������������������������������������������������������������������������������������  229 Fernanda Maria Policarpo Tonelli, Moline Severino Lemos, and Flávia Cristina Policarpo Tonelli 14 Pseudomonas as Backbone for Environmental Health ������������������������  239 J. A. Ruley, J. O. Galla, P. Massawe, J. L. C. Ladu, and John Baptist Tumuhairwe 15 Cyanobacteria  as Sustainable Microbe for Agricultural Industries����������������������������������������������������������������������  255 Shah Ishfaq, Jeelani Gousia, Syeed Mudasir, and Baba Uqab 16 Functional  Diversity of Endophytic Microbiota in Crop Management of Cucumis sativus L.������������������������������������������  269 Showkat Hamid Mir, Aadil Farooq War, Rezwana Assad, and Irfan Rashid 17 Nanoscience in Agricultural Steadiness ������������������������������������������������  285 Atin Kumar, Satendra Kumar, Rachna Juyal, Himani Sharma, and Mamta Bisht 18 Carbon  and Silver Nanoparticles for Applications in Agriculture������  297 Samiran Upadhyaya, Madhabi Devi, and Neelotpal Sen Sarma Correction to: Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry ��������������������������������������  C1 Murugaiyan Sinduja, Joseph Ezra John, R. Suganthi, S. Ragul, B. Balaganesh, K. Mathiyarasi, P. Kalpana, and V. Sathya Index������������������������������������������������������������������������������������������������������������������  317

About the Editors

 owhar Hamid Dar  PhD, is currently working as an G Assistant Professor in Environmental Science, Sri Pratap College, Cluster University Srinagar, Department of Higher Education (J&K). He has a PhD in Environmental Science with specialization in Environmental Microbiology (Fish Microbiology, Fish Pathology, Industrial Microbiology, Taxonomy and Limnology). He has been teaching postgraduate and graduate students for the past many years at Post-graduate Department of Environmental Science, Sri Pratap College, Cluster University Srinagar. He has more than 70 research articles (h-index 15; i-index 20; total citation >950) in international and national journals of repute and also has more than 20 books with international publishers (Springer, Elsevier, CRC Press Taylor and Francis, Apple Academic Press, John Wiley, IGI Global) to his credit. Moreover, he is supervising a number of students for the completion of degrees (PhD/Masters). He has been working on the isolation, identification and characterization of microbes for a decade to understand their utility for humans particularly in agriculture and industrial sectors.  His research is based to understand the pathogenic behaviour of bacteria and to particularly understand the impact of pollution on development of diseases in fish fauna in Kashmir Himalaya. He has received many awards and appreciations for his services towards the science and development. Besides, he also acts as a member of various research and academic committees. Further, Dr. Dar is Principal Investigator and Co-Principal Investigator for different R&D projects sanctioned by Govt. of India and Govt. of Jammu and Kashmir. xix

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About the Editors

Rouf Ahmad Bhat  PhD, has pursued his doctorate at Sher-e-Kashmir University of Agricultural Sciences and Technology Kashmir (Division of Environmental Sciences) and presently working in the Department of School Education, Government of Jammu and Kashmir. Dr. Bhat has been teaching graduate and postgraduate students of environmental sciences for the past 3 years. He is an author of more than 55 research articles (h-index 28; i-index 40; total citation 2050) and 45 book chapters, and has published more than 40 books with international publishers (Springer, Elsevier, CRC Press Taylor and Francis, Apple Academic Press, John Wiley, IGI Global. He has his specialization in Limnology, Toxicology, Phytochemistry and Phytoremediation. Dr. Bhat has presented and participated in numerous state, national, and international conferences, seminars, workshops, and symposium. Besides, he has worked as an associate environmental expert in World Bank-funded Flood Recovery Project and also the environmental support staff in the Asian Development Bank (ADB)-funded development projects. He has received many awards, appreciations, and recognition for his services to the science of water testing, air and noise analysis. He has served as an editorial board member and a reviewer of reputed international journals. Dr. Bhat is still writing and experimenting with diverse capacities of plants for use in aquatic pollution remediation. Mohammad  Aneesul  Mehmood  PhD, has his specialization in Limnology and Environmental Toxicology. He completed his doctorate with meritorious certificate from the Division of Environmental Science, Sher-eKashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar campus, Srinagar, J&K. He was awarded with Dr. Mumtaz Ahmad Khan Gold Medal and Shri Bhushan Memorial Gold Medal for his outstanding performance during his master’s programme both in curricular and extra-curricular activities. He was awarded with Late Sri N. Rama Rao Endowment (Highest Cash Prize) at 48th annual convocation of Bangalore University 2013 for securing top position in his master’s programme. He has qualified various state- and national-level competitive

About the Editors

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examinations in the subject of Environmental Science like UGC NET, JK-SET and ASRB-NET. He was also awarded with INSPIRE Merit Fellowship (JRF & SRF) by the Department of Science and Technology, GoI, during his doctoral programme. He was also awarded with Young Scientist Award at International Conference on Multidisciplinary Research and Latest Innovation 2018. He has also obtained his post-graduate diploma in disaster management with distinction grade from Indira Gandhi national Open University, New Delhi, in 2014. He has been teaching graduate and postgraduate students of Environmental Science from past many years. He has been supervising various students for their master’s projects within and outside Jammu & Kashmir in various colleges and universities. Furthermore, he has a number of publications in national and international journals of repute and a number of books with national and international publishers.

Chapter 1

Integrated Approaches to Agri-­nanotechnology: Applications, Challenges, and Future Perspectives Mir Zahoor Gul and Sashidhar Rao Beedu

Abstract  The agro-ecosystem is now under intense pressure because of exponential population growth, growing demand for food, excessive freshwater withdrawals and energy use, inordinate wastage of food, improper agrochemical utilization, and environmental degradation. Nanotechnology proved to be one of the most promising approaches and offers ample opportunities to overcome the flaws in conventional farming practices. Today’s agriculture has entered a new phase in which the development of new nano-devices and nanomaterials opens up prodigious applications in food manufacturing, processing, packaging, storage, and economic expansion. Numerous nano-based products are currently under research and development stage and, therefore, can be introduced in the coming years. However, at the same time, nanotechnology also brought uprising issues regarding biodiversity, health, environmental safety, regulation, safety, and approval of nanotechnology products. In this chapter, we overview several stupendous applications of nanotechnology in the food and agriculture sector, while also highlighting its unresolved issues and prospective merits. Keywords  Sustainable agriculture · Nanotechnology · Nano-fertilizer · Crop yield · Food processing · Waste management · Regulation

1 Introduction Recent agricultural practices attributed to the Green Revolution have vastly improved the world’s food supplies. Nonetheless, at the same time, they have also had an unintentional deleterious effect on the environment and ecological systems, thereby underlying the need for further sustainable agricultural approaches. Therefore, an existing system of agricultural production faces the overwhelming M. Z. Gul (*) · S. R. Beedu Department of Biochemistry, University College of Science, Osmania University, Hyderabad, Telangana, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_1

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task of satisfying the demands of a growing global population. In 2019, the global population increased from 2.5 billion in 1950 to 7.7 billion and is projected to rise to about 8.5 billion in 2030, 9.73 billion in 2050, and 11.2 billion in 2100 (United Nations 2019). This population explosion has greatly exacerbated the demands for food supplied by agriculture because plants are one of the key nutrient sources for human life. In the meantime, roughly 820 million people, primarily in developing and underdeveloped countries accounting for 11% of the global population, were reported to lack access to adequate food to lead a fairly healthy way of life in the year 2018, and an additional two billion people are anticipated to be in this segment by 2050 (Food Security Information Network 2018). To meet the estimated rising demands of 9.7 million people by 2050, world agriculture production must increase by approximately 60% (FAO et al. 2019). This troubling forecast becomes direr as climate change is anticipated to disrupt the patterns of agricultural production by prolonging the drought events and increasing daily average temperatures in various vulnerable agricultural productions of the world. Shortage of food is believed to cause greater mortality than the total due to diseases like AIDS, malaria, and tuberculosis (Food Security Information Network 2018). The world’s agricultural sector is facing immense challenges because of massive increase in population statistics, amplified global food demands, excessive freshwater withdrawals and energy consumption, extreme wastage of food, wasteful utilization of fertilizers and pesticides, environmental degradation, and climate change. Plant pathologists and other agriculturalists are facing daunting challenges in this regard. Different technical approaches are being applied to overcome these limitations/difficulties, but a majority of these approaches have their repercussions. Recent progress in science and technologies could be a potential approach to successfully overcome current production problems. The growing realization that existing farming practices would not be able to meet the ever-increasing demands of the world population and reclaim ecosystems harmed by the existing technologies paved the way toward the application of nanotechnology for sustainable agro-production. Thus, there are scrawling developments in the agricultural sector that can transform the contemporary agricultural system. Nanotechnology, which represents one of the exciting interdisciplinary research endeavors in the current era, has incredible potential to overcome many issues attributed to traditional agricultural practices. The waves of nanotechnology-based research have demonstrated the great promise of nanotechnology to improve the agriculture industry by proposing alternatives to agricultural and environmental issues to boost food productivity and security. A plethora of research studies on applications of nanotechnology have been conducted in the recent past highlighting its wide variety of applications in the field of agriculture (Chen et al. 2016; Prasad et al. 2017; Lv et al. 2018; Hakeem et al. 2021; Dar et al. 2022). Nanotechnology is a swiftly emerging and developing technology with novel applications to agriculture and food science. Quick and impactful nanotechnology developments for agriculture have resulted in new prototype experimental technologies and products. Development of a wide array of devices and tools, nanoscale fabrication of bulk molecules, and other environmentally friendly nano-platforms have the potential to

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enhance consumer health and well-being, shelf-life, bioavailability, efficiency, and stability, in processing and packaging with a real-time monitoring system. This ultimately aims to enhance agricultural productivity by increasing resource output and reducing related losses by tracking different environmental factors and enforcing targeted actions (Ditta 2012; Khot et al. 2012; Sekhon 2014; Fraceto et al. 2016; Singh et al. 2017). Therefore, nanotechnology has immense possibilities to revolutionize the agriculture sectors.

2 Overview of Multifarious Applications of Nanotechnology in Agricultural and Food Sector The application of nanotechnology to the agro-agriculture is multidisciplinary. Innovations in nanotechnology are cutting-edge research focusing on sustainable agricultural production. Several applications of nanotechnology in agriculture have already been explored and are in use in today’s advanced times (Fig. 1.1).

2.1 Precision Agriculture Nanotechnology embraces the role of information technology applied to commercial agriculture management. Nanotechnology offers the possibility of precision farming (i.e., increasing production with least input) in an era in which increased demand for sustainability requires a reduction in costs and elevated utilization of natural agricultural resources (Chen and Yada 2011). Precision farming has long been an intended target of improving agricultural production by diligently customizing soil and crop management to resemble the inimitable condition present in each soil despite retaining environmental worth (Baret 2015). It is used to achieve maximum output in terms of agronomic yield, while significantly reducing inputs (such as agrochemicals like fertilizers, pesticides, herbicides) by assessing various environmental variables and subsequently employing the targeted action (Servin et al. 2015; Fraceto et al. 2016). Precision farming supporting technologies typically include the Global Positioning System (GPS), Geographic Information System (GIS), and Remote Sensing (RS). By integrating GPS with fields, soil environments and plant growth developments, seeding, nutrients, pesticides, and water usage can be fine-tuned to reduce manufacturing costs and eventually improve productivity. Precision farming aims to eliminate agricultural waste; therefore, it tends to minimize the levels of environmental contamination. Other essential functions for nanotechnology-enabled devices will be automated sensing equipped with GPS for real-time tracking of soil condition and crop yield all through the field. The coalition of biotechnology and nanotechnology in sensors will establish extra sensitive equipment, enabling an earlier response toward the changes in the environment (Chen and Yada 2011; Cheng et al. 2016).

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Fig. 1.1  An illustrative pictorial representation of various applications of nanotechnology being explored in agricultural and food sector

2.2 Nanobiosensors Nanofabrication is a principal feature of modern advanced technology. Advancement in physical and material sciences, device fabrication, and manufacturing of nano-­ based products will enhance the growth of modern technologies. The nano-enabled biosensors have enormous potential for improving agricultural productivity. This innovative novel strategy to use nano-enabled biosensors would help farmers with improved fertilization management, reduction in agrochemical inputs, and proper planning of natural resources, thereby increasing the overall productivity of crops (Sekhon 2014; Omanović and Maksimović 2016). Nanobiosensors are the next-­ generation biosensors that have given rise to a broader prospect of increasing precision, sensitivity, and rapid response to sense the impairments compared to the conventional chemical and biological procedures (Dubey and Mailapalli 2016).

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Biosensors are the nano-analytical systems utilizing a biological sensor module integrated with a physicochemical transmitter to generate an electronic signal when the analyte of interest is in contact. It can be emphasized that nanobiosensors are advantageous in sensing and reporting the real-time information about the products from the time of manufacturing to the point of delivery. Owing to its unique chemical and electro-optical properties, these nanobiosensors can overcome the drawbacks of food packaging. Nanobiosensors can allow farmers to use inputs more effectively by projecting the plants’ nutrient or water status over fine spatial and temporal scales. It encourages farmers to use fertilizers, pesticides, and water only where and when necessary that ultimately reduces the input costs and environment safety. They can detect gasses, aromas, contaminants, toxic pollutants, and changes in the environmental conditions. One of the several prominent functions of nanotechnology-­based devices is to significantly boost the use of autonomous sensors that are linked to the Global Positioning System for live information. Reliable, affordable, and flexible portable nanobiosensors have been sought for food analysis and food safety applications, enabling monitoring of structure, smell, and taste of chemical substances as well as contamination by food spoiling, among additional applications (Chen and Yada 2011; Dasgupta et al. 2015). For example, a nanobiosensor based on atomic force microscopy tip functionalized with the acetolactate synthase enzyme was used for the detection of herbicide, metsulfuron-­ methyl (an acetolactate synthase inhibitor), through the acquisition of force curves (da Silva et al. 2013). These biosensors also facilitate the rapid identification and quantification of food pathogens and hence increase food safety for the consumers (Eleftheriadou et al. 2017). An exceedingly sensitive organophosphorus pesticide biosensor developed with surface functional carbon nanotubes designed with amino groups to monitor the proficient immobilizing process of acetylcholinesterase enzyme on the exterior of a smooth carbon electrode is used successfully to evaluate vegetable samples directly (Yu et  al. 2015). In addition, acetyl cholinesterase biosensor was successfully devised for detecting the organophosphate pesticide residues centered on the assemblage of multiwall carbon nanotubes (MWCN) onto the liposome bioreactors (Yan et al. 2013). Another sensitive acetylcholinesterase biosensor customized with hollow Au nanospheres with the detection confines of 0.06 μg/dm−3 for chlorpyrifos and 0.08 μg/dm−3 for carbofuran was successfully devised (Sun et al. 2013). The current high-tech advances in this area of technology are the production of luminescent nanocrystals that are quantum dots (QDs) being used for the biological recognition of molecules in fluorescent labeling. Quantum dots have more efficient luminescence, contracted emission spectra, and excellent characteristics of photostability; thus, they are superior compared to conventional organic dyes. Quantum dots are often used to identify causing agents of various plant diseases. For example, QD fluorescence energy transfer-based sensors have been designed to perceive lime broom disease of witches induced by Phytoplasma aurantifolia. The immune-­ sensor was designed and demonstrated to show extreme sensitivity and absolute specificity with a detection capacity of 5 ca. Phytoplasma aurantifolia per milliliter

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(μL) (Rad et al. 2012). Innovations in nanobiosensor and nanoprobe technologies are expected to flourish, as these nanomaterials offer a wide array of detection techniques. In conclusion, nanobiosensors are versatile with advanced and enhanced features that can be employed to thwart pest epidemics and subsequently keep a vigil on soil characteristics and thus support sustainable agriculture by improving the productivity of crops (Dubey and Mailapalli 2016; Mufamadi and Sekhejane 2017).

2.3 Nano-agrochemicals Agrochemicals including fertilizers, pesticides, and herbicides play a vibrant role in improving plant’s growth and crop’s productivity. The use of these chemicals to maximize agricultural productivity has contributed to the uncontrolled release of pollutants in the earth’s environment. In addition to crop protection from multiple pests and diseases and increasing yields, these agrochemicals result in other associated issues such as negative effects on target flora and fauna, dispersion and residues, soil microbial health disturbance, and thus soil structure and soil physicochemical properties. In such a situation, it becomes a major obstacle in developing a sustainable agriculture system (Guo et al. 2018; Lateef et al. 2019). The smart agrochemicals with controlled release mechanisms could provide a viable solution to this challenge by using delivery-based/carrier-based systems to regulate the release of fertilizers or pesticide’s active ingredients coordinated with the crop growth cycles. This will greatly minimize fertilizer/pesticide waste and ensure a steady or sustained release during the crop’s developmental stages (Calabi-Floody et al. 2018; Hagab et al. 2018). The intensifying global trend toward nanotechnology-­ based agricultural products has resulted in an inevitable revolution in nano-farming (Ghormade et al. 2011; Mukherjee et al. 2016). Nano-farming, therefore, aims to achieve cost-effective, eco-friendly, efficient, commercially viable agriculture production by reforming traditional methods and strategies to minimize chemical inputs and current ecotoxicological concerns by developing advanced nanocomposites of multiple agrochemicals (Mukherjee et al. 2016; Kim et al. 2018). Such nanocomposite materials synthesized using metallic, polymeric, and inorganic material are expected to enhance these intelligent nano-systems capable of capturing and immobilizing nutrients’/pesticides’ active ingredients and ensuring their gradual release into the soil to strengthen their effectiveness (Cătălin Balaure et al. 2017). One of the modern approaches to find solutions related to the applications of fertilizers and pesticides is the controlled release (CR) strategy, which facilitates the coordinated and customized delivery of agrochemicals that regulate plant development, improve target activity, and make them efficient for crop demand (Derosa et al. 2010; Mani and Mondal 2016; Chhipa 2017).

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2.3.1 Nano-fertilizer Fertilizers are the chemical additives used to improve plant productivity and the safety of plants. These chemicals play a key part in growing agricultural production by up to 34–40%, particularly after high-yield and fertilizer-responsive crops have introduced. Conventional fertilizers currently contribute to the tune of 50% of any crop’s agricultural productivity. Excessive use of higher doses of fertilizers does not always assure better agricultural yield but leads to severe issues such as soil degradation and surface and underground water pollution. The efficiency of the use of nitrogen, phosphorous, and potassium remained constant 30–35%, 18–20%, and 35–40%, respectively, which means a large proportion of added fertilizers remain in the soil and subsequently gain entry into the aquatic systems, thereby resulting in eutrophication (FAO 2017). Thus, the demand for alternative approaches to ensure sustainable nutrient use is increasingly gaining attention within the research world. In the given context of sustainable agriculture, the use of nanotechnology in the manufacturing and use of new fertilizers is looked at as one of the promising alternatives to increase soil fertility and agronomic crop yields to meet the challenging demands of food supply and environmental protection (Sekhon 2014). Nanotechnology has begun to attract more targets in the field of agriculture, especially to develop unique nano-fertilizers to increase the effectiveness and bioavailability of the existing fertilizers and to minimize the loss of such materials to the ecosystem (Sasson et al. 2007). Nano-fertilizers are nutrients consisting of nanostructured formulations, in whole or in part, that can be supplied to plants so that active ingredients can be effectively absorbed or release. These nano-fertilizers may possess nano Zn, SiO2, Fe, and TiO2, ZnCdSe/ZnS core-shell QDs, InP/ZnS core-­ shell QDs, Mn/ZnSe QDs, gold nanorods, core-shell QDs, etc. Fertilizers can be augmented in three different approaches using nano-­techniques: nanomaterial encapsulation, coating of a thin protective nanoscale polymeric film, and nano-emulsions (in the form of nano-porous materials, nano-polymers, or nanocomposites) (Calabi-Floody et  al. 2018). However, one more category of nano-­ fertilizers includes alternative classification based on nutrients involved in the processing, which comprises (i) nanomaterials based on micronutrients, (ii) nanomaterials based on macro-nutrients, and (ii) plant growth enhancement of non-­ nutrient nanomaterials (Guo et al. 2018; Kah et al. 2018). These nano-fertilizers can enhance crop nutrient absorption efficiencies while increasing agricultural yields and minimizing the undesirable effects of conventional fertilizers since these nanomaterials can systematically delay the release of active constituents to the specific biological needs of the crop and related environmental triggers of the respective environment (Sekhon 2014; Liu and Lal 2015; Solanki et al. 2015; Abobatta 2018). A minute particle size, higher surface to volume ratio, sorption efficiency, and regulated release kinetics promote the efficient absorption of such nanostructures into the plant cell and tissues as well as the controlled release of loaded nutrients at the specified targets, rendering them the most appropriate choice for the design and development of “smart fertilizers” or “smart delivery systems” (Rose et al. 2015; Solanki et al. 2015; Kim et al. 2018). There are very few systematic studies on the

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impact of smart nano-fertilizers applying under field conditions. Nano-fertilizer foliar application results in greater performance in the use of nutrients and has provided a quick response to the growth of several crops such as Ocimum basilicum, Oryza sativa, Lycopersicon esculentum (tomato), Cucumis sativus (cucumber), Zea mays (maize), wheat (Triticum aestivum) and alfalfa, (Delfine et al. 2005; Liu and Lal 2015; Abdelaziz and Abdeldaym 2018; McCauley 2019). Biopolymers, for example, proteins, starch, and chitosan, are widely preferred owing to their biocompatible features and their nontoxicity toward humans and the environment (Kim et al. 2018). One of the main benefits rendered by nano-fertilizers is the enhanced proficiency of the supplied nutrients with possible low levels of application to minimize environmental hazard pollution efficiently and potentially decrease the complexity of crop production to ensure economic prudence for the farmers (Kim et al. 2018). 2.3.2 Nano-pesticides Although there are many alternative methods available, the use of pesticides is a common practice in commercial agriculture for pest control. However, only a small proportion of applied pesticide (0.1%) serve the purpose of reaching the targeted pests/insects, while the remaining, that is, 99.9% pollutes the ecosystem which has severe repercussions for both the food chain and human health (Carriger et al. 2006; Bhattacharyya et  al. 2016). Besides the adverse effects on nontarget species, the pervasive presence of pesticide residues has led to the pesticide resistance in plants in addition to insects and other pathogens (Rai and Ingle 2012). Biopesticides have been found to reduce the perilous effects of conventional pesticides; however, their use is restricted by their sluggish and environmentally dependent competence against the pest. Nano-pesticides have added a new dimension in the field of plant protection management and described plausible possibilities to overcome all these drawbacks. Nano-pesticides are, therefore, essential for the efficient and sustainable management of various pests and can reduce synthetic chemicals and associated environmental perils. To boost their efficacy, the nano-pesticides function differently from their conventional counterparts. The benefits of nanomaterial formulations, such as insecticides and insect repellents, are improved applicability because of advanced surface area, higher solubility, induction of systematic activity due to their extremely small particle size, high mobility, lower levels of toxicity (due to removal of organic solvents), etc. (Sasson et al. 2007; Khot et al. 2012; Bhattacharyya et al. 2016). Nanoencapsulation has been employed to enhance insecticidal value to safeguard the active compounds from environmental factors and to facilitate persistence. These nano-pesticide formulations can provide means of regulating pesticide delivery and help in achieving bigger implications at reduced application rates and a relatively low dosage (Chhipa 2017; Bhatia and Bhatia 2019). It is widely believed that nano-pesticides can improve evident bioavailability of poorly water-soluble active compounds and eventually release the active ingredients to prevent degradation (Kah et  al. 2013; Kah and Hofmann 2014; Dubey and Mailapalli 2016).

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Nanoencapsulation of pesticides is indeed at present the most promising technology for the safety and security of plant species toward insect pests (Hussain et al. 2017). With nanoencapsulation strategies, the chemical release can be reduced in controlled situations, thus limiting the current dosage application and increasing performance (Balaji et al. 2017). Moreover, these nanoencapsulated pesticides are target specific and, therefore, reduce the effective doses. Nano-pesticides play a crucial role in water and energy conservation, as their application is less frequent, and they have limited quantities as compared to traditional pesticides. They also augment pesticide efficacy and agricultural produce by increasing yields at the same time limiting input costs of labor and minimizing agricultural wastes. 2.3.3 Nano-herbicide In the present agricultural production system, weeds are the biggest menace and inflict serious obstacles in agronomic yield/productivity by using nutrients that are otherwise available for crop plants. The uncontrolled application of synthetic herbicides has promoted the cumulative residual levels, resulting in pollution and herbicide resistance in target species (Vandermaesen et al. 2016; Alfonso et al. 2017). Nano-herbicides are, therefore, now formulated utilizing nanotechnology to achieve effective weed control and herbicide distribution. These nano-herbicides play a pivotal role in eradicating the weeds from agricultural fields and crops in an eco-friendly manner without leaving behind any toxic traces in the soil and environment (Alejandro and Rubiales 2009). It is indicated that these nano-herbicides possess chemical stability, bioavailability, solubility, photodecomposition, and soil absorption characteristics. Nano-herbicides rely mostly on biodegradable polymers in combination with different metallic nanoparticles which are mostly used nanocarriers for the delivery of herbicides into the appropriate target weeds, thus resulting in enhanced crop yield (Vandermaesen et al. 2016). Target-­specific herbicide-laden nanoparticles have been designed for the delivery in the roots of weeds. These nanocomposites gain entry into the root system, translocate to cells and therefore into the root system of the weeds, translocate to cells and impede metabolic pathways like glycolysis, and ultimately result in the death of the plant (Nair et al. 2010; Ali et al. 2014).

2.4 Crop Improvement Nanotechnology when applied in agricultural biotechnology has tremendous scope for crop improvement. Nanobiotechnology tools offer the industry the option of modifying the existing genes and even produce quite different organisms. Because of the presence of a rigid outer cell membrane, the surface-functionalized silica nanoparticles were previously considered to lack any applicability for the delivery of desirable entities in the plant cell or tissues. However, this technology involves

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the use of specialized nanoparticles, nano-capsules, and nanofibers to inject the molecular cargo especially DNA inside the plant cells (Sekhon 2014). An important modification in the usually used gene gun technique for plant transformation is to synthesize even smaller gold particles for capping the nanoparticles which not only stopped chemical leakage but also caused an increment in weight of the nanoparticles increasing their efficiency of delivery into the plant cells. Mesoporous silica nanoparticles with 3 nm pores capped with gold nanoparticles are handy in transporting DNA (gene) into leaves and intact plant cells. The concomitant introduction of the inducer chemical is helpful in this procedure for elicitation of the gene expression in plants under precise control release factors (Torney et al. 2007). This application of nanotechnology has opened windows of new possibilities and remarkable breakthroughs in plant biology and agriculture. Along with the imaging agents, the agriculture biotechnology scientists can now deliver anticipated or desirable genes in crop plants with the induction of precise control devoid of any toxic effects and marking of the corresponding intracellular events. With the aid of mesoporous nanoparticles, there is also the possibility of the introduction of multiple genes in plants simultaneously and releasing or expressing them at will (Poddar et al. 2017; Priyadarshan 2019). Cellular injection with the aid of carbon nanofibers containing foreign DNA has been involved in the genetic modification of golden rice. There have also been successful genetic and chemical transformations using nanotechnology in Arabidopsis, tobacco, and corn plants without any detrimental effects (Galbraith 2007; Sekhon 2014). Stable transgenic developments can also be avoided, if desired, by tightly binding the DNA with nanoparticles so that it does not get detached and integrated to the genome of the recipient but transiently expresses only at the delivery sites (Poddar et al. 2017). Apart from stable and transiently expressive site-specific genetic transformations, nanoparticle introduction can alter the expression of some specific genes. NanoAl2O3 treatment caused stimulation of miR395, miR397, miR398, and miR399 micro-RNAs in tobacco (Burklew et al. 2012). Similarly, nano-TiO2 treatment was found to upregulate the expression of Rubisco activity in addition to antioxidant enzymes such as SOD (superoxide dismutases), catalase, and other peroxidases in the chloroplast of spinach (Lei et al. 2008). A Carbon-based nanoparticle Fullerol (C60OH20), when deposited and accumulated in various tissues of the bitter melon vegetable crop, was found to lead to a remarkable increase in total biomass and fruit yield which includes number, weight, length, and overall size. Well-known antidiabetic constituents insulin and charantin were enhanced by 91% and 20%, respectively, while anticancer lycopene and cucurbitacin-B was increased to 82% and 74%, respectively (Kole et al. 2013). Owing to the efficient RNA binding and cell membrane penetration ability, the recent advancement in siRNA-loaded chitosan nanoparticle delivery vehicles has opened a new platform for crop improvement for facilitating target-specific control of insects and pests (Zhang et al. 2010). Another recent but promising modified tool of genetic engineering is nanomaterial-­ based delivery of CRISPR/Cas9 single-guide RNA (SgRNA) for plant genome editing. However, its progress is impeded by the low efficiency of delivery (Miller et al. 2017; Shang et al. 2019).

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2.5 Postharvest Processing Over the years, the continuous accumulation of agricultural waste or by-products in nature and their disposal has become a major problem and real challenge (Bello et  al. 2017). Nanotechnology aims at providing realistic solutions to agricultural waste management. The abundance and broad diversity of agricultural residues rendered them as an exciting and promising source of energy. Gasification, pyrolysis, transesterification, and hydrolysis are the main strategic ways of conversion of biomass to biofuels. Nanotechnology research into the conversion of biomass has played a crucial role in enhancing product quality and attaining optimum conditions. In biofuel processing, nanocatalysts provide a clean and environmentally friendly strategy that performs higher catalytic conversion and selectivity via inexpensive methods and milder operating conditions (Akia et al. 2014; Nasrollahzadeh et  al. 2018). Also, the use of nano-engineered enzymes has received enormous attention as a viable means way to reduce environmental and industrial contaminants and to translate these contaminants into possibly useful products such as biopolymers and bioplastics (Amulya et al. 2016; Emadian et al. 2017). Liquid biofuels are also reliant on cellulosic feedstocks in the second-generation conversion which converts to ethanol and biodiesel (Bhatia 2014; Zhang et al. 2016b). Waste material from spent tea could be used to produce biofuel, bioethanol, etc., via (і) gasification process (which generated 60% liquid extract, 28% gas fuels, and 12% charcoal, along with gaseous residues that comprise 53.03% ethane (C2H6), 37.18% methanol (CH3OH), and 4.59% methane (CH4)), (іі) transesterification process which provided 40.79% biodiesel (ethyl ester), and (ііі) generation of 57.49% bioethanol by Aspergillus niger (Mahmood and Hussain 2010). Abundant lignocellulosic biomass also generated from the wastes of agriculture with immense potential for the formulation of various functional nanomaterials (Hu et al. 2010). Biopolymer-based nanocomposites, for example, starch, proteins, and carbohydrates, are safe and eco-friendly than synthetic chemicals. The husks from rice and wheat are the harvest by-products that can be explored as raw materials to produce sustainable energy, superior nano-silica and biochar, and other high-impact products (Liu et al. 2015). Implementing mass nano-silica production through nanotechnology and biochar production processes can alleviate increasing apprehensions regarding farm waste disposal (Carmona et al. 2013; Liu et al. 2013). Nanotechnology is also being used to convert cotton waste into cellulose nanofibers with the help of electrospinning (Liu and Wu 2016). These nanomicrofibers can be used in multiple areas including nanomembrane, electronic and optical equipment, protective clothing, nano-agrochemicals, and biomedical applications (Zameer Ul Hassan et al. 2013; Liu and Wu 2016; Mostafa et al. 2018). The captivating features like porosity, high surface to volume ratio, and safety of these nanofibers render them rational entities to establish a wide array of applications (Noruzi 2016). Because of its outstanding features, unique chemical structure, excellent biocompatibility, and nano-cellulose derived from agricultural wastes has attracted huge interest in the production of advanced medical equipment in the

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recent past (Lin and Dufresne 2014). Nano-silica that is copiously present in rice husk has been utilized in controlling the insect pests and synthesis of silica nanomaterials conjugated with validamycin and subsequently used for the controlled delivery of water-­soluble pesticide (Liu et al. 2006; Carmona et al. 2013). Biochar, a porous material rich in carbon, is being generated under oxygen-­ limited conditions from a thermochemical conversion of biomass (from agricultural waste), called pyrolysis (Srinivasan et al. 2015; Tripathi et al. 2016). It offers a great opportunity to transform agricultural waste as well as other harmful chemicals into a renewable source of energy. The research carried out so far highlights biochar as a valuable product for mitigating catastrophic climatic changes and suggests its extensive application in agriculture, water purification and management, construction, etc. (Woolf et al. 2010; Xu et al. 2012; Das and Sarmah 2015).

2.6 Food Industry Most of the products from the food industry (such as fresh vegetables, fruits, dairy products, and various processed foods) are either perishable or semi-perishable. The increasing consumer issues about food safety and health benefits are driving the scientific community to improve the quality of food without compromising on its nutritional value. Nanotechnology offers a variety of applications in food processing, food packaging, food safety, and tracking and tracing of food and food products. 2.6.1 Food Processing Food processing is the transformation of raw resources into the food and its other forms via multiple approaches and translates it into a consumable state, and these procedures are being programmed in such a way to safeguard the food’s color, texture, flavor, and consistency. Nanotechnology has also established its competence in maintaining the safety and quality of food. The intervention of nanotechnology in food processing has resulted in the design and production of new and unique food products with upgraded solubility, thermal stability, and oral bioavailability. Nanotechnology increases the shelf-life of various food products and helps to prevent the severity of food waste associated with the microbial infection (Pradhan et al. 2015). Nanocarriers are used as delivery systems in packaged foods to transport dietary supplements without distorting their basic structure. The functional properties are maintained by encapsulating simple solutions, colloids, emulsions, biopolymer matrices, and others into the food products (Abbas et  al. 2009). Nanoencapsulation offers several advantages in food processing, including delivery of the desired component, entrapment of odor, and unwarranted components in the food, thereby playing a significant role in food preservation. Furthermore, the depletion of nutrients in the food can be inhibited with nanoencapsulated dietary supplements and other probiotics that have a significant advantage over the conventional

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use of similar substances. Similarly, nano-emulsions retain the flavors proficiently and avert them from oxidation and enzymatic reactions. Nano-emulsions are known to have antimicrobial activity, and due to this reason, they are used for decontaminating food packaging articles. In addition to antimicrobial properties, nanoparticles can also be used as a carrier for the delivery of antioxidants, enzymes, flavors, anti-browning agents, and other materials (Weiss et al. 2006; Pradhan et al. 2015; Adeyeye and Fayemi 2019). 2.6.2 Food Processing Food packaging is one of the most significant and essential steps for food safety. Naturally occurring substances, toxic gases, and water vapors are impervious to no packing material (Siracusa et al. 2008; Robertson 2013). The integration of nanotechnology will delay some biochemical processes like oxidation-reduction reactionsand therefore help in prolonging the product’s shelf-life of food products. Recent developments in food packing facilitate the use of biodegradable polymers that can be integrated or coated with nanomaterials for better mechanical or functional characteristics (Cha and Chinnan 2004; Berekaa 2015). Packaging has a major role in the nanofood systems in preventing the post product loss, in addition to extending the shelf-life of both fresh and stored agricultural produce. Nanomaterials used in food packaging have several potential benefits like enhanced mechanical barriers, detection of microbial infestation, improved nutrient bioavailability, and so forth. The aim of creating polymer composites from many inorganic or organic fillers is to provide more mechanical and thermostable materials for packaging with cost-effectiveness. Among the many unique nanomaterials, nano-clay is among the most versatile material for food packing owing to its excellent mechanical, thermal, and barrier properties along with the low cost. Besides, nano-coatings on food contact surfaces serve as barriers for microbial manifestation and keep it safe for human consumption. Other nano-based materials such as polyamide, polyvinyl, and polypropylene have found use in food packaging (Ali et al. 2014). Inorganic nano-based materials of certain metals and metal oxides like Ag, Fe, TiO2, ZnO, MgO, and SiO2 and carbon nanoparticles are being successfully incorporated into plastics for the manufacture of food storage containers, which serves as disinfection agents, mitigating harmful bacterial growth. It is interesting to note that TiO2 is ubiquitously utilized as a disinfectant because it produces highly reactive oxygen species that can help to get rid of the microbial pathogens due to toxicity effects (Sekhon 2014). Many other applications of nanotechnology in food packaging include detection of pesticide and infectious agents, owing to the ultra-­ sensitive nature of these nano-materials that are also under active research considerations (Banerjee et al. 2016; Zhang et al. 2016a, 2017; Kearns et al. 2017; Perçin et al. 2017; Sahoo et al. 2018; Sun et al. 2018a, b). Nanotechnology is, therefore, a progressive innovation, as it serves in agricultural biosecurity and food safety (Bumbudsanpharoke and Ko 2015).

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2.6.3 Identification, Tracking, and Tracing of Agri-foods Nanotechnology could even facilitate agri-food processing industries to provide authentication and track and trace attributes of food products to avoid counterfeiting, to prevent adulteration and misdirection of consumer foods intended for a definite market. In agriculture, nano-barcodes are used for both biological and nonbiological applications (Ditta 2012). The significant biological applications of nano-barcode are identification (ID) tags that are used for multiplexed gene expression studies and intracellular histopathology. In the coming years, more efficient identification of fast, cheaper application of plant gene trait techniques is intended through improvements in gene sequencing based on nanotechnology (Branton et al. 2008). It has been proven that this technique of decoding and identifying diseases by multiple pathogens in an agricultural field can be tagged and detected simultaneously with the help of fluorescent-based tools (Li et al. 2005). The nano-barcode ID tags have found its use in nonbiological systems. These nano-based tags have been used in agricultural foodstuff and other goods such as husbandry products for the authentication as well as tracking. This nano-barcode technology thus develops new ID technologies and therefore increases traceability in the food trade sector and will become a vital weapon for the development of safe global agri-food business. It helps to establish the strategies to preserve not just the freshness of agricultural products like vegetables and fruits, but their quality and safety as well. Nanotechnology also offers complex hidden nano-barcodes with encrypted batch information on different food items and packaging to assist with tracking and tracing (Li et al. 2005).

2.7 Water Quality Management The irrigation system plays a substantial part in agriculture. The efficient use of freshwater and cross-contamination of groundwater is one of the most important challenges among all sustainable agricultural practices. Among the prominent pollutants that are responsible for the contamination of agricultural water include water-borne pathogenic microorganisms, runoff agricultural chemicals, various inorganic compounds, heavy metals, and other complex compounds and many other complex compounds that gain entry into the water resources because of natural leaching and man-made activities (Fatta-Kassinos et al. 2011). In addition to affecting crop yield, polluted water also poses a lethal effect on soil fertility (Chong et al. 2010). The water pollutants from agricultural wastewaters pose a grave risk to human health and the Earth’s other ecosystem. The elimination or detoxification of these pollutants is not always viable, as the traditional approaches such as chemical and UV treatments, filtration, and desalination are not feasible in the far-off areas. Moreover, these methods are hampered by technical barriers as well as high costs (Zhang and Fang 2010; Oller et al. 2011). To

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counter this issue, modern, safe, and economical technologies are needed to treat this large quantity of wastewater. Recent developments in nanotechnology have allowed us to search for commercially viable alternatives for wastewater treatments. The desirable properties of nanomaterials for the wastewater treatment comprise excess surface area meant for adsorption, high photocatalytic property, the antimicrobial ability for sterilization, super magnetism for particle segregation, and other distinctive electronic and optical features for water quality monitoring. 2.7.1 Water Filtration/Purification Nano-adsorbents offer substantial gains over conventional adsorbents owing to their extremely high specific surface area, short intra-particular diffusion, and adjustable pore diameter as well as structure. Several nanomaterial surfaces can be characterized to target specific pollutants, attaining high selectivity. Therefore, these nano-­ adsorbents can be easily incorporated into the current treatment procedures like slurry reactors, filters, or absorbers by loading to porous granules. Carbon nanotubes (CNTs) are being pursued as an alternative for activated carbon since they deal with the efficient removal of both chemical and metal pollutants from water. The cost-effective nanosheets of graphene oxides have also emerged as another promising nonabsorbent for metal and organic pollutants. Nanomaterials synthesized from metal oxides (TiO2) are promising, effective, and affordable adsorbents and have shown profound efficiency in the degradation of a wide array of water pollutants such as organochlorine, halogenated herbicides, azo dyes, nitro-­aromatics, and so forth (Ahmed et al. 2014). A good number of nanomaterials like nano-Ag, nano-ZnO, nano-TiO2, nano-­ Ce2O4, CNTs, and fullerenes possess the strong antimicrobial potential and can be used for point-of-use water disinfection. Such nanomaterials inactivate pathogenic microbes by discharging toxic metal ions (e.g., Ag+ and Zn2+) or reactive oxygen species (ROS) resulting in membrane perturbation with minimal fewer tendencies to create harmful disinfection by-products. Carbon nanotubes and other carbon-­ based nanomaterials (e.g., graphite, graphite oxides) are used in filters due to their fibrous structure, good conductivity, and excellent antibacterial abilities (Khin et al. 2012). Another strategy employs sunlight and nano-photocatalysts to break down organic pollutants and inactivation of pathogens (Li et  al. 2014). Fullerenes, CNTs, and TiO2 are highly photosensitive materials and can generate ROS (e.g., HO., 1O2) under the influence of UV-A irradiation. Upon activation by visible light, amino-­fullerenes and fullerol generate reactive oxygen species which is highly specific to pollutants and thereby results in water decontamination of water. A critical feature of integrated water purification and reuse paradigm is membrane technology. The introduction of nanoscale features and nanomaterials into membranes provides many persuasive possibilities, including high selectivity and antifouling capabilities. Membranes and nano-mesh remove a wide variety of

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contaminants from brackishness, sea, and wastewater by providing a pore-sizedependent physical barrier. The three membrane nanotechnologies such as thinfilm nanocomposite (TFNC), aligned CNTs, and biomimetic membranes have demonstrated great potential in mitigating the challenges associated with water filtration and purification (Hoek et al. 2014). Nanofiltration membranes possess exclusive charge-dependent mechanisms which facilitate segregation of various ultra-small particles from the aqueous phase with tremendous accuracy. Another remarkable application of nanomaterials in water treatment, storage, and distribution system is fouling mitigation and control of membranes as well as other membranes. Antimicrobial nanomaterials (nano-Ag, nano-ZnO, nano-TiO2, nano-Ce2O4, CNTs, and fullerenes) along with photocatalytic nanomaterials have been introduced into the polymeric membranes to enhance resistance against fouling (Li et al. 2008; Khin et al. 2012). 2.7.2 Desalination Given the inadequate availability of freshwater both above and below the ground, the desalination of seawater offers a great opportunity to convert unusable saline water to freshwater. The conventional process of desalination is based on reverse osmosis (RO) which is economically not a viable choice owing to high energy requirements and infrastructure costs. Many innovations have been explored as a possible replacement for conventional RO membranes in the desalination process. The advent of nanotechnology offers new avenues to advance water desalination approaches. Carbon nanotubes, silica, zeolites, and graphene with high permeabilities are emerging nanomaterials with huge potential to overcome the sustainability issues of present membrane desalination techniques. The frictionless CNT channels with precisely regulated pores could concurrently facilitate the faster mobility of water molecules and present a remarkable ability to reject salt ions. Likewise, nanopores of graphene monolayers could also facilitate rapid water flow that exceeds that of polymer-based RO membranes. Recent studies have shown that graphene oxide membrane flux has ten times better efficiency than those of commercially available nanofiltration membranes. Biomimetic and bioinspired membranes have recently been perceived as a leading material with efficient and cost-effective avenues for membrane desalination. Significant research over the years has demonstrated the fascinating properties of aquaporins (AQPs) based on nanocomposite membranes. The amalgamation of AQP into the polymer vesicles by surface imprinting approaches could address the fragility of biomimetic bilayers while retaining the outstanding sodium and magnesium salt refusal and quick transport capabilities. Hence, the integration of nanotechnology with membrane technology has managed to bring innovative developments in water desalination (Humplik et al. 2011; Ahmed et al. 2014; Goh et al. 2016).

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2.8 Soil Remediation Land degradation represents a serious threat to agriculture that adversely affects soil functions and productivity. Agricultural land is being ruined due to the excessive and indiscriminate use of agrochemicals like heavy metals, fertilizers, pesticides, and herbicides. Approximately, 30% of the land is either degraded or polluted, with the degree of degradation rising sequentially (Abhilash et al. 2013). The soil pollutants such as heavy metals, pesticides, and POPs (persistent organic pollutants) diminish soil fertility, make it unfavorable for crop production, and consequently lead to great economic losses. Moreover, these pollutants withstand environmentally and bioaccumulate as they go up the food chain and decomposition in the environment (Gavrilescu 2009; Lu et al. 2015). Human beings are exposed to soil toxicity directly by consuming plants, or these pollutants can enter into the human body via the food chain, resulting in severe consequences for human health and life. As a result, many of the polluted and degraded farmlands are abandoned as inappropriate for crop production, triggering huge losses to agricultural output. Nanotechnology which is rapidly evolving has been perceived as offering innovative solutions to such global soil conservation hurdles. Nanotechnologybased approaches offer cost-effective advantages over conventional chemical and physical remediation strategies. Therefore, substantial efforts have been made toward the development of novel materials for soil detoxification. Nanomaterials’ unique properties and efficacy make them highly feasible for the soil remediation, as they possess a high surface area to volume ratio, which usually results in higher sensitivity. The different applications of nanomaterials for soil cleanup involved (a) nanomaterials for converting heavy metals to their lesser toxic forms, (b) nanomaterials for the degradation of pesticides and persistent organic pollutants (POPs), (c) nano-­sensors for the detection of pesticide residue, and (d) nanomaterialbased bioremediation of soil. Inorganic (zerovalent iron NPs (nZVI), AgNPs, AuNPs, bimetallic NPs, TiO2 NP, titanate nanotubes (TNTs), etc.), carbonaceous (fullerene, multi-­walled nanotubes (MWCNTs), graphene, etc.), and polymeric nanomaterials are among the various materials that have been effectively used for soil remediation (Pan and Xing 2012; Cai et al. 2019). Due to their size and unique properties, these nanomaterials possess high surface area; thus larger sites of sorption render them excellent adsorbents (Khin et  al. 2012; Gong et  al. 2018). Metal- or metal oxide-­based nanomaterials are extremely effective adsorbents and are widely used for soil remediation. Several other important features of these nanomaterials include modification at lower temperature levels, interparticle diffusion distance, highly configurable pore size, and unique chemical structures (Tang et al. 2014). Such features make them fascinating catalysts that help both the chemical reduction process and catalysis to alleviate the level of pollutants. TiO2 are photosensitive, consequently used for their ability to remove organic pollutants often from various media including soil. Ag-doped TiO2 nanofibers showed increased photodegradation ability than TiO2 nanofibers. nZVI has been successfully used to degrade dichlorodiphenyltrichloroethane (DDT) and its

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metabolites, hexavalent chromium – Cr(VI) – Pb, and Zn from the contaminated soils due to its high surface area, high reactivity, and reducing ability. Carbon-based nanomaterials have also been used to remediate soils through photocatalytic methods. Graphene oxide (GO) has also shown catalytic capabilities toward various pollutants including volatile organic compounds and heavy metals. Furthermore, oxidized CNTs can also be good Cd2+ adsorbents and have a great role to play in environmental reclamation. In addition, various polymeric nanomaterials (such as amphiphilic polyurethane NPs) have been synthesized and characterized for the remediation of polynuclear aromatic hydrocarbons (PAHs) from soils and therefore play an important role in environmental remediation. Therefore, nanomaterials have shown great promise in on-site remediation of contaminated soils on a large scale, thereby reducing the need for transportation, treatment, and disposal after remediation. This makes nano-remediation a less time-consuming and cost-effective approach for soil remediation (Jiang et al. 2018; Cai et al. 2019).

3 Key Challenges Notwithstanding the enticing development of nanotechnology in a variety of disciplines, its agricultural applications were not translated to achieve growing international desires predominantly due to concerns about biosafety and shallow awareness. Some of the key challenges associated with the application of agricultural nanotechnology are discussed in the nest sections.

3.1 Toxicity Although nanotechnology has exciting potential to be extensively used in all areas of agriculture, its novelty and speed create instability about the long-term effects of nanoparticles on the environment and human health (Miralles et al. 2012; Gardea-­ Torresdey et al. 2014). The use of nanomaterials in the form of nano-pesticides and nano-fertilizers acts as an important gateway that can pollute the food chain, since plants are interacting closely with soil, water, and the environment, and thereby results in nanotoxicity (Kim et al. 2018). Different approaches have been suggested for controlling toxicity and avoiding contamination of the food chain, including safer and more efficient use of nanomaterials, illustrating the interactions, fate, and toxicity of these nanostructures in the environment (Mishra et al. 2017). The studies on the toxic effects of these nanomaterials are very important because of the increasing application of various nanomaterials in the agricultural and food sector industries. This will enable us to comprehend the real impacts of nano-chemical usage and helps to alleviate toxicity, therefore making it a sustainable approach (Kim et al. 2018).

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3.2 Risk Assessment Risk assessment of the effects of agrochemicals on humans is not just an easy process due to the wide range of substances used in agriculture, disparities in exposure doses, and geographic and meteorological conditions of agricultural locations where these agrochemicals have been applied (Bolognesi 2003; Pastor et al. 2003; Damalas and Eleftherohorinos 2011). The recent trend in excessive use of nanomaterials into the agricultural system has raised specific concerns regarding their safety and unintended consequences for human environmental health. Therefore, the risk assessment and risk reduction variables associated with the application of nanotechnology in the agricultural warrant special attention and ought to be thoroughly analyzed at the earliest. Nano-specific risk analysis is a herculean task as the assumptions used to understand the risks of traditional agrochemicals, along with the test methods, modeling paradigms for complex environmental behavior, and possible human use, may not be suitable for nanomaterials (Damalas and Eleftherohorinos 2011). Also, assessing internal exposure to nanomaterials and their initial biological changes could be significant in understanding the relationship between nanomaterials and toxicity, and it appears to be an important factor for comprehensive risk assessment. There have been severe environmental issues like dichlorodiphenyltrichloroethane (DDT), carbamates, pyrethroids, or neonicotinoids in recent human history, which was forced to happen due to lack of a systematic assessment of environmental risks in advance (Aktar et al. 2009; Nicolopoulou-Stamati et al. 2016). In the absence of quantitative information, a qualitative framework for the risk assessment of nanotoxicity and exposure is very important, to identify and manage risks associated with nanotechnology that are already in use and those to be developed in near future. A credible and detailed risk assessment before the widespread implementation of nanotechnology-­based applications is the first line of defense for ensuring environmental safety and human health. In this perspective, toxicology is required in identifying risks of nanomaterials and their fate in the environment and simultaneously evaluating their physicochemical features that affect nanomaterial toxicity.

3.3 Public Awareness and Acceptance As an evolving technology, public expectations and awareness of nanotechnology are yet another critical issue that will influence the realization of nanotechnology strategies in the field of agriculture, as in the case of genetically modified (GM) crops (Scheufele and Lewenstein 2005; Bennett and Radford 2017). Public understanding and acceptance are critical elements in progressing nanotechnology, and this innovation’s development is complementary to the socioeconomic impacts. Public awareness of nanotechnology’s benefits and challenges will contribute to greater acceptance of this new technology. A very well-developed communication

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strategy to sensitize the buyers toward the facts and risks of nanotechnology needs to be planned meticulously. This is very significant to ensure that adequate knowledge is accessible on the issues and advantages of nanotechnology in agricultural-­ related activities, safeguard of the environment, protection of general public, and workforce from both unrealistic hopes and social stigma associated with these technological innovations (Scheufele and Lewenstein 2005; Bennett and Radford 2017). Highlighting the latest information about both risks and benefits, in a timely and transparent manner, will have a positive impact on the nanotechnology innovations and at the same time will reduce the likelihood of polarized public discussions that turns on speculations (Parisi et al. 2015).

3.4 Regulatory Policies As there are severe uncertainties pertaining to the nanoparticles and their applications, the regulatory procedures must be well defined to avoid unguarded synthesis and application of nanomaterials in the environment, agriculture, and food chain. Regulation plays an important and consequential role in the implication of nanotechnology as well as in product management. It also represents formal sources of public understanding and information and references. The existing regulatory policies related to specific strategies of nanotechnology in any area are inadequate and share a similar framework worldwide which covers all the facets of applications, threats, safety concerns, and disposals. When it comes to specific nanomaterials, it needs a thorough assessment and revision of existing policies. Regulatory policy framing, nevertheless, is challenging considering the scale of agricultural practices, which include numerous organisms (plants, pets, and humans), a myriad of microbiomes (soil, plants), climatic variations, soil morphology and compositions, factors in nanomaterial designs, and social interaction. It is imperative to highlight that the nanoparticle-based products are not flourishing due to the instability of regulatory frameworks and differing opinions across the globe; therefore, they face challenges in reaching the market.

4 Future Perspectives Global food production continues to experience from several issues and challenges such as population explosion, climate change, shrinking landscape, depletion of resources, and environmental pollution and pandemics. In this context, the existing farming practices need to be strengthened in order to improve productivity under adverse conditions by alternative novel technologies and developments. Nanotechnology embraces a thrilling and broad scientific frontier that is progressing rapidly and spreading its wings in almost all dimensions of agricultural practices. This advanced technology has not only changed the dynamics of traditional

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agricultural approaches by making them more innovative and achieved improved productivity but also greatly contributed to the development of new tools and methods, novel products, efficient packaging and storage strategies, and enhanced efficiency of its allied fields. However, the applications of nanotechnology are still in its infancy, and in the years to come, agri-food nanotechnology is expected to be an economic driving force in achieving and sustaining global food security and safety. Nanotechnological applications in agriculture are in tumultuous evolution and will continue to advance as the shortfalls in the existing approaches are being identified as the prime targets advancements. Further research studies on the design and development of new stable bio-­ composite nanomaterials with better dispersion, high selectivity, less toxicity, higher photoreactivity, and well-understood toxicokinetic and toxicodynamic are required for long-term solutions for sustainable agricultural production. Several other major areas need more attention in future research, including the development of biochemical sensors, intelligent feed, reduction in postharvest losses, comprehensive approach for deduction of pollutants, enhancement of food quality, the bioavailability of nutrients, and food packaging and coding (Rodrigues et al. 2017). There is a growing need for active public debates on nanotechnology’s benefits and challenges. Uncertainty and undesirable perception related to nanotechnological approaches ought to be treated seriously. Information sharing through outreach programs is also important to aggressively endorse this technology and go beyond negative perception about the nano-enabled materials. Similarly, the country government’s food administration department must endorse the regulatory framework to develop safe and appropriate marketing of nano-agricultural products. Therefore, comprehensive efforts need to be made to forward and develop future research focused on identified knowledge gaps. It is not too late before technology would be the central dimension in ousting food insecurity in the modern era by introducing sustainable agricultural production.

5 Concluding Remarks Nanotechnology, being the novel frontiers of the twenty-first century, promises to increase food production sustainably and improve the quality of life. The introduction of nanomaterials and their applications in different domains of agriculture have significantly transformed canvass of agriculture by innovations, rapid growth, and enormity to satisfy global food demands. However, we are still at the very initial phase of applicative aspects of this field, and it is necessary to address several concerns with great scientific or practical importance. To overcome the existing obstacles, safe-by-design techniques, green chemistry principles of new technologies, awareness about the benefits and challenges of nanotechnology applications, and support of regulatory policies are very crucial for better exploitation of this technology and visualizing the dream of sustainable agriculture. Hence, improved research endeavors, ably supported by public funding, need to work to remove the potential

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bottlenecks of nanotechnology applications by developing environmentally safe nano-agricultural systems. Acknowledgments  Mir Zahoor Gul (MZG) acknowledges the financial support in the form of research associateship from the Council of Scientific and Industrial Research, New Delhi, India (vide award letter No. 09/132(0883)/2019-EMR-I). The author MZG is also thankful to Dr. Karuna Rupula, Associate Professor & Head, Department of Biochemistry, Osmania University, for her encouragement and support.

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Chapter 2

Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry Murugaiyan Sinduja, Joseph Ezra John, R. Suganthi, S. Ragul, B. Balaganesh, K. Mathiyarasi, P. Kalpana, and V. Sathya Abstract  Biological treatment is a method that employ to degrade organic waste. Because of their metabolic activity, microorganisms can survive in every severe situation on Earth. Bioremediation is an all-inclusive action of microorganisms in the destruction, immobilisation or detoxification of various chemical wastes and harmful elements from the environment. Because of their specialised use, all bioreThe original version of this chapter was revised. The correction to this chapter is available at https://doi.org/10.1007/978-3-031-32967-8_19 M. Sinduja (*) Environmental Science, National Agro Foundation, Chennai, Tamil Nadu, India J. E. John Environmental Science, Tamil Nadu Agricultural University, Coimbatore, India Tamil Nadu Climate Change Mission, Department of Environment and Climate Change, Tamil Nadu, Chennai, India R. Suganthi Environmental Science, Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore, India S. Ragul Plant Breeding and Genetics, Plant Variety Examination Research Associate (PVERA), PPV&FRA, Ministry of Agriculture, New Delhi, India B. Balaganesh Soil Sciences, Department of Agriculture, Karunya Institute of Technology and Sciences, Coimbatore, India K. Mathiyarasi Division of Environment Science, Indian Agriculture Research Institute, New Delhi, India P. Kalpana Soil Sciences, National Agro Foundation, Research & Development Centre, Anna University Taramani Campus, Chennai, Tamil Nadu, India e-mail: [email protected] V. Sathya Environmental Science, Tamil Nadu Pollution Control Board, Chennai, Tamil Nadu, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023, Corrected Publication 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_2

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mediation strategies have their own pros and cons to choose based on the requirement. Increased waste products and depleting natural resources have shifted human focus to efficient green and clear production systems. Understanding the mechanisms of degradation, is critical to eliminating the need for additional pretreatment of lignocellulosic chemicals in the waste mixture and facilitating the commercialisation of organic waste technology. In addition to that, health of the soil and a measure of a complex series of biological, chemical and physical interactions driven by the nature of organic waste added to it must be explored to successfully utilize the technology. Effective microorganisms boost the beneficial microbial population and improve soil chemical and physical properties, allowing for long-term crop production. This chapter discusses the convergence of microbial technology, as well as the functions of microbiota in attaining sustainability in organic waste degradation and utilisation in the agricultural business. Keywords  Microbiota · Immobilisation · Degradation · Organic waste · Sustainable agriculture

1 Introduction Sustainability in agriculture refers to the long-term preservation of soil productivity through the use of natural resources without harming the environment. The maintenance and protection of natural resources, particularly a diversified and functional microbial community in the soil, is critical for sustainable agriculture (Umesha et al. 2018). Environmentalists are beginning to adopt integrated soil management, which emphasises the management of ecosystem functioning through nutrient cycling, waste management and soil microbial diversity management (Naeem et al. 2002). Given a precise set of environmental and cultural conditions, microorganisms’ distinctiveness, as well as their frequently unpredictable nature and biosynthetic capabilities, has made them plausible candidates for tackling exceptionally challenging challenges (Wu et al. 2012). Sustainable agriculture is a farming method based on ecological principles, which is the study of the interactions between organisms and their environments (Rastegari et al. 2020). Nonetheless, despite significant success in applying microbial technologies to different agricultural and environmental challenges in recent years, they have not been universally acknowledged by the scientific community since it is sometimes difficult to reliably recreate their beneficial effects (Trivedi et  al. 2021). The United Nations established the 2030 Sustainable Development Goals in January 2016 to achieve environmental, social and economic growth through green approaches and cleaner industrial technology (Akinsemolu 2018). A wide range of microbial enzymes are involved in the biodegradation of an organic substance, changing both manmade and natural hydrocarbons into intermediate products that may be less dangerous than the parent chemicals. Because biodegradation is a step-by-step process, the intermediate molecules are transformed into carbon dioxide, water and soluble inorganic chemicals through further processing or degradation. Indigenous microorganisms are a type of intrinsic microbial consortia that lives in the soil and on the surfaces of all living things,

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inside and out, and have the capacity to biodegrade, fix nitrogen and improve soil fertility, act as phosphate solubilisers and promote plant growth (Kumar et al. 2018). Without these bacteria, life on our vibrant planet would be bleak and depressing for the survival of the human species. Microorganisms are the most diverse and numerous natural resources, but due to their smaller size, they are being overlooked. Recently, efforts have been made to incorporate microbial diversity into soil classification and management programmes (Rao and Patra 2009). The organic fraction of solid waste has been identified as a significant resource capable of being transformed into useful products by microbial-mediated transformations (Damtie et al. 2021). There are other strategies for treating organic waste, but anaerobic digestion appears to be a promising strategy. The anaerobic treatment of solid organic waste is less common than the aerobic procedure, owing to the longer time required for biostabilisation (Hakeem et al. 2021; Fernandez et al. 2022). The mechanism is also vulnerable to large quantities of free ammonia produced by anaerobic breakdown of nitrogen-rich protein components. The specific activity of methanogenic bacteria was discovered to decrease with increasing ammonia concentrations (Lee et  al. 2019). The chemical content and structure of lignocellulosic materials slow the biodegradation rate of solid organic waste. Hydrolysis of complex organic materials to soluble molecules has been shown to be the rate-limiting step in anaerobic processes for wastes with a high solid content (Wang and Wang 2018). As a result, various physical, chemical and enzymatic pretreatments are necessary to increase substrate solubility and speed of solid organic waste biodegradation. Nonetheless, even with this limited data, considerable changes in the diversity of essential microorganisms engaged in nutrient conversions, antibiosis, plant disease control and growth promotion occur in response to various soil management strategies used in intensive agriculture (Bonanomi et  al. 2018; Dar et  al. 2022). This chapter will describe the role of bacteria in the long-term breakdown of organic waste and its application in agriculture.

2 Organic Waste Generation and Its Sources Human development and growth depend greatly on agriculture. This is a result of the production of fibre and food, both of which are essential to human life on Earth. However, the production of a lot of wastes like animal manure and crop residues is also a part of agriculture. These wastes are typically difficult to dispose of and frequently degrade the quality of the environment. Hence, they are dumped on open fields or burned in the majority of the regions across the world, while those left on the field are subject to wetting and dry processes that may occasionally result in anaerobic conditions leading to bad odour and facilitate the spread of epidemic diseases (Lokeshwari and Swamy 2010). According to Aiyelari et al. (2011), burning agricultural wastes could have a negative impact on both human health and the environment due to the release of greenhouse gases into the atmosphere that could have an impact on global warming. The effects of this phenomenon include

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potential for chaotic weather patterns, food insecurity, starvation and malnutrition (Preston and Leng 1989). In recent years, agricultural production has advanced beyond the emphasis on high-yield production to improved food quality, human nutrition and environmental quality through practices that enhance food security while advancing environmental health and sound ecology. Rodale (2011) suggested that the goal should be an agricultural management system that has the ability to preserve or improve soil quality and the environment rather than concentrating on higher yields, which will eventually exhaust soil nutrients. The majority of agricultural wastes, according to Lokeshwari and Swamy (2010), contain biodegradable hemicellulose and cellulose materials, which when decomposed improve soil qualities and supply crops with nutrients. They can be processed properly to become marketable materials or used as a source of energy, bedding, manure, mulch, compost, organic matter or plant nutrients. With the expansion of the population, waste generation is rising daily, which has an immediate impact on the environment and the economy. The agricultural and municipal solid waste (MSW) sectors in India contribute the most to waste production while its improper handling harms the environment and poses health risks. As a result, managing organic waste is crucial given the rising demand for energy. Agro-waste comes in a variety of forms depending on the source and accessibility in the environment. As a result, these wastes can be divided into four main generations according to their capacity to produce various products (ElMekawy et al. 2015): First generation  This group includes a variety of food crop classes, including sorghum, corn, rice and wheat. The direct use of these crops as a primary feedstock of interest is frequently linked to the production of energy and a variety of goods. The competition between this generation’s use in the production of fuel and food is one of its greatest problems. Production of fuel is thought to have a higher return on investment than that of food. Second generation  This generation typically consists of lignocellulosic wastes that can be used to produce bioenergy using various waste beneficiation techniques such as the following: 1. 2. 3. 4.

Sugarcane bagasse Wood chips Crop residues Organic waste

This kind of waste is linked to the removal of significant barriers present in first-­ generation biomass. Third generation  Microalgal biomass is used as a feedstock in energy source production systems. As a result, its cultivation can be accomplished with ease in lagoons and open ponds using wastewater that contains a nitrogen-rich agro-waste compound.

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Fourth generation  This kind of biomass is produced by metabolically modified organisms like bacteria, including algae produced as a result of cleaner disposal, or by emission control techniques like CO2 capture systems. This raises the generation’s value because it can be used to produce high-value goods with higher requirements for polymeric hydrocarbon content or other bioenergy products. According to the Solid Waste Rule (2016), waste should be divided into three different streams by the generator and stored in appropriate bins: domestic hazardous, biodegradable and non-biodegradable wastes. The Ministry of Urban Development (MUD) aimed at achieving sustainable municipal solid waste management (MSWM) system based on 3R principles, such as reduce, reuse and recycle, with appropriate systems of collection, segregation, processing, transportation and disposal with the introduction of the Solid Waste Rule (2016) of the Ministry of Environment, Forest and Climate Change (MoEF& CC). The MSWM system in India still does not fully follow every link in its chain. Only 21.45% of MSW is treated, and the remainder is still being dumped in landfills, according to the Swachh Bharat Mission (SBM) database and State-by-State status of implementation of various components under SBM (up to September 2016). As per the direction given by the local authorities from time to time, the segregated wastes should be given to the authorised waste pickers or waste collectors. Municipalities are primarily in charge of waste collection. However, one of the biggest issues is the segregation component. The majority of urban local bodies (ULBs) lack the resources, the capacity and the necessary action plan to implement and enforce the solid waste rule. After China, India is the second largest producer of paddy in the world. Currently, India produces around 130 million metric tonnes (MT) of rice straw and 98 million MT of paddy. Nowadays, on average 50% of rice straw is used as animal feed, and the other 50% is simply thrown away with other solid wastes. India also generates about 50 million MT of cane trash from its 350,000 MT of cane production, which has the potential to be used to make fuel with the right processing. Cane trash, which has no commercial use and is entirely burned to reduce volume, has a very high silica content. Other agricultural wastes are also available in India, including maize, cotton, millets, pulses, sunflower and other stalks, groundnut shells and coconut trash. Due to crop cycle and time constraints, farmers frequently burn large amounts of biomass, which increases haze, contributes to global warming and has a negative impact on the environment and human health. In India, MSW’s primary physical components are recyclable, compostable and inert. Around 40–60% of Indian MSW is biodegradable, 30–50% is inert waste and 10–30% is recyclable (Kumar et al. 2009). He also found that the nitrogen content of MSW is 0.64 ± 0.8%, the phosphorus content is 0.67 ± 0.15%, the potassium content is 0.68 ± 0.15% and the C/N ratio is 26 ± 5.

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3 Mechanisms of Microbial Degradation of Organic Wastes Bianchi (2011) stated that natural organic matter (NOM) is the planet’s greatest reactive source of reduced carbon (C), and the transformation and breakdown of NOM are of vital importance because of their effects on the global carbon cycle and ecosystem C flow (Heimann and Reichstein 2008). In a wide range of environments including soil, sediment, the ocean and freshwater, microorganisms are important mediators in the generation, mobilisation, transformation and storage of NOM (Xue et al. 2016). In the context of microbiology, “biodegradation” refers to the breakdown of all organic materials by living things, primarily bacteria, fungi, protozoa and other organisms. By definition, biodegradation means “the transformation of a substance into new compounds through biochemical reactions or the actions of microorganisms such as bacteria”. Hazardous toxic pollutants are changed into less toxic or nontoxic materials through this naturally usual process. Secondary metabolites, intermediate molecules or any breakdown products from one species can feed another, serve as a source of energy and carbon for that organism and continue the process of decomposing remaining organic matter (Eskander and Saleh 2017). As nearly every waste product created by other living things is degraded or eliminated with the aid of some of its enzymes, microorganisms play a crucial role in biogeochemical cycling and help recycle nutrients. Therefore, waste does not exist from a microbiological standpoint (Eskander and Saleh 2017). Organic wastes are substances that may biodegrade and are primarily produced by both plants and animals. Fruit waste, food waste, grass clippings, cow manure, human waste, abattoir waste, paper trash and agricultural leftovers are some types of organic waste. These wastes are frequently disposed of by landfill disposal, incineration or composting. As a result of varied disposal methods, greenhouse gases including methane and carbon dioxide are frequently produced. The disposal techniques must be closely watched because poor disposal practices can cause serious environmental issues like drain clogging, insect infestations, air pollution in the vicinity of the landfill site, leachate contamination of nearby reservoirs and frequently burning in the landfill site. Microorganisms use different pathways for degrading organic wastes. Depending on the type of microorganisms, either they may consume the entire organic molecule in a process called “ultimate biodegradation” or they will consume only a portion of it, destroying the full parent component. During the energy-producing phase of metabolic activity, oxygen is used, which causes the “mineralisation” process, which immediately produces carbon dioxide, water and mineral salts.

4 Types of Biodegradations A biochemical process, “biodegradation”, is mediated by microorganisms. Based on microbial involvement and respiration behaviour, biodegradation is classified as aerobic biodegradation and anaerobic biodegradation. Aerobic biodegradation

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refers to the process by which microbes convert complex organic substances to simpler ones in the presence of oxygen, while in the latter anaerobic process, the process occurs in the absence of oxygen. An electron acceptor, which is itself reduced, often oxidises an organic substance (which loses electrons) (which gains electrons). Oxygen serves as the electron acceptor in an aerobic environment or a poisonous environment. Aerobic respiration is defined as the oxidation of organic substances along with the reduction of molecular oxygen. Microorganisms can utilise organic compounds or inorganic anions as alternate electron acceptors in anaerobic environments (the absence of oxygen). Anaerobic biodegradation can occur under fermentative, denitrifying, iron-reducing, sulphate-reducing or methanogenic conditions.

4.1 Aerobic Biodegradation of Organic Wastes Composting is indeed the technique used to turn organic wastes into valuable products via the aerobic route. It is defined as the biological metabolic action of microorganisms such as bacteria, fungi and actinomycetes under ideal circumstances over some time to produce a stable end product. The final output is called compost. The stoichiometries involved in the composting process are as given below.

Liwarska-Bizukojc and Ledakowicz (2003) The processes involved during the waste stabilisation stage are hydrolysis, oxidation, biomass synthesis and endogenous respiration (Ramana and Singh 2000). The initial process is hydrolysis, which is the breakdown of complex substrates like sugars and amino acids by enzymes produced by microbes like bacteria. Oxidation reactions are carried out to meet the energy requirements of the newly generated microorganisms. Oxygen is the terminal electron acceptor in the aerobic process. Subsequently, microbial proliferation occurs and leads to biomass synthesis. 4.1.1 Phases of Aerobic Composting The composting process is characterised by rapid decomposition in the initial stage leading to a temperature rise followed by slower decay of the remaining substrates. The initial phase is dominated by mesophilic organisms which thrive in the temperature range of 20–40  °C.  The mesophilic stage is dominated by bacteria and fungi. They encourage organic decomposition during composting by releasing several substrate-based hydrolytic extracellular enzymes like cellulases, xylanases, amylases, ligninase and laccase that break down the complexly structured molecules (i.e. plant polymers, cellulose, hemicellulose and lignin) and produce

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water-­soluble compounds (Echeverria et al. 2012). These reactions supply the substrate for biomass generation required for further stages of composting. The composting pile’s temperature rises as a result of the mesophilic organisms’ tendency to emit heat during their metabolic processes. The mesophilic species die as a result of the temperature increase, and a new population of creatures known as thermophilic organisms takes their place in the compost pile that can adapt to higher temperatures. They can endure temperatures greater than 40 °C. The pasteurisation and stability of the compost are aided by this step, which may witness temperatures reaching 65 °C. When temperatures naturally climb to 55 °C, harmful pathogens are killed (Ravindran and Sekaran 2010), and weed seeds and pathogens are destroyed (Zhang and Sun 2014) if high temperatures persist for 3 days, helping to produce a higher-quality product. Complex substrates, including lignin, lipids, cellulose and hemicellulose complexes, break down during this phase. Due to nutrient depletion in the medium, bacteria begin to eat their protoplasm through endogenous respiration. Cells die and lyse as a result of this event. As a result, between 5% and 80% of the components of the cell are oxidised. In the end, the population of thermophiles decreases with the decrease in the availability of substrates, the mesophilic microbial community once again proliferates and this phase of composting is called the curing or maturation phase. A reduced temperature and a decline in microbial activity mark the cooling phase. Mesophilic microorganisms recolonise the compost pile, degrading the remaining sugars, cellulose and hemicellulose to produce humic-­ like compounds (Albrecht et  al. 2010). The rate of organic matter breakdown declines after that, while the rate of humification and polymerisation of the organic compounds rises. This ensures the effective production of an amorphous dark-­ brown humus-rich material that may be directly applied to plants.

4.2 Anaerobic Biodegradation of Organic Wastes Anaerobic digestion (AD) is a multiphase microbial-driven complicated biochemical process that is widely used to generate biomethane. The process is the same as aerobic composting, but the difference is that here anaerobes play the major role and convert organic wastes to methane and carbon dioxide. AD involves four main phases hydrolysis, acidogenesis, acetogenesis and methanogenesis. 4.2.1 Steps Involved in the Anaerobic Process The hydrolysis phase involves breaking down the complex organic molecules like polysaccharides, proteins and lipids to low molecular weight and simpler water-­ soluble monomers like glucose, amino acids and fatty acids by the action of hydrolytic enzymes produced by facultative anaerobic bacteria. The first step is very crucial as more complex materials are first broken down. Ventorino et  al. (2018) stated that fermentative bacteria make use of the extracellular enzymes connected to

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their cell wall, including cellulase, protease and lipase. The most prevalent phyla of bacteria include Firmicutes, Actinobacteria, Bacteroidetes, Chloroflexi and Proteobacteria, which are reported to be the primary hydrolytic fermentative bacteria implicated in the AD process (Luo et al. 2018; Yadav and Vivekanand 2021). Streptococcus and Enterobacter are the principal taxa involved in hydrolysis, with Bacteroides, Lactobacillus, Propionibacterium, Sphingomonas, Sporobacterium and Bifidobacterium also participating (Yadav et al. 2022).



 C6 H10 O5 n  6H 2 O  C6 H12 O6  polysaccharides   glucose 

Then the fermentative microbes termed acidogenic bacteria produce volatile fatty acids (VFAs) like acetic acid, propionic acid and formic acid from the monomers along with the production of H2S, CO2 and NH3 (Dhanya et al. 2020). Bacteroidetes, Firmicutes and Clostridium are the dominant phyla in the process while the Ruminococcus, Paenibacillus and Clostridium are the most active genera in the acidogenesis phase. Out of all phases in AD, acidogenesis is the most important phase. The formation of VFA follows many different pathways depending upon the end product, but pyruvate plays a major role in the formation of each VFA. These metabolic pathways are classified as acetate-ethanol, propionate, butyrate, mixed-­acid and lactategenerating metabolic pathways based on the end product (Zhou et al. 2018). Only formate, acetate and H2/CO2 may be directly absorbed by methanogens as a substrate for methane synthesis. Propionate, butyrate, ethanol, butanol, lactate and other products must be oxidised syntrophic acetogens into formate, acetate and H2/CO2. The fatty acids produced from the acidogenesis phase are converted to acetate, hydrogen and CO2 by acetogenic bacteria. The phase proceeds with two types of organisms, namely, acetogenic bacteria, that produces acetate from VFAs, and the other group of organisms called acetate-degrading organisms, which oxidise the acetate to produce H2 and CO2. The final step is the conversion of acetate or H2 to methane by methaneforming microorganisms belonging to archaea. The acetoclastic methanogens convert acetate to CH4, while another group of methanogens called hydrogenotrophic methanogens reduce CO2 and H2 to CH4.

CH 3 COOH  CH 4  CO2  acetoclastic methanogenesis 



CO2  4H 2  CH 4  3H 2 O  hydrogenotrophic methanogenesis 



Methanosaeta, Methanosarcina, Methanococcoides, Methanosalsus and Methanogenium are some of the predominant genera involved in AD (Kong et al. 2019; Yadav and Vivekanand 2021).

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5 Microbial Intervention in the Breakdown of Organic Wastes Sustainable degradation stresses the importance of the development of new technologies for the environmental management of organic waste due to the escalating anthropogenic activities. Microbes, indigenous as well as inoculated, play a prominent role in the degradation of organic wastes either by (1) aerobic or (2) anaerobic method of degradation (Fig. 2.1 and 2.2). Oxygen is the key factor in controlling the nature and rate of degradation. Microbes are responsible for mineralisation of plant nutrients and depolymerisation of complex molecules by extracellular enzymes along with heat generation (Bernardi et al. 2018; Holman et al. 2016; Kutu et al. 2019). Recycling of organic wastes results in the generation of organic manure,

Fig. 2.1  Mechanisms involved in organic waste degradation

Anaerobic degradation

Methane CO2

Aerobic degradation

Compost , CO2 Heat, H2O

Organic waste

Fig. 2.2  Basic schema of microbial breakdown of organic wastes

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animal feed, liquid fertiliser, biogas, peat alternatives, etc. Microorganisms such as Bacillus, Pseudomonas, Flavobacterium, Mycobacterium, Xanthobacter, Nocardia, Trichoderma, Phanerochaete, Cyanobacteria and many more are actively involved in the degradation of organic waste (Hassan and Sabreena 2022). Microbes are either applied in pure or mixed cultures to accelerate the rate of disintegration. Mostly multiple consortiums are inoculated to accelerate the maturation which is effective (Duan et al. 2020; Abdel-Rahman et al. 2016). In some cases, mixed cultures resulted in unfavourable results in contrast to other findings. For instance, commercial inoculants such as EM and LDD1 were used against food scraps with dry leaves which denied the introduction of mixed consortia (Karnchanawong and Nissaikla 2014). Time of inoculation also plays a dividend role in decomposition. Mostly, cultures are introduced at the initial stage. Some researchers reported the inoculation at different phases such as cooling phase to reduce the effect of high temperatures (Zhao et al. 2016), inoculation of trichoderma at maturation phase and suppressed fusarium wilt (Bernal-Vicente et al. 2012) in case of composting. Microbial enzymes such as cellulose, hemicellulase, amylase and laccase act on the complex molecules rich in lignin, cellulose and hemicelluloses which also inhibit the growth of fungal pathogens.

5.1 Aerobic Degradation Bioconversion of organic wastes with oxygen is termed to be aerobic degradation. This group of microorganisms utilise oxygen in order to feed nutrients from the organic matter developing into cell protoplasm (Cadena et  al. 2009; Mehta and Sirari 2018). Forest is a best example for aerobic degradation where leaf litters and other plant and animal residues get converted into stable organic matter. In most of the waste treatment processes, aerobic degradation is used as a pretreatment process followed by anaerobic digestion. The major advantages are fast degradation, reduction in volume of wastes, detoxification of organic wastes, no odour, no emission of greenhouse gases and other volatile organic compounds (Gómez et  al. 2012). Table 2.1 enlists some of the microbes associated with the aerobic breakdown of different organic wastes. In general, organic waste comprises of 40–60% protein, 25–50% carbohydrates and 10% fats and oils. Basic biochemical reactions in the breakdown process were hydrolysis, oxidation, cell synthesis and biomass generation followed by endogenous respiration (Ramana and Singh 2000). A massive breakthrough in aerobic degradation is greenhouse gas emission reduction. For instance, at a swine farm in the USA, replacing lagoon technology with aerobic technique resulted in 96.9% reduction in greenhouse gas emission (methane from anaerobic decomposition and nitrous oxide from handling and storage) from 4972 tonnes of carbon dioxide equivalent to 153 carbon dioxide equivalents (Vanotti et al. 2008).

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Table 2.1  Microbes in aerobic degradation of organic wastes Microorganism Bacillus, Brevibacillus, Paenibacillus, Pseudomonas and Klebsiella Bacillus paralicheniformis and Bacillus velezensis Bacillus and Halobacillus Aspergillus and Penicillium Terrisporobacter Enterococcus, Pseudomonas and Idiomarina Trichoderma, Phanerochaete, Aspergillus, Penicillium and Azotobacter

Substrate/type of waste Food waste

References Ren et al. (2021) Msarah et al. (2020)

Food waste

Roslan et al. (2021)

Farm and food waste

Chander et al. (2018)

Wood chips

Jia et al. (2021)

Piggery waste Food and sewage sludge

Wei et al. (2022) Chen et al. (2021)

Rice straw and cattle manure

Greff et al. (2022)

5.2 Anaerobic Degradation Anaerobic degradation involves the conversion of complex molecules into simpler products under anoxic conditions. It tends to benefit us with energy-rich products rather than aerobic degradation. Similar to aerobic degradation, anaerobic microbes feed on organic wastes without oxygen and develop their cell protoplasm (Cayuela et al. 2012). Anaerobic digestion mainly involves four stages (1) hydrolysis, breakdown of polysaccharides to monosaccharides with the aid of hydrolytic bacteria and its enzymes (xylanase, cellulose, glucosidase, peptidase); (2) acidogenesis, sugars and amino acids to alcohols and ketones; (3) acetogenesis, alcohols to acetic acid; and (4) methanogenesis, generation of methane (Methanobacterium, Methanosarcina, Desulfovibrio, Methanococcus, Methanobrevibacter, Methanothrix and Methanospirillum). Table 2.2 enlists microbes in anaerobic decomposition of wastes into compost, biogas, biodiesel, enzyme recovery, liquid fertiliser, etc. Engineered microbial consortia are also encouraged for product generation. Jiang et al. (2020) developed an anaerobic coculture for butanol production from hemicelluloses by combining Clostridium acetobutylicum and Thermoanaerobacterium saccharolyticum. Coculture was developed from methanogen and anaerobic fungi, and performance was compared with native microbes (Gilmore et al. 2019). These technologies got the attention of scientific community, and several researches were being carried out to manage the waste into getting desired end product.

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Table 2.2  Microbes in anaerobic degradation of organic wastes Microorganism Pseudomonas aeruginosa and Klebsiella pneumoniae Bacillus thuringiensis, Brevibacillus borstelensis and Bacillus licheniformis Firmicutes, Bacteroidetes and Proteobacteria Rhizomucor Rhizopus and Fusarium Actinomyces, Bifidobacterium, Clostridium, Propionibacterium and Staphylococcus

Substrate/type of waste Waste cooking oil Food waste

References Sharma et al. (2022) Liu et al. (2018) Awasthi et al. (2018)

Wheat straw waste

Jin et al. (2022)

Orange peel and oatmeal Vegetable waste

Yang et al. (2015)

Sewage sludge

Cyprowski et al. (2018)

Sabater et al. (2020)

6 Utilisation of Value-Added Products from Sustainable Microbial Degradation in Agriculture The past few decades witnessed a soar in food production due to the advent of the green revolution. This boosted grain production and increased agrochemicals’ use to increase crop yield. Though there was an increase in food grain production, poverty and hunger could not be eradicated because of land degradation problems, deforestation, etc., to increase the agricultural land availability for feeding the rising human population. This, together with the usage of agrochemicals, exacerbated the concerns of deteriorating human health by contaminating neighbouring reservoirs and remaining in the soil for extended periods. In addition, the cost of those products went so high that marginal farmers could not afford them. As a result, the globe needs a cost-effective and eco-friendlier product that can preserve both the ecology and human health at the same time (Fig. 2.3). Thus, sustainable agriculture emerged as an alternative concept that is not only eco-friendly but also lowers the farmers’ expenditure on agriculture. It refers to agriculture’s ability to contribute to general well-being over time by producing enough food and other commodities and services in economically effective and successful, socially responsible and ecologically sound ways. This practice involves the combined use of agriculture and livestock practices in a way that reduces the need for external inputs, thereby increasing the health of the environment and consumers. It accounts for practices that manipulate the local natural processes like nutrient cycling and nitrogen fixation. Composting is one such practice that recycles the organic waste produced by the farm, thereby returning the nutrients to the soil.

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Time reduction in initial lag phase Enhance the degree of humification

Reduce the production cost

Beneficial microbes Enhances the properties of final product

Enzymes

Accelerates the rate of decomposition

Fig. 2.3  Significance of microbial degradation of organic wastes (Chi et  al. 2020; Fang et  al. 2019; Wang et al. 2019; Gou et al. 2017)

(i) Compost Compost is an ideal alternative solution for fertilisers as it has a great effect on microbial activity in the soil and its organic matter content (Garcia et  al. 2017). Healthy soil is when it contains higher microbial activities, and it is a key factor in nutrient recycling through enzymatic activities (Bünemann et  al. 2018; Li et  al. 2015). Compost application was found to be an effective method for enhancing the rhizosphere microbial activities of the soil, which also increases plant growth and yield (Sayara et al. 2020). This is because the compost slowly releases nutrients into the soil so that microbial growth can be sustained for longer periods. Also, the compost supplies microorganisms that are capable of transforming the complex substrates into nutrients. These microbes often form a framework in the soil for creating a natural immune system for the plant. Compost addition also improves the soil structure, decreases the bulk density and increases soil porosity, thereby increasing the exchange of gas and water transfer, reducing erosion and evaporation, increasing cation exchange capacity and facilitating improved drainage conditions. (ii) Biofertiliser Biofertilisers are live microbial inoculants that contain bacterial/microbial strains that are capable of fixing nitrogen, mobilising nutrients like phosphorus and

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improving plant health, drought and salt tolerance, etc. Biofertilisers can be grouped into various categories like nitrogen-fixing, phosphorus- or potassium-mobilising, zinc-­solubilising, microbial strains that promote iron or sulphur uptake and plant growth-­promoting rhizobacteria (Pathak et al. 2017). Rhizobium, blue-green algae (BGA), Azotobacter, etc., are nitrogen-fixing biofertilisers; Pseudomonas, Bacillus and arbuscular mycorrhiza (AM) fungi are examples of phosphorus-mobilising biofertilisers. Thiobacillus and Pseudomonas fluorescens are examples of sulphate and iron uptake biofertilisers, respectively. Nitrogen-fixing biofertilisers like Rhizobium can add up to 50–100 kgs of N/ha per year, and BGA can add up to 20–30 kgs of N/ ha per year (Asoegwu et al. 2020). Phosphate-mobilising or phosphorus-­solubilising biofertilisers/microorganisms (bacteria, fungi, mycorrhiza, etc.) convert the insoluble form of soil phosphate into soluble forms by secreting several organic acids and can solubilise/mobilise about 30–50 kg P2O5/ha under optimal conditions, increasing crop yield by 10–20%. Rhizobacteria colonise the plant roots and inhibit the growth of pathogenic microorganisms and stimulate plant growth, and endomycorrhizal fungi like AM improve the overall plant growth characteristics like plant height, root diameter and total dry weight. These growth parameters in the plant are also due to the phytohormone production by rhizobacteria like Acetobacter diazotrophicus, Azospirillum lipoferum and Azospirillum brasilense which produce indole-3-acetic acid, gibberellic acid and abscisic acid, respectively (Pathak et al. 2017). (iii) Biopesticide To get higher yields from crops to meet the growing population, pest control is very important. Conventional pesticides are disadvantageous because they leave more residues in the soil and kill beneficial insects also. Thus, biopesticides that are based on microorganisms are effective in protecting non-target organisms and humans (Gaši and Tanovi 2013). There are many different biopesticides each having a specific target, and their formulations also vary. Over 100 bacteria have been identified and listed as biopesticides, but more attention is given to Bacillus thuringiensis since this is widely used for insect control. Over 1000 viruses that infect insects have been identified like NPV capable of infecting 525 insects. Examples of entomopathogenic fungi are Beauveria brongniartii and Nomuraea rileyi which are capable of infecting Coleopteran and Lepidopteran insects, respectively (Thakre et al. 2011; Townsend et al. 2010). By-products from agricultural processes, namely, rice straw, wheat straw, stumps, husk, grass seed straw, barley straw, flax coil seed, corn stalks, sugarcane bagasse, sorghum stalks, hemp fibre, Sabai grass, reeds, cotton staples and stem fibres, are available throughout the year. Some by-products are recycled as fertiliser, feed or fuel, and some are considered as wastes. A significant amount is still being misused. To turn this waste into value-added products, a strategy is required. This conversion procedure should be technologically efficient, cost-­ effective and simple to use. Microbial degradation of agricultural wastes is one of the cost-effective and efficient technologies to produce value-added goods from the agricultural wastes. Crop waste and residues; by-products of the fruit and vegetable processing industries; by-products of the sugar, starch and confectionary industries;

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by-products of the grain and legume milling industries and the oil industry; and by-­ products of distilleries and breweries are all examples of agro-wastes. The handling and technology utilised for processing agro-wastes are mostly determined by their nature. (iv) Animal Feed The problem with animal feed in most underdeveloped nations is the scarcity of protein sources, despite significant efforts to find alternative supplements. Crop residues are good source of fibre and lacking in protein, carbohydrates and fat. As a result, the traditional strategy of raising cattle farming by augmenting forage and pasture with grains and protein concentration may not be sufficient to fulfil future meat protein requirements. The use of grain and protein for human diet will compete with the use of grain and protein for animal feed. These issues can be avoided by feeding wastes to domesticated animals (Hussein and Sawan 2010). Many of the basic ingredients used in feed production are items that might be better utilised in human nutrition (Brum et al. 1999). As a result, it is preferable to employ lower-­ quality materials as the primary component of animal diets (Table 2.1). Most agro-­ industrial wastes and food industry residues, on the other hand, are lacking in nutrients such as proteins and vitamins and high in fibre with low digestion. Such materials are not suited for non-ruminant animals and, in some situations, have such low digestibility that they are not even good for ruminants (Lima et al. 2000). In the face of this issue, a potential solution exists: the use of microorganisms, primarily fungi, to convert agro-industrial wastes into products with higher nutritive value, particularly in terms of protein and vitamin contents and increased digestibility. Large-scale cultivation of fungi, bacteria and seaweed can be used as feed. These microorganisms are highly appealing feedstuffs because they can be grown on agro-­ industrial wastes and produce enormous volumes of cells rich in proteins that often contain all of the essential amino acids, as well as vitamin and mineral levels that are favourable (Brum et al. 1999). Furthermore, the growth of microorganisms on lignocellulosic wastes can provide all of the hydrolytic enzymes commonly used in feed preparation and make minerals more accessible for absorption by the animal. The nutritional value and utility of a microbial protein are determined by its composition. Proteins must be nontoxic, free of antinutritional chemicals and easy to digest. Various agro-industrial leftovers, such as potato residues, rice bran, cassava residues and coffee shells and pulp, among others, produce microbial protein. World’s productions of some agro-industrial wastes to animal feed are given in Table 2.2. Protein enrichment of apple bagasse is possible with three yeasts: Saccharomyces cerevisiae, Candida utilis and Torula utilis. Each yeast species produced a threefold rise in crude protein content, as well as a doubling of fat, vitamin C, minerals, fibre and ash (Joshi and Sandhu 1996). Enrichment of beet pulp, wheat bran and citrus residue utilises the fungus Neurospora sitophila with the goal of employing these residues as animal feed. After 5 days of fermentation, the protein content of beet pulp increased by 15%, wheat bran by 13% and citrus residue by 7% (Shojaosadati et al. 1999).

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(v) Methane Anaerobic methane production is preferred from agricultural wastes due to its use of renewable energy sources, little residual waste output and low cost. This method generates nutrient-rich waste that can be utilised as a soil conditioner or fertiliser (Kiran et  al. 2014). Methane has an energy content of 55.5  MJ/kg. Anaerobic digestion generates methane by biodegrading organic waste and decreasing it. Several aspects influence methane synthesis in this process, including alkalinity, pH, organic loading rate, nutrients, reactor type, volatile fatty acids, C:N ratio, operation temperatures, ammonium ions and substrate properties (Park et al. 2018). The accumulation of volatile fatty acids and a drop in pH reduce the formation of methane gas during anaerobic digestion. Combining a microbial electrolysis cell (MEC) with an anaerobic digestion reactor increases methane production rate by 1.7 times when compared to the anaerobic digestion reactor alone. MEC accelerates the decomposition of volatile fatty acids, concentrated organic wastes and non-­ degradable organic debris, resulting in increased methane output. When MEC crosses a low voltage in the reactor, electrons produced by exoelectrogenic bacteria generate methane at the cathode. Waste pretreatment could be an effective technique for boosting protein/lipid digestibility, lowering acidification rates and changing biological and physicochemical features, minimising process inhibition and increasing methane recovery. Physical (grinding), thermal, acid and alkali treatments, high-pressure treatment, pulse discharge of high voltage, microwave-assisted, micro-aeration and biological treatment are all typical pretreatment methods. The optimum pretreatment procedures for anaerobic waste digestion are thermal treatment followed by alkali treatment. Alkali pretreatment increased methane yield by 25%, and when paired with heat treatment, the yield increased to 32%. Fifty-four different fruit and vegetable wastes produced 180–732 mL methane per gram of volatile solid. Furthermore, by utilising 95.1% volatile solids, fruits and vegetables waste in a two-stage anaerobic digester yielded 530 mL per gram of volatile solid. According to Hou et al. (2022), low salt concentrations boosted acidification and hydrolysis while suppressing methanogenesis, but high quantities hindered both methanogenesis and acidification. (vi) Enzymes Enzymes are protein biomolecules that act as catalysts in chemical processes. Agricultural by-products’ value addition encompasses the biotransformation of wastes into valuable products as well as the manufacture of crude enzymes utilising biowaste as a substrate. Agricultural wastes are typically made up of starch, cellulose, hemicellulose, lignin and cellulose and pectin. These substrate composition and enzyme production in the agricultural wastes are listed in Tables 2.3 and 2.4. Enzymes are utilised in various industries, particularly the food industry, to produce both classic products and new molecules. Three key enzymes derived directly from fruit waste are papain (from papaya), bromelain (from pineapple) and ficin (from figs). Each is a protein-degrading enzyme having numerous

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Table 2.3  Composition of agro-industrial residues Agro-industrial residues Corn cobs Sugarcane bagasse Wheat straw Rice straw Sunflower seed hull

Lignin (%) 6.1 25 8.9 12.56 29.40

Cellulose (%) 33.7 50 32.9 35.45 24.10

Hemicellulose (%) 31.9 26 24 23.78 28.60

Table 2.4  Enzyme production from different agro-industrial wastes Support Sugarcane bagasse Wheat bran

Microbial strain Trichoderma versicolor, Flammulina velutipes and Aspergillus niger Ganoderma, Aspergillus niger and Aspergillus niveus Wheat straw Phlebia radiata and Bacillus subtilis Banana skin Trametes pubescens and cellulolytic and pectinolytic enzyme Grape pomace Aspergillus awamori Corn fibre Fusarium proliferatum Cauliflower Aspergillus niger waste Soybean hulls Trichoderma and Aspergillus Apple pomace Aspergillus niger

Enzyme MnP, laccase MnP, pectinolytic, cellulase and beta-glucosidase Laccases, MnP, pectinases, glucoamylase and catalase Lip, MnP, laccase and protease Laccase Pectinases Beta-xylosidase Glucoamylase Cellulolytic enzyme Cellulases and pectinases, beta-­ fructofuranosidase and ethanol

applications, including laundry detergents, leather tanning and beer making. In addition to these three traditional enzymes, several additional industrially essential enzymes are being produced. Solid-state and semisolid fermentation processes are widely employed in the production of a wide range of enzymes from fruit and vegetable waste. Many of these fungal and bacterial species have been discovered to be extremely beneficial in the fermentation process; for example, Aspergillus sp., Pseudomonas sp., Bacillus sp. and Trichoderma sp. are important. On a large scale, the above said enzymes are produced from many fruit wastes, such as bananas, potatoes, dates, citrus fruits and mango kernels. Cellulases have been successfully produced by fermentation using a combination of microbes from grape pomace, banana waste, kinnow residues and palm kernel cakes. Invertase, pectinases, tannases, xylanases, proteases and laccases have also been successfully produced by fermentation using a combination of microbes. Fungi or yeasts produce 50% of accessible enzymes, and bacteria produce 35%, while plants and animals produce 15%.

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7 Innovative Application of Microbial Organic Waste Degradation The management of organic waste is crucial for the sustainability of the environment and the economy, but it is influenced by socioeconomic, political and environmental factors. Since recycling is becoming more popular than landfilling, various researchers have proposed the zero waste idea, taking sustainability into account. Anaerobic digestion is regarded as an economical and environmentally responsible technology to address the imbalances in the ecosystem brought on by the accumulation of organic substantial waste due to the environmental restrictions on energy generation from biodegradable solid waste (Bouallagui et al. 2005). The production of biogas from various biodegradable materials can be divided into four processes: (1) hydrolysis, (2) acidogenesis, (3) acetogenesis and (4) methanogenesis. An optimistic carbon resource to be used in a more aware and renewable global economy is biodegradable organic waste (Adl et  al. 2015). They are accepted to be widely used for biofuels such as biogas, biohydrogen, bioethanol and value-added products due to their abundance and diversity in terms of structural and compositional characteristics, which are related to their origins (acetic acid, lactic acid, etc.). Anaerobic digestion has emerged as one of the most promising technologies in recent years for achieving high bioenergy yields. The hyperthermophilic bacteria are highly capable of metabolising complex substrates during the AD process (Zhang et  al. 2015). Thermotoga, Thermotogaceae and Pseudothermotoga are examples of the family of hyperthermophilic bacteria that are recognised as producing hydrogen from a variety of organic substrates. Thermotoga and Pseudothermotoga species in particular have enormous potential for degrading organic wastes. Additionally, P. elfii and T. neapolitana are capable of breaking down complex substrates (Esercizio et al. 2021). The final portion of organic waste fed into digesters that could not be utilised by microorganisms during the anaerobic degradation process is known as biogas residual (digestate) (Lawal-Akinlami and Shanmugam 2017). As a result of the anaerobic digesters’ residual dead microbial flora, the digestate also contains mineralised matter (Janke et al. 2015). Digestate increases soil aggregation, maintains structure and provides aeration, all of which increase crop yield (Klimiuk et al. 2010). Microbial fuel cells (MFC) could be another option for generating power from various livestock while simultaneously reducing pollution and maintaining the potential for biofertilisers (Choi 2015). In MFC, the substrate-dwelling bacteria were capable of electrical charging, and these so-called electro active bacteria produced electricity. Utilising readily available biodegradable materials, MFC could produce 2–50% more energy. MFC would run under similar circumstances to conventional anaerobic digesters. MFC, however, performs better than anaerobic digesters at lower temperatures (30–20 C). MFC bacteria can release electrons onto the anode electrode and then react with an electron acceptor in the cathode chamber (Saheb-Alam et  al. 2019). Microbial fuel cells have the ability to generate

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electricity, but the advantage of microorganisms on the electrodes has allowed for the development of numerous systems for various purposes.

8 Advances in Recycling of Agricultural Wastes The agricultural wastes are considered as potential resources. Potential supplies include agricultural straw and livestock faeces. Inappropriate agricultural waste disposal not only pollutes the environment but also wastes a significant amount of important biomass resources. Recycling and utilising agricultural wastes are seen as critical steps in protection of the environment, energy structure and sustainable agriculture. In recent decades, agricultural wastes are becoming major causes of pollution, and the problems produced by poultry and animal excrement have received worldwide attention (Liu et al. 2015). Random straw burns and livestock waste in agricultural country have resulted in a slew of environmental issues. In recent years, a considerable amount of agricultural waste has been created each year all over the world (Wang et al. 2015). Agricultural waste increased at a rate of 5–10% each year on average. Random abandonment and inappropriate exploitation would also result in air pollution, soil degradation and other negative effects. The combustion of manure and straw produces a large amount of toxic gas, smoke and dust, severely damaging our air environment (Varma et al. 2015; Karak et al. 2015). Many diseases, parasite eggs, heavy metals and other contaminants can be found in animal faeces. A portion of agricultural leftovers have even been discharged straight into water, resulting in substantial contamination of the aquatic ecosystem. The presence of agricultural waste was unique in each region. There are several options for dealing with agricultural waste material. Some of these wastes have recently been put to better use. Some of these agricultural solid wastes could be used as additions in cement, water glass, paper manufacture, ethanol production, animal feed, electricity and biogas generation, heavy metal removal, mulching, organic fertilisers and compost. Recycling agricultural solid wastes to create valuable products is an efficient way of handling them. This can be accomplished by the following: 1. Organic manure/compositing 2. Substrates for the development of edible fungus 3. Nontraditional feed ingredient 4. Traditional soap production 5. Alternative energy and biofuel production 6. Silica production Agricultural solid wastes can be used as animal feed through sterilising, fertiliser through composting and bioenergy through anaerobic digestion. These wastes are good candidates for compositing because of their high organic matter and nutrient content, but their high salt, moisture and oil concentration may make composting

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difficult (Yangyang et al. 2016). As substrates, mushrooms were grown on various agricultural solid wastes (Akintola et  al. 2019). Production of agricultural solid waste to feed cattle is a recycling method as well as a low-cost source of feed for generating animal-source protein. Mycomeat is a nontraditional feed component which is made from agricultural solid waste. Mycomeat fed various agricultural solid wastes to albino rats and advocated processing of the wastes to achieve a better result (Oluwaseun and Oluseun 2018). The processing of agricultural solid wastes could increase their value for pig feed (Adebiyi et  al. 2019). The effect of dried sweet orange (Citrus sinensis) peel on humoral immune response in broiler chickens (Pourhossein et al. 2019) as well as maize replacement and its effect on growth performance in broiler chickens. Across the globe, traditional methods for turning agricultural solid waste into valuable items existed. Cocoa pods that could end up as agricultural waste are usually permitted to decompose naturally and nourish the soil, or they are used to make black soap, which can be used for dishwashing or bathing. Anaerobic digestion can turn agricultural solid waste into green energy. The high protein and fat content of these wastes may hamper anaerobic digestion stability, as well as the lack of effective technology required for biogas residue disposal (Tsai et al. 2007). However, pretreatment techniques such as mechanical (sonication), oxidative (ozone), chemical addition (acid or alkali), thermal osmotic (freezing and sodium chloride treatment) and biological (enzyme addition) can improve the physical and chemical properties of wastes, enhancing their solubilisation of organic particles, sterilisation effect and promotion of subsequent recycling (biogas production). Despite the many challenges that its production faces, biofuel and bioenergy are gaining popularity as a sustainable renewable energy source that promotes rural and regional development, reduces CO2 emissions, creates job opportunities and replaces energy from nonrenewable fossil fuels with green energy (Nguyen et al. 2010). Silica may be found in agricultural solid waste. Using chemical, thermal and microbiological processes, silica has been extracted from agricultural solid wastes such as corn cob, rice husk, bagasse and rice straw (Shim et al. 2015). Although dietary sources are low in silicon and may need to be supplemented in diets through other means, silicon quantity decreases with age and tends to be greater in plants than animal sources (Martin 2018). Agricultural solid wastes (high in cellulose, hemicellulose, lipids, starch and proteins) produced in huge quantities and burned on open fields or allowed to accumulate in some poor countries could be directed into biofuel production. Key stakeholders and political leaders, particularly in developing countries, should collaborate with researchers to scale up biomass conversion to alternate energy sources or biofuel output. This is projected to not only reduce the health risk posed by open-­ field agricultural solid waste burning or dumping but also to boost energy generation and reduce waste disposal economic losses.

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9 Challenges and Future Perspective Several researches have shown that microbial inoculants improve management of nutrients and plant diseases indicating their crucial role in future agricultural management systems. Apart from plant growth promotion, the use of bioinoculants for organic waste degradation has become a trustable solution to the modern world (Skariyachan et al. 2015). Organic wastes are generally bulky in nature; hence the time and space required for microbial degradation reduce their potential application. The search for fast-degrading strains and methods to optimise the process is crucial for improving the practicability of the technology. The complex soil-plant-­ microbe interactions are yet to be elucidated in detail that questions the viability of the microbial inoculants in the long run (Finkel et al. 2017; Mukhtar et al. 2018; Tabassum et al. 2017). The emission of greenhouse gases from the waste conversion facilities is recorded in humungous levels that are to be addressed by further research in the near future. Several new organic compounds are synthesised and utilised in various sectors that are mostly preservatives and have resistance to microbial degradation (John et al. 2023; Backer et al. 2018; Goss et al. 2013), which are very tough to be addressed with the existing practices and procedures for degradation of organic waste. However, biotechnological tools could offer more efficient and hardy microorganisms that could work in combination with some specific compounds or as mixed microbial cultures. The cost of genetically modified microbial inoculum and the regulations that are yet to be formulated for utilising in waste degradation hampers the path to sustainability. One of the major challenges for energy generation and product formation from municipal or other organic wastes is lack of awareness about segregation of organic and inorganic fraction. The secondary metabolites and enzymes synthesised by microbes can be explored for degradation of organic waste due to their high effectiveness and target-oriented approach. The utilisation of cost-­ friendly thermal-assisted composters could renovate the waste management especially municipal solid waste. However, while opting for a decentralised composting framework, a state legislation on community composting should be in place to avoid additional environmental damage. Hence, further research to identify socioeconomic characteristics and optimised location-based technology for successful processing of organic waste and exploiting in agriculture is needed.

10 Conclusion The amount of waste generated due to anthropogenic activity mostly ends up being a burden to the environment. This chapter has undoubtedly shown that microbial inoculants could improve management organic waste while improving the sustainability of agricultural sector. The anaerobic methods of conversion offer many attractive end products than aerobic methods. The prospects of energy generation through anaerobic microbial technologies could turn tables in the present energy

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crisis. However, several aspects of aerobic management outweigh the anaerobic means of waste conversion like duration and simplicity. The use of microbes to produce pesticide and biofertiliser can possibly reduce the use of agrochemicals. Soil degradation due to agriculture could be potentially eliminated through these technologies. Nevertheless, further research is needed to improve the efficiency and rate of waste management to reach the goal of waste-free process with environmentally enhancing microbial inoculants. Biotechnological researches for efficient microorganisms that are compatible with many types of waste and adaptable to the environment are expected in the years to come. In meeting the goal of sustainable agriculture ecosystem, the use of microbial inoculants technology could be adopted. Acknowledgements The authors are grateful to the Director, National Agro Foundation, Taramani, Chennai, and the Division of Environmental Science, Tamil Nadu Agricultural University, Coimbatore, for providing support for this work.

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Chapter 3

Microbial Degradation of Toxic Agri-wastes Archit Mohapatra, Davood Ahmad Dar, and Priti Raj Pandit

Abstract With development in the field of agriculture, man has continuously sought to improve his livelihood by transforming nature to provide food in terms of both quality and quantity for better and long life. The adoption of lobal mechanization, urbanization, and various natural processes of modern technology for the cultivation of crops and rearing of animals has led to the release of harmful chemical compounds. These toxic compounds are both organic and inorganic and get accumulated into the biosphere. These chemical compounds are the major sources of contamination of environment and causes of diseases. Various approaches have been adopted for the management of the wastes which cause environmental problems. As a major concern owing to this, there has been a growing interest in finding an eco-friendly and sustainable approach. Modern concepts of waste management visualize these wastes in different perspectives where wastes are considered as valuable precursors. The optimal utilization of these wastes is considered as an emerging area of interest with the purpose of finding an effective and efficient way of the management of wastes. Biotechnology plays an important role in utilizing the wastes as valuable products. This chapter highlights the biotechnological approaches and strategies to remove and convert the wastes into less toxic or beneficial products such as manure production and energy production and some value-added products. Keywords  Agriculture waste · Biotechnology · Bioremediation · Bioconversion

1 Introduction Agriculture refers to the production of food, feed, cereals, and other related goods through cultivation of desired crops. Being a tradition method of obtaining food for survival, agriculture still contributes to the development of the nation with some A. Mohapatra · P. R. Pandit (*) Gujarat Biotechnology Research Centre, Gandhinagar, Gujarat, India D. A. Dar Government Degree College, Beerwah, Budgam, Jammu and Kahmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_3

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advancements of the technologies for the production. With ever-increasing population, there is a need for the increase of the agriculture production which leads to the development of high-yield variety and use of synthetic chemical fertilizers and pesticides which enrich the soil and improve the plant health (Kibblewhite et al. 2008). Agriculture waste can be defined as waste produced at every step of operation of agriculture (United Nation Report 1997). Agriculture waste includes crop harvest waste; organic waste from livestock; runoff water from field; heavy metals and pesticides entering the soil, air, and water reservoir; and salts and slit runoff from field. Depending upon the various aspects of waste generation such as coverage and location of land used for agriculture, the quality and composition can be determined. The desirous nature of humans for increasing production by using these chemicals indiscriminately affects the whole ecosystem which includes generation of waste with potential pollutants, pollutes the groundwater, and destroys soil structure and health of plants and animals (Power 2010). Conversion of unusable or waste lands into agriculture field and groundwater for irrigation and overuse of water and chemical fertilizer have irreversible adverse effects on the environment. With time, using of the chemical fertilizer repetedly affects the soil by deterioration of nutrients and microbial community (Pretty and Bharucha 2014). If the chemical fertilizer is being used in a concentration more than what is required, then it starts getting accumulated in the food chain which passes from one to another and affects the health of ecosystem as a whole (Lal 2015). Biological wealth of the agriculture field is deteriorated, and there is an urgent need to sustain it for a long time to protect the environment and provide the food security to rural livelihood and health of each member of the food chain who either linked directly or indirectly (Frison et al. 2011; Pradhan et al. 2015). The rate of deterioration of environment quality generates concern toward the foods which are supposed to provide the nutrient required for their proper health (Hossard et al. 2014; Pradhan et al. 2015). FAO’s (Food and Agriculture Organization) (2017) report suggested that most of the countries reduce their dependence on chemical fertilizer. Initiatives were taken to use alternative way of supporting the soil and provide the nutrients required for the proper growth and development of the plants. In order to manage waste produced from the agricultural field and sustain the environment by reducing the dependence on the chemical fertilizer, biotechnology came into picture. According to the convention on biological diversity, biotechnology is defined as the technology developed to produce living organism or derivatives with desired function (FAO 2000). With its development, many researchers were trying to develop new product of interest according to the problem they faced using biotechnology and extended the definition. Modern biotechnology is known for its application in almost all fields from waste management till medical treatment (Ezejiofor et al. 2013). Biotechnology is also known to provide the solution to problem faced at every step in the field of agriculture. It starts with the selection of the seeds with the high productivity till the management of the waste generated from the field to protect environment. Due to the alarming increase in the environment pollution from the waste generated, the use of the heavy machinery that releases pollutants, use of chemical fertilizer, etc., are needed (Ezejiofor et  al. 2013). Biotechnology has various applications not only to manage the waste and reduce the

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pollution but also process the waste to produce some value-added products such as enzymes, important organic compounds, single cell proteins, and animal feeds. Further it is used in the production of organic bio-fertilizer, food additives, aroma compounds, and secondary antibiotics, and it is an alternative form of energy that releases the stress from the nature. An alternative way of increasing the productivity is to recycle and reuse the agriculture waste generated into organic manure that enriches the soil for better productivity (Schröder et  al. 2018). This way, one can improve the soil quality by supporting the microbial community having specific function and its biodiversity (Gattinger et al. 2012; Lori et al. 2017). It was found that the mixture of composted material applied along with bacterial bio-fertilizer enhances the soil structure and microbial diversity which leads to better productivity (Zhen et al. 2014). Low carbon in the soil will unable to support the growth of microbial diversity which in turn affects the productivity. Therefore, there is an urgent need to provide organic matter which can support the beneficial microbial community to convert the nutrient to enrich the soil and provide utilizable nutrients and tolerance (biotic and abiotic) to crops (Zhang et al. 2016). Agriculture wastes generated during cropping season and postharvest are generally considered as wastes and create environmental problems. If considered as a potential source for organic carbon and applied in the cropland, they can improve the production (Han et al. 2017; Hakeem et al. 2021). Due to the lack of information about how microbial community plays an important role in the management of waste and improvement of crop yield, if understood, microbial community can integrally manage the agriculture waste by converting the complex organic matter into simpler or utilizable form to plants which reduce their dependence on organic carbon from chemical fertilizer and protect environment at the same time (Han et al. 2017). It has been found that biotechnology when applied in compost preparation by using agriculture waste and desired microorganisms can be a boon to human race and sustain environment. Another most important application is the production of alternative source of energy using agriculture waste and biotechnology as catalyst. From the past few decades, the demands for the energy have increased with its cost, and large part of it is fulfilled through the use of nonrenewable source of energy. These natural nonrenewable sources are not only limited, but using them for the production of energy affects the environment adversely (EIA 2013). As per earlier discussion, biotechnology has a solution and has been applied for the production of renewable energy in the rural area since this field has not been understood clearly. Bioenergy involves the production of energy using microorganisms and waste generated from the agriculture. Biogas, bio-hydrogen, bio-methane, bio-kerosene, bio-diesel, etc., are included in the bioenergy which is considered to be an alternative source of energy with significant merits (Kaparaju et  al. 2009; Cheng et  al. 2011). Biotechnology provides such facilities and techniques with unique and potential way to bioremediation for the waste management and concurrent bioenergy production. The main purpose of this chapter is to highlight the problems faced in the field of agriculture and its waste management. The chapter mainly enlightened the techniques developed in the field of biotechnology to manage the waste and convert it into a useful form which will be beneficial to human race and sustainable toward the environment.

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2 Biotechnology for Agriculture Waste Management As per definition provided, biotechnology is a branch of science that deals with the application, knowledge, and procuring solution in the field of biological sciences and related problems (Ezejiofor et al. 2013). Although the definition changes with its application, particularly how the technologies developed will have an effect on their work atmosphere. Biotechnology when applied in the field of waste management, as reported by OECD (Organisation for Economic Co-operation and Development 2005), is defined as “technology developed to processing of waste and converting into a form which has least effect on environment.” All the technologies developed involve the use of living organisms like yeast, bacteria, fungi, and algae which degrade the waste materials by utilizing them for their own metabolism resulting into a new product (Ezejiofor et al. 2013). Environmental pollution is an alarming issue which is faced by many countries, and agriculture waste plays an important role in it. With the advancements in the field of biotechnology, many applications offered to treat the waste generated before realizing the environment. Ezejiofor et al. explain the methods one can use for the management of waste and that is by removal of wastes and converting them into value-added product.

2.1 Bioconversion of Agriculture Waste for Energy Using clean energy produced from the agriculture waste is the most effective method for disposal and sustainability (Xie et al. 2019). The emergences of this field were particularly the rise of cost associated with the production and supply of energy, management of waste generated, and more importantly the protection and sustainability of the environment which is interdependent for the management of natural resources (Brennan et al. 2010). Reliance on the natural resources which are unsustainable results in both depletion and emission of gases which have an effect on environment globally (Erakhrumen 2014). A remarkable advancement in the techniques involves the energy utilized from the agriculture waste which include crop straw, crop-processed residues, livestock breeding waste, etc., into different forms such as pyrolysis gas, bioenergies (biogas, bio-gasoline, bio-diesel, bio-hydrogen, bio-fuel), electricity, and more (Wie et al. 2020; Dar et al. 2022). 2.1.1 Anaerobic Digestion for Biogas Anaerobic digestion is a well-known technology for converting all sources of biomass such as organic wastes into a highly energetic form called biogas (Holm-­ Nielsen et al. 2009). Table 3.1 shows the different kinds of agriculture waste utilized for biogas production (Table 3.1). Anaerobic digestion takes place inside the digester

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Table 3.1  Production of biogas from agriculture waste Agriculture waste Rice straw

Corn straw Wheat straw Switch grass

Pretreatment Involve messing and passing through Sieve eight times Rice straw and piggery waste water Involve messing to a size from 3 to 5 mm Mixture of 5% W/W NaOH and solid (meshed and passed through Sieve) Wheat straw from horse bed Spent wheat straw –

Biogas production (mL/g VS) 325.3 231 350 372.4 55–60 150 117

References Gu et al. (2014) Mussoline et al. (2012) Lei et al. (2010) Zhu et al. (2010) Cui et al. (2011) Cui et al. (2011) Brown et al. (2012)

which converts waste into biogas which is a renewable source of energy, and the solid residues left in the digester can be utilized in the field to enrich soil. There are two possible perspectives to sustain environment using anaerobic digestion such as energy production, irrespective of wastes used, and production of bio-fertilizer (De Meester et al. 2012). The increased demand for food leads to an extensive production of agricultural crop and livestock which makes the generation of waste unused and stay scattered (Gadde et al. 2009; Hossain and Badr 2007). A method was proposed which helps to quantify the residues by residue characteristic factors and to determine the energy potential of these residues in the anaerobic digestion (Rahman et al. 2012). The gases released from the anaerobic digestion of the organic waste called biogas. This is promising technique to meet the need of energy globally and simultaneously providing multiple benefits to environment (Jiang et al. 2011; Rehl and Müller 2011; Tambone et al. 2010). The process of digestion in the anaerobic digestion chamber involves an integrated system of microorganisms and raw material to be processed under specific condition as explained in Fig. 3.1 (Lyberatos and Skiadas 1999). In order to obtain maximal biogas production factors like microbial community, operational conditions applied and the raw materials provided must be managed properly (Munk et al. 2010; He et al. 2007).

2.2 Factors Affecting Production of Biogas Using Anaerobic Digestion 2.2.1 Temperature The life cycle of anaerobic digestion involves stages such as thermophilic and mesophilic digestion and rate of digestion; load-bearing capacity and productivity were found to be better in thermophilic than mesophilic digestion (Mao et al. 2015).

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Complex material rich in Lipids, Carbohydrates and proteins Extracellular enzymes

Simpler material such as simple sugar, aminoacids, fatty acid Acidogenic bacteria Intracellular enzyme

Slurry / Solid residues/ undigested solids

Organic acids and Alcohol Acetogenic & Hydrogenic bacteria

Acetates

carbon dioxide, H2 Methanogenes CH4

Fig. 3.1  Life cycle of anaerobic digestion for biogas production (Lyberatos and Skiadas 1999)

The main disadvantages of thermophilic anaerobic digestion are acidification and less stability, and activity of methanogens is low and costly and may be sensitive and increased susceptibility to environmental factors (Mao et al. 2015). As compared to thermophilic system, mesophilic system provides better process stability and rich microbial community, but the biodegradability and biogas yield are low (Bowen et  al. 2014). As suggested by Mao et  al. (2015), optimal condition for anaerobic digestion would be hydrolysis or acidogenesis at higher temperature and then followed by mesophilic condition for methanogenesis. 2.2.2 pH The optimum pH for anaerobic digestion would be around 6.8–7.4 at which the growth and metabolic activity of most of the organisms is active (Fang and Liu 2002). Zhang et al. (2009) suggested that the rate of hydrolysis is correlated with pH. It should be noted that pH for both acidogenic and methanogenic microorganisms is optimum. Zhang et al. (2009) suggested that optimum pH for acidogenesis is in the range 5.5–6.5. Optimum pH for methanogenesis is 7 (Lee et al. 2009) and below 6.6; the activity of the methanogens is greatly affected (Zhang et al. 2009). Due to the different optimum range for two stages of anaerobic digestion, separate

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hydrolysis/acidification and acetogenesis/methanogenesis system is suggested for maximum production of biogas and degradation of waste (Kim et al. 2003). 2.2.3 C/N Ratio C/N ratio is the soul component reflecting the nutrient level of digestion and is directly linked to the production of biogas. High C/N ratio affects the biogas production by proving less nitrogen for the maintenance of cell biomass, whereas low C/N ratio also affects the production by insufficient utilization of carbon source due to increased ammonia production and toxicity to methanogens (Mao et al. 2015). For appropriate digestion, C/N ratio of 25 is widely used (Zhang et al. 2013; Yen and Brune 2007; Punal et al. 2000). C/N ratio can be a limiting factor for incomplete digestion of agriculture waste such as livestock manure or crop straw (Mao et al. 2015). 2.2.4 OLR In order to obtain biogas on a daily basis, one must have fed the digester continuously with amount of volatile solid which is known to represent the OLR (organic loading rate). From the above information, it can be denoted that with increases in the OLR, biogas production increases, but it might affect the yield or productivity at the same time (Mao et  al. 2015). The environment inside the digester is affected when introducing the new material on a daily basis. Extremely high OLR being an inhibitory factor for the bacteria leads to affect the process of methanogenesis and increased irreversible acidification by the hydrolysis/acidogenesis bacterial activity (Mao et al. 2015). Rincón et al. (2008) observed that abundant bacteria present at low OLR are firmicutes and at high OLR are Gammaproteobacteria, Actinobacteria, Bacteroidetes, and Deferribacteres.

3 Utilization of Waste for Soil Productivity The management of agriculture waste is a challenge for the developing countries. Effective waste management involves recycling and composting of the crop residues and organic wastes resulting in the production of organic manure with enriched nutrients that can transfer back to soil to regain its fertility (Dadhich et al. 2011). Options of recycling and composting and applying onto soil are techniques which help to reduce the dependence on chemical fertilizer. The compost prepared will improve not only the productivity but health of ecosystem (Gaind and Nain 2010). The application of the compost starts its effect from the the root till the shoot which ultimately improves the productivity (Pandey et al. 2009; Gaind et al. 2006; Lata et  al. 2005). Micro- and macronutrients along with carbon source play a very

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important role in the development of soil structure and compost prepared from the agriculture waste which is known for providing multiple benefits (Vasanthi and Kumaraswamy 2000). Lata et al. (2005) developed the compost using crops such as chickpea, pigeon pea stover, and mustard stover and microorganisms (bacteria, fungus, and actinomycetes) which are an improved method of compost preparation. From the experiment conducted by Dadhich et al. (2011), it showed that the productivity of rice crop along with the soil microflora is improved with the application of compost prepared from the crop residues along with chemical fertilizer in limited concentration.

4 Conclusions For a long time, these wastes generated from agriculture field are always considered as useless entity and disposed of by either land filling or burning which affect the productive topsoil layer. The advancement of technology not only in the field of technique but the knowledge and understanding depends on how nature by its own ability can recycle the waste and convert it into worthwhile products and remove the dependence on the chemical fertilizer. By using chemical fertilizer, the rate of productivity increases, but the health of humans, soil, and microflora starts getting deteriorated with the same rate. Biotechnology answers the question that how these wastes generated can be converted into useful product that not only helps in the management of the environment but protects the environment and sustains the resources for future generation. This field of science using the techniques developed will help to produce animal food and feeds, provide bio-fertilizer to enrich the soil, and provide alternative renewable energy, bio-fuel, biogas, etc., from the waste which earlier was considered as useless. Energy utilization from the agriculture waste is considered a boon to the human race because of the increase in the demand of the energy and depletion of natural resources. With the appropriate optimization and reducing of the limiting factor, biogas, bio-methane, and bio-hydrogen can be produced in a rate that reduces the dependence and effect on nature. The major benefit of bioconversion of organic waste into bio-fertilizer will make the soil ready to use with the enriched nutrients that support soil productivity and presence of microbial community which are useful for immunization of plants against both biotic (pathogens and pest) and abiotic (drought, light, etc.) stresses for better farming. This review was solely based on bringing out the techniques which were developed to manage the waste generated in the agriculture field, converting them into a form which serve so many purposes and protect the environment from harmful effect and sustaining it.

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Chapter 4

Introduction of Biofertilizers in Agriculture with Emphasis on Nitrogen Fixers and Phosphate Solubilizers Mir Sajad Rabani, Insha Hameed, Mahendra K. Gupta, Bilal Ahmad Wani, Mudasir Fayaz, Humaira Hussain, Anjali Pathak, Shivani Tripathi, Charu Gupta, Meenakshi Srivastav, and Moniem Benti Ahad Abstract  The demand for food resources is continuously increasing due to the expanding population, environmental limitations, and adverse effects of different synthetic inputs. The agricultural industry plays a pivotal role in survival of countries by feeding the population and their economic growth. Thus, the industries have approached newer scientific technologies in order to make it more efficient and maintain its quantity and quality. Various strategies have been adopted from time to time to meet the growing demands of food especially from plants. Meanwhile, biofertilizers are emerging as a boon and alternative to combat this problem due to their availability, cost-efficiency, and eco-friendly approach. These biofertilizers play a significant role in agricultural systems by improving plant nutrition uptake, soil quality, and thus crop production. Biofertilizers propose a sustainable solution for this crisis by limiting the use of synthetic fertilizers and meeting the demand of expanding population. They act as a link for different nutrients present naturally in M. S. Rabani (*) · M. K. Gupta · A. Pathak · S. Tripathi Microbiology Research Lab., School of Studies in Botany, Jiwaji University, Gwalior, Madhya Pradesh, India I. Hameed School of Studies in Environmental Science, Jiwaji University, Gwalior, Madhya Pradesh, India B. A. Wani Plant Reproductive Biology, Genetic Diversity and Phytochemistry Research Laboratory, Department of Botany, University of Kashmir, Srinagar, Jammu and Kashmir, India M. Fayaz · H. Hussain Ethnobotany, Phytodiversity Conservation, Plant Tissue Culture and Taxonomy, Department of Botany, University of Kashmir, Srinagar, Jammu and Kashmir, India C. Gupta · M. Srivastav School of Studies in Microbiology, Jiwaji University, Gwalior, Madhya Pradesh, India M. B. Ahad Department of Zoology, Central University of Kashmir, Ganderbal, Jammu and Kashmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_4

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the soil, atmosphere, and water; make them available for plant use; and act as supplement to agrochemicals. Being important elements of sustainable farming, ­biofertilizers play a leading role in maintaining soil health, quality, and functioning. They have the potential to convert insoluble and immobile forms of nutrients into soluble and mobile components, thereby making them readily available for plant uses and promoting their growth as well. Moreover, they can protect the plants against different environmental stresses like drought and other soilborne diseases that limit the crop production. This chapter highlights the benefits of using biofertilizers in attaining sustainability agricultural systems and suggests for the commercial production of biofertilizers with their applications. Keywords  Demand · Population · Food · Biofertilizers

1 Introduction The exponential growth in population increased the demand for food production especially from plants. Simultaneously, there is a dire need to attain food security for this increasing population across the world by enhancing crop yield and production. As a result, productive and intensive agricultural practices are performed by the addition of pesticides and synthetic fertilizers such as nitrogen, potassium, and phosphorus (Schultz et  al. 1995). On the other hand, the overreliance of modern agricultural systems on excessive input of chemical fertilizers has deteriorated the soil and water quality directly or indirectly. The excessive and nonjudicious uses of the synthetic fertilizers have also caused reduction in microbial biodiversity and imbalance in functioning of ecosystems (Socolow 1999; Youssef and Eissa 2014). The production of synthetic fertilizers results in emission of carbon dioxide and nitrogen pollutants which are then deposited in terrestrial ecosystems. Moreover, excessive use of synthetic fertilizers into soil gets stored in plants and sometimes causes heavy losses because of high nitrate and phosphorus levels that lead to water pollution (Vance 2001) and other types of environmental pollution (Mosier et al. 2004; Nash et al. 2012). Considering the negative effects of synthetic fertilizers, it is necessary to reduce their use in crop fields without any severe effect on production and yield. Therefore, the inclusion and use of renewable, safe fertilizers known as biofertilizers offers a sustainable alternative for these harmful synthetic chemical fertilizers. Moreover, sustainable agriculture could be attained without compromising with the natural resources and future generation to fulfill their needs (Wang et al. 2015; Calabi-Floody et al. 2018). Thus, biofertilizers open up new horizons of industrialization in the agricultural systems which can regulate and supply nutrients to plants without negative effects on ecosystem (Mishra and Dash 2014). Biofertilizers are generally referred to as microbial inoculants which are artificial multiplied cultures of some soil-associated microorganisms capable of enhancing the soil fertility, nutrient status, and production of crops. In other words, biofertilizers are the substances that contain live microbes which after their application to

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soil, seed, or plant surfaces inhabit the rhizosphere and promote the plant growth by enhancing the nutrient bioavailability to plants (Vessey 2003). It is an advanced organic farming system into which useful microbes are incorporated in the crop fields. In a broader sense, the biofertilizers may contain all organic resources for growth and development of plants that are rendered in accessible form for plants through plant microbe interactions (Khosro and Yousef 2012). The microbial biofertilizers use different mechanisms to improve the soil nutrient status of plants. They have the potential to fix atmospheric nitrogen, solubilize and mobilize insoluble forms of phosphate, and thus promote growth and development in plants (Bhat et al. 2010). The preparation of biofertilizers includes selection of the microbes beneficial for the soil and plants. The packaging of biofertilizers is ensured with a longer shelf life, safety, and well-being of the user and environment (Brar et  al. 2012). Their application is attracting the agriculturalists due to their nutrient status and relatively lesser impact on environment (Hari and Perumal 2010). They are renewable resources that can replace the chemical fertilizers and are easier to processes that include pulverization, packing, sterilization, and transport. Biofertilizers supply nutrients and microorganisms which might be already present in the soil in lesser quantities or not present at all. They speed up and boost the certain processes of microbial activities via different mechanisms and thus supply adequate and balanced quantities of nutrients to soil and plants. They are useful in enhancing the crop yield by utilizing the synthetic fertilizers more efficiently and protect the crops from pathogens and soilborne diseases. Numerous microbes including bacteria, cyanobacteria, and fungi have been identified that can stimulate plant growth. Bacteria, such as plant growth-promoting rhizobacteria (PGPR), can confer benefits to plants by various mechanisms. The chief mechanisms displayed by PGPR that can promote growth of plants are nitrogen fixation, phosphorus solubilization, and the increase in nutrient uptake or production of certain phytohormones (De Freitas et al. 1997; Goldstein et al. 1999).

2 Biofertilizers in Alleviating Environmental Stress Tolerance in Plants Changing climate has increased the concurrence of various abiotic and biotic stresses. The main constraints that affect the crop production and cause major loss to the crops globally are these stresses (Suzuki et al. 2014). Since, there is a dire need to enhance crop production to meet the increasing demand for food. Simultaneously, we need to find sustainable solutions to combat both abiotic stresses (drought, heavy metals, extreme temperatures, pH, and salinity) and biotic stresses (pests and pathogens). Various techniques have been used for crop improvement under different stresses, where microbes are of principal importance which act as bio-protectants (Yang et al. 2009). Microbiomes associated with plants like plant growth-promoting microorganisms (PGPM) have the capability to promote plant

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growth and enhance stress tolerance, maintain plant nutrition, and act as a means of biocontrol against phytopathogens. They are receiving a considerable attention of agronomists and environmentalists as candidate organisms employed to deal with multiple kinds of stresses (Ma et al. 2011, 2016). Thus, they open up new horizons in understanding PGPM-induced stress tolerance in plants, suggesting that their application can play a critical role in alleviating stress tolerance and improvement in food production (Ilangumaran and Smith 2017). Salinity stress limits the agricultural productivity worldwide due to its effects on seed germination and plant development besides growth and crop yield (Munns and Tester 2008; Carmen and Roberto 2011; Paul and Lade 2014). It also hampers the rate of photosynthesis, increases photorespiration, and causes nutrient imbalance that results in various deficiencies (Munns 2002). Studies have shown the potential of certain PGPMs to improve salt stress tolerance in plants (de Zelicourt et al. 2013; Miliute et  al. 2015). An increase in nodulation and biomass was observed in Trifolium alexandrinum inoculated with Rhizobium trifolii under salt stress conditions. A Pseudomonas aeruginosa was found to resist biotic and abiotic stresses (Pandey et  al. 2012; Hakeem et  al. 2021). Further, Pseudomonas putida RS-198 strain improved the growth and germination rate under alkaline and highly saline conditions by enhancing the K+, Mg2+, and Ca2+ uptake and decreasing Na+ absorption (Yao et al. 2010). Inoculation of salt-tolerant rhizobia in crop plants has been reported to enhance crop production under salinity stress (Ahmad et al. 2012, 2014). They use a variety of mechanisms to combat with salt stresses. Enhanced growth was observed in plants inoculated with arbuscular mycorrhizal fungi (AMF) under salinity stress. Further, Piriformospora indica, an endophytic fungus, was found to confer salinity stress tolerance in crop plants (Ansari et al. 2013). Studies have demonstrated that inoculating PGPR separately or with AMF like Glomus intraradices or G. mosseae showed improved nutrient uptake and improved physiological processes in Lactuca sativa under stressed conditions and enhanced shoot biomass was found in same plant inoculated with P. mendocina under salinity stress (Kohler and Caravaca 2010). Researchers have shown that PGPMs stimulate and increase production of antioxidative enzymes in plants that are subjected to various abiotic stresses. The PGPMs are supposed to confer tolerance in plants to a variety of abiotic stresses in particular salt stress (Nautiyal et  al. 2008; Zhang et  al. 2008; Chakraborty and Chakraborty 2015). Temperature stress is thought to be one of the most essential abiotic stresses that limits crop yield and production. It is the rise or decline in temperature than the critical range that is sufficient enough to cause irreversible damage to plants (de Zelicourt et al. 2013; Hasanuzzaman et al. 2013). Studies have demonstrated that PGPRs, namely, Bacillus polymyxa BcP26, Mycobacterium phlei MbP18, and Pseudomonas alcaligenes PsA15, produced calcisol that conferred tolerance in plants against extreme temperatures and salt stress (Egamberdiyeva 2007). Water is also an important factor that regulates agricultural production and development. Both the stresses attributed to water including water logging and drought produce negative effects on crop yield and growth. Combination of AMF and nitrogen-­fixing bacteria has been reported to assist legume crops to prevail over

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drought stress. Studies have demonstrated that application of Pseudomonas sp. to basil plants enhanced their antioxidant and photosynthetic pigment content and also exhibits profound effects on seed germination and growth under water stress conditions (Liddycoat et al. 2009). The rate of photosynthesis and antioxidative response of paddy plants increased after inoculation with AMF (Ruiz-Sanchez et al. 2010). Further, the addition of Bacillus megaterium or Pseudomonas putida in combination with AMF has been proven to be effective in enhancing drought stress (Marulanda et al. 2009). Further, Achromobacter piechaudii has been reported to enhance biomass of pepper and tomato crops under salt and water stresses (Murphy et al. 2003). An exopolysaccharide producing strain Pseudomonas putida GAP-P45 imparted drought stress tolerance in sunflower by biofilm formation on root surfaces (Chakraborty and Chakraborty 2015). Heavy metals are inorganic pollutants that result from industrial wastes, pesticides, agrochemicals, and mining (Marchiol et al. 2004). Their persistent and nondegradable nature poses a serious threat to soil microflora (Krujatz et al. 2012), plants (Wani and Khan 2010), and environment (Cheung and Gu 2007). For instance, photosynthetic activity of legume host and nitrogenase activity of rhizobia is negatively affected by cadmium and reduces its nodulation potency (Ahmad et al. 2012). Reports also revealed that zinc badly affected the association of Rhizobium leguminosarum and pea plants by declining rhizobial population, nodulation, and its growth (Chaudri et al. 2000; Dar et al. 2022). Besides legumes, rhizobia may also increase growth of nonlegumes as well and play a role in phytoremediation of contaminated sites under stressed conditions. Using rhizobia in combination with legume plants is an environment-friendly and cost-efficient technique for phytoremediation under unfavorable conditions (Kang et al. 2018). Soil rhizospheric bacteria play a vital role in mitigation of heavy metal stresses (Hassan et al. 2017). The beneficial soil microorganisms (BSMs) possess unique metabolic functions that help them to overcome various kinds of stresses including metal stress, thus making these BSMs very important for agronomy. Application of BSMs has been proven beneficial for bioremediation under changing environment (Nautiyal et  al. 2013; Tiwari et al. 2016). The volatile organic compounds (VOCs) synthesized by several microorganisms and microbial biofertilizers can alleviate stress tolerance and resistance against diseases in plants and thus help in controlling a number of pathogens. Biofertilizers increase disease resistance in plants by producing various antimicrobial substances and hydrolytic enzymes and stimulate plant defense mechanism (Kang et al. 2006; Duan et  al. 2009; Samavat et  al. 2011). Researchers have recognized numerous antimicrobial and several VOCs produced by Paenibacillus polymyxa and Verticillium longisporum in response to each other’s VOCs that contributed significantly in understanding the mechanisms of VOCs involved in the interaction between phytopathogens and their antagonistics (Rybakova et al. 2017). PGPRs are the alternatives for chemical agents which act as biological protective agents and provide resistance to crop plants against various phytopathogens. They can provide resistance against various phytopathogens by producing certain bioactive compounds in addition to growth-promoting agents (Backman and Sikora 2008).

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Bacillus subtilis GBO has been reported to induce defense-related pathways. It has been demonstrated that Bacillus subtilis N11 in combination with compost controls Fusarium invasion on banana roots. Exploiting PGPRs have been found very effective in the management of cucumber mosaic, viruses of tomato and pepper, etc. Studies have also shown that mycorrhizae incorporation with bacteria imparts resistance against fungal pathogens in crops and also inhibits the growth of certain pathogens like Rhizoctonia solani and Pythium sp., Fusarium oxysporum, Armillaria obscura, and Heterobasidion annosum (Khalil and Labuschagne 2002; Riedlinger et al. 2006). Reports based on studies suggest that addition of AMF and Pseudomonas fluorescens to soil can minimize the growth of pathogen causing root rot disease of Phaseolus vulgaris and increase its yield (Neeraj 2011). A study, which isolated hydrogen cyanide producing Pseudomonas fluorescence strain and stated its role as a biocontrol agent, increases root and shoot length and seed germination rate of crops like barley, rye, and wheat (Heydari et al. 2008). A few strains of Pseudomonas were found to confer plant tolerance against stresses by producing 2,4-­diacetylphloroglucinol (DAPG) (De Souza 2003). Rhizobia have been reported to secrete bioactive compounds like zeatin (Boiero et  al. 2007), hydrogen cyanide, pyrrolnitrin, tensin, viscoinamide (Bhattacharyya and Jha 2012), and antibiotics like phenazines (Krishnan et al. 2007); thereby, they are useful in biocontrol of pathogenic microorganisms (Triplett et al. 1994). They can also produce bio-stimulatory compounds which can induce systemic resistance in plants (Singh et al. 2006).

3 Biofertilizers in Nitrogen Fixation and Nitrogen-Fixing Microbes Nitrogen (N) that constitutes 78% of the atmospheric gas is among the most limiting mineral elements available for plant growth due to its difficulty of fixation and uptake (Valentine et al. 2010). Most organisms cannot use the molecular form, that is, dinitrogen (N2) form of nitrogen. Some prokaryotic microorganisms, which can form different associations with plants, have the capability to convert this molecular nitrogen into usable forms like ammonia and nitrates through biological nitrogen fixation. Nitrogen is further used by plants for the synthesis of vitamins, proteins, and other metabolic compounds (Dos Santos et al. 2012; Nyoki and Ndakidemi 2018). Since then, nitrogen bioavailability in the usable forms such as ammonia and nitrates is limited. The modern agriculture practices are over dependent on synthetic nitrogen fertilizers in order to achieve maximum crop yield (Galloway et  al. 2008). These fertilizers emit greenhouse gases, require a huge amount of fossil fuels (Erisman et al. 2007), and cause soil acidity (Arma 2016), and majority of the applied fertilizers are lost due to leaching, therefore causing problems to mankind and ecosystem as well (Olivares et al. 2013). Thus, nitrogen biofertilizers offers a sustainable and eco-friendly alternative for agricultural sustainability (Farrar et al. 2014), which are

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categorized into various forms on the basis of their nitrogen-fixing ability. Nitrogenfixing microbes are used in biofertilizer applications as living fertilizers composed of microbial inoculants or cluster of microbes which can fix atmospheric nitrogen. They are categorized into free-living bacteria such as Azospirillum, Azotobacter, Anabaena, Beijerinckia, Clostridium, Klebsiella, and Nostoc and cyanobacteria and symbionts such as Azolla, Frankia, and Rhizobium (Gupta 2004). The nitrogen fixation in Medicago sativa by free-living bacteria has been reported to vary from about 3–10  kg  N  ha1 (Roper et  al. 1995). Further, bacterial species like Azotobacter chroococcum has been reported to fix about 2–15 mg of nitrogen per gram of carbon source used in culture media. Also, free-living bacterial symbionts like Frankia have been reported to fix nitrogen in both host and nonhost plants (Smolander and Sarsa 1990). Studies have also revealed that the leaf spray- and seed-soaking inoculation of Beijerinckia mobilis and Clostridium sp. has stimulated the growth in crops like barley and cucumber by fixing atmospheric nitrogen and production of certain plant growth-promoting substances (Polyanskaya et al. 2002). Free-living cyanobacteria harnessed in paddy fields in India have been observed which can supply about 20–30 kg N ha−1 under suitable circumstances (Kannaiyan 2002). The nitrogen-fixing bacteria associated with nonlegume plants includes certain species from genera Acetobacter, Achromobacter, Alcaligenes, Arthrobacter, Azomonas, Bacillus, Campylobacter, Corynebacterium, Clostridium, Desulfovibrio, Derxia, Beijerinckia, Enterobacter, Erwinia, Herbaspirillum, Klebsiella, Lignobacter, Methylosinus Mycobacterium, Rhodospirillum, Rhodopseudomonas, and Xanthobacter (Wani 1990). The nitrogen fixation capability of bacterial biofertilizers of rhizobia group like Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium, and Sinorhizobium having symbiotic or other relations with plants can vary up to 450 kg N ha−1 depending on type of strain and host plant species (Stamford et al. 1997; Vance 1998; Unkovich and Pate 2000). These rhizobial biofertilizers can be applied in certain forms including powder, liquid, and granular form with carriers like charcoal, peat, and mineral soil (Stephens and Rask 2000). Frankia has the capability to form root nodules and thereby nitrogen fixation in several plants as well (Torrey 1978; Dawson 1986; Huss-Danell 1997; Wall 2000) and form symbioses with certain nonlegumes like Alnus, Casuarina, Myrica, and Rubus. Moreover, leaves of certain plants like Ardisia build up unique cavities that harbor bacteria like Xanthomonas and Mycobacterium with nitrogen-fixing capability; thus, the leaves serve as a source of nitrogen fertilizers (Miller 1990). Cyanobacteria is another important group of organisms used as biofertilizers. Numerous cyanobacteria like Anabaena, Tolypothrix, and Nostoc can fix atmospheric nitrogen with the help of unique structures called heterocysts (Saikia and Bordoloi 1994; Kumar et al. 2010). Due to this feature, cyanobacteria are used as biofertilizers in the rice fields in China, India, Japan, Vietnam, etc. (Sahu et  al. 2012). Nitrogen fixed from the heterocysts may be released as ammonia, amino acids, vitamins, polypeptides, etc., in the surrounding environments by the microbial decomposition of the dead cells and making nitrogen accessible to plants; likewise, few cyanobacteria have been reported to produce the biologically fixed nitrogen (Subramanian et al. 1994). It has been reported in the literature that the

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cyanobacteria can fix about 22.3–53.1 kg N ha−1 that can reduce the application of chemical nitrogen fertilizers by 50–75% (Issa et al. 2014). Some important blue-­ green algae are Anabaena, Anabaenopsis, Aphanothece, Aulosira, Calothrix, Cylindrospermum, Nostoc, Oscillatoria, Phormidium, Plectonema, and Tolypothrix. Among which, only few like Anabaena variabilis, Nostoc muscorum, Aulosira fertilisima, and Tolypothrix tenuis have been found to have applications as biofertilizers. Some cyanobacteria like Anabaena, Nostoc, and Trichodesmium have been reported significantly contributing to about 36% of the total nitrogen fixation and enhancing fertility of soils for the cultivation of paddy across the world (Kundu and Ladha 1995; Irisarri et al. 2001). The estimated turnover of nitrogen in the biosphere varies from about 100–200 million metric tons per year, where about 66% arrives from biological sources mainly from blue-green algae (BGA) (Pabbi 2015). Studies have reported that the application of cyanobacterial biofertilizers could also be expanded to several other crops and vegetables as well (Osman et al. 2010; Bidyarani et al. 2016). Studies have also demonstrated that 23 crops in a row can be grown effectively for continuous 12 years with the application of cyanobacteria only without applying any other synthetic nitrogen fertilizers (Watanabe et  al. 1977). However, physicochemical, climatic, and biotic factors play a significant role in the total nitrogen fixation by blue-green algae, for instance, soil alkalinity favors the nitrogen fixation by cyanobacteria (Roger and Kulasooriya 1980). Meanwhile, plants can use fixed nitrogen when it is present extracellularly in the form of extracellular products or by mineralization of their intracellular components through microbial breakdown (Pabbi 2015). Crops inoculated with cyanobacteria use nutrients efficiently from the soil due to slow liberation of fixed and metabolized nitrogen. Nitrogen fixation by cyanobacteria works on a switch on mechanism and is regulated by its concentration, when its level goes down beneath the threshold level, that is, about 40  ppm due to excessive utilization and loss from the soil (Pabbi 2015). Studies have shown that approximately 90% of the nitrogen accumulated by blue-green algae is derived from the atmosphere (Inubushi and Watanabe 1986). Further, it has been observed that apart from urea, all other nitrogenous fertilizers when used in excess have harmful effects; however, optimal doses of these fertilizers exhibit beneficial effects on growth and development of cyanobacteria (Watanabe 1973). Besides nitrogen fixation, cyanobacteria are also known for plant growth promotion and their possible use in reclamation of barren soils or other ecosystems disposed by floods (Bashan et  al. 1998). BGA can also provide plant growth regulators, proteins, minerals, and vitamins. There are certain symbiotically competent cyanobacteria which act as a soil conditioner and have some exceptional features that make these to be included in plants of economic importance. The symbiotic cyanobacteria occur in two basic types of associations mainly, that is, extracellular and intracellular. These BGA are not confined to roots only but to host plant tissues as well. The main host plants are bryophytes, cycads, Gunnera (an angiosperm), Azolla (water fern), and fungi, all of which are extracellular. Contrasting to rhizobia, most symbiotic BGA have their unique mechanism of nitrogenase production. Besides contributing to nitrogen fixation, cyanobacteria can

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also supply fixed carbon to non-­photosynthetic parts of the host as well. Among other symbiotic associations, the association of a BGA (Anabaena azollae) with a fern (Azolla) makes a unique beneficial relationship of biological and economic importance. It is used as a fertilizer commercially in different fields especially for growing rice. Azolla also provides an inhabiting space for Anabaena in its aerial dorsal lobes of leaves. This Anabaena in return provides nitrogen that is required by Azolla for its growth. Symbionts of Azolla-Anabaena azollae are being employed as green manures since ages in paddy fields in China and other Asian countries to enhance production (Deepali 2017). Azolla can form green mats on water surfaces and are decomposed to ammonia, thereby generating enormous amount of biofertilizers. Acetobacter diazotrophicus and Herbaspirillum sp. are associated with plants like maize, sugarcane, and sorghum but did not form any endophytic symbioses and have less close association with roots (Triplett 1996; Boddey et al. 2000); others include Azoarcus sp. with Leptochloa fusca (Malik et al. 1997); certain species of genera Azospirillum, Alcaligenes, Bacillus, Enterobacter, Klebsiella, Herbaspirillum, and Pseudomonas with maize and rice (James et al. 1997); and Azospirillum with a better host specificity with a variety of annual and perennial plants (Bashan and Holguin 1997). Reports based on different studies have revealed that Azospirillum improved the growth and production of crops like carrot, cotton, eggplant, oak, pepper, rice, sugar beet, sunflower, tomato, and wheat due to its nitrogen-­fixing capability and production of some plant growth-promoting substances (Okon 1985; Okon and Labandera-Gonzalez 1994). Production of Azospirillum to be used as biofertilizer is an environmental benign technique that can be applied by effortless peat formulations (Vande Broek et  al. 2000). The biofertilizer from Acetobacter diazotrophicus has been reported to fix about 150  kg  N  ha−1 annually which meets 70% requirement for sugarcane (Boddey et al. 1995). Legumes can fix the atmospheric nitrogen by making symbiotic relations with rhizobia present in root nodules of these crops and are thought to be important candidates to maintain the soil health and fertility. A part of the nitrogen fixed by legume crops can be transferred to adjacent nonnitrogen-fixing crop plants by a process called nitrogen transfer (Fustec et al. 2009). It is the movement of nitrogen from a donor legume plant to other nonlegume receiver plants (Pirhofer-Walzl et al. 2012). This N-transfer is beneficial for effective utilization of fixed N, reduces N losses, and maintains the biomass production (Thilakarathna et al. 2016). The nitrogen fixation in legumes is a complex process which can contribute significantly to sustainable agriculture. It is mediated by a variety of chemical signals between legume host and rhizobia which provide fixed nitrogen to host plant and in return gets carbon compounds as a source of carbon and energy (Lodwig et  al. 2003; Andrews et al. 2009; Hungria and Kaschuk 2014). Rhizobia are highly specific to their host plant where they carry out nodulation and fix nitrogen. For many years, scientific community was of the view that a legume crop can make association with one strain of rhizobium only. For instance, Bradyrhizobium japonicum was thought to make association with soybean only (Rodriguez-Navarro et al. 2010). Later on, a

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number of reports suggested that there are a numerous species from genera like Bradyrhizobium, Rhizobium, Mesorhizobium, and Sinorhizobium which can form symbiotic association with soybean and fix nitrogen (Biate et  al. 2014). This nitrogen fixation is the chief process that contributes for plant nitrogen availability; however, it may vary with physicochemical parameters of soil (Giller 2001), mineral nitrogen present in soil (Thies et al. 1991), native rhizobial inhabitants, and other environmental factors as well (Al-Falih 2002; Liu et al. 2011). Applications of Rhizobium are important that confer several benefits to agriculture in legumes and other host plants (Sahu et al. 2018). An endophytic strain, Paenibacillus polymyxa P2b-2R, has the ability to fix nitrogen and promote growth in a number of host plants like Brassica napus L. (Anand et al. 2013; Padda et al. 2016). Recent studies have revealed that inoculating maize and wheat plants with Pseudomonas protegens Pf-5 X940 enhanced the nitrogen content and biomass in the host plant (Fox et al. 2016).

4 Biofertilizers in Phosphate Solubilization and Phosphate-Solubilizing Microbes Phosphorus (P) is the second essential limiting mineral nutrient after nitrogen in plants which plays a significant role in processes including photosynthesis, respiration, energy transfer processes, transmission of genetic material, cell division, and synthesis of nucleic acids and phospholipids. It regulates the processes of nitrogen fixation, signal transduction, and protein synthesis in plants (Fernandez et al. 2007; Khan et al. 2010; Richardson and Simpson 2011; Pande et al. 2017). The concentration of P is very high in the soil, but it is present in forms unavailable for plants (Schachtman et al. 1998). Crop yield and production are affected by applications of phosphorus due to its role in growth and reproduction like processes. Despite the fact that P is present in sufficient quantities in soil, it becomes inaccessible to plants often due to their ability of absorbing soluble forms of phosphorus, that is, mono (H2PO4−) and dibasic phosphate (HPO42−) (Jha et al. 2012). Most of the crops contain 0.1–0.5% P and it is absorbed in the form of primary orthophosphate ions (H2PO4−) mainly; however, certain plant species take it as secondary orthophosphate ions (HPO42−) from the soil. In order to meet the plant phosphorus requirements, synthetic phosphate fertilizers are applied to the crop plants. But the chemical phosphate fertilizers have various limitations such as the release of toxic hydrogen fluoride gas during their manufacture (Sharma et al. 2013), accumulation of heavy metals in soil and plants, eutrophication and hypoxia of lakes and other water bodies (Lugtenberg et al. 2013), etc. These P fertilizers when applied to soil become inaccessible to plants because of complexation with calcium carbonate (CaCO3) in alkaline calcareous soils (Leytem and Mikkelson 2005) and with sesquioxide in acidic soils (McLaughlin et al. 2011). Thus, it needs to be converted into free form from its bound and complex form for regular consumption (Corona et al. 1996). Phosphorus

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is extremely a reactive macronutrient which can form complex derivatives by binding with aluminum, iron, potassium, and oxygen. More than 80% of the applied synthetic fertilizers used for enhancing crop production remain in unavailable forms like aluminum (Al-P), calcium (Ca-P), and iron (Fe-P) in most soils (Dotaniya et al. 2013, 2014), where the Al-P and Fe-P constitute about 1–25% of total P that is present in acidic soils generally and the Ca-P comprises about 40% in neutral or calcareous soils. The mobility of P ions is quite slow and in most of the cases plant roots take it from a distance of 2–4 mm while other nutrients are taken over from long distances. There are several bacterial strains that are capable of converting phosphorus in the simplest forms available for plant growth. Soil microorganisms play a vital role in phosphorus bioavailability in soils (Sharma et al. 2013) using different mechanisms including lowering of soil pH by producing organic acids, siderophores, and release of hydroxyl ions (OH−) and enzymes (Barroso et al. 2006; Glick 2012). The microbes also mineralize the phosphorus by decomposing organic compounds and make P available to plants (Rodrigues et al. 2006) by producing phosphatases and phytases (Maougal et al. 2014). Rhizobia have been found to avail the inorganic phosphate to plants through solubilization and organic phosphate by decomposition (Tao et  al. 2008). Phosphate-solubilizing microbes (PSM) offer a cost-efficient and environmentally benign alternative to synthetic fertilizers. Studies have demonstrated the ability of various bacterial species to solubilize inorganic P compounds, such as dicalcium phosphate, tricalcium phosphate, hydroxyapatite, and rock phosphate. The important phosphate-solubilizing bacterial genera are Achromobacter, Agrobacterium, Bacillus, Burkholderia, Enterobacter, Erwinia, Flavobacterium, Micrococcus, Pseudomonas, and Rhizobium. The average content of phosphorus in soil is about 0.05%; however, it is only a minute fraction of including bacteria, cyanobacteria, and fungi which have the capability of solubilizing inorganic P and mineralizing organic phosphorus, making it accessible to plants (Yandigeri et al. 2011; Long et al. 2018). Although phosphate-­ solubilizing microbes are cosmopolitan in nature, however, their quantity may vary depending on the source of isolation and soil type (Chen et al. 2006; Vessey 2003; Awais et al. 2017). The phosphorus-solubilizing bacteria (PSB) like Bacillus and Pseudomonas can enhance the P availability to plants in the soil by mobilization of the unavailable phosphate (Richardson 2001). The bacteria and some fungi such as Penicillium and Aspergillus dissolve phosphates bound to soil by producing organic acids of low pH. Reports have suggested that the application of economical rock phosphate with Bacillus megaterium increased the yield of sugar and juice quality of sugarcane by about 12.6% and reduced the P requirement by 25% (Sundara et al. 2002). Studies have also revealed that isolates such as Acinetobacter sp. and Bacillus sp. from Phyllanthus amarus exhibit salt tolerance and P-solubilizing properties and thus reduce consumption of fertilizers. Studies had shown that inoculation of bacterial strains increased P content, seed germination rate, and biomass and promoted higher vigor index, phenolic content, and antioxidant activity of the crops as well (Joe et al. 2016).

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Numerous strains of rhizobia have been reported to solubilize inorganic P and mineralize organic P in soil (Khan et al. 2010) such as Rhizobium (Egamberdiyeva et al. 2004), Bradyrhizobium (Afzal and Bano 2008), Mesorhizobium (Rodrigues et  al. 2006; Chandra et  al. 2007), and Sinorhizobium (Bianco and Defez 2010). Studies have demonstrated that the bacterial strains like Achromobacter, Aerobacter, Erwinia, Micrococcus, and Pseudomonas have the ability to solubilize phosphate compounds (Rodriguez and Fraga 1999; Chen et al. 2006; Mishra and Dash 2014). It is said that rhizospheric bacterial strains have strong phosphate-solubilizing potential compared to that of non-rhizospheric regions. The familiar mechanisms used for phosphate solubilization include production of organic acids like “acetic acid, citric acid, gluconic acid, lactic acid, 2-ketogluconic acid, malic acid, oxalic acid, succinic acid, and tartaric acid” (Patel et al. 2015) and production of extracellular enzymes like nonspecific phosphatases, phytases, and C-P lyases (Bloemberg and Lugtenberg 2001). Phosphate-solubilizing ability is commonly found among rhizospheric microbes, and some recognized competent PSMs are Aspergillus niger, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus atrophaeus, Kluyvera cryocrescens, Paenibacillus macerans, Penicillium sp., and Pseudomonas aeruginosa. The phosphate solubilized by the microbes enhanced the crop yield up to 70% (Verma 1993). Improvement in crop yield has been observed by the applications of phosphate-solubilizing biofertilizers due to effective solubilization of inaccessible and insoluble phosphorus present in the soil (Ponmurugan and Gopi 2006). About 50% reduction in the synthetic P application was seen by using phosphorus-­ solubilizing biofertilizers and PGPR without any harmful effect on crop yield (Yazdani et al. 2009). Sugarcane yield was found enhanced by 12.6% with the inoculation of PSB (Sundara et al. 2002). Also, studies have shown that inoculation with Pseudomonas fortinii increased the growth and P content in two alpine Carex species (Bartholdy et  al. 2001). Applications of Rhizobium co-inoculated with PSM (Perveen et al. 2002) or AMF (Zaidi et al. 2003) have been reported to increase plant growth in P-deficient soils. Further, improvement in growth and crop yield was observed by the inoculation of PSB with nitrogen fixers such as Azospirillum (Belimov et al. 1995) and Azotobacter (Kundu and Gaur 1984) or with AMF (Kim et al. 1997). The mycorrhizae have been also reported to increase phosphate uptake and other micronutrients. Studies have suggested that the inoculation of mycorrhizal fungi helps the plants to efficiently use the soluble form of phosphate from the inorganic fertilizers by increasing root phosphate-absorbing sites because of the presence of extraradical mycelium (Khan et al. 2007). It is also reported that mycorrhizal fungi engages other microbes on their surfaces by producing significant hyphae biomass in soils and helps in the release of inorganic phosphate in the soil (Zhang et  al. 2018). Reports have recommended that fructose exudates of AM fungi Rhizophagus irregularis helped Rahnella aquatilis to increase the expression of phosphate genes and the rate of phosphatase release (Zhang et  al. 2018). Similarly, studies have revealed that the interaction of PSB and AM fungi increased the inorganic P uptake in wheat plants (Yousefi et al. 2011). Some other species of fungi used as biofertilizers

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are Acaulospora sp., Amanita sp., Boletus sp., Gigaspora sp., Glomus sp., Laccaria sp., Pezizella ericae, Pisolithus sp., Rhizoctonia solani, Sclerocystis sp., and Scutellospora sp.

5 Application of Biofertilizers Biofertilizers are provided as conventional carrier-based microbial inoculants that are cheap, environmentally benign, and easy to produce. The frequently used biofertilizers are nitrogen-fixing bacteria (Azotobacter, Rhizobium), cyanobacteria (Anabaena), PSB (Pseudomonas sp.), and AM fungi. Likewise, PGPB, rhizobacteria, and other cellulolytic microorganisms are also used in biofertilizer formulations. Their production involves culturing of microbes, processing and mixing carrier materials, and packaging. The principal carrier materials used for making biofertilizers should be cost-effective, easily available, and easy to process, should be nonhazardous and organic in nature with efficient water-holding capacity, and contain higher microbial cells and support their survival for long period of time. The carrier materials generally used are peat, charcoal, farmyard manure, vermiculite and soil mixture, etc. However, they may have drawbacks of having low shelf life, temperature sensitivity, and chances of contamination and are less efficient by lower cell counts. Accordingly, liquid formulations are developed for biofertilizers such as Acetobacter, Azospirillum, Azotobacter, and Rhizobium, which are although costly, but have the benefits of being easy to produce, higher cell counts, long shelf life, free of contamination, survival of up to 45  °C, and greater competence in soil (Ngampimol and Kunathigan 2008). Meanwhile, the biofertilizer applications include seed treatment, root dipping of seedlings, and soil applications.

5.1 Seed Treatment It is a valuable and commonly used treatment employed for all kinds of biofertilizers (Sethi et al. 2014). The seeds are thoroughly mixed and evenly coated in a slurry and air-dried, before 24 h of sowing. The coating for liquid biofertilizers depends upon the quantity of seeds; it can be done either in plastic bags for small quantities or buckets in case of large quantities. The treatment of seeds can be done with more than one inoculant as well. For example, nitrogen fixers like Azospirillum, Azotobacter, and Rhizobium can be used with phosphorus-solubilizing microorganisms which do not show any antagonistic effect on each other (Chen 2006). Seed treatment using Rhizobium is done for various pulses such as chickpea, cowpea, green gram, groundnut, and soybean; Azotobacter for barley, wheat, oat, mustard, sesame, linseeds, sunflower, castor, pearl millets, finger millets, and kodo millet; forage crops and grasses; and Azospirillum or PSB for rice, maize, and sorghum (Taylor and Harman 1990).

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5.2 Root Dipping of Seedlings This type of treatment is familiar for plantation crops including banana, cereals, cotton, grapes, fruits, sugarcane, tobacco, trees, and vegetables. Here seedling roots are dipped in a biofertilizer suspension for adequate time period which varies from crop to crop, for example, about 20–30 minutes of treatment is given to vegetable crops before transplantation and 8–12 h for paddy (Barea and Brown 1974).

5.3 Soil Application Here, biofertilizers are directly added to soil either singly or in combination with others. A combination of PSB, cow dung, and rock phosphate is left overnight, and its moisture content is maintained to about 50%; after which it is applied to the soil (Pindi and Satyanarayana 2012). Biofertilizers employed for this type of application are Azotobacter and Rhizobium (Hayat et al. 2010).

6 Conclusion Due to exponential rise in population, agriculture faces several unexpected environmental challenges especially in countries based on agriculture for their economy. Sustainable agriculture is of dire need in the present era to fulfill the demand of food for growing population across the world. Sustainability in agricultural system and other aspects is necessary for combating problems related to crop production and yield. Agricultural production and yield need to be increased in the modernized ways without deteriorating the ecosystem quality and existing natural resources. Thus, biofertilizers offer an eco-friendly approach for sustainable agricultural systems that are considered as cost-efficient and renewable sources of plant nutrients. The biofertilizers in sustainable agriculture are of vital importance in the present context of high costs of synthetic fertilizers and the dangers linked with them. They play a vital role in enhancing crop yield, nutrient uptake efficiency, and soil quality and in reducing the use of synthetic fertilizers, thereby maintaining crop production and quality. In order to maintain and improve the crop production, the integrated approach of plant-microbe interaction is of vital importance. Manufacturing of biofertilizers needs a considerable attention of researchers for their wide applications and promotion in agricultural fields. Furthermore, the screening and identification of efficient microbial strains need to be explored. The economic benefits, production, utilization, and storage conditions of biofertilizers need to be addressed so as to use them on a large scale and for sustainability in agriculture. This chapter highlighted the role of biofertilizers for attaining agricultural sustainability. Moreover, the biofertilizers open up new horizons in the

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agriculture and other important governmental sectors which can meet the challenges of food insecurity as well.

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Chapter 5

Biofertilisers and Biopesticides: Approaches Towards Sustainable Development Toyeeba Hassan and Gowhar Rashid

Abstract  The application of synthetic fertilisers and pesticides in Indian agriculture has sharply increased in recent years, reaching alarming levels in some regions with serious consequences for public health, the environment and groundwater aquifers. As a result of the widespread use of dangerous pesticides and chemical fertilisers on crops, agriculture systems were no longer sustainable, cultivation expenses rose quickly, farmer income stagnated and the risk to the health and safety of food worsened. The health of the soil has significantly declined as a result of the indiscriminate and unbalanced use of synthetic fertilisers, particularly urea and chemical pesticides, and a lack of access to organic manures. Target-specific biopesticides do not leave behind hazardous residues. Therefore, it is crucial to employ environmentally friendly techniques for controlling pests and diseases as well as increasing soil fertility. Among the alternate sources of plant nourishment, biofertilisers have come to light as promising eco-friendly supplements for healthy plant growth. They have enormous promise for supplying nutrients to plants while reducing the need for chemical fertilisers. A cost-effective method of managing agricultural output and environmental balance is provided by the proper use of bioinputs, which aid in restoring the health of the soil. A variety of biofertilisers have been created as a result of bacteria and fungus, which met the nutrient needs of crops and also boosted agricultural production. The most efficient way to influence the majority of components of sustainable agriculture has been found to be through the use of organic pesticides via integrated pest management (IPM). So if applied with the required knowledge, skill and research agriculture, biopesticide-driven IPM would promote sustainable agriculture. The potential, worth and limitations of biopesticides for sustainable agriculture are examined in this chapter along with the connection among sustainable developments and sustainable agriculture.

T. Hassan Centre of Research for Development, University of Kashmir, Srinagar, J&K, India G. Rashid (*) Department of Medical Lab Technology, Amity Medical School, Amity University, Gurugram, Haryana, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_5

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Keywords  Biopesticides · Integrated pest management · Chemical · Agriculture · Environment · Pests

1 Introduction Human population has doubled in the past 40 years and food production has also doubled (Vance et al. 2000). This extraordinary rise in food supply and demand is mostly attributable to the nutrition of plants. The usage of commercial fertilisers composed of man-made materials has increased crop production. An abrupt increase in the usage of chemical fertilisers has coincided with the growth in agricultural productivity over the past three decades, raising severe concerns. The use of fertiliser containing phosphate (P) and nitrogen (N) has also nearly doubled (Vance et al. 2000). The increased use of fertilisers and economically productive systems has led to a decline in soil characteristics and surface and groundwater quality, along with increased environmental pollution, decreased diversification and suppressed ecosystem function (Socolow 1999). Sustainable agriculture methods are obviously urgently needed on a worldwide scale. It has long been known that biopesticides and biofertilisers have significant potential for advancing sustainable agriculture. Globally, organic farming has risen to the top of the priority list due to the increasing need for secure and healthy food, lengthy sustainability and concerns about environmental contaminancy brought on by the uncontrolled use of agrochemicals. Although using chemical inputs in agriculture is unavoidable to meet the growing need for food worldwide, there are particular crops and niche markets where organic production can be encouraged to get access to the domestic export market. The improper usage and inadequate application of chemical pesticides have given rise to a significant issue, namely the presence of pesticide remnants in food. The majority of insecticides now in operation have a tendency to linger in plants for a long time. They join the food chain as well. In India, the issue of pesticide residue already poses a severe risk to the environment and public health. It is obvious that using synthetic pesticides in agriculture excessively is a big concern. Alternative, ecologically friendly plant protection techniques must be used, such as integrated pest management (IPM) methods that include biopesticides and biofertilisers. Biofertilisers are thought to be a very important alternative plant food source. These preparations, which contain live or latent cells of effective strains of bacteria, algae or fungi, are applied to seed, soil or composting areas in order to increase the number of these microorganisms and speed up the microbial processes that boost the availability of nutrients that plants can readily absorb. They are biologically active products with the capacity to supply nutrients to plants. In essence, they are bioinoculants that, when given to plants, enhance their development and productivity (Kawalekar 2013). They are an important part of organic gardening. Biofertilisers greatly enhance soil fertility by biological nitrogen fixation, either alone or in combination with plant roots. Additionally, they produce soil-based plant development factors and solubilise insoluble soil phosphates. Numerous researchers have noted that the

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addition of biofertilisers significantly improves fertility of soil, yield-attributing traits and ultimately final yield. Additionally, their use in soil increases soil biodiversity and reduces the need for synthetic fertilisers alone. The role and importance of biofertilisers in agricultural sustainability have been addressed by a number of authors (Biswas et al. 1985; Wani and Lee 1995; Katyal et al. 1994). Applying biofertilisers is the only option to increase soil nutrients for the preservation of soil health and potential crop production. Biopesticides and biofertilisers are crucial components of organic farming, a production method that often avoids the use of synthetic pesticides, fertilisers and other chemicals. Agriculture has a negative impact on numerous pests, such as bacteria, fungi, weeds and insects, thus reducing productivity and producing poor quality of products (Kumar 2012). The extensive use of synthetic pesticides has been the most popular approach of pest management since the 1960s. Dichloro-diphenyl-­ trichloroethane (DDT), along with other organophosphate and carbamate insecticides, was first used as a pesticide in the 1940s (Nicholson 2007). After that, by heavily utilising inputs like chemical fertilisers and pesticides, among other things, crop production techniques developed during the Green Revolution might had improved food output in developing countries. Even though the use of agrochemicals greatly increased agricultural productivity, they also had negative effects on the soil’s health, the water’s quality and the quality of the produce, and they gave rise to issues like insect resistance, plant genetic variation, toxic residues in food and feed, and food and feed safety. Additionally, reliance on chemical pesticides and their indiscriminate application had a negative impact on the ecosystem in a number of ways (Al-Zaidi et al. 2011). The development of substitutes for these synthetic agricultural inputs is increasingly crucial. The present challenge is to maximise output from limited natural resources while protecting the crop from post-harvest wastage and minimising environmental harm. Utilising biopesticides and biofertilisers can be quite helpful in finding a sustainable solution to these problems. The naturally occurring combinations of compounds that manage pests through nontoxic and environmentally beneficial means, such as biopesticides and biofertilisers, are not newer technology. Since the dawn of human civilisation, they have been utilised in numerous ways. The use of biopesticides has a lot to offer in agricultural and public health initiatives (Kumar and Singh 2015). In the upcoming decades, population expansion and resource demands are anticipated to exacerbate India’s nutritional and health problems. The country will overtake China as the most populated nation in the world by 2050 when its population, which is currently 1.26 billion, is projected to increase to 1.6 billion (Holden et al. 2016). The effects of climate change, water scarcity and declining soil fertility owing to land degradation have all been linked to India, making it one of the nations most sensitive to these issues (Roberts 2001). Deserts would eventually emerge as a result of intensive land farming without preservation of soil fertility and soil structure. Soils would become alkaline or saline if irrigation was not done with drainage in mind. Because of the harmful residues left behind in the grains or other edible portions, the excessive use of pesticides, fungicides and herbicides may have a negative impact on the biological balance and increase the prevalence of cancer and other disorders. Unscientific mining of subsurface water would hasten the rapid depletion

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of this priceless capital resource, which has been ours, thanks to centuries of natural farming. In broad contiguous areas, the quick substitution of multiple locally adapted types with one or two high-yielding strains might lead to the spread of dangerous diseases capable of eradicating entire fields, as occurred during the Irish Potato Famine of 1845. As a result, the introduction of exploitative agriculture without a thorough understanding of the various effects of each change made to traditional agriculture and without first developing a sound scientific and training foundation to support it may ultimately result in an era of agricultural disaster rather than prosperity. In order to maintain food security and nourishment for everyone, now and in the future, sustainable agriculture sector is agricultural development that helps to improve resource efficiency, strengthen resilience and secure social assets of agriculture and food systems. Because they use a lot of resources, agriculture systems have extensive interactions with the environment and natural resources. Agriculture occupies over 50% of India’s total land area and consumes 90% of the nation’s total water withdrawals (Sims et al. 2015). Due to weather variability that can interfere with crop cycles, it is one of the industries that not only helps to cause climate change but also suffers one of the harshest effects from it. India’s agricultural systems are in charge of providing farmers’ livelihood security and achieving food security. Both of these tasks must be completed in light of a diminishing base of natural resources, a deteriorating environment and the impacts of global warming on agriculture and assets. By 2030, India would not have enough food for everyone if current trends continue. If total factor productivity (TFP) continues to expand at its current rate, India’s domestic production will only be able to supply 59% of the nation’s food needs by 2030 (Nash et al. 2017).

2 Strategies for Sustainable Agriculture Development Utilising biotechnological methods to find and select suitable locations, crops and soil variants for N-fixing, P and Zn emulsifying and absorbing (mycorrhizal) to adapt varied agroclimatic conditions, providing technical training on production and technical advice and projects’ quality control to producers and rendering to manufacturers, exchanging cultures among their efficiencies for countries with the same environmental conditions, assessing during the best strain for a specific crop, monitoring the interaction of cultures stored to prevent organic mutants, providing organisational training to extension workers and farmers technology and disseminating information through mass media are all examples of ways to advance science (Kumar and Singh 2015). Sustainable agriculture seeks to achieve a balance between the needs of the present and those of future generations without compromising either by taking ecosystems into account when using natural resources (Burton 1987). However, Rachel Carson’s widely read book The Silent Spring (Carson 1963), which highlighted the damage agriculture causes to the environment, helped usher in a new era of global consciousness in the 1960s. Furthermore, Garret Hardin argued in his 1968 book Tragedy of the Commons that the rational pursuit of

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individual interests eventually compromises collective interests and depletes the planet’s natural resources (Hardin 2009; Frischmann et al. 2019). According to the insightful computational simulation of Meadows et al. (1972), if a man does not set a growth limit tied to the usage of the unquestionably finite natural resources, economic and social collapse will result. Their forecasts came true 40 years later when global pollution and the issues that come along with it began to pose a danger to sustainable development. The first UN Conference, held in Stockholm in 1972, was intended to address how human activity affects the environment and how it relates to economic development, based on the theories of resource depletion and pollution (Maurer and Bogner 2019). Finding a unifying principle to encourage and direct the worldwide populace to protect the human environment was also essential. The World Conference in 1979 gradually centred on the influence, evaluation and contributions of human and natural sources, as well as the implications of climate change for human society. The human development index, which takes into account both social and economic achievements, emerged as a result. The Brundtland’s (“Our Common Future”) report (1987), which stated that the collection of technology, social organisation and the biosphere’s ineffective status is a means of mitigating the impacts of human activities, provided the simplest and most widely accepted definition of sustainable development. The macroeconomic sector and the ecosystem were connected by the United Nations Conference’s Agenda 21 drought plan from 1992. The report focused on outlining how the ecosystem is deteriorating and how to use this knowledge to establish policies for sustainable development. This paradigm situates sustainable development on the triangle basis of the economy, society and environment, and if it were to be pursued with true intent, it would definitely promise a far more prosperous future via greater standard of living and secure habitats (Blandford 2011). In addition to the Steward W.  C. framework and the Steward W. C. self-sustaining agriculture’s five domain concepts (economic, sociocultural, technological, environmental and public policy), sustainable agriculture can also be viewed in the context of the 12 Green Chemistry Principles and the 17 Sustainable Development Objectives (United Nations) (Marteel-Parrish and Newcity 2017; Anastas and Warner 1998). When one conceptualises sustainable agriculture along the three axes, what is meant are agro-practices that link ecologic healthiness (effective utilisation of precious resources; protection of air, land and water contamination; and decline of health hazards), commercial feasibility (dependable and lucrative manufacturing actions) and public acceptance (consciousness, enhanced quality of life and equality). With this in mind, the tripod’s three components will gradually receive equivalent attention (Zhen et al. 2005). The Pollution Prevention Act of 1990 established the concept of “green chemistry”, which Joseph Breen, Tracy Williams and Paul Anastas developed in 1998 (Tundo and Griguol 2018). Since then, the concept has gained prominence in theory, development and practice. The adjective “green” denotes benign solvent and catalyst/ reagent, and energy consumption components are associated with a reaction. To protect the environment and its receivers, including man, this entails implementing the most inventive and safe safety measures in accordance with some scientific understanding. This means adopting the safest innovative measures in line with

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Fig. 5.1 Three-­ dimensional concepts showing sustainable development in agriculture

some elements of chemical knowledge to protect the environment and its receptors including man (Ivanković et al. 2017). The flow chart for sustainable agriculture is shown in Fig. 5.1.

3 Pests and Their Associated Diseases Food production has been a deliberate preoccupation since the Tertullian era (300 AD) to sustain the nation’s rising population. According to the UN, there will be 9.15 billion people on Earth in 2050. There will be 7.70 billion people living in the planet in 2020, up from 6.9 billion in 2010 and 2.25 billion in 1970, suggesting a population growth rate of 0.8 billion people every 10 years (Alexandratos and Bruinsma 2012). According to current figures, global demand can be met by agro-­ production, but third-world nations’ contributions are appallingly low because of a confluence of causes, including poverty and the failure of sections of society and leaders to modernise agriculture. And as a result, a significant portion of the global population—hundreds of millions—experiences pervasive hunger (Fan and Rosegrant 2008). 820 million people around the world experience hunger, which is ironically close to the target population that the “world without hunger” programme aims to reach by 2030 (Sobiczewski 2008). In the absence of crop pests, the regional and worldwide enhancement of the total agricultural production would have performed better. The following symptoms, among others, may be brought on by phytopathogenic bacteria: galls, leaf spots, blights, overgrowths, wilts, specks, soft rots, chlorotic halos, cankers and scabs. Relatedly, some of the illnesses they bring about include brown rot, fire blight, bacterial soft rot, black rot of cabbage and walnut bacterial blight (Mergenthaler et  al. 2020). Although this is not always the case, plant illnesses brought on by fungi can be identified by the specific plant organ they damage and the sort of symptom they produce. These allow us to differentiate between the following fungal diseases: damping-off disease, powdery mildew, downy mildew, vascular wilts, root and foot rots, rusts, galls, dieback and anthracnoses (Brown and Ogle 1997). Tobacco mosaic virus, plum pox virus, yellow leaf

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curl virus, potato virus X, African cassava mosaic virus, brome mosaic virus, cauliflower mosaic virus and potato virus Y are a few prominent plant viruses (Scholthof et al. 2011). Nematodes are creatures that resemble worms, and some of them are reported to parasitise plants. Root knots, yellow patches, yellow dwarfs, lesions, root-tip swelling, stem rot, flagging, cyst, stubby-root and corky ringspots are all known to be caused by them (Mduma et al. 2015). Dodder and mistletoe are wellknown plant parasites. The most dangerous pests are thought to be insects. An estimated 0.5% of all insects are crop pests, but they also provide four important ecological functions: pollination, nitrogen cycling, decomposition and predation (Jankielsohn 2018). According to Bartomeus et al. (2014), insect pollination contributes 9.5% to agricultural output yield while being responsible for 72% of crop reproduction globally. The intentional human actions including removal of vegetation to make room for crops and animal production to ensure food security compromise the ecosystem and its functions and contribute to an active manifestation of pests (Losey and Vaughan 2006). When biodiversity is distorted, it has an immediate cascading impact that drives insects to aggressively compete with people for resources like space and food. Pests have unquestionably significant economic effects on the world as a whole. To put it simply, the world must battle with about 40,000 pest species in order to produce enough food for the growing human population.

4 Biopesticides The main objective of the green revolution was to increase crop yields at all costs. Agriculture that increases yields without damaging the environment is increasingly prioritised. A crucial element of sustainable agriculture is the use of biopesticides. They are particular varieties of pesticides produced using resources such as specialised minerals, plants, animals and microorganisms. Microbial pesticides have an active ingredient that is a microbe, such as a bacterium, fungus, virus or protozoan. Microbial pesticides can control a number of pests even though each active ingredient is quite specialised for the pest(s) it is meant to control. For instance, some fungi kill specific insects while others manage specific weeds. The most widely employed microbial insecticides are subspecies and strains of Bacillus thuringiensis or Bt. Each strain of this bacteria targets and eliminates just one or a limited number of closely related insect larvae species, and it produces a variety of protein combinations. While some Bts are specifically designed to prevent fly and mosquito larvae, other Bts are used to control moth larvae on plants. The type of Bt that releases a protein that can connect to a receptor in the gut of a larva and cause the insect larvae to starve determines which insect species it will target. Plants create pesticides called complete genome that has been incorporated into the plant which results in plant-incorporated protectants (PIPs). For example, scientists can alter the genetic structure of the plant to introduce the gene for the Bt pesticidal protein. The plant, not the Bt bacterium, then produces the chemical that kills the pests. Pests are

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controlled by biochemical insecticides, which are natural substances. Traditional insecticides, on the other hand, frequently contain synthetic materials that either directly kill or inactivate the bug. Biochemical pesticides include insect sex pheromones that hinder mating and other fragrant plant extracts that attract insect pests to traps (Kumar 2012). Natural organisms or bio-based formulations known as biopesticides are thought to work in a variety of ways to control pests (Tijjani et al. 2016). They come from microbes (Bacillus thuringiensis, Verticillium lecanii, Neodiprion sertifer), insects (Trichogramma spp.), plant parts or extracts (such as a finely crushed flower of Chrysanthemum cinerariaefolium) and animals (nematode, Heterorhabditis spp.) (Pavela 2014; Rodgers 1993). The widely accepted definition, however, deviates in that natural materials should be considered chemical pesticides if they can affect the nervous system of pests (Marrone 2019). Similar to nicotine, which is a rapidly acting nerve toxin, sabadilla; pyrethrins, which disrupt normal nerve impulse transmission; and fluoroacetate, which affects the nervous system by causing glutamic acid depletion, are all potent pesticides that damage insect nervous systems (Oguh et al. 2019). However, the majority of the literature labels these substances as botanical insecticides. A biopesticide can also be thought of as its chemical counterpart. Phytosanitary biocontrol agents or bioproducts include biopesticides designed to control herbivorous insects or pests (Brudea et al. 2012).

4.1 Biopesticides’ Categories and Their Modes of Action Biopesticides might be microbial, biochemical or plant-incorporated protectant (PIP) based. The following five categories can be used to categorise their modes of action according to the biological processes they influence: growth regulators, gastrointestinal irritants, metabolic toxins, neuromuscular toxins and non-specific multi-site inhibitors (Sparks and Nauen 2015). Some of the mechanisms of action, particularly with regard to biochemical biopesticides, are still not fully understood. Microbial biopesticides use antagonism, predation, parasitism and antibiosis to maintain control (Mishra et al. 2018). A natural material must have a nontoxic mode of action in order to qualify as a biochemical biopesticide. Plant-incorporated defences depend on the integrated chemical, which might come from either plants or microbes (Ivase et al. 2017). 4.1.1 Microbial Biopesticides Microbial biopesticides are substances produced by bacteria, fungus, viruses, protozoa and nematodes that affect pest activity through pathogenicity, competition or inhibitory toxins. Multifactorial microbial generalists and hyperparasitic microbial specialists are two major categories into which these agents fall. While specialists focus on a specific issue, generalists manage a larger variety of pests. More than 3000 microorganisms, including greater than 100 bacteria, 800 fungi,

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1000 protozoa, 1000 viruses and 2 significant groups of nematodes (Steinernema, 55 species, and Heterorhabditis, 12 species), have been identified as disease-causing agents in insects (Dowds and Peters 2002). The benefits of this class of biopesticides include precision (non-pathogenic to nontarget), synergisms (which could be used with agrochemicals), environmentalist (their distillate has no negative impact on the environment), permanent impacts (the microorganism becomes an essential component of the insect species or its biodiversity displaying the inhibitory effects) and betterment in plant growth (Nawaz et al. 2016; Hakeem et al. 2021). 4.1.2 Biochemical Biopesticide Biochemical biopesticides are compounds containing active ingredients that come from nature and are used to manage pests using methods that are safe for humans, the environment and the host. A natural substance can meet the criteria for being a biopesticide if it has the following properties: attractant, deterrent, repellent, antifeedant, suffocant, confusant, arrestant and desiccant (Kumar 2012; Leahy et  al. 2014). Since they are natural, these chemicals must be separate or combined bioactive elements from the natural world. However, a synthesised duplicate that is exact in both structure and function with respect to a natural substance possesses the same mode of action (Stankovic et  al. 2020). Some artificial equivalents of naturally existing compounds now predominate the market due to a number of circumstances. Although the term “toxic” is ambiguous, a drug is considered harmless if its active ingredients do not directly cause the target pest’s physiology to change in a way that causes direct mortality of the target host (Fenibo et  al. 2022). Botanical extracts have bioactive components that, in entomopathogenic fungi, can inhibit hyphal growth, change the mycelial structure, alter the cell wall, divide cytoplasmic membrane and separate the cytoplasmic membrane. Plant extracts change the way that insect pests consume, lay their eggs and mate. They also stop the insects from reproducing, growing and developing (Lengai and Muthomi 2018). Essential oils function as deterrents to oviposition, repellents and antifeedants. Additionally, they have compounds in them that have larvicidal, ovicidal and insecticidal effects, interfering with all phases of insect metamorphosis (Sarma et al. 2019). 4.1.3 Plant-Incorporated Protectants A gene put into a plant through transgenesis creates a biopesticide known as a plant-­ incorporated protectant (PIP). PIP makes the plant unfit for an assault rather than requiring the pest to be killed (Ibrahim and Shawer 2014). The guarded plant might occasionally serve as a deterrent or disrupt the normal metabolism of the insect pests when they consume PIPs. After being consumed, PIP gets through digestive and physical obstacles to reach the target area, where it performs. The disturbance of gut activity has been a reoccurring problem in the development and identification

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of PIPs since it has been shown that the digestive system significantly influences insect sensitivity and vulnerability (Nelson and Alves 2014). Since insecticidal proteins, more importantly Bt, can be used in PIPs, they are being investigated for use in pest management (Koch et al. 2015). Since 1902, when the silkworm (Bombyx mori) was the target of Bacillus thuringiensis’ insecticidal activity, researchers have been looking for Bt strains that can effectively control insects (Jisha et al. 2013). The efficient, varied and selective insecticidal proteins of Bt are frequently utilised as models in PIP biotechnology; nevertheless, Schwnek et al. (2020) have shown that Bt exhibits non-negotiating harmful potentials. The Cry proteins (endotoxins), an insecticidal crystal protein made by Bt, are varied and demonstrate insect selectivity, and they are specific to Lepidoptera, Coleoptera and Diptera, for example (Maciel et al. 2014).

4.2 Advantages of Biopesticide Biopesticide is gaining popularity due to its advantages for the environment, target specificity, effectiveness, biocompatibility and usefulness in integrated pest management (IPM) programmes. So one of the potential approaches to regulate environmental contamination is biopesticide. The possibility of using biopesticides to protect the environment is well understood, but interest had also increased because of the growing market for organic foods. There are some opportunities for biopesticides to be used as a part of IPM in some crops and niche areas, despite the need to utilise agrochemicals to meet the always rising needs for food, feed and fodder. Environmental safety may benefit from the greater use of biopesticides in agricultural and health programmes (Kumar 2012). Typically, biopesticides are less hazardous by nature than traditional pesticides. Biopesticides frequently only affect the target pest and closely related organisms, in contrast to diverse agrochemicals, which may harm a number of organisms, including birds, insects and mammals. Traditional pesticide pollution problems are often avoided by using biopesticides, which often act in incredibly tiny quantities and frequently disintegrate swiftly (Kawalekar 2013).

4.3 Biopesticide Prospects and Limitations When conventional synthetic pesticides and biopesticides are compared closely, comparable parallels emerge, especially in terms of potency. Conventional pesticides are easy to use, effective against the intended pests and quick to start working and have a lengthy residual effect (Felsot and Rack 2007). A substantial proportion of synthetic pesticides now have placement limits because of their harmful effects. According to Jensen (2015), just 250 active components of conventional pesticides were permitted in 2009, down from around 1000 in 2001. From 70 in 2000 to 28 in

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2012, the quantity of new synthetic pesticides has similarly reduced (McDougall 2013). Due to the bad impacts that are slowly killing off the dubious practice of applying synthetic pesticides, there is now a greater need for alternative pesticides to combat them. Because of its selectivity and less toxicity in comparison to chemical pesticides, the use of biopesticides typically has few or no negative impacts on humans, nontarget creatures or the environment. The use of biopesticides in place of synthetic pesticides is predicted to increase agricultural yields in the near future (Leng et al. 2011; Arora et al. 2016; Dar et al. 2022). The application of chemical pesticides, which have shown to be successful both quantitatively and qualitatively, in combination with biopesticides appears to be an operational compromise at the moment (Ujagir and Byrne 2009). Although it is not the best option, it does have advantages over using only these synthetic pesticides in that it reduces pollution and other negative impacts. The usage of biopesticides has several great advantages, one of which is that they are environmentally friendly. Their presence in the air, water and terrestrial ecosystems is absent or low because they are readily biodegradable and leave behind few traces. Biopesticides’ high specificity ensures that they only kill the intended pests while promoting the growth of beneficial species like pollinators, predators and parasitoids for the benefit of the protected crops as a whole.

4.4 Present Status Only 2% of plant protectants used globally today are biopesticides, but their growth rate has been trending upwards for the past 20 years. Over 3000 tonnes of biopesticides are thought to be produced year globally, and this number is rising quickly. The usage of biopesticides is rising rapidly worldwide, at 10% a year. Only one entomopathogenic bacteria, Bacillus thuringiensis, is the source of almost 90% of the microbial biopesticides. In contrast to just 60 equivalent products in the EU, there are about 200 products available on the US market. In 30 OECD (Organisation for Economic Co-operation and Development) nations, more than 225 microbial biopesticides are produced (Hubbard et al. 2014). About 45% of the biopesticides sold are used in the NAFTA (North American Free Trade Agreement) countries (the United States, Canada and Mexico), whereas just 5% are used in Asia (Bailey et  al. 2010). Nonetheless, the regulatory framework established for chemical pesticides has always been predominantly used to biopesticides. Most nations have altered their policy to encourage the use of biopesticides while reducing the usage of conventional pesticides. The biopesticide sector was burdened with high prices, which served to establish obstacles to market entry. Although various technological and policy deficiencies have been discovered for the efficient use of biopesticides, they must be effectively addressed at the national level. To prevent overuse of conventional pesticides and encourage the use of biopesticides, policy measures must be increased (Kumar and Singh 2015). We really have to increase public knowledge of the advantages of switching to biopesticides for pest management needs among landowners, producers,

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government bodies, decision-makers and the general public because protection of the environment is a priority for everyone (Kumar and Singh 2015).

4.5 Recent Advances Biopesticide research is still regarded as new and developing. Numerous domains, including product production, formulation, distribution and commercialisation, require in-depth research. In addition to the ongoing search for new biomolecules and enhancements to the effectiveness of the currently employed biopesticides, recombinant DNA technology is being used to augment the efficacy of biopesticides. Innovative hybrid molecules are being developed in an effort to produce the subsequent generation of biopesticides. Instead of previously only being harmful when injected into a predator’s prey, a toxin that is not harmful to living organisms can now be combined with a carrier protein to make it poisonous to insect pests when ingested (Fitches et al. 2004). The amplified product may be produced in a microbial environment as a recombinant protein that may be scaled up for use in industrial manufacturing and commercial formulations. The development of biopesticides as acceptable, successful and efficient pest management solutions also employs other cutting-edge techniques.

5 Biofertilisers Chemical pesticides and fertilisers have significantly increased agricultural production during the past 50 years, yet they are relatively new to modern agriculture. Their quick response and low price allowed them to quickly become the centre of attention. Their harmful consequences on the environment, plants, animals and people deflected attention from the need to protect eco-friendly plant life. Additionally, the problem of insects developing resistance to typical pesticides has not yet been resolved. As a result, techniques like integrated pest management (IPM) have become more significant (Al-Zaidi et al. 2011). The word “biopesticide” refers to the employment of advantageous microorganisms as a pesticide. In order to restore the health of the soil and enable it to survive on sources other than chemical fertilisers, the concept of biofertilisers was developed. Biofertilisers include nutrition accessibility methods that incorporate biological functions. The word “biofertilisers” refers to specific microorganisms, such as bacteria, fungus and algae, that can transform soluble phosphate and potash in the soil into forms that plants can utilise or fix nitrogen from the atmosphere. A biofertiliser’s function in preserving long-­ term soil fertility and sustainability is crucial since it is affordable, environmentally friendly and renewable. With the aid of a nitrogen fixer and a phosphate solubiliser, the biofertiliser binds 20–40  kg of nitrogen each hectare. By being employed to ensure yield and keeping the cost of soil fertility down, the biofertiliser causes the soil very productive for high-quality output (Al-Zaidi et al. 2011).

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5.1 Types of Biofertilisers Most biofertilisers fall into one of two subgroups: those that fix nitrogen or those that solubilise phosphate. Nitrogen-fixing biofertilisers transform air nitrogen into other versions which plants can easily use. Rhizobium, Azotobacter, Azospirillum, blue-green algae (BGA) and Azolla are a few of them. Others can fix nitrogen on their own; however, Rhizobium needs symbiotic interaction with the plant rhizosphere of legumes to do so. Microorganisms that dissolve rock phosphate, such Bacillus, Pseudomonas and Aspergillus, among others, release organic acids that improve plants’ ability to absorb phosphorus. Others include zinc solubilisers and phosphate mobilisers. Biofertilisers that fix nitrogen, such as Rhizobium, Azospirillum and Azotobacter, BGA, phosphate-solubilising bacteria and phosphate-­mobilising mycorrhiza, are commonly used. The efficiency of biofertilisers on diverse crops, in different agro-climatic areas, has been the subject of extensive investigation. The yield of most crops can be significantly impacted by the use of biofertilisers. However, it has been discovered that their efficacy varies widely, mostly dependent on the kind of soil, the weather and the farming techniques (Kumar and Singh 2015).

5.2 Advantages of Biofertilisers Nutrients are renewable; maintain soil health and boost grain yields by 10–40%; add to chemical fertilisers and/or replace them by 25–30%; decompose plant waste and stabilise the soil’s C:N ratio; enhance the soil’s structure, texture and water-­ holding ability; and have no negative effects on plant development or soil fertility by stimulating plant growth through the secretion of growth hormones and facilitating nutrient mobilisation and solubilisation, this approach offers an eco-friendly, non-polluting, and cost-effective method (Kumar and Singh 2015).

5.3 Current Status of Biofertiliser Development The primary and instruct objectives of implementing biofertilisers to root system must be to supply micronutrients and create favourable growing conditions for the development of crops when utilised as a human corpse; to replace conventional and improve the effectiveness of nitrogen fertiliser and then decrease the quantities of fertilisers applied even while preserving the very same agricultural output; and to reduce the negative effects of agrochemicals. Contrarily, adding biofertilisers to soil has secondary advantages such as boosting seedling survival after transplantation, speeding up flower emergence, extending the life span of roots, neutralising and decomposing hazardous substances stored in soil and encouraging root growth (Aggani 2013).

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5.4 Future Perspective of Biofertilisers Due to excessive use of chemical fertilisers by farmers during intensive agricultural operations, excess nutrients, particularly P, accumulate in soils. The development of effective and long-lasting biofertilisers for agriculture crops, so that the application of inorganic fertiliser could be greatly decreased to prevent further environmental issues, should therefore receive important scientific attention. It is going to be important to do short, moderate and protracted research in order to overcome this bottleneck and to do so short-, medium- and long-term research. To do this, soil biochemists, horticulturalists, agronomists, plant specialists, even dietitians and marketers must collaborate (Aggani 2013). The following are the most crucial and specific research needs to be highlighted: 1. Choosing multi-functional biofertilisers that are efficient and affordable for a range of crops 2. Quality assurance system to make sure of the research on the benefits of plant microbial interaction in inoculants and their field use 3. Research on the microbiological survival of biofertilisers in stressed soil environments 4. Agronomic, soil and financial evaluation of biofertilisers for various agricultural production systems 5. Transferring technological know-how for optimal formulation and commercial biofertiliser production 6. The establishment of the “Bio-fertilizer Act” and strict rules for use and quality control in the market (Yuan et al. 1995; Lin and Chang 1987)

6 Conclusion To boost and maintain the production of agricultural fields, the most efficient plant-­ microorganism relationship must be discovered utilising an integrated approach. The current trend of low chemical input agriculture systems will help achieve the objective. For growers to have the opportunity to learn about the impacts of biofertilisers and be willing to utilise them, the Council of Agriculture (COA) sponsored a number of events and seminars on the topic. Growing attention is being generated by recent developments in the field of biofertilisers as a result of their usage of environmentally friendly fertilisers that support sustainable agriculture practises. These biofertilisers use living microorganisms that form symbiotic connections with the plants or are an inoculation of microorganisms that promotes plant development by boosting the primary nutrient availability to the host plant and also maintains soil fertility. Similar to the use of chemical pesticides, the use of biopesticides has emerged as a potential solution to limit the use of these chemicals due to the numerous drawbacks associated with them, such as genetic alterations in plant populations, food poisoning and other health issues.

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In the years to come, biofertilisers will be crucial in enhancing nutrient supplies and crop availability. They are inexpensive, environmentally beneficial agriculture inputs. By fixing atmospheric nitrogen, mobilising fixed macro- and micronutrients and converting insoluble phosphate in the soil into forms available to plants, they serve a crucial role in preserving long-term soil fertility and sustainability. The only way to increase soil organic carbon for the maintenance of soil quality and future agricultural productivity is to apply biofertilisers. Consent for Publication  As the chapter did not cover any personal or individual data, audio or videos, there was no need for publication permission. Conflict of Interest  The authors declare no conflict of interest.

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Chapter 6

Credibility of Biofertilizers Towards Restoration of Fertility Phenomenon in Degraded Soil Environs J. A. Ruley

, J. O. Galla, T. A. Basamba, and J. B. Tumuhairwe

Abstract  Three decades to come, evidence is rife that different areas worldwide will be more populous than now. A whopping 25% rise in population will see planet Earth host close to ten billion people. This will cause a spectacular increase in the number of mouths to feed; hence providing insights that sustainable management of our resources is a prerequisite. Soil is the core of the resources that man must preserve and conserve. Directly, it is a base factor for agricultural prosperity and increased productivity, while indirectly, human and animal health are impacted by deteriorated soil health. The interventions adopted to improve soil fertility to match the raising numbers of people such as intensification by smallholder farmers and large-scale players through green revolution have caused unacceptable levels of soil degradation leading to infertility. Common to observe in the different environments are chunks of wasteland, yet formerly, these areas served as national, regional or international food baskets and salad bowls. To cushion against the looming predictions of human disaster caused by hunger and intense food insecurity, novel interventions capable of promoting sustainable livelihoods via agricultural production and biofertilizers inclusive, have been tested and proven. Biofertilizers are beneficial microorganisms packaged in a carrier medium which is applied in the soil to introduce and supplement limiting essential nutrients, remediate polluted soil, suppress pathogens and scavenge and chelate heavy metals, among others. The actions of the biofertilizers may involve a single package, dual or consortium. In this chapter, an appraisal is made of biofertilizer use for restoration of fertility in degraded soil environs. An inside-out analysis is provided using stair case argumentation, and further insights are provided on the way forward.

J. A. Ruley (*) · J. O. Galla Department of Agricultural Sciences, University of Juba, Juba, South Sudan T. A. Basamba Department of Agricultural Production, Makerere University, Kampala, Uganda J. B. Tumuhairwe Department of Agricultural Production, College of Agricultural and Environmental Sciences, Makerere University, Kampala, Uganda © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_6

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Keywords  Soil · Soil fertility · Beneficial microorganisms · Essential nutrients · Restoration · Sustainable management

1 Introduction Human life on Earth is dependent on well-performing agriculture, and therefore, the sector is the greatest source for support life on Earth (Nabyonga et  al. 2022). In 2013, the United Nations (UN) anticipated a big rise in global population by 2050 (Mahawar et al. 2020). In 2020, while the world’s population was 7.8 billion people (International Institute of Sustainable Development [IISD] 2020), by 2050, the number is expected to swell to 9.9 billion, representing a 25% increase (IISD 2020). The most increase is expected in Africa (Aloo et al. 2021). These statistics imply that by 2050, the world is likely to face the worst case of food insecurity ever recorded in history (Mahawar et al. 2020). This worry is justified by the putative fact that additional mouths must be fed. Hence, more problems are anticipated to bedevil mankind. Therefore, scientists especially in the agricultural sector such as plant breeders, agronomists, soil scientists and agromicrobiologists are tasked to work out the possible solutions to avert the anticipated crisis. Aloo et al. (2021) note that agriculture is the most important pillar for attainment of food and socio-economic security in most if not all states running an agrarian economy. This need is even more urgent as soon as now in Africa where on average, more than 65% of the active workforce ekes a living from the sector either directly or indirectly (Aloo et  al. 2021). Moreover, a proportionately greater contribution to the GDP of about 30% is contributed by the sector (Aloo et al. 2021). Sad to note however is that today, the sector is grappling with several challenges, decline in soil fertility inclusive (Hakeem et al. 2021; Verma et al. 2022).

2 Soil-Agricultural Production Nexus Soil is a major medium through which agricultural productivity is achieved (Nabyonga et  al. 2022). Incidentally, soil is a nonrenewable or finite resource of nutrients (Aleminew and Alemayehu 2020; Jatav et al. 2021). Despite this characteristic, in different environments, soil has been massively degraded by both natural and man-made factors leading to soil infertility (Abebe et al. 2022). Depletion of the soil fertility has become an acute problem (Mishra and Arora 2019; Ruley et  al. 2022). The major causes of infertility are anthropogenic activities that have caused both degradation and infertility (Mishra and Arora 2019). Cognizant of this challenge and the linkages between soil fertility, agricultural productivity, food insecurity and poverty, many policy makers and subject matter experts are a crush programme of ensuring that soil health is reinstated lest the worst human disaster befalls planet Earth by 2050 when the world’s population is anticipated to explode

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by 25% (Abebe et al. 2022). On this basis therefore, maintenance of soil fertility forms a bedrock on which the better performance of the agriculture sector anchors (Gholamhosseinian et al. 2021; Ruley et al. 2022; Dar et al. 2022). With burgeoning population and even more increase expected, efforts have to be taken to ensure that better strategies are designed to improve and enhance the agricultural yields (Kaur and Purewal 2019). The adoption of green revolution and intensification of farming practices are case examples of efforts taken to cater for the increasing population via the window of increased agricultural production. One of the salient features of green revolution and intensification is increased use of chemical fertilizers to replenish lost soil nutrients. Green revolution and intensification have high-affinity chemical fertilizer use (Atieno et al. 2020). For a long period of time, addition of chemical fertilizers has been applauded as a good solution for increasing agricultural production (Gholamhosseinian et al. 2021). However, practically, chemical fertilizers are not the best. One of the major drawbacks is its injurious effects on soil especially after large-scale use (Kaur and Purewal 2019). These fertilizers have caused a major decline in soil quality (Kaur and Purewal 2019) leading to soil infertility and productivity (Shabbir et al. 2019). What is more to say, continuous use of chemical fertilizers also destroys soil biota (Boraste et al. 2009) leading to decimation of soil fauna and microbial communities (Atieno et al. 2020). Equally, continuous use increases soil salinity (Pankaj 2020), induces soil structure instability (Abinandan et al. 2019) and leads to pest resistivity (Kumari and Singh 2020). Consequently, there is a marked reduction in soil fertility and a drastic drop in farmer productivity (Atieno et al. 2020). Declining soil fertility is a global challenge. At present, it is reported that more than 500 million hectares of land in the tropics and more than 33% of Earth’s land surface are covered with unhealthy soil (Atieno et al. 2020). Atieno et al. (2020) define soil health as the ability of soil to function as living system leading it to support and sustain health plant and animal life in addition to her functions of improved water and air quality. Further, health soil is able to have balanced and stable physicochemical and biological properties (Atieno et al. 2020). What is more to say, in such a state, there are successful nutrient cycling, improved soil structure, improved water availability and holding capacity and ease in suppressing crop pests and diseases (Atieno et al. 2020). Such soil is believed to be fertile since the aforementioned attributes are determinants of luxuriant crop plant growth as well as potential yield enhancers (Patil and Solanki 2016). Given the fact that sustainable crop production hinges on good soil health, efforts must thus be made to ensure that the available cultivable soil is well maintained (Boraste et al. 2009). By doing so, insurance for the worst days to come by engendering sustainable production of crops will have been enhanced (Boraste et al. 2009). The restoration of the agricultural soils turned marginal lands holds a special place in the realization of the 2030 United Nations SDGs 1 (no poverty), 3 (good health and well-being), 6 (clean water and sanitation), 13 (climate action) and 15 (life on land) (United Nations University 2018). Among others, it will solve the triple problems of feeding the burgeoning population, mitigating the spate of climate change and reducing the current magnitude of biodiversity degradation (Atieno

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et al. 2020). To meet the growing demand for food sustainably, it is advisable that safer organic and nano-fertilizer technologies be adopted for improved soil productivity and environmental sanitation (Nabyonga et al. 2022; Das et al. 2019). The use of biofertilizers is one window of opportunity available (Ibeh et  al. 2019). Biofertilizers provide a lasting solution for restoration of the wastelands because they are a mix of growth-specific nutrients for boosting agroproduction and protecting or maintaining the environmental conditions (Kaur and Purewal 2019).

3 Biofertilizers and Soil Health Also called a microbial inoculant, Boraste et al. (2009) and Simarmata et al. (2016) define biofertilizers as a preparation made up of either live or latent cells of efficient strains of nitrogen-fixing microorganisms, phosphate-solubilizing microorganisms or cellulolytic microorganisms that is either applied to seeds, soil or composting areas intended to increase the number of such microorganisms so that they can accelerate the microbial process through which the available nutrients can easily be assimilated by plants. In the strictest meaning of the term, biofertilizers are not supposed to be confused with fertilizers that are applied directly to crop plants to supply the limiting nutrients (Boraste et al. 2009). Rather, biofertilizers are cultures of microorganisms. The selected microorganisms for biofertilizer production are called beneficial organisms (Ortiz and Sansinenea et al. 2022; Atieno et al. 2020) or plant growth-­promoting rhizo-microorganisms (PGPR) (Atieno et  al. 2020). The main ones are bacteria and fungi. These are packed in a carrier material (Boraste et al. 2009). Therefore, it is imperative to note that the critical inputs in the making of biofertilizers are microorganisms.

3.1 History of Biofertilizers The current widespread use of biofertilizers has a rich history dating to the twentieth century (Boraste et al. 2009). Pioneer efforts were made by Hellriegal and Wilfarth whose scientific works in the 1980s made a revelation that atmospheric nitrogen was fixed in leguminous plants (such as beans, ground nuts and peas, among others). However, this discovery anchored on the works of Beijerinck, a Dutch scientist, who in 1888 made a scientific breakthrough and confirmed that a root nodule bacteria called Rhizobium existed naturally in the leguminous plant root nodules that was responsible for the fixation of atmospheric nitrogen in the soil (Boraste et al. 2009). In 1895, the first commercial biofertilizer called ‘Nitragin’ was launched (Chakraborty and Akhtar 2021). This broke the ground for extant research on biofertilizers that has attracted even more scholarship in the twenty-first century. The ultimate goal of applying biofertilizers is to increase and boost the economic

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viability of the adopting farmers leading to higher levels of productivity (Boraste et al. 2009). The reasons for deployment of biofertilizers are sixfold: firstly, to supply the limiting nutrients to crops; secondly, to boost the availableness of soil nutrients; thirdly, to boost plant growth; fourthly, to parasitize and suppress the plant pathogens especially those that are soilborne; fifthly, to cleanse soils of pollutants through rhizoremediation; and lastly, to improve the soil structure by gelling the soil aggregates and particles together (Seneviratne et al. 2011). These benefits and many more are realizable when the microbial biofertilizers are applied in high densities to the soil. Putting high densities aside, the applied microbial fertilizers must be viable and in active form (Seneviratne et al. 2011). In relative and absolute terms, biofertilizers are affordable to farmers, effective and a desirable source of plant nutrients that is renewable (Atieno et al. 2020; Boraste et al. 2009). When the farmers decide to use biofertilizers on a large scale, they are capable of scaling down the cost of buying inorganic nitrogen fertilizers by 25–30% and phosphorous by 25% hence saving a large fraction of money that they have been spending on buying these inorganic soil amendments (Simarmata et al. 2016). The only limiting factor is that they have not been popularized and are yet to be known let alone adopted by bigger numbers of farmers (Atieno et al. 2020). The most used microorganisms in production of biofertilizers are bacteria, fungi and blue-green algae (Boraste et  al. 2009). These organisms are added to the rhizosphere of the plants to enhance their activity in the soil.

3.2 Application of Biofertilizers to Soil Biofertilizers have more than one mode of application to the soil (Boraste et  al. 2009). They can be applied alone or in combination. Once applied in combination, they form a consortium (Boraste et al. 2009). Quite often, consortia are preferred over individual application especially where the corrective requirement is synergistic (Eris et  al. 2022; Ghosh et  al. 2022; Yadav et  al. 2021). For best results, we incorporate the beneficial microbes in carrier materials (Seneviratne et al. 2011). Biofertilizers are majorly packaged in two ways, solid carrier-based and liquid-­ based biofertilizers (Dey 2021). In comparison, liquid-based biofertilizer carry more benefits than solid carrier-based and are by far more cost effective and easy to apply (Dey 2021). In selecting the carrier materials among the various available alternatives, several factors have to borne in mind. They are as follows: 1. The carrier material should not be toxic to the inoculant bacteria strain. 2. The carrier material should have a high and better moisture absorption capacity. 3. It should be less technical to manufacture as well as free of any lump-forming materials.

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4. The materials should be easy to sterilize so that any foreign materials that could affect the diligence of the inoculant is got rid of. 5. It should be available whenever needed. 6. It should be affordable. 7. It should have good adhesive potential to seeds in case the inoculant is to be applied to seeds. 8. It should have a good pH-buffering capacity. 9. It should not be toxic to plants (Seneviratne et al. 2011).

3.3 Beneficial Microorganisms for Biofertilizers As earlier noted, the specific microorganisms applied to soil as biofertilizers are known as PGPR.  Much as Seneviratne et  al. (2011) provide three categories of microbial biofertilizers: plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF) and rhizobial biofertilizers. In this chapter, the distinction between the above types is handled following the classification scheme of Atieno et al. (2020). According to Atieno and colleagues, two broad categories of PGPR are commonly reported in scholarly studies. These are symbiotic PGPR and free-living PGPR (Atieno et al. 2020). 3.3.1 Symbiotic Beneficial PGPR As the name suggests, symbiotic PGPR mutually interact with a restricted selective plant species. They include Rhizobium and AMF. 3.3.1.1 Rhizobium This strain of bacteria is a member of the bacterial family Rhizobiaceae (Nosheen et  al. 2021). According to Young et  al. (2021), the bacteria belonging to the Rhizobium leguminosarum are regarded as a species complex. They are excellent at playing the symbiotic nitrogen fixation in the soil environment (Nosheen et  al. 2021) and are adept at fixing N in both leguminous and non-legume plants. The specific role played by these microorganisms in leguminous plants is the fixation of about 300 kg N/ha/year. Notably, these species in the soil environment are resigned at transforming molecular nitrogen to ammonia and making it utilizable by plants for production of proteins, vitamins and other nitrogens (Nosheen et  al. 2021; Schulte et  al. 2021). The nodules formed by rhizobium on some legume-eating plants not only increase plant nutrition and growth but also soil fertility (Gulshan et  al. 2022). For non-legumes, rhizobia influence the structuring, health and

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appearance of the root systems while also impacting on the physiology of the entire plant system (Nosheen et al. 2021). 3.3.1.2 AMF Arbuscular mycorrhizal fungi (AMF) are natural biofertilizers in degraded soils. Berruti et al. (2016) noted that the AMF are root obligate biotrophs that have a symbiotic relationship with about 80% of plants. In the first place, they are considered as natural biofertilizers given their potency in providing the host plants with water, nutrients and pathogen protection. In return, they obtain photosynthetic products from the hosts (Berruti et al. 2016). Much as AMF are ubiquitous soil microorganisms (Atieno et al. 2020), quite often, they are deficient in a soil ecosystem due to anthropogenic activities. Thus, soil ecosystems that lack AMF cannot function properly as they will lack the mentioned requisite and important plant growth requirements. It is important to note therefore that in degraded soil ecosystems, once low abundance of AMF has been confirmed, their re-establishment provides an excellent alternative to application of conventional fertilization practices, hence leading to sustainable agriculture (Berruti et al. 2016). AMF are re-introduced as propagules in the soil environment. Besides positing the limiting nutrients, the other notable potential benefits of introducing AMF in degraded soils for soil fertility restoration include protection of plants from abiotic stresses (Berruti et al. 2016). Among others, AMF improves drought and salinity tolerance among plants while also enabling plants to withstand the stresses ushered in by flooding. Also, AMF enhance plants to withstand the toxicity of high concentrations of heavy metals in a soil ecosystem such as Fe, Cu and Zn. The increased tolerance levels protect the plant roots and shoots from the deleterious effects of toxic heavy metals that would lead to stunted growth and lowering of the possibility of withering. AMF have metal transporters which play a key role in heavy metal homeostasis (Berruti et al. 2016). Notable examples include a Zn transporter common in Glomus intraradices (GintZnT1) identified by González-Guerrero et al. (2005) and Cu, Fe and Zn transporters in Rhizophagus irregularis genome (Tisserant et  al. 2013). However, much as the above transporters have been identified, their functional characterization and the potential specific roles played in heavy metal homeostasis are not discussed as they are beyond the scope of this chapter. Last, the reintroduction of AMF in a degraded soil environment reportedly improves soil structure as well as soil particle aggregation (Leifheit et al. 2014, 2015; Rillig et al. 2015). 3.3.2 Free-Living Beneficial PGPR The free-living PGPR have both direct and indirect stimulant effects on plants growing in their rhizosphere. They include Azotobacter, Azospirillum and Azomonas. The major difference between this category and the symbiotic PGPR is that while the former does not establish mutualistic interactions with plants, the latter does.

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Rhizobia and Azotobacter slightly differ with regard to N fixation. While Rhizobia interacts with the plants when fixing N, Azotobacter fixes N without forming mutual interactions with the plants. This accounts for why the efficiency of N fixation is higher for rhizobia than all other free-living PGPR (Atieno et al. 2020). For this reason, the inoculants of these free-living PGPR are not commonly used. 3.3.3 Other PGPR Other PGPR with notable effect on direct and indirect growth and development of plants include Alcaligenes, Aspergillus, Bacillus, Klebsiella, Lactobacillus and Trichoderma. While these have not attracted extant scholarship, Atieno et al. (2020) note that they are known for facilitating the uptake of both macro- and micronutrients by the plants, synthesizing phytohormones such as cytokinin and auxins for root system development and shielding the plants from the harmful effects of pathogens. Bashan et al. (2014) and Atieno et al. (2020) cited the example of secretion of siderophores and antimicrobial metabolites that immunize the plants from the soilborne pathogens. The case examples of the all categories of PGPR above have a cornucopia of roles they play in the restoration of soil fertility including solubilization and mobilization of nutrients, fixation of nutrients and secretion of plant growth-promoting substances such as antibiotics, siderophores and other hormones (Atieno et  al. 2020), Besides, they catalyse the decomposition of organic matter while also steering the degradation of pollutants in the soil environment such as PAHs. What is more to say, the beneficial microorganisms outcompete the soil pathogens, hence minimizing the incidences of plant diseases (Simarmata et al. 2016). Several studies have also shown that they improve soil structure by secreting polysaccharides which are gelling substances that help to hold soil particles together (Atieno et al. 2020; Patil and Solanki 2016). Therefore, in degraded soils where it is anticipated that the soil biota is either in meagre quantities or trace, discoveries overtime have shown that several strains of useful soil microorganisms can be introduced to aid the crop plants in absorbing the required nutrients for luxuriant growth (Boraste et al. 2009). Important to note is the fact that the helpful microorganisms create an enabling environment for the plants to absorb nutrients. However, the very strains of microorganisms may be less abundant. In such environments, human interventions are necessary. These are preceded by studies to establish the communities available followed by interventions to isolate those that are efficient in improving the rhizosphere for plant growth. The less abundant but desirable strains are then cultured and added directly to the soil or through seeds. The mass multiplication of the effective strains of the selected microorganisms takes place in laboratory settings. The choice of this environment according to Chakraborty and Akhtar (2021) is that the process of preparing biofertilizers involves mass cultivation of microbes and maintenance of a standard culture pH and temperature, ensuring that the right cell count is maintained as well. Boraste et al. (2009) professes that the cultured microorganisms, for efficiency, must be packed in

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some carrier material to ease their application in the soil. The packaged microorganisms become biofertilizers. Chakraborty and Akhtar (2021) mention the need for ensuring effective delivery and promoting efficacy as key motivations for choosing a suitable carrier material. The most commonly used packaging or carrier materials are peat and lignite powder. Boraste et al. (2009) cited the decision to use the said carrier materials and others at large as the need to prolong the shelf life of the biofertilizers. Stakes are even high that with the resurgence of genetic engineering especially with the ‘omics’, the possibility of producing mutant and genetically engineered microbes as a sustainable solution to agriculture has been made possible as these are believed to be more responsive compared to wild type.

4 Types of Biofertilizers 4.1 Nitrogen-Fixing Biofertilizers The N biofertilizers fix nitrogen in the soil through mutual interaction with the plants. More specifically, this type of biofertilizers is a correcting factor in the soil as they help in boosting the concentrations of N in the soil. It is important to note that much as N is a limiting factor for plant growth, with plants requiring a certain amount to thrive in the soil, the use of N biofertilizers is crop specific. According to Aseogwu et al. (2020) and Mahmud et al. (2021a), rhizobia biofertilizers are applied for legumes while Azotobacter or Azospirillum are specifically applied to non-­ leguminous crops. For cereals such as lowland rice, blue-green algae are the best for use, while for sugarcane, Acetobacter produces excellent results.

4.2 Phosphorus Biofertilizers Like N, P is a limiting nutrient for plant growth (Asoegwu et al. 2020; Mahmud et al. 2021a). Once the P biofertilizers have been applied to the soil, they help to correct the P levels through solubilization and mobilization. The solubilizers release insoluble phosphorus in soil, help to fix needed clay minerals in the soil and also secret organic acids as well as lowering the soil pH so that the bound phosphates in the soil are dissolved. The strains of bacteria that do so include Bacillus, Pseudomonas, Penicillium and Aspergillus. On the other hand, the mobilizers play a role of transferring P from the soil to the root cortex such as AMF. A stark difference exists between N and P biofertilizers in a way that while N biofertilizers are plant specific, P biofertilizers are not. Actually, quite often, they are used as consortium for all crops with Rhizobium, Azotobacter, Azospirillum and Acetobacter as proven in Phosphotika by Aseogwu et al. (2020).

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4.3 Potassium Biofertilizers After N and P, K is the second most abundant and important mineral element that confers necessary nutrients to plants (Nosheen et al. 2021). Despite its abundance in the soil, K is a limiting nutrient such that only 1–2% is available for use by plants (Gautam et al. 2022; Mahmud et al. 2021b; Nosheen et al. 2021). For this reason, the continuous K replenishment of soil solution is required accounting for why K biofertilizers must be applied to the soil to cater for this deficiency (Nosheen et al. 2021). These biofertilizers are influential in the soil environment and support luxuriant plant growth, root development, growth and development of seeds and consequently higher yields (Mahmud et al., 2021a, b; Tallapragada and Matthew 2021). Like P, K biofertilizers play a dual role of solubilization and mobilization. The former convert insoluble K in the soil into soluble forms with the aid of Bacillus spp. and Aspergillus niger, Arthrobacter spp., Cladosporium, Sphingomonas aminobacte, B. edaphicus and B. mucilaginosus, while in the latter process, potash is mobilized from potash from the elementary or mixture of potassium into a form that is easily absorbed by plants which can be easily aided by B. mucilaginosus (Gautam et al. 2022; Nosheen et al. 2021).

4.4 Sulphur Biofertilizers Much as sulphur belongs to micronutrients, it is an essential nutrient for plant growth (Gulshan et  al. 2022; Nosheen et  al. 2021). Sulphur is needed in high amounts by plants because it is part of the macromolecules that regulate the enzymatic activities of the plants (Gulshan et al. 2022). Priming their importance, Saha et al. (2018) argue that any deficiencies lead to chlorosis and consequently a decline in the productivity of the plants. Besides this, the presence of sulphur in the soil fans the potential and efficiency of N and P fertilizers leading to better performance of the plants (Nosheen et al. 2021). Furthermore, the availability of sulphur in adequate amounts in the soil environment improves certain biological and physical properties of the soil such as soil buffering from high pH values and elimination of sulphur pollution in the soil (Nosheen et al. 2021). Sulphur compounds existing in the soil in a reduced form exist as pollutants in the soil environment. The sulphur-­ oxidizing microbe includes Xanthobacter, Alcaligenes, Bacillus, Pseudomonas, Thiobacillus sp., Thiobacillus thioparus and T. thiooxidans. These oxidize sulphur to nutritious sulphates for plant uptake (Gulshan et al. 2022; Nosheen et al. 2021).

4.5 Zinc Biofertilizers As is the case with the preceding case of sulphur, zinc is a micronutrient for plants. However, it is an essential micronutrient (Nosheen et al. 2021; Saboor et al. 2021; Saleem and Khan 2022). The deficiency of zinc in soil impedes crop growth (Saboor

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et al. 2021). Zinc-rich food is widely recommended by physicians and nutritionists especially in the developing countries where zinc malnutrition is worrying. According to Saleem and Khan (2022), the limited availability of Zn in crop plants and more so in the cereals is linked to the increased and continued used of inorganic fertilizers. Besides, waterlogging and deviations in the soil physicochemical properties such as the increase in alkalinity and presence of insoluble forms of Zn in soil contribute to shortage of requisite zinc for plant uptake (Saleem and Khan 2022). It is envisaged that by 2025, if the above predisposing factors of unavailability of zinc for plants are not looked into, there is a possibility of zinc deficiency by a factor of 21% (from 42% to 63%) (Nosheen et  al. 2021). Yellowing of leaves, chlorosis, retarded root growth development, impeded water intake and transport and reduced leaf development are all characteristics of plants growing in Zn-deficient soils (Nosheen et al. 2021; Saboor et al. 2021). The microbial inoculants that perform Zn solubilization in soil include Mycorrhiza, Saccharomyces spp., Burkholderia spp. and Acinetobacter spp. while several genera of rhizobacteria such as Pseudomonas spp. and Bacillus spp. bring about a reported increase in the availability of Zn in the soil (Nosheen et al. 2021).

4.6 Compost Biofertilizers Compost biofertilizers, the third category, are used to enrich compost and enhance the bacterial processes responsible for breaking down compost waste. Cellulolytic fungal cultures, Phosphotika and Azotobacter, are the frequently used cultures. This process supports the production of organic fertilizers such as vermicompost. According to Aseogwu et al. (2020), vermicompost contains N, P, K, SOM, S, hormones, vitamins, enzymes and antibiotics. These ingredients boost soil fertility. Characteristically, these ingredients make organic fertilizers natural crop boost and a restorative solution to wasteland arising from illicit use of chemical fertilizers.

5 Net Advantages of Biofertilizers Over Chemical Fertilizers Much as conventional agriculture holds promise for meeting the feeding requirements of the increasing population, the possibility of attaining sustainable livelihoods is diminishing at a marathon speed (Bhardwaj et al. 2014). The cause of the declining possibility is the massive and uncontrolled use of chemical fertilizers and pesticides. Another recent development that underlines the critical need for a departure from the use of the chemical fertilizers is the emphasis on bio-safety with several projects undertaken in different countries to achieve the same. Organic production is emphasized in every effort to produce ‘nutrient-rich high-quality food’. This has even made the need to replace the chemical fertilizers with biological-­ based organic fertilizers so urgent than ever (Bhardwaj et al. 2014).

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Microbial biofertilizers by comparison with chemical fertilizers are far better. According to Seneviratne et al. (2011), they post a considerably low level of potential risk on environment and human health. Besides, their application is a much more targeted activity, while on the third front, the biofertilizers are highly effective even when applied in small quantities. Last but not the least, they have the ability of self-multiplication. The soil environment is home to the beneficial microorganisms (Bhardwaj et al. 2014; Ruley et al. 2020a, b, 2022). It has been proved by several studies that the rhizosphere is a residence to over ten trillion microbial cells per gram of root. Besides, more than 30,000 prokaryotic species that have plant growth-­ promoting potentials are found in the same zone. Given the high concentration of collective genome of rhizosphere microbial community enveloping plant roots than that of the plants, the zone is known as microbiome (Bhardwaj et al. 2014). The use of biofertilizers enhances achievement of biosafety (Baweja et al. 2020). Chemical fertilizers cannot. Although chemical fertilizers and pesticides are considered as critical farmland tools and major conduits through food security is hoped to be achieved, they alter the soil health equation (Baweja et al. 2020). Asoegwu et al. (2020) argue that remnants of chemical such as nitrates in situations of low concentrations of oxygen can be denitrified by bacteria to form nitrogen and nitrous oxide. Nitrous oxide is a dangerous greenhouse gas. For example, it depletes the ozone layer leading to abrupt changes in climate. The changes in climatic patterns indirectly affect the quality of soil. It is eminent to note therefore that the use of chemical fertilizers causes variations in both biotic and abiotic factors leading to soil degradation and threatens the lives of microflora and other organisms. Therefore, the use of chemical fertilizers leads to the outcome of these effects outlined above. The replacement of chemical fertilizers with microbial biofertilizers enhances achievement of biosafety (Baweja et al. 2020). Biofertilizers protect lithosphere; improve biosphere by protecting air, water, soil pollution and eutrophication; and enhance yields of agriculture produce (Chakraborty and Akhtar 2021). Evidence of this matter is provided by Simarmata et al. (2016) that correct application of biofertilizers translates into a 25% increase in the yields of various crops. In nutrient-deficient soil environment, the biofertilizers add macronutrients such as N, P, K and S, the reason why they are classified according to these macronutrient plant requirements. Besides, the macronutrients is a suite of micronutrients that are introduced in the soil environment including siderophores, antibiotics, enzymes and antifungal and antibacterial substances. What is more to say, the biofertilizers secret and release plant growth regulators (Chakraborty and Akhtar 2021). As noted by Atieno et al. (2020), biofertilizers can be inoculated with other agricultural practices for better outcomes. Comporting views are raised by Seneviratne et al. (2011) that the use of microorganisms or their dominant spores to identify and develop soil inoculants has been an ongoing scientific activity for a long period of time.

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6 Roles of Biofertilizers in Protecting the Soil Environment Degraded soil environments are best reclaimed using biofertilizers (Asoegwu et al. 2020). This is possible through a number of ways: bioremediation, provision of nutrient supplements, boosting quality of the degraded soil, dilution of the toxicity contents of chemical fertilizers and piecemeal release of soil nutrients (Asoegwu et al. 2020). Soils contaminated with PAHs become hydrophobic and consequently infertile (Ruley et  al. 2020a, b, 2022). However, they can be restored to support arable farming when they are bioremediated using excellent phytoremediation plant species such as Medicago sativa, Hyparrhenia rufa and Oryza longistaminata, among many other proven plant species (Mishra and Arora 2019; Ruley et al. 2019). The best results are released when the phytoremediation species are deployed with excellent microorganisms whose scanty communities can be squared through inoculation. The chelating and biodegrading potential of microbial communities is amplified when organic manures are applied with phytoremediation species and microbial inoculants as proven by Ruley et al. (2020a). Factoring this into consideration, microbial fertilizers provide the best solution of for eco-restoration of the polluted soils (Raina et al. 2020). Biofertilizers are excellent supplements for organic matter adjustments and soil fertility renovation (Bhardwaj et  al. 2014). They provide supplement nutrients which may not be present in soil or are existing in meagre quantities (Asoegwu et al. 2020). This observation rhymes previous findings that the biofertilizer application leads to a rise in concentrations of SOM, N, available P and K (Banerjee et  al. 2011). Soil bulk density, porosity and water-holding capacity are greatly improved by these soil nutrients (Alhassan et al. 2021; Bamboriya et al. 2022; Srivastava 2021). The use of bioinoculation with consortium provides better supplements when compared to dual or single inoculation. Evidence is provided by Garikapati and Sivasaththivelan (2013) who established that Trichoderma viridae+Pseudomonas fluorescence  +  Azotobacter chroococcum consortia improved the soil health and served as an excellent remedy for restoration of infertile soils. The use of biofertilizers therefore helps to eco-restore degraded soil by providing the limiting nutrients in the soil while also improving the natural environment in the rhizosphere immensely (Singh et al. 2020). Biofertilizer production improves quality of soil through conversion of organic waste into nutrient-rich manures. This applies mainly to compost biofertilizers, and by doing so, biofertilizer production helps to reduce on the quantity of wastes disposed of in the soil environment. Furthermore, this process helps to decrease nutrient overspill or leaching while providing better ways of managing crop residues in the environment. In some environments where chemical fertilizers continue to be used under intensification especially in urban and peri-urban areas, the use of microbial inoculants plays a dilution role which in essence, lessens the amounts of chemical fertilizers used while also squaring the efficiency of the  applied fertilizers (Asoegwu et al. 2020; Abo-El-Ghait et al. 2022).

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Aseogwu et al. (2020) noted that most biofertilizers secrete auxins, cytokinins, biotins and vitamins which are essential requirements for better growth of plants. As well, the biofertilizers are known for secreting antibiotics which parasitize the plant pathogens, consequently eliminating them. Soil environments benefit from the mutualistic interactions of plants and resident rhizobacteria communities (Ruley et al. 2022; Saini et al. 2021). The symbiotic relationship between the root systems and rhizobacteria enables the  plants to access the limiting nutrients, while also, the  rhizobacteria are sustained by the root exudates such as mucilage (Mahmud et al. 2021a). Resultingly, the biochemical properties of the rhizosphere are modified leading to improvement in soil health. Biofertilizers are reservoirs of plant nutrients (Hussain et al. 2021) and an excellent biological soil fertility management technique (Ghumare et  al. 2014) manifested in the long-lasting effects on soil. For example, they encourage slow release of nutrients to the soil (Asoegwu et al. 2020; Kumar et al. 2022). Unlike the chemical fertilizers whose benefits are imparted to the soil for a season, the application of biofertilizers leads to the release of nutrients to the plants for more than one season. This slow release of nutrients not only sustains plant life but also restores soil fertility. The degraded soils that have been deserted by the farmers on the account of prevalence of plant pathogens are reclaimed using biofertilizers. According to Aseogwu et al. (2020) and Dong et al. (2019), application of biofertilizers provides a biocontrol for pythium root rot, rhizoctonia root rot, chillwilt and parasitic nematode. This minimizes the incidence of soilborne diseases, hence improving the soil environment for crop plant production.

7 Limitations of Using Biofertilizers for Restoration of Soil Fertility in Degraded Lands The law of unity of opposites applies to use of biofertilizers. Their invention and consequence are without some limitations. According to Ghumare et al. (2014) and Mahmud et al. (2021a), the acceptability of biofertilizers among some farmers has continued to be low due to their limited effectiveness with regard to providing quick and spectacular responses. Their effects are not quickly realized compared to use of chemical fertilizers. Similar views are shared by Bhardwaj et al. (2014) and Odoh et al. (2020). Secondly, their production requires sophisticated technology and adequate qualified personnel that may be lacking in many countries. Thirdly, limited efforts have been taken to increase on their popularity. The limited awareness and adoption are explained by the different inoculation methods. Fourthly, biofertilizers are difficult to store especially where good quality carrier materials are in short supply. The other dimension of difficulty in storage is explained by their short shelf life. Fifthly, there is also a limitation of lack of region-specific indigenous microbial strains. Mahmud et al. (2021a) noted that this is a major pitfall of biofertilizers since

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they are not only crop but also soil specific. What is more to say, an excellent microbial strain of one region cannot perform well in another region. Conclusively, all the said limitations have impacted on adoption of biofertilizers.

8 Conclusion The need for rejuvenating the wasteland for arable farming has manifested in all nations (Hussain et al. 2021). This calls for selection and use of the most appropriate soil management and conservation techniques lest the risk of food security will bite the increasing population (Hussain et  al. 2021). Biofertilizer application to degraded soils provides a ray of hope for soil scientists, environmentalists, agronomists and microbiologists to redeeming the large expanses of land that have been reportedly lost through use of unfriendly agronomic practices such as use of chemical fertilizers and other practices at large such as extraction of crude oil that has caused pollution overtime. The golden opportunities unfolded by the recent developments in computer science, plant breeding, biotechnology and omics have been and continue to be regarded highly as key players in the advancement of the activities leading to the effective production of the biofertilizers. This has, for example, made it possible to realize high throughput from the application of biofertilizers. Worth noting, further opportunities of producing biofertilizers that not only have multiple functionalities but also increased shelf life is anticipated.

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Chapter 7

Macrophytes as Biofertilizer for Agriculture: Concept and Applications Shabeena Farooq, Shah Ishfaq, Syeed Mudasir, and Baba Uqab

Abstract  Urbanization and industrialization have provided many economic benefits but at the same time have led to global food insecurity due to reckless use of land resources. The remaining land resources are under tremendous pressure of fulfilling the human needs which has resulted in the use of chemical fertilizers leading to the degradation of soil quality. Accumulation of various chemicals in soil leading to its degradation has paved a new way to use biofertilizers instead of chemical fertilizers. Use of biofertilizers and biopesticides in agriculture is a growing science using biomass for its production using different microbial consortia. Macrophytes best fit for biofertilizer use as the aquatic environment is many times higher than the accessible land and much of the dryland is being used. Biotechnological interventions like solid-state fermentation, cell immobilization, etc. can be fruitful in obtaining the benefits from macrophytes to be used as biofertilizers in soil-plant systems. Using biofertilizers in place of synthetic fertilizers is not only cost effective but also environmental friendly. It adds to soil fertility, nitrogen fixation and pollution control in addition to lot of more benefits it provides to soil-plant complex. Keywords  Biofertilizers · Macrophytic biofertilizer · Biostimulants · Ecofriendly techniques · Biopesticides · Solid-state fermentation

1 Introduction Traditional farm management depends heavily on fertilizers to support crop growth; however, the widespread usage of currently available inorganic and chemical-based fertilizers can present a significant challenge to human health and the S. Farooq · S. Ishfaq Department of Environmental Science, University of Kashmir, Srinagar, India S. Mudasir Abdul Ahad Azad Memorial Degree College Bemina, Srinagar, India B. Uqab (*) Sri Pratap College of Sciences, Srinagar, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_7

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climate. Huge usage of artificial fertilizers to promote agricultural growth has culminated in global land, water and air contamination. Around the same period, this condition intensified the worries of customers regarding the quality and health of food processing, which prompted a resulting rise in the price of food goods due to the spike in fertilizer prices. It is broadly accepted that the only solution is to improve the productivity of plant-beneficial microorganisms that play an important role in maximizing the distribution of nutrients otherwise unavailable to plants under conditions of undisturbed soils. Hence, fertilizer research focuses on shifting to microbial exploitation as a more environmentally friendly method to sustainable farming. The biotechnological toolbox includes microorganisms like microalgae, cyanobacteria, endo- and ecto-mycorrhizal fungi, rhizobacteria and others that may exist in association with higher plant species. Biofertilizer is an important and growing intervention in green farming activities (Bloemberg et al. 2000). A biofertilizer is a material that includes living microbes that colonize the rhizosphere in the inside of the plant when applied to seeds, plant surfaces or soil and stimulate growth by increasing supply or availability of primary nutrients to the host plant (Kevin 2003). Biofertilizers add nutrients via the natural phenomena of fixing nitrogen, solubilizing phosphorus and enhancing plant growth by the synthesis of elements that promote growth. This can be anticipated that biofertilizers can limit the usage of conventional synthetic fertilizers. Microbes in the biofertilizers maintain the normal nitrogen cycle of the earth and create organic plant content. A popular scientific name for these helpful bacteria is “plant growthstimulating rhizobacteria” (PGPR), and they perform many functions. Thus, by providing the organic nutrients by microbes and their by-products, they are highly beneficial in enhancing soil quality and fulfilling plant nutritional requirements. Therefore, biofertilizers provide no toxic contaminants to the living earth. Biofertilizers are commonly described as the organic molecules of active microbes to foster crop, plant or soil bacterial consortia growth by critical nutrients like nitrogen, phosphate, potassium and other nutrients. Biofertilizer is a promising, cost-effective, eco-friendly, renewable resource of plant nutrients to supplement synthetic fertilizers and also help to remediate contaminated soils. Biofertilizers and biopesticides offer a lasting solution to reduce the need for synthetic fertilizers by meeting the increasing demands of the population (Kannaiyan 2002). Instead of chemical agents, the usage of biofertilizers and biopesticides is expected to reduce impacts on land, climate and water, which therefore has the ability to enhance public health and safety. Not only are they rich in nutritional quality but they often enrich the soil with active microbiota. Biofertilizer increases the efficacy of fertilizers using a carrier material that are mounted by microbes. Biofertilizer-based abatement of contaminated areas is a critical and effective path to ecologically sustainable growth.

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2 Microbiota for Biofertilizers Biofertilizers including rhizobium, azotobacter, azospirillum and blue-green algae (BGA) have long been in use. Rhizobium’s interdependent nitrogen fixation with legumes adds greatly to a complete fixation of nitrogen. Inoculation of rhizobium is a well-known agricultural method meant to ensure sufficient nitrogen. Azotobacter may be found in crops such as wheat, corn, mustard, cotton, potatoes and other plant crops. Inoculations of azospirillum are suggested primarily for sorghum, millets, maize, sugarcane and wheat. Blue-green algae like cyanobacteria, Nostoc, Anabaena, Tolypothrix and Aulosira repair atmospheric nitrogen, which are used as inoculations for paddy crops cultivated both in upland and in lowland conditions.

3 Aquatic Plants as Biofertilizers The growing focus of the planet nowadays is centred on aquatic residues, as the underwater environment on earth is many times higher than the accessible land and much of the dryland of the whole globe and surfaces is being used. Macrophytes are an important part of any aquatic ecosystem. They help in regulating the nutrient dynamics of an aquatic system and help in remediating pollutants and excess nutrients. Macrophytes store up huge concentrations of nitrogen and phosphorus in their tissues, and once added as fertilizer nutrients, they can boost soil quality. The use of biofertilizers has already become widely known, trying to grow a minor crop which offers nutrients to a major crop, although relatively new to aquatic science. Co-composting of macrophytes along with the sewage sludge can effectively improve soil resulting in enhanced photosynthesis levels and nutrient content in plants. It also raises soil moisture dramatically, which is among the most critical variables in soil-plant system. In addition, the usage of macrophyte compost as a fertilizer will reduce the expense relative to importing synthetic fertilizers. Macrophytes like Phragmites australis and Typha angustifolia display huge potential for recycling as composting material. Azolla sp., a free-floating aquatic fern which fix nitrogen in a mutually beneficial relationship with Anabaena azollae, is commonly applied to rice fields as a biofertilizer. Because of the biological nitrogen-­ fixing capacity of its symbiotic heterocyst cyanobionts, Azolla is used worldwide as a biofertilizer particularly in rice fields (Sood et al. 2012). A variety of abiotic and biotic factors have quite a significant impact on nitrogen fixation through biofertilizers. Anabaena in combination with Azolla adds up to 60 kg/ha/season of nitrogen and even enriches agricultural soils. Due to its possible usage as an alternative to conventional fertilizers, biofertilizer use has acquired broad attention. Thus, these provide green and environmentally sustainable alternatives for modern farming, in

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particular through integrated nutrient management (INM) and integrated plant nutrition network (IPNS), which can contribute to sustainable economic development. Addition of microbes can play a vital role in preparation of biofertilizers, and excessive use of chemical fertilizers can be minimized (Bashan et al. 2014; Owen et al. 2015). Microbial cultures and products are now commonly used in agriculture. In addition, soil productivity enhancement and conservation of microorganisms are projected to be a common method (Vassilev et al. 2013; Hakeem et al. 2021).

4 Cyanobacteria as a Potential Biofertilizer Cyanobacteria or blue-green algae have been studied for its potential for biofertilizer applications. They have the capacity to aerate the soil as well as increase its capacity to hold water and can also add vitamins (Song et al. 2005). Besides it can be applied along with water fern Azolla to soil that is deficient in nitrogen (Moore 1969). Cyanobacteria in symbiosis with aquatic plants can enhance nitrogen-fixing ability, for example, Azolla-anabaena complex can be used as a nitrogen-enriching biofertilizer for rice fields.

5 Steps in Developing a Macrophytic Biofertilizer Key steps in the development of a biofertilizer include the following: 1. Selection, collection and processing of macrophytes 2. Isolation, selection and characterization of a specific indigenous microbe with efficient functionality for a specific soil-plant system 3. Development of a method to ensure the persistence of microbes under normal as well as stressful soil conditions 4. Composting and co-composting trial tests of macrophytes, additives like sludge and microbes 5. Field applicability tests 6. Application of biotechnological know-how for production of biofertilizers on industrial scale 7. Development of a quality control system 8. Final field applicability tests with guaranteed benefits as claimed Furthermore, the emphasis of research efforts is now on the isolation and selection of plant-beneficial microbes and their subsequent usage under regulated conditions under soil-plant systems.

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6 Biotechnological Interventions for Preparation of Macrophytic Biofertilizer 6.1 Solid-State Fermentation Solid-state fermentation (SSF) is defined as the processes that occur in a solid matrix (inert support or substrate) in the absence of free water of the substrate needs moisture to sustain microbial growth and metabolic activity (Singhania et  al. 2010; Thomas et al. 2013). SSF puts greater focus on the growth of a broad variety of bioprocesses including bioremediation, biodegradation of hazardous waste, biological detoxification of agro-industrial waste, large-scale processing of enzymes, secondary metabolites, organic acids, antibiotics, biopesticides, biofuels, biosurfactants and aromatic substances and biotransformation of biomass and its residues for enrichment of nutrient (Hölker and Lenz 2005). The fibre arrangement of macrophytes is comparatively looser in comparison to land plants, and so it is simpler to decompose through microbes. Since microbially induced waste treatment by SSF is the preferred method for both the mass production of biocontrol products and for inocula production for biofertilizer, it can also be used for horticultural purpose by mixing the final biomaterial from SSF with potting mixtures. Various in vitro experiments also demonstrated that some fungi are capable of synthesizing phosphate ions from poorly soluble P-bearing inorganic compounds. The P-solubilizing function can be described by the biochemical efficiency of the microorganisms to generate and release metabolites like organic acids that chelate cations (mainly calcium) attached to phosphate by their hydroxyl and carboxyl groups, and the latter are transformed into soluble forms (Kpomblekou-a and Tabatabai 1994). In addition, biotechnological interventions can enhance plant growth, biological activity and soil properties through introduction of biotechnological products into soil-plant system, but this system is still in its initial stages of research. SSF-based growth and formulations could be generated utilizing nitrogen fixing and other microorganisms with specific characteristics like P-solubilization, biocontrol, lignocellulolytic behaviour, etc. In such a largely unexplored system, a significant range of microbial mixtures could be produced under SSF conditions, which could contribute to a new kind of biofertilizer.

6.2 Immobilization and Co-immobilization Cell immobilization is a biotechnological technique that is widely utilized in biofertilizer preparation. The immobilization of microbial cells has many benefits over free cell structures for fermentation processes, such as higher yields due to reduced metabolic activity and durability, greater isolation facilities, better process monitoring and minimal contamination exposure (Vassilev and Vassileva 1992). In particular, formulations focused on encapsulation (trapping) in polysaccharide beads give excellent cell defence against biotic and abiotic stress factors for agricultural and

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environmental applications (Vassilev et  al. 2012). Immobilized cell technologies require the use of two to more microorganisms, in the same way as solid-state fermentations. Co-immobilization was commonly observed to minimize cost of production and resolve issues related to process parameters, fertilizer usage, oxygen requirement, etc., between co-cultures (Hickert et al. 2014). Various experiments have shown the possibility of co-immobilization of plant beneficial microbes as well as co-encapsulation of microbes, mycorrhizal fungi, N-fixing microbes and P-solubilizing microbes which have been proven to increase the positive effects of the participants in the immobilized system (Vassilev et al. 2001, 2005). Subsequently, different combinations between plant beneficial microbes and biocontrol microbes and stimulants for plant development, such as plant extracts or active microbial metabolites, may be produced to produce highly efficient, multifunctional products that reflect a stable substitute inoculum preparation for sustainable farming use.

6.3 Elicitation and Biostimulants Another important tool that can be contemplated and progressively used especially in combination with benefits of the above biotechnological approaches is the combination of plant and plant beneficial microorganisms with elicitors as well as biostimulants. Elicitation is defined as the induced or improved biological synthesis of (secondary) metabolites attributable to the introduction of limited quantities of trace amounts of a material to a cellular system (Radman et al. 2003). In general, it is possible to distinguish a wide variety of elicitors based on the type and structure (physical and chemical, biotic and abiotic, etc.), but it will involve biological elicitors, for example, oligosaccharides obtained from microbes and seaweeds. Elicitors are responsible to induce defensive responses in plants interacting with pathogens. The increase in the production of secondary metabolites in plant cell cultures by elicitation resulted in the creation of an economically significant biotechnological research area. It is important to note that same elicitor can provoke different effects on different biological objects, for example, sodium alginate, carrageenan and chitosan purified from seaweeds are efficient elicitors of plant defence response (Mercier et al. 2001), stress alleviators and growth promoters (Aftab et al. 2011; Hashmi et al. 2012) and biostimulants of plant-microbe origin (Palacios et al. 2014). Both SSF and immobilized cell systems can be utilized in the study of stress tolerance range of plant-microbe systems and their metabolism (Zafra et al. 2014) which in turn will result in production of biofertilizer products with a wide range of tolerances to drought condition, temperature fluctuations and changes in salt concentrations and pH. It is also important to note that the preparation of inoculum is just one step in soil-plant-microbe system in sustainable farming (Eisenhauer 2012). Microbial biofertilizers being heterotrophic hence need organic carbon for metabolic activity and growth in soil (Vassilev et al. 2001). Animal manure and compost and their mineralization by microbes are vital for nutrient delivery to the crops. The nutrient delivery depends on factors like soil microbiota, temperature, moisture, chemical composition, etc. (Fornara and Tilman 2009).

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6.4 Benefits The aquatic plants are the cause of poor C:N ratio of plant biomass. Biofertilizers based on water weeds will serve as the correct remedy for testing their inadequacy but would also render the soil filled with nutrients. Biofertilizers comprise mostly of selected living microbial cells that provide nutrients to the plants via their root system. The microbes in such fertilizers use different pathways to supply the plants with nutrients. They are capable of fixing nitrogen and ammonia, solubilizing phosphates, mobilizing phosphates and fostering rhizobacteria (Bhat et  al. 2010). Packaging suitability is guaranteed for longer shelf-life and the protection of the product and the consumer (Brar et al. 2012). Biofertilizer use is becoming prominent due to nutritive value and less negative impacts (Ajmal et al. 2018). Being a renewable resource, biofertilizers can be widely used instead of synthetic fertilizers. They are much easier and cheaper to process and handle through pulverizing, neutralizing, sterilizing, packing and shipping. Biofertilizers enhance the microbial biota to soil which provides sufficient and balanced nutrient content to soil and plants. These microbes maintain the habitat of the soil and increase the yield by 20–30% replacing the chemical fertilizers by 30%. These also facilitate utilization of chemical fertilizers more effectively and help control various soilborne diseases. Similarly, natural materials are being used to develop biopesticides to fight plant pests (Balachandar 2012), for example, Bacillus thuringiensis or Bt is a bacterial strain used as a biopesticide. Biological interventions in pesticide and fertilizer preparations are gaining importance since 1995 with the USA, Canada, Mexico and European Union being the largest consumers while Asian countries using only 5% of the sold biopesticides (Kumar et al. 2017).

6.5 Application of Macrophytic Biofertilizers High microbial diversity in a small unit volume of soil are responsible for a number of interactions (Rosselló-Mora and Amann 2001) which may be bidirectional or unidirectional (West et  al. 2006), for example, quorum sensing (Manefield and Turner 2016) and oxalate-carbonate pathway (Martin et al. 2012). These interactions are responsible for enhancement in soil nutrient content and availability. Biofertilizers facilitate the microbial diversity in soil which in turn lead to a wide variety of its applicabilities. 6.5.1 Soil Fertility Algal biomass along with fungal and bacterial consortia is used in biofertilizer application. These however have greater efficiency in detoxification of pollutants but can also maximize the availability of N, P and K in the soil system (Saadatnia and Riahi 2009; Galhano et al. 2009).

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6.5.2 Nitrogen Fixation Biofertilizers based on the cyanobacterial consortia have the capability to fix the nitrogen that higher plants can uptake easily (Kumar 2016). Azolla-Anabaena symbiosis is the best example of N-fixing complex that has the capability to renew the nitrogen content by reducing inorganic nitrogen requirements to minimum (Vaishampayan et  al. 2001). Cyanobacteria-based biofertilizers have higher N2 recovery than chemical fertilizers in a soil-plant system (Valiente et al. 2000) and also have the ability to produce by-products like that of Tolypothrix sp. under tropical conditions (Velu et al. 2015). 6.5.3 Production of Plant Growth Biostimulants Biofertilizers enhance the biomineralization by facilitating the plant-microbe interactions to release metabolites that in turn enhance plant growth and nutrient availability as in case of few algal metabolites (Sangha et al. 2014). 6.5.4 Biopesticidal Substances Algae may be used as nematicidal agent, where cyanobacteria extracts and exudates have also been observed to suppress hatching and induce immobility and mortality of in vitro parasitic nematodes in juvenile plants (Holajjer et al. 2013; Hashem and Abo-Elyousr 2011). There has also been research on antifungal and antibacterial behaviours where filtrate from culture has hydrolytic action against phytopathogens. 6.5.5 Pollution Control Using macrophytes for biofertilizers can prove to control water pollution as well as soil pollution. Harnessing macrophytes in a controlled manner from a water body can reduce the organic load required to decompose the macrophytes in a water body. Besides, the macrophytes have been found to accumulate the nutrients that will help in abatement of eutrophication of water bodies. As already described, biofertilizers can be used instead of chemical fertilizers, hence reducing the negative impacts on soil system. Besides, the microbes present in the biofertilizer can help in the remediation of various toxic components from soil, thus leading to reclamation.

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7 Conclusion and Recommendations Macrophytes being an important element of any aquatic system may also result in adding up more nutrients to the system if allowed to decompose in the water body. Macrophytes can be a good source of nutrients for the soil-plant systems when properly managed. Studies on the use of macrophytes as biofertilizers need further elaboration as biofertilizers and biopesticides are expected to be the subject of research worldwide and are referred to be the remedy for pests, insects and weeds and are less toxic to human well-being and the climate. USEPA (US Environmental Protection Agency) found almost no negative consequences of the techniques used for formulation of biofertilizers and allowed the selling and delivery thereof. Various countries have been amending their laws to prohibit the utilization of chemicals and encourage the promotion of biopesticides. But the expense of production and price constraints has become a concern for the sector because of the rising demand of synthetic fertilizers. Another big challenge that serves as an obstacle to encouraging biofertilizers and biopesticide is that the public and lawmakers are still uncertain regarding its mode of operation, consequences and regulatory concerns. Therefore, its significance is also not generally known. To recognize the value of biofertilizers, there is a need to build understanding among growers, policymakers, government and manufacturers. In order to encourage the usage of biofertilizers and biopesticides in agriculture, they have to be made increasingly productive and reliable so that they can perform their role in introducing sustainability to the farming sector. Farmers have to be trained in utilizing fertilizers efficiently to mitigate runoff and potential negative effects. Besides, the universities and other research institutions must focus their research towards the sustainable agriculture as it is a possible solution to food security and environmental problems.

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Chapter 8

Potential Role of Biofertilizers in Fruit Crops Mohammed Tauseef Ali, Umar Iqbal, Sheikh Mehraj, Zahoor Ahmad Shah, Sharbat Hussain, M. A. Kuchay, and Owais Ali Wani

Abstract Fruit crops rely on nutrients for their proper growth, development, production, and quality. As the world’s population is increasing day by day, demand for fruit is swelling, thus putting enormous pressure on soil nutrients to produce quality fruit. Vitamins, dietary fiber, sugars, nutrients, etc. are important sources from fruit for human nutrition. The nutrients used for nutrition can be either chemical (fertilizers) or organic, such as biofertilizers. However, chemical fertilizers provide rapid results but at the cost of harming the environment. Moreover, the area expansion and the productivity of fruit crops have increased according to demand and have incorporated high-yield varieties. As a result, huge quantities of nutrients from these soils are removed by fruit crops. The continuous production of crops on these soils without proper nutrient management results in depleting the nutrient reserves in the soil. Consequently, in the coming years, nutrient-deficient soils will lead to a decrease in production and soil fertility. In order to ensure that fruit production systems are sustainable, minimizing chemical fertilizer input is necessary, and biofertilizer technology can compensate for that deficit. The application of biofertilizers in fruit crop nutrient management has exhibited significant improvements in the vegetative growth of fruit plants, fruit quality, production, plant nutrient uptake, and soil health. Therefore, biofertilizer practice in fruit crop cultivation for harnessing the prospective benefits of nutritional, environmental, and sustainable fruit production has become essential. Keywords  Biofertilizer · Fruit · Growth · Quality · Yield · Uptake · Health M. T. Ali (*) · U. Iqbal · S. Mehraj · S. Hussain · M. A. Kuchay Division of Fruit Science, Sher-e-Kashmir University of Agricultural Sciences & Technology of Kashmir, Shalimar, India Z. Ahmad Shah Division of Agricultural Extension and Communication, Sher-e-Kashmir University of Agricultural Sciences & Technology of Kashmir, Shalimar, India O. A. Wani Division of Soil Science, Sher-e-Kashmir University of Agricultural Sciences & Technology of Kashmir, Shalimar, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_8

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1 Introduction Biofertilizer is a material containing beneficial live microorganisms; mobilizes nutrient availability through biological processes when applied to soil, roots, or seeds; and aids in microflora growth and soil health development. Biofertilizer usage gradually rises as the prices of inorganic fertilizers surges, in addition to improving crop productivity. Microbes applied as biofertilizers boost nutrient availability, discharging hormones that stimulate plant growth, minimizing pathogen damage, and imparting abiotic resistance (Pathak et al. 2017). Bacteria, fungi, and cyanobacteria represent the key groups of microbes used for biofertilizer manufacture, as they have mostly symbiotic relationships with plants. Microbial fertilizers that supply nitrogen and phosphorus form a vital group (Thomas and Singh 2019). In total, 1.30 billion out of 7.41 billion people depend on agriculture, and 6.38 billion hectares of the Earth’s surface are occupied by the human population (Gouda et al. 2018). Many factors regulate soil content, namely organic carbon, nitrogen, phosphorous, potassium, and moisture content, besides various living and nonliving factors. The excessive application of fertilizers, specifically nitrogen and phosphorus, has resulted in soil pollution by decreasing exchangeable bases and pH, therefore reducing the productivity of crops from the unavailability of nutrients (Gupta et al. 2015; Hakeem et al. 2021; Dar et al. 2022). Fulfilling the worldwide demand for food has led to the indiscriminate usage of inorganic fertilizers, damaging microbial habitats and beneficial insects. Further, the excessive use of chemical fertilizers has made crops susceptible to diseases and has decrease the fertility of soil (Tilman et al. 2002; Aktar et al. 2009). To overcome the scarcity of available nutrients in soil and meet food demands, the productivity of crops has to be increased but by taking a safe, environmental, and sustainable approach. One approach is biofertilizers, which are ecofriendly and cheap, and their cumulative effect improves soil fertility (Mahdi et al. 2010; Singh et al. 2011). Bhardwaj et al. (2014) stated that using biofertilizer improves crop yields by about 10–40%, by increasing the fixation of nitrogen, protein content, essential amino acids, and vitamins. The benefits of using biofertilizer include having an economical and excellent nutrient source, secreting plant growth hormones, and stabilizing inorganic fertilizers’ negative impacts (Gaur 2010). Ahemad and Kibret (2014) reported that a soil ecosystem consists of various microorganisms that perform key biological processes, resulting in the mobilization of nutrients and crop production sustainability. The low crop productivity among poor farmers from developing nations is due to poor soil fertility. Hence, increasing crop productivity and soil fertility can be achieved through proper soil quality involving biofertilizers (Khosro and Yousef 2012). The continuous cultivation of fruit crops in the soil gradually decreases soil nutrients. However, the speed of removing nutrients is faster than that of replacing them. The nutrition requirements of fruit crops is high; in order to meet that requirement and the requirements for sustainable fruit production systems, the application of biofertilizers, along with the judicial use of inorganic fertilizer, is necessary. Therefore, this chapter highlights the impacts of applying biofertilizer to fruit crops on plant growth, the physicochemical properties of fruit, fruit production, and nutrient uptake in plant and soil health.

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2 Biofertilizer Types Related to Nitrogen and Phosphorous Nutrition 2.1 Free Living: Nitrogen-Fixing Biofertilizers Nitrogen is an essential macronutrient that plants require in large amounts. It is an important constituent of chlorophyll and proteins; hence, it is required for proper plant growth and development. One of the important free-living bacteria is Azotobacter, which fixes nitrogen and comes under the family Azotobacteriaceae. It is found frequently in the alkaline and neutral soils. It fixes atmospheric nitrogen in nonleguminous crops, such as fruits and vegetables. It does not require a host or any symbiotic relationship. Azotobacter has been found to release plant hormones, vitamins, and extra-bioactive substances that can provide protection against root pathogens. Further, the uptake of the minerals in plants and the promotion of growth in the roots have also been reported (Mahanty et al. 2016).

2.2 Symbiotic: Nitrogen-Fixing Biofertilizers The rhizobiaceae family contains the best symbiotic fixers of nitrogen and has been extensively used for crops. It consists of various genera: Rhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium, Sinorhizobium, and Allorhizobium. In a host plant that has Rhizobium bacteria, root nodule formation takes place, wherein symbiotic Rhizobium bacteria live. Atmospheric N2 gas is basically fixed in the root nodules because Rhizobium reduces the N2 to NH3, subsequently used by the plant to produce various proteins, vitamins, and nitrogen-containing compounds. Nitrogenase, an enzyme, carries out N fixation (Mahanty et al. 2016). Nif genes are present both in free-living microorganisms and in symbiotic microorganisms for nitrogen fixation (Black et al. 2012). Legumes are less dependent on nitrogen fertilizers thanks to the nitrogen-fixing ability of Rhizobium, whereas nonlegume crops are dependent on nitrogen fertilizers.

2.3 Associative: Nitrogen-Fixing Biofertilizers Bacteria that coexist with the higher plants form close associative symbioses, and at the root surface, many live on and occasionally pierce into the root tissues, but no visible nodule or outgrowth on the root tissue is produced. For instance, Herbaspirillum spp. and Acetobacter diazotrophicus are associated with sugarcane, sorghum, and maize (Triplett 1996), while Bacillus, Enterobacter, Azospirillum, Herbaspirillum, Rhizobium, Klebsiella, and Pseudomonas are associated with rice and maize (James 2000).

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2.4 Phosphorus-Solubilizing Microbes Phosphorus (P), a macronutrient, plays important functions in the growth and development of crops. Phosphorus concentration is high in soils; however, a major portion of it is in unattainable forms, and therefore, nitrogen becomes a limiting plant nutrient. In the soil, it is present at the levels of 400–1200 mg/kg (Kour et al. 2020). Although it is in higher concentrations, its insoluble, immobilized, and precipitated forms make up about 95–99% of the total P; thus, in plants, absorption becomes tough. Plants absorb phosphate in monobasic (H2PO4−) and dibasic (HPO4−2) ion forms (Gouda et al. 2018). About 20–80% of immobilized phosphorous in the soil is present in organic matter (Hariprasad and Niranjana 2009). Phosphatesolubilizing microbes are known to change phosphorus from an insoluble form to a soluble one, resulting in improvements in the growth of plants. This conversion involves various mechanisms, such as acidification, exchange reactions, and chelation. Phosphorous solubilizers secrete acid phosphatases and phytases, enzymes that play vital roles in the solubilization of phosphorus in the soil (Kumar et al. 2013; Relwani et al. 2008). Some Bacillus and Pseudomonas species showed phosphorous-solubilizing traits, isolated from different crop rhizospheres (Mishra et al. 2014). Various genera of phosphate-solubilizing microbes include Enterobacter, Beijerinckia, Bacillus, Burkholderia, Pseudomonas, Rhizobium, Microbacterium, Arthrobacter, Mesorhizobium, Erwinia, Flavobacterium, Serratia, and Rhodococcus (Oteino et al. 2015). Cyanobacteria and species consisting of Nostoc, Scytonema, and Anabaena have also been used for phosphorus solubilization in soil (Mishra et  al. 2014). Fungi that are found to solubilize inorganic phosphates include Penicillium, Aspergillus, and Paecilomyces.

2.5 Phosphorous-Mobilizing Fungi Plant roots and fungi form symbiotic relationships called mycorrhizal associations. About 90% of the terrestrial species of plants form symbiotic relationships with arbuscular mycorrhizal fungi (AMF) (Gadkar et al. 2001). The mycorrhizae group plays critical roles in phosphorus mobilization. Mycorrhizal fungi facilitate nutrient absorption in the plants by spreading the mycorrhizal hyphae system beyond the rhizosphere. Most of the plants are not dependent on the mycorrhizal associations, but the production of plants that have grown in low P-soils and that have been inoculated with mycorrhiza has increased (Kour et  al. 2020). Arbuscular mycorrhiza fungi are present in the soil, and most terrestrial plants, such as various fruit crops, cereals, and vegetables, have symbiotic relationships with it (Dalpe and Monreal 2004). The popularity of arbuscular mycorrhiza fungi as biofertilizer is increasing with the passage of time thanks to their role in improving soil fertility, aggregate stability of soil, and promoting plant health. Therefore, the application of AMF will help improve the crop yield and simultaneously reduce fertilizer and pesticide

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consumption. Moreover, when the seedlings of Litchi chinensis were inoculated with AMF, an increase in IAA (indole-3-acetic acid) concentration in the seedling roots was observed, compared with the controls (Yao et al. 2005).

3 Effect of Biofertilizers on Fruit Plant Growth Applying the treatment containing 75% N (inorganic source) + 12.5% N through vermicompost + 12.5% N through FYM + biofertilizers (Azotobacter and phosphate-­ solubilizing bacteria—or PSB) to plum cv. Kala Amritsari resulted in a maximum plant height increase (0.27 m), a plant height percentage increase (4.91%), a leaf area increase (13.13 cm2), a chlorophyll index of 23.88, and an annual shoot growth of 70.63 cm (Kamatyanatti et al. 2019). Krishna et al. (2018) stated that supplying papaya cultivar Arka Prabhat with the treatment—50% recommended dose fertilizer (RDF) + 50% recommended dose Nitrogen (RDN) through vermicompost + biofertilizers—resulted in the best stem circumference (35.58 cm), leaves per plant (46.98 no.), leaf area per plant (11.05  m2), and canopy spread (199.55  cm (EW) and 191.08  cm (NS)). According to Poonia et  al. (2018), various biofertilizers (Azotobacter and PSB) and vermicompost treatments on mango plant cv. Dashehari showed that the treatment involving 3 kg of vermicompost plant−1 with biofertilizers (50 g of Azotobacter per plant−1 + 50 g PSB per plant−1) recorded significantly higher values compared with other treatments—on metrics such as girth of rootstock, girth of scion, shoot number per plant−1, shoot node number per plant−1, and percentage of proliferation in plant height. Singh et  al. (2018) reported that in rough lemon, enhancements in the germination of seeds, growth of seedlings, chlorophyll content, growth of roots, epidermises of roots, thickness of the cortical region, and diameter of phloem and xylem were registered after treatment with soil + FYM + cocopeat with Azospirillum + AMF. Mosa et al. (2018) reported that when apples (cv. Topaz bioproducts, Florovit Natura, Florovit Eko, and Vinassa) were accompanied by four bacteria species (Klebsiella oxytoca, Pseudomonas fluorescens, Rhizobium sp., and Pantoea sp.), the volume and surface area of shoots, main stems, and roots and tree trunk thickness greatly improved compared with inorganic fertilization (NPK) as the control. Sau et  al. (2017) investigated the Himsagar variety of mango in order to evaluate the effect of chemical, organic, and biofertilizer fertilization sources on growth for two consecutive seasons. According to the results, treatment comprising biofertilizers (Azotobacter chorococcum + Azospirillum brasilense + Glomus mosseae) and accompanied by 3% Panchagavya significantly produced plants with the maximum plant height and the maximum spread of canopy, while the lowest findings were found with the control plants (no fertilization), followed by those using only chemical fertilizers. Mamta et al. (2017), while assessing the consequences of combining inorganic nutrients, organic manure, and biofertilizers on the growth performance of papaya seedlings, reported that the highest plant growth (32.42 g/plant) was obtained under dual inoculation with Azotobacter strain 3 + PSB + 75% NP + 100% K compared with uninoculated treatments and controls (13.82  g/plant).

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Furthermore, they stated that a double inoculation of Azotobacter and PSB was better than a single inoculation of either and was obviously better than no treatment at all. Hosseini and Gharaghani (2015) studied AMF species inoculation consisting of Rhizophagus intraradices, Claroideoglomus etunicatum, and Glomus versiforme on apple rootstock (M.7, M.9, and MM.106) growth. Glomus versiforme–inoculated plants showed better maximum stem diameter, shoot height, biomass, and leaf size compared with other species of AMF.  Substantial variations in rootstock growth were also noticed: the most growth was observed in MM.106, whereas the least was observed in M.9. In strawberries, the highest plant spread (25.64 cm), plant height (20.26 cm), leaf number (54.30), and leaf area per plant (97.87 cm2) were recorded thanks to a treatment comprising vermicompost + Azotobacter + PSB + AMF, while the lowest values of the same parameters were observed in the controls (Singh et al. 2015). Hassan (2015) reported that for strawberries, a treatment consisting of effective microorganisms (photosynthetic bacteria, lactic acid bacteria, fungi, and ray fungi) and biofertile (Azotobacter chroococcum, Bacillus polymyxa, Azospirillum brasilense, Pseudomonas putida, and Enterobacter agglomerans) significantly improved plant height, number of leaves per plant, crown diameter, leaf area, and plant dry weight in comparison to controls, which were treated with only tap water spray. Hassan et al. (2015) examined some combinations of organic fertilizers (sheep manure and poultry manure) with biofertilizer containing three microbes, namely Azotobacter chroococcum (nitrogen-fixing bacteria), Bacillus megaterium (phosphorous-­releasing bacteria), and Bacillus circulans (potassium-releasing bacteria), at a ratio of 1:1:1, during three successive seasons (2012, 2013, and 2014) in Egypt on 15-year-old olive trees (cv. Manzanillo). The results revealed that a combination of PMB2—poultry manure + biofertilizer (2 L/tree)—was the best treatment to increase flowering density, sex expression, and pollen grain germination. Kumar et al. (2014) reported that in aonla plants grafted in the year 2011, treating them with AMF and Azospirillum showed the highest plant height (94.66 cm) and shoot diameter (1.68 cm) after 90 days of transplanting them. Further, the same treatment also produced the highest root length (26.50 cm) and root number (55.33) after 120 days of transplanting. Singh et al. (2013) noticed something in apple variety Lal Ambri: The use of biofertilizers in a combination consisting of Azotobacter + Azospirillum + arbuscular mycorrhizal fungi (AMF) showed significant growth in plant height (44.70  cm), tree cross-sectional area (9.25  mm2), shoot extension (22.80 cm), leaf number per plant−1 (76.30), and the laterals of shoot plants−1 (4.43), followed by dual inoculation and sole inoculation, while these were observed the least in controls (no cultures). Godage et al. (2013) stated that at the harvesting stage of guava cv. Allahabad Safeda (Psidium guajava L.), maximal plant height (3.80 m), primary branch girth (28.67 cm), and north–south (5.13 m) and east–west (5.20 m) tree spread were found after a treatment containing 75% N  +  75% P2O5  +  100% K2O  +  Azotobacter 5  ml tree−1  +  PSB 5  ml tree−1. According to Raman (2012), inoculating stratified apple seeds involves Pseudomonas striata, Azotobacter chroococcum, and Trichoderma viride and their combinations; the maximum seed germination percentage and the seedling survival rates were improved after a dual inoculation of Azotobacter chroococcum + Trichoderma viride compared with other

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treatments. Moreover, premier seedling length and diameter were associated with a triple inoculation combination: Pseudomonas striata  +  Azotobacter chroococcum + Trichoderma viride. Sharma et al. (2012) reported that Royal Delicious seedlings under minimum inorganic fertilization when inoculated with G. fasciculatum delivered significant enhancement in the vegetative characteristics of the plants, such as plant height, stem diameter, leaf area, and total root length. Singh and Singh (2009), while working on strawberry (cv. Sweet Charlie), reported that the maximal plant height, leaf area, leaf chlorophyll content, leaf number, total biomass, and crown plant−1 were noticed with treatment comprising Azotobacter + Azospirillum  + 60 kg N ha−1 + 100 ppm GA3. In citrus plants, plant height, stem diameter, the number of leaves, and dry mass were significantly improved through G. versiforme colonization (Wang and Xia 2009). Ojha et al. (2008) found that custard apple seedlings inoculated with G. fasciculatum exhibited the highest chlorophyll content throughout the growth season compared with the uninoculated seedlings. Furthermore, plant height and weight and the freshness and dryness of the roots and shoots were also significantly higher in seedlings treated with G. fasciculatum compared with the uninoculated seedlings. Aseri et al. (2008) noticed 7–10-day earlier sprouting from pomegranate cuttings when inoculated with biofertilizers, whereas uninoculated cuttings took 8–10 days longer. The maximum improvement in leaf area (27.40–57.60%) was recorded with A. brasilense inoculation, followed by a combination of A. chroococcum + G. mosseae. Total chlorophyll content and shoot dry weight (16–36%) were also enhanced upon biofertilizer inoculation. In strawberry cv. Senga Sengana, plant spread (24.21  cm) and plant height (23.30  cm) reached their maxima after treatments comprising poultry manure + Azotobacter  +  wood ash + phosphate-solubilizing bacteria + oil cake (Nowsheen et al. 2006). Singh and Singh (2004) found that banana plants showed significant improvements in growth when inoculated with VAM, as compared with the uninoculated plants.

4 Effect of Biofertilizers on Fruit Quality Gupta et al. (2019) reported that for guava cv. Allahabad Safeda, a treatment of 50% RDF + 10 kg FYM + Azotobacter + PSB (100 g/P) showed the highest significant effect on TSS (10.29 °Brix, 10.72 °Brix), total sugars (7.07%, 7.22%), ascorbic acid (212.10, 191.90), and pectin content (1.15%, 1.18%) during both seasons (rainy and winter), as compared with controls (RDF: 100%; NPK: 180, 90, and 90 g), within a high-density planting system. Singh et  al. (2018) stated that in guava cv. L-49, among inorganic and biofertilizer combinations, the highest significant TSS (9.95 °Brix), total sugars (6.40%), reducing sugars (3.73%), and nonreducing sugars (2.67%) were noticed after treatments containing 75% RDF  +  Azospirillum (250 g/tree) + PSB (250 gm/tree). Baraily and Deb (2018) reported that in pineapple (cv. Kew), a treatment of 30  t/ha FYM  +  75% of RDF of NPK + biofertilizers (Azotobacter  + PSB) has shown the best results in obtaining maximum TSS

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(13.93  °Brix), TSS–acidity ratio (20.18), and total sugars (12.96%). Mosa et  al. (2018) stated that for apple plants from MM-106 rootstock planted in pots in Poland, fruit firmness and TSS increased thanks to various bioproducts enriched with microbial inoculum, comprising Glomus mosseae and G. intraradices (mycorrhizal fungi) and Bacillus subtilis and Pseudomonas fluorescens (plant growth–promoting bacteria). Bashir et al. (2017), while working on pear cv. Carmen at high densities, having rootstock Quince C planted with a spacing of 3 × 3 m, revealed that treatment comprising 75% nitrogen + 75% phosphorous + Azotobacter + PSB + VAM + vermicompost (7 kg tree−1) resulted in the best qualities of fruits, such as the highest organoleptic rating on the hedonic scale (3.43, 3.45), the most total soluble solids (17.36 °Brix, 17.42 °Brix), and the most total sugars (15.06%, 15.12%) during the 2015 and 2016 experimental years, respectively. Sau et al. (2017) reported on mango cv. Himsagar: the highest total sugars (13.41%) and TSS (19.70  °Brix), with 10 days extended shelf life, were reported after treatment with Azospirillum brasilense + Azotobacter chorococcum + Glomus mosseae + Panchagavya 3%. Das et al. (2017) revealed that a treatment containing A. brasilense + AMF showed maximum TSS (10.30 °Brix), total sugars (7.85%), and reducing sugars (4.37%). Similarly, A. brasilense  +  AMF also showed maximum nonreducing sugars (3.48%) and ascorbic acid (153.44 mg/100 g) with less acidity (0.27%), whereas the fruit treated with chemical fertilizers were found to have a maximum acidity of 0.38%. The fruit from the control plants recorded the minimum for all the biochemical parameters. Ennab (2016) reported that Eureka lemon trees that are treated with 75% NPK tree−1 + 27.5 kg farmyard manure year−1 + Azotobacter 25 g tree−1 + Azospirillum 25 g tree−1 + Bacillus circulans 25 g tree−1 produced higher values of vitamin C (44.46  mg/100  ml juice, 49.83  mg/100  ml juice) compared to the controls (1000:250:500 g N, P2O5, and K2O tree−1 year−1) in both seasons of 2014 and 2015, respectively. When banana cv. Grand Naine is treated with biofertilizers, it produces fruit with similar quality, greater sugar, and ascorbic acid contents to those treated with inorganic fertilizers (Vazquez-Ovando et al. 2012). When biofertilizers are applied in combination, such as Azotobacter + Azospirillum + AM + PSM, they result in the best fruit size in mango cv. Himsagar. Moreover, treatment comprising 500:250:250 g NPK/tree + FYM (50 kg) + Azospirillum (250 g) delivered top fruit quality (Singh and Banik 2011). Kundu et al. (2011) stated that in the Amrapali cultivar of mango, using chemical fertilizers alongside biofertilizers (Azotobacter, Azospirillum, and VAM) resulted in better fruit quality values compared with using only inorganic fertilizers. Abdelaal et al. (2010) stated that inoculating Washington navel oranges with Pseudomonas fluorescens (strain 843) under Egyptian conditions resulted in enhancing fruit quality and retarding nematode survival in soil. Mahendra and Singh (2009) revealed that upon treatment, consisting of FYM  +  100% NPK + Azotobacter + PSB in ber cv. Banarasi Karaka, the highest length, width, and weight of fruit and biochemical properties such as TSS, reducing and nonreducing total sugar, and the lowest acidity were registered. According to Singh and Singh (2009), combinations of biofertilizer and bioregulator had significant effects on the chemical compositions of the strawberry cv. Sweet Charlie. A double inoculation of

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Azotobacter and Azospirillum supplemented with nitrogen (50% of the standard dose) and GA3 (100 ppm) produced fruits with maximum total sugars (8.55%), TSS (8.96 °Brix), and ascorbic acid (59.22 mg 100 g−1). Umar et al. (2009) reported on strawberry cv. Chandler plants: after a treatment containing 25% nitrogen through FYM + 75% nitrogen (urea) + Azotobacter provided the best fruit biochemical qualities for TSS, total sugars, anthocyanin, and ascorbic acid content. Dey et al. (2005) revealed that using biofertilizer significantly improved the physicochemical characteristics of guava (L 49) compared with the controls. Using vesicular-arbuscular mycorrhiza resulted in the highest vitamin C (151.8 mg 100 g−1) amount, the highest TSS (10.10 °Brix), and the best TSS–acid ratio.

5 Effect of Biofertilizers on Fruit Yield Kamatyanatti et  al. (2019) reported that in plums cv. Kala Amritsari, the highest flower number per foot of shoot (87.19), fruit set number per foot of shoot (32.58), fruit set final (20.50%), fruit weight (12.35 gm), and fruit yield on a per-tree basis (53.43 kg/tree) were significantly better upon a treatment containing 75% N + 12.5% N (vermicompost) + 12.5% N (FYM) + biofertilizers. Gupta et al. (2019) reported on guava cv. Allahabad Safeda: a treatment containing 50% RDF  +  10  kg FYM + Azotobacter + PSB (100 g/plant) showed significant improvements on the number of fruit/plant−1 (32.60, 31.45), fruit weight/plant−1 (122.60  g, 152.15  g), fruit yield/plant−1 (4.00  kg, 4.79  kg), and fruit yield/hectare−1 (53.16 q, 88.34 q) during the rainy and winter seasons of cultivation, respectively, compared with the controls (RDF: 100%); (NPK: 180, 90, and 90 g). Krishna et al. (2018) reported that when papaya cv. Arka Prabhat was supplied with a treatment consisting of 50% RDF  +  50% RDN through vermicompost + biofertilizer, it produced the highest fruit yield/plant (22.73 kg) and fruit yield/hectare (56.82 t). Baraily and Deb (2018) reported that for pineapple (cv. Kew), a treatment containing 7.5 t/ha vermicompost + 75% RDF of NPK + biofertilizer provided the best results for yields: 67.26 t/ha. Dwivedi and Agnihotri (2018) reported that treating guava cv. Allahabad Safeda with 50% NPK  +  25  kg FYM  +  Trichoderma  +  Pseudomonas provided the best results for fruits per tree (187), fruit weight (236 g), and fruit yield (28.6 kg/tree), while in the controls (with no fertilizers), fruits per tree (128), fruit weight (192 g), and fruit yield (20.20 kg/tree) were the lowest. Mosa et al. (2018) reported that in apple cv. Topaz, fruit yield and fruit weight were significantly increased thanks to the addition of bacteria species (Pseudomonas fluorescens, Pantoea sp., Rhizobium sp., and Klebsiella oxytoca) to the bioproducts: Humus UP, Fertigo (manure), Humus Active + Aktywit PM, yeast, and Biofeed Amin in comparison to NPK (control). Sau et  al. (2017) reported that using biofertilizers containing Azospirillum brasilense + Azotobacter chorococcum + Glomus mosseae + Panchagavya 3% on mango cv. Himsagar provided the highest fruit weight (237.12  g) and fruit yield (42.14 kg/plant). Das et al. (2017) reported that dissimilar sources of biofertilizers significantly influenced fruit retention, fruit yield per plant, and fruit yield per

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hectare for the guava plant. The highest fruit retention (56.30%), fruit yield/plant−1 (41.37 kg plant−1), and fruit yield/hectare−1 (11.50 t ha−1) were noticed after treatment with a combination of A. brasilense + AMF, while the controls (no fertilization treatment) recorded minimum fruit retention (45.20%), fruit yield/plant−1 (25.20 kg plant−1), and fruit yield/hectare−1 (7.00 t ha−1). In strawberries, using biofertilizers (Azotobacter  +  PSB  +  AM) and vermicompost increased the highest flower number/plant (64.23), fruit set/plant (50.63%), and whole fruit weight/plant (311.26  g). The minimum flower number/plant (44.97), fruit set/plant (31.25%), and whole fruit weight/plant (136.59 g) were registered in the controls (Singh et al. 2015). Hassan et al. (2015) reported that during the three consecutive seasons of 2012, 2013, and 2014, olive trees treated with PMB2 (poultry manure + biofertilizer 2 l) registered the highest yield per tree (58.61, 28.03, and 75.17 kg per tree, respectively), whereas using only sheep manure gave the lowest values of yield per tree during those three seasons (43.47, 20.14, and 60.40  kg per tree, respectively). Similarly, in three seasons, PMB2 treatment also gave the highest fruit weight, 6.75, 9.31, and 6.07  g, during the first, second, and third seasons, respectively, among treatments. According to Singh and Singh (2009), maximum fruit set (84.28%) and fruit yield (94.26 qha−1) were obtained for strawberry cv. Sweet Charlie after a treatment containing Azotobacter + Azospirillum + 50% N of the recommended dose + 100 ppm GA3.

6 Effect of Biofertilizers on Nutrient Uptake in Fruit Plants Srivastava et al. (2019) reported that in Nagpur Mandarin oranges, the maximum leaf nutrient levels for nitrogen (2.52%), phosphorous (0.38%), and potassium (1.72%) were observed more after treatments consisting of 100% RDF  +  VAM (500 g per plant) + PSB (100 g per plant) + Azospirillum (100 g per plant) + T. harzianum (100 g per plant) than after other treatments. Singh et al. (2018) reported that the highest leaf N content (13.2%) in rough lemon over uninoculated (control) was obtained under treatment: Azospirillum + PSB + AMF. Moreover, a maximum increase in leaf K (9.2%) and P (17.4%) content was recorded after a combined treatment of Azospirillum + AMF. Mamta et al. (2017) stated while assessing the combined effect of inorganic nutrients, organic manure, and biofertilizers in papaya seedlings on nutrient uptake that the N content in papaya shoots varied from 25.62 to 43.76 mg/seedling under different treatments at 120 DAT. The N uptake in shoots was found to reach its maximum after a treatment of Azotobacter strain 3 + PSB + 75% NP + 100% K (43.76 mg/seedling), followed by Azotobacter strain1 + PSB + 75% NP + 100% K (42.41 mg/seedling), which were significantly higher than those of controls—25.62 mg/seedling at 120 DAT. Das et al. (2017) reported that in guava cultivation in the Indo-Gangetic Plain of West Bengal, India, the N content in leaves significantly varied, from 1.21% to 1.64%, and the application of A. brasilense + AMF resulted in the highest value. Moreover, the highest leaf contents for P

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(0.49%) and K (1.19%) were also observed in the same treatment. Sau et al. (2017) stated that in mango cv. Himsagar, treatment consisting of Azospirillum brasilense + Azotobacter chorococcum + Glomus mosseae + Panchagavya 3% displayed the highest leaf, N (1.97%), P (0.99%), and K (1.09%) percentages. Further, chemical fertilizer and the control plants recorded minimum results. Bakhshi et al. (2017) reported that in Kinnow Mandarin oranges, the maximum N leaf content (2.57%) was obtained after two treatments: (1) Azotobacter  +  100% N as urea and (2) Azotobacter  +  25% N as vermicompost and 75% N as urea. Leaf phosphorus reached its highest level, 0.19%, under Azotobacter + 50% N as vermicompost and 50% N as urea. Similarly, the maximum leaf phosphorus level, 0.18%, was obtained with treatment consisting of Azotobacter + 75% N as vermicompost and 25% N as urea. The treatment Azotobacter + 100% N as vermicompost registered the highest leaf potassium (1.56%), while the lowest leaf potassium content was obtained under the control. The maximum leaf calcium (4.31%) was recorded after a treatment containing 25% N as vermicompost + 75% N as urea + Azotobacter, followed by plants receiving 50% N as vermicompost and 50% N as urea + Azotobacter. Two treatments, namely 25% N as vermicompost + 75% N as urea + Azotobacter and Azotobacter + 50% N as vermicompost + 50% N as urea, registered the highest leaf magnesium content (0.46% each). For nutrients, the highest fruit N content (0.06%) was achieved under two treatments (100% N as urea + Azotobacter and 25% N as vermicompost + 75% N as urea + Azotobacter). The fruit phosphorus reached its highest level, 0.025%, after a treatment consisting of Azotobacter + 50% N as vermicompost + 50% N as urea. The highest fruit potassium content (0.092%) was recorded after a treatment consisting of 100% nitrogen as vermicompost + Azotobacter. The calcium content (0.033%) was the highest after two treatments: 25% N as vermicompost + 75% N as urea + Azotobacter and 50% N as vermicompost + 50% N as urea + Azotobacter. Ennab (2016) reported that in Eureka lemon plants, the maximum leaf nitrogen content during both seasons, namely 2014 (2.76%) and 2015 (2.79%), was recorded after the application of 75% NPK tree−1 + 27.5 kg farmyard manure year−1 + Azotobacter 25 g tree−1 + Azospirillum 25 g tree−1 + Bacillus circulans 25 g tree−1, whereas the controls (N, P2O5, and K2O) produced 1000:250:500 g tree−1 year−1. Hosseini and Gharaghani (2015) reported that inoculating 1-year-old apple plants with arbuscular mycorrhizal fungi (AMF) significantly improved the concentrations of N, P, Ca, Mg, Zn, and Fe in their leaves compared with the uninoculated plants (controls). Hassan (2015) reported that in strawberry cv. Sweet Charlie, the total N, P, and K percentages of plant foliage were progressively and significantly improved through the use of biofertilizer types (photosynthetic bacteria, lactic acid bacteria, certain fungi, yeasts, and ray fungi) and specific biofertilizers (Azotobacter chroocooccum, Bacillus polymyxa, Azospirillum brasilense, Pesudomonas putida, and Enterobacter agglomerans) when used in combination with NPK (100% recommended dose) as mineral fertilizers or organic (compost), compared with other treatments. Singh et al. (2013) reported that inoculating apple seedlings with bioinoculants (Azotobacter  +  Azospirillum  +  AMF), either alone or in combination, significantly improved the total N of leaves by 2.22% in Red Delicious and 2.20% in Lal Ambri, respectively, compared with the

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uninoculated plants (controls). Raman (2012) reported in apple seedlings that the maximum contents of leaf nutrients N, P, K, Cu, and Zn were recorded after being inoculated with Azotobacter chroococcum + Pseudomonas striata + Trichoderma viride. Kundu et al. (2011) reported that in pruned mango cv. Amrapali, treatment consisting of NPK (100%) + VAM + Azotobacter caused better leaf nitrogen, phosphorus, and potassium contents: 1.56–1.88%, 0.14–0.15%, and 1.11–1.21%, respectively. Dutta et al. (2010) revealed that treating litchi cv. Bombai with FYM, 50 kg tree−1 + Azotobacter; 150 g + VAM, 100 g + N; 500 g + P2O5, 250 g + K2O; and 500 g tree−1 year−1 through fertilizer produced the highest leaf nitrogen and potassium contents. Singh and Singh (2009) investigated strawberry cv. Sweet Charlie and stated that inoculating it with Azotobacter + Azospirillum + 50% N (standard dose) + GA3 (100 ppm) resulted in the highest N (2.94%) and Mg (0.31%) contents, while the highest Zn (68.19 ppm) content was recorded after a treatment featuring only one change from the above treatment, namely 75% N in place of 50% N (standard dose). Wu and Zou (2009) stated that the AMF inoculation in citrus seedlings significantly increase leaf K, P, Mg, Ca, Mn, Cu, and Fe and root K, P, Fe, Ca, Cu, and Zn contents compared with the uninoculated controls. Khosravi et al. (2009) reported that young apple plant (M.9) roots were inoculated with Azotobacter chroococcum, consisting four strains. The AFA146 strain among the four was a valuable strain in that the uptake of nutrients was increased, such as K, Mg, Mn, Fe, B, and Zn. Similarly, increases in the root nitrogen uptakes of N, P, K, Mn, and Zn were recorded. Aseri et al. (2008) revealed the uptake of various nutrients (N, P, K, Ca, Mg, Cu, Mn, and Fe), which were the highest in pomegranate seedlings under Indian Thar Desert conditions upon inoculation with A. chroococcum + G. mosseae. Ojha et  al. (2008), while working on mycorrhizal custard apple seedlings, stated that the phosphorus levels in shoot and root tissues remained higher than those in nonmycorrhizal-treated seedlings. Further, the older the plant became, the more phosphorous content was recorded.

7 Effect of Biofertilizers on Soil Health–Holding Fruit Plants Hazarika and Aheibam (2019) reported on soil that contained lemon plants: At the harvest stage, treatment consisting of 75% N through FYM + 25% through inorganic fertilizers + Azotobacter + PSB + KSB showed the maximum organic carbon content (0.90%) and available P (27.90  kg/ha), compared with other treatments. Deshmukh et al. (2018) reported that in acid lime orchard soil, the maximum organic carbon content was noted after treatment consisting of 75% RDF (450:225:225 g NPK) + FYM, 50 kg per plant + AMF; 500 g per plant + PSB, 100 g per plant + ZnSO4; and 200 g per plant, during both seasons, namely the first (0.56%) and second seasons (0.58%) of the experiment. Poonia et al. (2018) revealed that adding Azotobacter 50 g + phosphorus-solubilizing bacteria (PSB) 50 g + vermicompost 3 kg per plant affected soil health parameters and resulted in a reduction in the soil pH, a reduction in electrical conductivity (EC) compared with other treatments, and

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an improvement in soil fertility status, especially available N (341.87 kg ha−1), P (24.92 kg ha−1), and K (362.81 kg ha−1) for mango cv. Dashehari orchard soil, by the end of the experiment. Aseri et al. (2008) reported that biofertilizer inoculation in the soil of pomegranate significantly improved the activities of alkaline phosphatase, dehydrogenase, nitrogenase, and fluorescein diacetate hydrolysis in the rhizosphere in comparison with those of the uninoculated plants (controls). Further, root colonization percentage via AMF was boosted by 15–38% over the control after 4 months of inoculation. Kumar et  al. (2018) expressed that the physicochemical properties of soil, such as soil reaction, soil organic carbon content, available N and P contents, and dehydrogenase activity in apples after 3 years, were significantly affected by different treatments. The treatment consisting of 75% RDF + 25% N through FYM  +  microphos in apple brought about the highest SOC (10.9 g/kg), DHA (18.4 μg TPF/hr./g soil), and diethylenetriaminepentaacetic acid (DTPA) for extractable zinc (0.80 mg/kg). Similarly, the highest N (334 kg/ha) and P (24.2 kg/ ha) values were recorded under the same treatment. Singh et al. (2018) reported that in rough lemon, regardless of the potting combination used, a treatment of Azospirillum + AMF produced the maximum media organic carbon, phosphorus, and potassium contents: 4.33%, 0.39%, and 459.33 ppm, respectively. Ennab (2016) reported that on Eureka lemon plants, the application of a treatment consisting of 75% NPK/tree + 27.5 kg farmyard manure per year + Azotobacter 25 g per tree + Azospirillum 25 g per tree + Bacillus circulans 25 g per tree resulted in the highest availability of nutrient contents in mg/kg of soil for specifically N (159.63), P (15.11), K (165.24), Fe (33.24), Zn (19.85), and Mn (10.92), by the end of the experiment, compared with the controls (1000:250:500 g N, P2O5, and K2O per tree per year). Wang et al. (2016) reported that in apple cv. Fuji, soil treatment containing biofertilizer application produced the highest soil organic matter content per soil depth: 13.79, 15.26, and 9.50 mg/g at depths of 0–20, 20–40, and 40–60 cm, respectively. Similarly, for total N, values of 2.19, 2.44, and 1.51 mg/g were found to be the highest at the depths of 0–20, 20–40, and 40–60 cm, respectively. Furthermore, the activities of invertase and catalase were also increased after the same treatment. Adak et  al. (2014) stated that when guava was treated with vermicompost (10  kg)  +  N, P, and K (120, 60, and 50  g per tree per year, respectively) + Azotobacter + PSM + Trichoderma harzianum + organic mulching, it resulted in the highest organic carbon content and available N, P, K, Fe, Zn, Cu, and Mn contents when compared with the application of only chemical fertilizers and FYM. While working on 1-year-old Red Delicious and Lal Ambri cultivars on MM-106 rootstock, Singh et al. (2013) stated that the use of bioinoculants (Azotobacter + Azospirillum  + AMF) significantly improved the availability of nutrients such as N, P, and K in soil compared with the controls (uninoculated plants). Mir et  al. (2013) revealed that in pomegranate orchard soil, treatment consisting of biofertilizers (80 g/tree), FYM (20 kg/tree), vermicompost (20 kg/tree), Crotalaria juncea L., green manure, and the recommended dose of fertilizers (RDFs) N, P, and K delivered the highest water-holding capacity (60.31%), porosity (60.27%), particle density (2.25%), bulk density (0.97%), organic carbon (1.90%), soil pH (6.89), N (405.56%), P (22.02%), K (419.00%), Mn (61.95 ppm), Fe (66.92 ppm), Cu (3.25 ppm), and Zn (2.33 ppm).

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Enhance soil fertility

Improve soil health

Non-bulky

lmprove fruit quality

Improve fruit yield

Cheaper than chemical fertilizers

Biofertilizers

Act as bio-protectant to stresses

Enhance plant growth

Secrete plant growth hormones

Reduce pressure on chemical fertilizers Environment friendly

Fig. 8.1  Beneficial effects of biofertilizer use in fruit crops

Gogoi et al. (2004) stated that in banana orchard soils, treatment consisting of RDF of NPK + Azospirillum + PSB resulted in the highest increase in available soil P2O5 (30.30 kg/ha) and soil K2O (242.42 kg/ha) (Fig. 8.1, Table 8.1).

8 Limitations of Biofertilizer Use in Fruit Crops I. Precise Strains for Diverse Agro-climatic Regions Biofertilizer strains are usually crop specific as well as soil climatic and agro-climatic. Therefore, a region-specific strain shortage becomes a limitation for a biofertilizer’s wide use and better performance (Mahdi et al. 2010). II. Low Carrier Material Reserves Preparation of biofertilizers is usually based on carriers containing an inoculation of effective microorganisms. Charcoal, perlite, peat, etc. are granular forms of carrier materials generally suggested for soil inoculation (Mazid and Khan 2014). The lack of quantity and quality among carrier materials in India hampers the popularity of using biofertilizers among Indian farmers (Mahdi et al. 2010). III. Antagonistic Constraints The presence of hostile microorganisms in soil constraints the efficacy of biofertilizers.

Table 8.1  Biofertilizer application exhibiting highest values on fruit crop characteristics

Biofertilizers AMF

Plant BA/ vegetative BNC growth BA +

AMF + A. chroococcum

BA

Pear

Azotobacter + PSB + VAM

BNC *

Plum

Azotobacter + PSB

BNC +

Azotobacter + AMF + PSB

BNC +

Azotobacter + PSB + AM

BNC +

Azotobacter + Azospirillum

BNC +

Mango

Azotobacter + PSB

BNC + BNC *

Banana

Azotobacter chorococcum + Azospirillum brasilense + AMF AMF

+

*

*

Azospirillum lipoferum + Bacillus megaterium + Frateuria aurantia + Glomus intraradices Azotobacter + PSB

BNC +

+

*

BNC +

*

*

Azotobacter + PSB + KSB

BNC +

+

*

Pomegranate A. chroococcum + G. mosseae

BA

+

*

*

Guava

Azotobacter + PSB

BNC *

+

+

A. brasilense + AMF

BA

*

+

+

Pineapple

Azotobacter + PSB

BNC *

+

+

Ber

Azotobacter + PSB

BNC *

*

+

Aonla

AMF + Azospirillum

BA

+

*

*

Custard Apple

Glomus fasciculatum

BA

+

*

*

Crop Apple

Strawberry

Papaya

Lemon

BA

+

Fruit yield TSS References * * Hosseini and Gharaghani (2015) * * Sharma et al. (2012) + + Bashir et al. (2017) + * Kamatyanatti et al. (2019) * * Thakur et al. (2016) + * Singh et al. (2015) + + Singh and Singh (2009) * * Poonia et al. (2018) + + Sau et al. (2017) Emara et al. (2018) Krishna et al. (2018)

Mamta et al. (2017) Hazarika and Aheibam (2019) Aseri et al. (2008) Gupta et al. (2019) Das et al. (2017) Baraily and Deb (2018) Mahendra and Singh (2009) Kumar et al. (2014) Ojha et al. (2008)

BA biofertilizers used solely in the experiment, BNC biofertilizers used with other nutrients in the experiment, AMF arbuscular mycorrhizal fungi, PSB phosphate-solubilizing bacteria, KSB potassium-­solubilizing bacteria + indicates highest value in the experiment * indicates either the character was not evaluated or does not exhibit the highest value in the experiment

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IV. Production Restrictions Biofertilizers have an affinity for mutating during fermentation; therefore, their quality lowers, while production costs increase. To minimize such changes, more research is needed (Mahdi et al. 2010). V. Financial Restrictions High-tech instruments and equipment are needed for the manufacture of quality biofertilizers. VI. Technical Resource Persons There is a dearth of effective technical expertise and experts at production sites for quality maintenance. VII. Logistics Restrictions The storage and transportation of biofertilizers currently take place at inadequate facilities. A duration of only 6 months is the usual life span of biofertilizers when prepared with common carriers such as peat or lignite. Exposing biofertilizers to high temperatures during transportation and storage restricts their efficiency (Mathur et al. 2010). VIII. Little Awareness Owing to a lack of awareness of the advantages of using biofertilizer, farmers resist adopting this technology in fields. IX. Trust Limitations The low shelf life of biofertilizers makes retailers prone to selling outdated products through illegal ways, which has led farmers to doubt their efficacy. X. Farm Field Restrictions No rapid response from biofertilizers on crops, because of the prevalent soil conditions, such as alkalinity, acidity, pesticides, water logging, drought, etc. decreases the performance of the biofertilizers compared with that of inorganic fertilizers. Further, when farmers use defective techniques for soil, seed, and seedling inoculation, this hampers biofertilizers’ performance levels.

9 Biofertilizer Application Methods The biofertilizer method of application depends on the type of crop and its growth stage. The ultimate aim of following different methods of using biofertilizer is to place the microbes close to the root zone so that it has the maximum activities near it and so that it can provide the maximum benefits to the growing plant. Different methods of using biofertilizers are presented next. I. Soil Soil application is commonly followed in fruit crops. Biofertilizers are thoroughly mixed with FYM, compost, or pulverized soil before they are used in soil. Mixed preparation is placed near the root zone of the plant. Biofertilizers Azospirillum lipoferum, Bacillus megaterium, Frateuria aurantia, and Glomus intraradices were applied in papaya at a rate of 5 g plant−1 mixed with 2 kg of

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FYM, and they were applied to the plants at the time of planting (Krishna et al. 2018). Here, 10 g each of Azotobactor and PSB was mixed with 500 g FYM during pineapple planting (Baraily and Deb 2018). II. Seedling This practice of treatment is applicable for transplanting crops. This practice ensures a heavy load of microorganisms on the root system. Seedlings are dipped in a prepared solution for a certain period of time, varying from crop to crop, before transplanting. Runner strawberry plants were thoroughly dipped in 10% guar slurry inoculated with Azotobacter and Azospirillum before planting (Singh and Singh 2009). After dipping the apple seedlings for 15 minutes in microbial suspensions, the root was immediately planted in the soil (Singh et al. 2013). III. Seed One common, economic, and effective technique applied for all forms of inoculants is seed treatment (Sethi et al. 2014). However, in fruit crops, seed treatment is infrequently used because most of the fruit crops are now clonally propagated. Furthermore, this method can be used to develop healthy apple seedling rootstocks from seeds. Seed treatment facilitates the establishment of microorganisms very close to the root system, which is required for the effectiveness of biofertilizers. Seeds uniformly coated in slurry are subsequently shade-dried and then sown within 24 hours. In the case of liquid biofertilizer, a small quantity of seeds can be coated in a plastic bag or a bucket if the seed quantity is large. The advantage of seed treatment is that more than two biofertilizers, such as Rhizobium, Azospirillum, and Azotobacter, may be applied, in addition to phosphorus-solubilizing microorganisms, without any antagonistic effect (Chen 2006). A seed treatment of Rhizobium is practiced in peas and chickpeas; Azotobacter in wheat, oats; and Azospirillum or phosphorus-­ solubilizing bacteria in maize, rice, and sorghum (Taylor and Harman 1990).

10 Conclusion Biofertilizers nowadays form an important constituent of integrated nutrient management in fruit crops. They are a renewable and ecofriendly source of plant nutrients. Because India produces the second-highest amount of fruit in the world, there is huge demand for using inorganic fertilizers in fruit crop nutrition. The use of biofertilizer in fruit crops is gradually growing thanks to awareness among farmers. Biofertilizers provide their portion of nutrition to plants, hence relieving some of the pressure on inorganic fertilizers. Biofertilizers enhance nutrient availability and maintain soil health. Furthermore, they increase the production and productivity of fruit crops. However, their commercial use by cultivators in fruit crops is not usually seen, because of the limitations associated with them. In order to realize the full potential of using biofertilizers on fruit crops, more focus and research are needed to alleviate the limitations and to develop crop-, soil-, and

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climatic-specific strains so that their efficacy can be improved. At present, replacing all the inorganic fertilizers used in fruit crops with biofertilizers is not possible; however, that day may come in the near future.

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Chapter 9

Microbial Biofertilizers: An Environmentally-friendly Approach to Sustainable Agriculture Lukman Ahamad, Mohammad Shahid, and Mohammad Danish

Abstract  In modern-day agricultural practices, the application of microbes as biofertilizers is considered an important component of sustainable organic farming and ecofriendly practices, so biofertilizers are used instead of chemical fertilizers that cause environmental pollution, which severely affects human health. Microorganisms like plant growth–promoting rhizobacteria (PGPR), fungi, algae, etc., have also shown biofertilizer-like exertion in modern agronomic practices. These microbes live in the rhizosphere and have the movability to invade plant roots and enhance their development. Microbes’ positive impacts are achieved through various mechanisms, such as phosphorus solubilization, nitrogen fixation, plant nutrient and phytohormone development, antimetabolites to sustain root growth, pathogen defense, and recovery from stressful environmental conditions. This is the key reason why many microbes are increasingly being used. The goal of this review is to focus on the importance of microbial fertilizers and their advantageous effects on plants in promoting sustainable agriculture. Keywords  Microbes · Biofertilizers · Sustainable agriculture

1 Introduction In recent years, agricultural production has increased dramatically, day by day, due to increased population growth in the world and thus the growing need for food (Hassen et al. 2016). It has been estimated that at present, there are around seven

L. Ahamad · M. Danish (*) Department of Botany, Aligarh Muslim University, Aligarh, India M. Shahid Department of Agricultural Microbiology, Faculty of Agriculture Science, Aligarh Muslim University, Aligarh, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_9

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billion people living on Earth, who total nearly eight billion as of 2020 (Conway 2012). It is a noteworthy challenge to feed this large population. So far, generally, chemical fertilizers have been used to increase agriculture production, which has proven unsustainable and has become a great threat to nature, by polluting the air, water, and soil, leading to human health hazards (Szilagyi-Zecchin et  al. 2016; Hakeem et al. 2021; Dar et al. 2022). There are numerous options when choosing chemical fertilizers that may be acquired to reach sustainable crop production and environmental protection. Plant growth–promoting microorganisms (PGPMs), which move inside the rhizosphere, a dense, slender, and nutrient-rich area of soil positioned close by the root zone. It is characterized by the occupancy of various root exudation and extreme microbial activity (Zaidi et al. 2016). These microbial communities can be used as biofertilizers. Biofertilizers are extensively applied to boost those microbial methods that augment the presence of vitamins that can be effortlessly assimilated via vegetation. The fixation of atmospheric nitrogen and solubilizing insoluble phosphates brings plant growth–promoting substances to the soil to improve soil fertility (Mazid and Khan 2015). Exceptional microbiota participate in different biotic tasks and play crucial roles in the soil ecosystem, building soil potency to transport nutrients and to make the soil habitable for new crops (Ahmad and Kibret 2014). The interplay between microorganisms and roots extensively enhances the absorption of important compounds and obstructs the augmentation of toxic compounds. These organisms have more than one way to fertilize a plant and enhance its growth and development in an ecologically sustainable manner, which has attracted the interest of researchers all over the world in recent years (Hassen et al. 2016).

2 Mycorrhiza as Biofertilizers Mycorrhizae are obligate fungi that are abundantly present in the roots and soil of higher plants. They form an association with plant roots in a host and promote plant health by enhancing the acquisition of nutrients from the soil and increasing resistance to plant pathogens. Therefore, they can be used as biofertilizers and provide potential benefits to agriculture. The two main types of mycorhizas are ectomycorrhizas and endomycorrhizas.

2.1 Ectomycorrhizal Fungi Ectomycorrhizas have the most advanced symbiotic relationship that occurs between higher plants and fungi, where about 3% of seed-bearing plants are connected with most of a forest’s trees. In this type of association, the root system of the plant is entirely surrounded by a fungal sheath. The fungal hyphae penetrate between the outermost layers of cells forming the structure, called the “Hartig net.” This

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unique structure has a high surface area between the two symbiotic partners and acts as the site of nutrient uptake as well as exchange. Carbon (C) resources from the host plant are transported to the fungus in return for limiting nutrients. However, the fungus can either access them from the nutrient depletion zone surrounding the root system of the host (Smith and Read 2008) or release them from immobilized sources that are generally inaccessible to the plant. These fungi can also uptake a range of micro- and macronutrients, including iron, zinc, copper, manganese, phosphorus, potassium, calcium, magnesium, and sulfur and provide them to the host plants (Yadav et al. 2023).

2.2 Endomycorrhizal Fungi They are one of the most important known mycorrhizae, which differ from ectomycorrhiza in structure and function. The endomycorrhizae can form a hyphae network that can not only grow inside the host root but also penetrate the cell walls of root and become encircled in the cell membrane (Bonfante and Genre 2010). This phenomenon makes for a more invasive symbiotic association between the fungi and the host plant. The penetrating hyphae create greater contact with the large surface area between the fungal hyphae and the host plant. This association is better able to transfer nutrients, such as phosphate and nitrogen, and increases resistance to biotic and abiotic stresses. Endomycorrhizal fungi have further been classified as arbuscular mycorrhizal (AM) fungi, which play important roles as biofertilizers in sustainable agriculture. 2.2.1 Arbuscular Mycorrhizal Fungi AM fungi are soilborne microorganisms that form a symbiotic relationship between plants and fungi. The AM part of the name derives from the Latin word arbusculum and the two Greek words mycos and rhiza, which mean “little tree,” “fungus,” and “root,” respectively. These are root obligate biotrophs that exchange mutual benefits with about 80% of vascular plants and with approximately 90% of agricultural crop plants (Smith and Read 2008). The genera include Glomus spp., Gigaspora spp., Acaulospora spp., Entrophospora spp., Sclerocystis spp., and Scutellospora spp., which are commonly associated with a range of plants. These species are generally identified on the basis of their spores and sporocarps, which are generally formed in the soil surrounding the roots and inside the roots (Sullia 1991). AM fungi are considered natural biofertilizers because they provide the host with water; nutrients, such as inorganic phosphorus, nitrogen, and amino acids; and pathogen protection, in return for photosynthetic products (Vishwakarma et al., 2022; Berruti et al. 2016). Therefore, AM fungi, not the roots, are the main organs of nutrient acquisition by plants (Smith and Read 2008). AM fungi also provide tolerance to plants against pathogens and abiotic stress (Liu et  al. 2007; Marschner 1995). The AM fungi

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commonly known as biofertilizers are valid alternatives to conventional fertilization practices, especially for sustainable agriculture.

3 Other Beneficial Fungi as Biofertilizers Fungal biofertilizers have been utilized for agricultural purposes because of their ability to control plant diseases and increase crop production in an ecofriendly manner. In recent years, many fungal biofertilizers have been registered for their application in crop production. These fungal biofertilizers are plant growth–promoting fungi such as Trichoderma spp., enzyme-producing fungi for compost production, phosphorus (P)-solubilizing fungi, and potassium (K)-solubilizing fungi. These biofertilizers play important roles in improving plant growth, plant health, plant productivity, and the fertility of soils (Kaewchai et al. 2009). Phosphorus is present in soils in both organic and inorganic forms and is one of the essential elements for plant growth and development (Khan et  al. 2010). Phosphate-solubilizing fungi such as Talaromyces aurantiacus and Aspergillus neoniger can be used as as ecofriendly biofertilizers in subtropical bamboo ecosystems (Zhang et  al. 2018). However, K-solubilizing fungi, including Fomitopsismeliae RCKF7, Aspergillus tubingensis (Kasana et al. 2017), and other Aspergillus species, have been applied for their beneficial effects on crop productivity (Prajapati et al. 2013).

4 Algae as Biofertilizers Algae are simple photosynthesizing organisms ranging from microalgae (microscopic forms) to macroalgae (seaweeds). They help in retaining the essential nutrients and water in soil, which is required for the proper growth and development of plants. Nowadays, many algae, such as blue-green algae or cyanobacteria, red algae, and brown algae, have been used as potential biofertilizers in sustainable agriculture.

4.1 Blue-Green Algae Blue-green algae (cyanobacteria) are the simplest living autotrophic microorganisms that can make food materials from inorganic matter. These organisms are microscopic and are often found in aquatic environments (Abdelgani and Hassan 2006). Certain blue-green algae are in symbiotic relationship with other plants. Several features of blue-green algae include atmospheric N2 fixation and adaptability to extreme conditions, making them useful biofertilizer to improve the properties of soil (Abdelgani and Hassan 2006; Singh et  al. 2016). These organisms also secrete phytohormones as secondary metabolites, enhance the transfer of nutrients

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from soil to plants, cause soil to accumulate, and increase soil chemical properties (Malliga et al. 2002; Kheirfam et al. 2017). Some of the efficient nitrogen-fixing strains used as biofertilizers for food production across the agroclimatic regions of the world are Nostoc, Anabaena, Aulosira, Calothrix, Tolypothrix, and Scytonema (Prasad and Prasad 2001). Moreover, the beneficial effects of blue-green algae have been reported for various crops, such as radishes, cotton, barley, maize, chili, oats, tomato, sugarcane, and lettuce (Thajuddin and Subramanian 2005).

4.2 Red Algae Red algae are a specific type of species that are mostly found in freshwater lakes, and they are considered one of the oldest eukaryotic algae. They are red in color due to the presence of pigments known as chlorophyll A, phycocyanin, and phycoerythrin. Red macroalgae are also widely used as biofertilizer due to their high content of trace elements and other agricultural properties. Three red macroalgae, namely Laurencia obtusa, Corollina elongata, and Jania rubens, have been investigated for their N, P, and K contents and have been widely used as biofertilizers in agriculture. However, some red marine algae, such as L. obtusa, C. elongata, and J. rubens, have been used alone and in combination as biofertilizer to improve the growth of maize plants (Safinaz and Ragaa 2013).

4.3 Brown Algae Brown algae are complex macroscopic seaweeds that live in marine environments. Their brown color characterizes them due to the presence of the fucoxanthin pigment. These algae can be used as vital sources of biofertilizer in both their fresh and dried forms, and this use helps to enhance the biochemical properties of plants, such as lipids, carbohydrates, fibers, ash, phenol, proteins, and dietary fiber. These seaweeds are good sources of the micro-/macro-elements required for plant growth and development. Several studies have shown that seaweed extracts are effective fertilizers for many crops (Strik et al. 2004). The addition of different successive extracts of Asparagopsis taxiformis thallus powder to soil, as a biofertilizer, was shown to significantly increase the growth of Vicia faba (El-Barody et al. 2007). The foliar application of seaweed extracts enhanced the plant growth, drought and salt tolerance, the rate of photosynthesis, and resistance to fungi, bacteria, and viruses in many crops (Norrie and Keathley 2006; Sharma et  al. 2014). Seaweed extracts could be used as ecofriendly biofertilizers and replace chemical fertilizer, and they are essential for sustainable agriculture.

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Plant Growth–Promoting Rhizobacteria (PGPR) Beneficial soil bacteria that aggressively colonize the rhizosphere region and promote the growth of plants are termed plant growth–promoting rhizobacteria (PGPR) (Shahid et al. 2021a). They augment the growth and productivity of crops through numerous mechanisms, functioning directly and indirectly (Shahid et  al. 2017). Among the PGPR strains, the agriculturally important soil bacteria belong to the genera of Azotobacter, Azospirillum, Bradyrhizobium, Bacillus, Cellulomonas, Pseudomonas, Rhizobium, and Xanthomonas. Beneficial rhizosphere flora, involving the symbiotic bacteria, forms an intricate relationship with the roots of plants, including legumes, and successfully colonizes the root surfaces and consequently enhances the plant’s growth parameters via either (i) nitrogen fixation, (ii) phytohormone secretion, (iii) solubilizing the insoluble form of inorganic P and producing siderophore, and (iv) induced systemic resistance (Mukhtar et  al. 2020). The intrinsic and inherent properties of PGPR make them a best choice to use as biofertilizers in agriculture. Agricultural Importance of PGPR Soil microbial diversity plays a vital role in the recycling of plant materials via the decomposition of soil organic matter (Fan et al. 2019). In addition, soil microorganisms influence the productivity of crops and the health of plants by acting both as pathogens and as beneficial agents (Rosier et al. 2018). They improve agricultural productivity because they are involved in biofertilization, root growth stimulation, biotic/abiotic stress management (Shahid et al. 2023; Shahid et al. 2022b; Malviya et al. 2022; Shafi et al. 2023), and rhizoremediation (Bhardwaj et al. 2014). Many soil microbiota, including rhizobacteria (Singh et  al. 2019) and actinomycetes (Ansari et al. 2019), form symbiotic relationships with the roots of plants and provide nutrients like nitrogen and phosphorous (Zaidi et al. 2017). In this symbiotic relationship, plants provide carbohydrates to bacterial entities, while bacteria decrease the nitrous compounds in soil and make it available to plant systems. An exchange of nutrients between both symbiotic partners (bacteria and plants) during the synergy of N2-fixing Rhizobium has been reported (Zaidi et  al. 2017). Some bacteria colonize the root zone of plants and provide assistance/benefits such as plant tolerance to pesticides, heavy metals, and phytopathogens. In this regard, numerous workers have reported the beneficial effects of various groups of root-­ colonizing bacteria, such as Azotobacter (Banik et al. 2019), Rhizobium (Kopycińska et al. 2018), Burkholderia (Shahid et al. 2018), Bradyrhizobium (Schneijderberg et al. 2018), Mesorhizobium (Shahid et al. 2021c), Pseudomonas (Chiriboga et al. 2018), Kosakonia (Shahid et al. 2022a; Sun et al. 2018), and Bacillus (Mendis et al. 2018; Shahid and Khan 2017). Bacteria mitigate and alleviate the pesticidal toxicity in plants and soil systems through various mechanisms (Khan et al. 2020). The mitigation of abiotic/biotic pressures due to beneficial soil microbes is extremely valuable in agronomic practices, especially when in varying environments (Fig. 9.1).

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Supplementing

Plants growth

Organic matter decomposition

Biocontrol of soil-borne phytopathogen

Alleviating Abiotic stress in Plants

Supply of nutrients to plants

Soil micro flora

phytohormone production

Enhancing Nutrient Availability As Biopesticides and Biofertilizers

Fig. 9.1  Different functions of plant growth–promoting rhizobacteria (PGPR)

Plant Growth Promotion Mechanism by PGPR Plant growth–regulating/soil-beneficial PGPR can promote the growth of plants in both direct and indirect ways. On one hand, the direct enhancement of plant growth entails either supplying the growth-regulating substances to plants that are synthesized/released by bacterial species or enabling the uptake of certain nutrients from environments (Al-Shwaiman et al. 2022; Shahid et al. 2022c; Danish et al. 2022; Rizvi et al. 2017). The familiar direct growth promotion mechanism includes nitrogen fixation, phytohormone production, growth regulators, and P solubilization. The fixation of N2 by nonsymbiotic PGPR is one of the advantageous activities of PGPR and has been found to be exceedingly effective (Ahmed et  al. 2017). The activity of acetylene reduction (ARA) was detected in tomato plants (Lycopersicum esculentum) bacterized with Methylobacterium spp. (Jourand et al. 2004). In contrast, nitrogen fixation by rhizobia in plants other than legumes (non-­legumes) is uncommon/infrequent. On the other hand, the indirect mechanism of plant growth by PGPR happens when bacteria protect the plants from the deleterious impacts of one or more phytopathogens. Iron-chelating compounds—e.g., siderophore, synthesized by a number of soil microflora—may even be considered the direct factors promoting the growth of plants. The catecholate type of siderophore secreted by

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Plant Growth Promotion Mechanism by PGPR

Indirect Mechanisms Indir

Direct Mechanisms

Release of Biological Nitrogen Fixation (BNF) (Symbiotic and Asymbiotic)

Production of (e.g . Indole Phytohormone acetic acid, Gibberellins, Cytokinins , Abscicis acid and Ethylene)

Phosphate Solubilization

(e.g. Gluconic , Oxalic, Citric, Acetic, Latic , Malic and Ketogluconic etc.)

ACC Deaminase Activity

JJA, A, Et E

Siderophores

(e.g. Phenolate and Catecholate )

JA, JA, Et JA E

Production of Ammonia

Production of Cyanogenic Compounds (e.g. Hydrogen cyanide ) Antibiotic Production (e.g. kanosamine,

oligomycin A, oomycin A, phenazine-1-carboxylic acid, pyoluteorin

Production of lytic/cell wall degrading enzymes

Induced Systemic Resistance (ISR)

Fig. 9.2  A schematic representation depicting the mechanisms of growth promotion by PGPR

bacterial species solubilizes and sequesters the insoluble form of iron (Fe) in agricultural soil systems, and this solubilized form of siderophore is ultimately taken by the roots of plants and activates the growth regulatory enzymes of plants (Kurth et al. 2016). Furthermore, these chelating compounds (siderophore) are considered indirect factors in promoting the growth of plants by inhibiting/killing the growth of phytopathogens, by limiting the available Fe in soil systems (Shanmugaiah et al. 2015). Largely, PGPR may stimulate the growth and development of plants by using any one of such mechanisms or combination of them. Numerous bioactive compounds secreted/synthesized by plant-beneficial bacteria that promote the growth of plants have been reviewed. The direct and indirect mechanisms of PGPR-induced growth enhancement are illustrated in Fig. 9.2. PGPR as Biofertilizers Microbial preparation containing a sufficient number of active/viable cells that can enhance the growth of plants by producing active biomolecules is called biofertilizer. (Shahid et al. 2021b). Biofertilizers have several advantages over synthetic pesticides: They (i) are safer, (ii) cause less environmental damage, (iii) show much more targeted activity, (iv) are effective in small quantities, (v) multiply themselves

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(vi), decompose more rapidly than synthetic pesticides (vii), cause slow resistance development, and (viii) can be used in integrated pest management. In addition to augmenting the growth and health of plants, these microbial entities are used in the management of end products. Microbes play crucial roles in preserving food products and maintaining their quality. Many PGPR have been applied as biofertilizers, according to various workers. For instance, in an experiment conducted by Mehmood et al. (2018), it has been reported that plants exposed to auxin (IAA) and soil-beneficial bacteria for longer periods have developed their root systems exceedingly well, which in turn allows the plants to absorb sufficient nutrients from the soil, thus improving the overall performance of the plants. Additionally, a Rhizobium strain isolated from the root nodule of a legume produced a considerable amount (3 mg/ mL) of IAA in an L-tryptophan-amended medium, and when this strain was applied as a biofertilizer to plants, it enhanced the length, dry biomass, and nodule number of V. mungo (Pratibhan and Krishna 2016). The enhancement of the biological features of plants may be due to the phytohormone (auxin) synthesized by the bacterial strain, and it is well known that auxins elongate root initiation, cause cell elongation, and promote plant development. Similarly, the Enterobacter cloacae strain produced a considerable amount of IAA and other plant growth–regulating substances when cultured in a liquid medium and had positive impacts on the growth and yield of green gram even in a stressed environment (Widowati and Sukiman 2019). In a follow-up study, two PGPR strains, namely Bacillus sp. FOW1 and Lysinibacillus sp. FOW7, degraded pesticides, produced a considerable amount of growth-regulating substances in a pesticide-treated liquid medium, and improved the germinating ability, shoot length, root length, and overall performance of Trigonella foenum-graecum plants, even in those grown in soil supplemented with pesticides—as reported by Nathiya et al. (2020). Phosphate-solubilizing strains are also a group of PGPR that augment the growth of various crop plants, including vegetable and legume crops. Various reports have described how phosphate-solubilizing bacterial strains are used as biofertilizers. For example, two promising phosphate-solubilizing strains of Bacillus (B. aryabhattai S10 and B. subtilis ZM63) improved the N, P, and K contents by 142%, 90%, and 71%, in shoots of Vigna radiata (green gram) plants, respectively. Likewise, in a similar crop-based study, two PSB strains, namely Bacillus aryabhattai S10 and Bacillus subtilis ZM63, significantly improved the concentrations of N, P, and K in shoot tissues of Vigna radiata plants by 142%, 90%, and 71%, respectively (Ahmad et  al. 2019). Furthermore, in another study, ACC deaminase–producing and stress-tolerant PGPR strains of Bacillus, Acinetobacter, and Enterobacter increased the relative water content, plant height, leaf–stem ratio, fresh biomass, dry biomass, photosynthetic pigments, and N, P, and K contents of Medicago sativa plants (Daur et al. 2018). Conclusively, using microbial preparation–based biofertilizers would reduce the use of agrochemicals/pesticides in agricultural practices, which can be helpful in the remediation of environmental pollution (Table 9.1).

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Table 9.1  Some examples of PGPR used as biofertilizers in conventional soil and under stressed environments Plant growth– regulating PGPR/biofertilizers Environment substance Bradyrhizobium Pesticide ACC japonicum stress deaminase, EPS, IAA, siderophore, NH3, and HCN Cellulosimicrobium Conventional EPS, IAA, funkei soil NH3, siderophore, HCN, protease, catalase, and hydrolytic enzymes Conventional IAA, P Pseudomonas, soil solubilization, Bacillus, and siderophore, Enterobacter NH3, and EPS

Ensifer adhaerens

Pesticide stress

IAA, EPS, ammonia, HCN, and siderophores

Achromobacter spanius and Serratia

Pesticide stress

Siderophores, phosphorus, and indole acetic

Bacillus cereus and Conventional Extracellular Bacillus safensis soil enzymes, siderophore, IAA, and solubilized phosphate

Target crop Vigna radiata (green gram)

Action Increased the overall growth, yield, and productivity of plants Enhanced the length, dry biomass, and chlorophyll synthesis of plants

References Shahid and Khan (2019)

Capsicum Improved annuum (chili) the height and biomass of plants and increased their carotenoid content Glycine max Increased the (soybean) germination rate and plant growth rate Medicago Enhanced sativa (alfalfa) the symbiotic attributes and dry biomass of plants Lens culinaris Promoted (lentil) the length and dry biomass of plants

Veerapagu et al. (2018)

Phaseolus vulgaris (common bean)

Karthik et al. (2017)

Zhou et al. (2013)

Aroua et al. (2019)

Roy et al. (2018)

(continued)

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Table 9.1 (continued) Plant growth– regulating PGPR/biofertilizers Environment substance Rhizobium Conventional IAA, leguminosarum soil siderophore, EPS, ACC, HCN, and NH3

Burkholderia cepacia

Paenibacillus lentimorbus

Rhizobium

B. aryabhattai and B. subtilis

Target crop Action Pisum sativum Enhanced (pea) plant growth, dry matter, symbiotic features, plant nutrients, and seed features Pesticide IAA, Alleviated Cicer stress siderophore, the oxidative arietinum EPS, ACC, stress and (chickpea) HCN, and increased the NH3 overall growth of legumes Conventional ACC Lycopersicum Improved soil deaminase, plant growth esculentum IAA, NH3, and (tomato) by inhibiting fungal production of growth cyanogenic compounds Vigna mungo Enhanced Conventional Auxin, the length, soil cytokinin, and (black gram) dry biomass, IAA and nodule number of plants Conventional Phosphate Vigna radiata Improved soil solubilization, (green gram) the N IAA, NH3, and content up to 142%, the P siderophores content up to 90%, and the K content up to 71% in shoot tissues

References Shahid et al. (2019)

Shahid and Khan (2018)

Dixit et al. (2016)

Pratibhan and Krishna (2016)

Ahmad et al. (2019)

5 Conclusion Researchers have focused on microbial fertilizers for quite a long time. Microbial-­ based fertilizers promote the growth and development of plants and are also acceptable as alternatives to chemical fertilizers, which are excessively used and very harmful to the environment and to humankind. The idea of biofertilizer is not new;

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plenty of scientific research papers have been written on it. However, many questions remain unanswered. The wide range of technological challenges includes the fermentation method, the types of formulations, the population of microorganisms, and their method of release. The most essential but also most difficult part of studying and identifying both diverse biofertilizers strains and their properties is describing the actual mechanism through which they are useful in sustainable agriculture. More knowledge and more research are required to increase product quality, reliability, and practical usage. The increasing demands from farmers and planters to use biofertilizers will set the scene for new entrepreneurs to join in the production of biofertilizers, and this production needs more support from governments. Acknowledgements  The authors Lukman Ahamad and Mohammad Shahid have equally contributed and shared first authorship.

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Smith SE, Read DJ (2008) Mycorrhizal symbiosis, 3rd edn. Academic Press, Cambridge Strik WA, Arthur GD, Lourens AF, Novok O, Strand M, Van-Staden J (2004) Changes in seaweed concentrates when stored at an elevated temperature. J Appl Phycol 16:31–39 Sullia SB (1991) Use of vesicular-arbuscular mycorrhiza (VAM) as biofertilizer for horticultural plants in developing countries. In: Prakash J, Pierik RLM (eds) Horticulture-new technologies and applications. Current plant science and biotechnology in agriculture, vol 12. Springer, Dordrecht Sun S, Chen Y, Cheng J, Li Q, Zhang Z, Lan Z (2018) Isolation, characterization, genomic sequencing, and GFP-marked insertional mutagenesis of a high-performance nitrogen-fixing bacterium, Kosakonia radicincitans GXGL-4A and visualization of bacterial colonization on cucumber roots. Folia Microbiol 63(6):789–802 Szilagyi-Zecchin VJ, Mógor ÁF, Figueiredo GGO (2016) Strategies for characterization of agriculturally important bacteria. In: Singh DP, Singh HB, Prabha R (eds) Microbial inoculants in sustainable agricultural productivity. Springer, New Delhi, pp 1–21 Thajuddin N, Subramanian G (2005) Cyanobacterial biodiversity and potential applications in biotechnology. Curr Sci 89:47–57 Veerapagu M, Jeya KR, Priya Rand Vetrikodi N (2018) Isolation and screening of plant growth promoting rhizobacteria from rhizosphere of chilli. J Pharmacogn Phytochem 7:3444–3448 Vishwakarma SK, Ilyas T, Malviya D, Shafi Z, Shahid M, Yadav B, Singh UB, Rai JP, Singh HB, Singh HV (2022) Arbuscular Mycorrhizal Fungi (AMF) as Potential Biocontrol Agents. In Rhizosphere Microbes: Biotic Stress Management (pp. 197–222). Singapore: Springer Nature Singapore. Widowati T, Sukiman H (2019) Production of indole acetic acid by Enterobacter cloacea H3 isolated from mungbean (Vigna radiata) and its potential supporting the growth of soybean seedling. IOP Conf Ser Earth Environ Sci 308:012040. IOP Publishing Yadav B, Singh UB, Malviya D, Vishwakarma SK, Ilyas T, Shafi Z, Shahid M, Singh HV (2023) Nematophagous Fungi: Biology, Ecology and Potential Application. In Detection, Diagnosis and Management of Soil-borne Phytopathogens (pp. 309-328). Singapore: Springer Nature Singapore. Zaidi A, Khan MS, Ahmad E, Saif S, Rizvi A, Shahid M (2016) Growth stimulation and management of diseases of ornamental plants using phosphate solubilizing microorganisms: current perspective. Acta Physiol Plant 38:117 Zaidi A, Khan MS, Rizvi A, Saif A, Ahmed B, Shahid M (2017) Role of phosphate solubilizing bacteria in legume improvement. In: Zaidi A, Khan MS, Musarrat J (eds) Microbes for legume improvement, 2nd edn. Springer, Switzerland, pp 175–197 Zhang L-P, Fang X-M, Wu X-Q, Luan F-G, Zhang L-P, Fang X-M, Wan S-Z, Hu X-F, Ye J-R (2018) Isolation and characterization of two phosphate-solubilizing fungi from rhizosphere soil of moso bamboo and their functional capacities when exposed to different phosphorus sources and pH environments. PLoS One 13(7):e0199625. https://doi.org/10.1371/journal. pone.0199625 Zhou GC, Wang Y, Zhai S, Ge F, Liu ZH, Dai YJ, Yuan S, Hou JY (2013) Biodegradation of the neonicotinoid insecticide thiamethoxam by the nitrogen-fixing and plant-growth-promoting rhizobacterium Ensifer adhaerens strain TMX-23. Appl Microbiol Biotechnol 97:4065–4074

Chapter 10

Actinomycetes as Biofertilisers for Sustainable Agriculture Jeelani Gousia, Shah Ishfaq, Baba Uqab, and Syeed Mudasir

Abstract  Agriculture worldwide has gone through rapid shifts, i.e. from use of chemical fertilisers to bioactive fertilisers or biofertilisers. This shift demanded use of living species, like microorganisms and plants, for the production of the biofertilizers. Actinomycetes being ubiquitous microbes have various applications in sustainable agriculture. Actinomycetes are prokaryotic organisms that are classified as bacteria, but are unique enough to be discussed as an individual group. Actinomycetes have been studied for their role in nitrogen fixation, breakdown of organic matter, plant growth-promoting activity, production of various enzymes and bioremediation of different pollutants. All these properties have made actinomycetes a sustainable alternative to chemical fertilisers. Keywords  Actinomycetes · Biofertilisers · Nitrogen fixation · Bioremediation

1 Introduction All living beings require nutrients for their growth and development. A total of 17 plant nutrients (classified as major, minor and micro) are essential for proper development of the crops, each being equally important to the plants; however, each nutrient is needed in vastly different amounts (Brahmaprakash and Sahu 2012). The J. Gousia Centre of Research for Development, University of Kashmir, Srinagar, Jammu & Kashmir, India S. Ishfaq Department of Environmental Sciences, University of Kashmir, Srinagar, Jammu & Kashmir, India B. Uqab Sri Pratap College of Sciences, Srinagar, Jammu & Kashmir, India S. Mudasir (*) Abdul Ahad Azad Memorial Degree College Bemina, Srinagar, Jammu & Kashmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_10

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majority of plants take up these nutrients as inorganic ions, irrespective of the form in which it is applied to the soil. The long-established knowledge indicates that the soils manured regularly yield better. In most agroecosystems, crop production is dictated by nitrogen, as it is most often the limiting nutrient. Although nitrogen is present in large quantities in the atmosphere, plants cannot make use of nitrogen, due to its inert nature. Thus, nitrogen is made available in the form of fertilisers, produced by the chemical fixation of atmospheric nitrogen through the Haber-Bosch process. The intensive uses of such chemical fertilisers in agriculture, to improve crop yield, are increasing due to population explosion. These demands increase the costs with adverse effects on physico-­ chemical properties of the soils. Currently, there is growing concern regarding various environmental threats and hazards to the sustainable agriculture (Kumar et al. 2017). Therefore, the paradigm is shifting from using such chemical fertilisers towards the organic fertilisers. Recently, several organic fertilisers have been introduced acting as natural stimulators for growth and development of the plants (Khan et al. 2009). A specific group of such kind of fertilisers including products based on plant growth-promoting microorganisms (PGPM) named “biofertiliser” or “microbial inoculants” are prepared and used in place of hazardous chemical fertilisers.

2 Biofertilisers A biofertiliser is a product, containing specific microorganisms (living or latent), which apply direct or indirect desired beneficial effects on plant growth and crop yield through diverse mechanisms (Fuentes-Ramirez and Caballero-Mellado 2005). Biofertilisers are products which contain living cells of different and specific micro-­ organisms having the ability to convert nutritionally essential elements from unavailable to available form through various biological processes (Vessey 2003). Biofertilisers are typically, carrier-based microbial preparations, using beneficial microorganisms in a viable state, intended for seed or soil applications, to enhance plant growth by nutrient uptake and/or production of growth hormones. In India, popular as well as important microbial inoculants are those that supplement nitrogen, phosphorus and plant growth-promoting rhizobacteria (PGPR) (Brahmaprakash and Sahu 2012; Hakeem et al. 2021). Biofertilisers play a significant role in improving the soil fertility. Their application improves the soil structure and also minimises the intensive usage of harmful chemical fertilisers. Although biofertilisers do have certain limitations, such as unavailability of suitable strain of microorganisms, and lack of awareness among farmers, still dayby-­day, biofertilisers are replacing chemical fertilisers due to their advantages/ benefits of the former over the latter: • Cost-effective with high cost-benefit ratio • Eco-friendly properties, as they discourage the use of chemical fertilisers

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• • • • •

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Improves soil fertility by improving the soil structure Increases growth of plants and thus, crop yield Improves soil quality and health Helps plants to grow under stressed conditions Uses renewable resources of plant nutrient

Nowadays, biofertilisers are also seen as a promising approach in bio-controlling of various crop diseases against many soil-borne pathogens.

3 Microorganisms Used as Biofertilisers Various microorganisms and their association with specific crop plants are being exploited in the production of biofertilisers. Most biofertiliser components are nitrogen fixers (N-fixers), phosphorous solubilisers (P-solubilisers), phosphorus mobilisers (P-mobilisers), potash mobilisers (K-mobilisers) or plant growth-­ promoters with the combination of moulds or fungi. Most of the bacteria that are used in biofertilisers have close relationship with plant roots or rhizospheric soil. These biofertilisers aid in the efficient uptake of the nutrients from the growth medium. Nitrogen-fixers, present in the soil or the root nodules of the leguminous crops, fix the nitrogen and make it available to the plant. Phosphorous solubilisers help in solubilising the insoluble form of phosphates such as tri-calcium phosphate [Ca3 (PO4)2], iron phosphate (FePO4) and aluminium phosphate (AlPO4) into available form for the plant. Plant growth promoters produce hormones and various antimetabolites that promote plant growth, especially root growth. The biofertilisers or microbial inoculants also help in decomposing the organic matter when they are applied to the seeds and the soil, and thereby increase the crop yield. Different types of microbes solely or with associations have been used for the production of biofertilisers depending upon the desired effect one seeks to get from them. Some microbes find their application in agroecosystems very often and are popularly used in many parts of the world (Table 10.1). In addition to the already mentioned species, there are actinomycetes, which are also found to be helpful in the nitrogen fixation, production of plant growth-­ promoters, etc., and thereby aiding in efficient plant growth under stress conditions of dry and high pH soils.

4 Actinomycetes: Nature & Habitat Actinomycetes, is a non-taxonomic term for a group of common soil microbes, sometimes called “thread or ray bacteria”. The word “Actinomycetes” comes from two Greek words, “atkis” (meaning a ray) and “mykes” (meaning a fungus), having characteristics of both bacteria and fungi (Das et al. 2008), yet possessing ample

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Table 10.1  Some of the important and popular microbial biofertilisers used in agriculture S. No. Biofertiliser type Examples of microorganisms used Nitrogen fixers 1. Free living Anabaena spp., Klebsiella spp., Bejerinkia spp., Clostridium spp., Nostoc spp., Azotobacter spp. 2. Symbiotic Rhizobium spp., Frankia spp., Anabaena azollae, Acetobacter diazotrophicus 3. Associative Azospirillum lipoferum symbiotic Phosphate solubilisers 4. Bacteria Bacillus subtilis, Bacillus circulans, Bacillus megaterium var. phosphaticum, Psedomonas fluorescens, Pseudomonas striata 5. Fungi Aspergillus awamori, Pencillum spp., Trichoderma sp. Phosphate mobilisers 6 Arbuscular Acaulospora spp., Sclerocystis spp., mycorrhiza Glomus spp., Scuttellospora spp., Gigaspora spp. 7. Ectomycorrhiza Pisolithus spp., Amanita spp., Laccaria spp., Boletus spp. 8. Ericoid Perizella ericae mycorrhiza 9. Orchid Rhizoctonia solani mycorrhiza Potash mobilisers 10 Bacteria Bacillus spp., Pseudomonas spp. Zinc mobilisers 11 Bacteria

Rhizobium spp., Bacillus spp., Pseudomonas spp. Plant growth-promoting rhizobacteria (PGPR) 12. Bacteria Psedomonas fluorescens

References Bhattacharjee and Dey (2014), Itelima et al. (2018)

Bhattacharjee and Dey (2014), Itelima et al. (2018)

Bhattacharjee and Dey (2014), Kumar et al. (2017), and Itelima et al. (2018)

Bhattacharjee and Dey (2014) Bhattacharjee and Dey (2014), Kumar et al. (2017) Itelima et al. (2018)

distinctive characteristics to get delimited to kingdom bacteria. Like fungi, they are filamentous and have true aerial hyphae. Actinomycetes are prokaryotic organisms that are classified as bacteria, but are unique enough to be discussed as an individual group. Actinomycete numbers are generally one to two orders of magnitude smaller than the total bacterial population (Pepper and Gentry 2015). Actinomycetes are an important component of the total bacterial community under high pH conditions. A characteristic feature of this particular group of bacteria is that they are able to utilise a variety of substrates found in the soils, which includes even the less degradable insect and plant polymers such as cellulose, chitin and hemicellulose. Although,

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Table 10.2  Characteristics of actinomycetes (Pepper and Gentry 2015) Characteristics 1. Structure 2. Morphology 3. Size 4. Gram stain 5. Respiration 6. Habitat (a) Abundance in soils (b) Abundance in marine habitat

Prokaryotic Filamentous lengths of cocci 1–2 micron in diameter Gram positive Predominantly aerobic, can be anaerobic also Primarily soils; aquatic bodies (both fresh and marine) 106–108 per gram 5–40 CFU/ml

formerly they were recognised as soil microbes only, the importance of marine actinomycetes is also being recognised. Other characteristic features of actinomycetes are as follows (Table 10.2): Actinomycetes have ubiquitous distribution. They form persistent and stable microbial population in different ecosystems, especially soils. They have a important role in the cycling of organic matter in the terrestrial ecosystems (Veiga et al. 1983; Dar et al. 2022), due to their inherent capability of degrading and decomposing comparatively less degradable plant polymers, like, cellulose, chitin, etc. They thrive in almost all ecosystems. Actinomycetes are mostly found in soil, in the silt of different water bodies, in plant remains and in the air. They are the most abundant microbes that form thread-­ like filaments in the soils, and grow as hyphae (like fungi). Actinomycete population is abundant in upper surface layers of soils, with decrease in deeper layers (Takahashi and Omura 2003). They can adapt very well to the stress conditions around them, and have been reported to thrive in different temperatures (from 5 °C to as high as 60 °C), halophilic and other extreme environments with pH as high as value 10 (Groth et al. 1997). Some species are acidophilic, and have been found in acid forests and peat soils. Some species of actinomycetes have been reported to be present in psychrophilic conditions of Antarctica, like, Cryobacterium psychrophilum (Suzuki et al. 1994). Actinomycetes perform a lot of functions. Some of the special functions are as follows: 1. They act as source of various natural products and antibiotics, like, streptomycin, gentamicin, erythromycin, rifamycin, etc. 2. They produce geosmin, a special compound that gives water and soil a characteristic earthy odour. 3. They can carry biological nitrogen fixation with non-legume associated Frankia sp. 4. They can degrade complex organic molecules. 5. They can inhibit the growth of various plant pathogens.

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5 Actinomycetes as Potential Candidates for Nitrogen Fixation For recycling of the agricultural wastes microorganisms are the potential candidates (Singh and Nain 2014). The basic demand of the plant is for NPK, hence good and suitable sources are required for the supply of these basic nutrients to the plant. Bacteria play a vital role in agricultural fields, as they lead to both the carbon cycle and the decomposition. Bacteria, especially actinomycetes, are known for breaking many chemical compounds (Bhatti et al. 2017). Nutrient concentrations are influenced by bacterial groups and it is valid that land management has direct influence on bacterial communities’ composition and this can change the domination of decomposers from bacterial to fungal species. Nitrogen is fixed by actinomycetes with non-leguminous plant connections and nitrogen is easily accessible to the other plants in the proximity as well (Bhatti et al. 2017). The host plant’s nitrogen requirements are almost being fulfilled by the Frankia. Bacteria especially from the Frankia family of actinobacteria are very significant for the fixation of nitrogen and the natural nitrogen cycle relies entirely on these bacteria. Three processes are important in the nitrogen cycle and these include ammonification, nitrification and de-­nitrification. In all the three processes, bacteria plays a vital role. Specific organisms of the Frankia family of actinobacteria and their host plants which are reported to have a symbiotic relationship fix approximately 15% of the world’s nitrogen each year. So this family of bacteria and their symbiotic relations are the primary mechanisms of nitrogen fixation worldwide and that will undoubtedly grow more relevant when we adapt to climate change (Jose and Jha 2016). Thus actinomycetes may be the potential candidates to be used for nitrogen fixation.

6 Role of Actinomycetes in the Decomposition of Organic Matter Soil has a number of microorganisms and actinomycetes are the key community known to generate hydrolytic enzymes, which plays a significant role in organic matter recycling (Mohan and Vijayakumar 2007). Actinomycetes hold the ability to break down compounds such as cellulose and lignin, and it even has the capacity to break down chitin. Once such materials are broken down they provide nutrients to the plant. Composting is the process which is responsible for the decomposition of organic matter and high temperatures are needed for such process. Thermophiles and thermo-tolerant microbes especially actinomycetes possess the ability to be used for the decomposition of organic material as they have tendency to withstand high temperatures. The high temperature in composting is needed to kill viruses and pathogenic bacteria. Oxygen is the basic need of actinomycetes as they are aerobic in nature thus the compost where actinomycetes are being used should be well

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aerated (Bhatti et al. 2017). Fresh-grown substrates are the sites for the growth of actinomycetes but the rate of growth is slow as compared to that of other bacteria and fungi. Hence actinomycetes have the tendency to break organic matter and hence provide us the best option to be used in composting.

7 Actinomycetes as Plant Growth-Promoting Bacteria Being an essential part of the environment and also an important class of bacteria, actinomycetes inhabit the rhizosphere and interact with the plants (Gerretsen 1948). The association of these bacteria with the plant characterises such bacteria as plant growth-promoting rhizobacteria (PGPR) (Bhatti et al. 2017). With these properties they support the plants and their development actively. The process of synthesising plant growth regulators and increasing plant supply of nutrients and minerals allows actinobacteria a specific alternative (Katz and Baltz 2016). The actions of bacteria such as the solubilisation of phosphates, the development of siderophores and the fixation of nitrogen are closely linked to the efficiency and profitability of crops and actinobacteria (Gerretsen 1948). Another feature of actinobacteria is that they establish the biotic balance and do not damage the environment (Gomez-Escribano et al. 2016). Metabolite production that enhances plant development, and resistance to unfavourable environmental conditions for actinobacteria has also been studied (Fett et al. 1987). In the context of the above events, actinobacteria can be known as potential plant fertilisers.

8 Actinomycetes: An Excellent Candidate for Growing Healthy Crops Actinomycetes are an extensive and diverse community of microorganisms with a gram-positive origin and DNA with a high percentage of G + C content (51–73%) (Ghai et al. 2012) The actinomycetes play a significant role in the supply of nutrients and minerals as they impede both rhizoplane and rhizosphere, as well as the mechanisms of bioremediation (Amoroso et al. 2013), nitrogen fixation and decomposition of organic compounds (Genilloud et al. 2011). The bioactive compounds of these bacteria are very much useful in plant growth and production (Saif et  al. 2014). Other properties of the actinomycetes are as follows: 1. They have strong genomic and metabolic polyvalence properties. 2. They can be genetically modified quickly (Pogell et al. 1991). 3. They exhibit strong growth rates and comparatively faster colonisation performance. 4. They exhibit high level fo tolerance to heavy salts (Vassilev et al. 2012).

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Given these characteristics, actinomycetes were typically less explored species in agricultural technology, among diverse soil microflora (Qin et al. 2011).

9 Enzymes Produced by Actinomycetes Actinomycetes have the ability to produce enzymes like cellulases, amylases, chitinases, proteases, pectinases and xylanases. These enzymes have a wide applicability in industries like food and biomedicine; paper and pulp; detergents and textiles. Some of the strains are summed up in the following table (Table 10.3): In addition actinomycetes produce lipases (Streptomyces exfoliates), peroxidases, lacases (Nocardia spp.), dextranase, nitrile hydrase (Pseudonocardia thermophila) and cutinase (Thermobifida fusca).

10 Bioremediation by Actinomycetes Actinomycetes have been studied for their role in bioremediation of various pollutants such as metals, polymers and xenobiotics. Actinomycetes use these contaminants for their growth and metabolism. Actinomycetes like Streptomyces sp. has the ability to remediate heavy metals like cadmium, chromium, and iron from wastewater (Majdah and Ahmed 2016). Another actinobacteria, Thiobacillus sp., is used for the treatment of metal leachates (Macaskie et al. 2005). They have also the ability to detoxify xenobiotics such as hydrocarbons (Pseudomonas sp), dyes (Anoxybacillus pushchinoensis, Pseudomonas and staphylococcus), plastics (Brevibacillus borstelensis), lignins (Cellulomonas fimi) (Del-Pulgar and Saadeddin 2014); petroleum refinery effluents (Pseudomonas sp. and Azotobacter vinelandii). Table 10.3  Enzymes produced by actinomycetes and their applications (Mukhtar et al. 2017) Enzyme Amylase Cellulase Protease Chitinase Pectinase Xylanase

Actinomycete strain/s Streptomyces erumpens Thermobifida fusca Streptomyces ruber Thermobifida halotolerans Streptomyces pactum Streptomyces thermoviolaceus Streptomyces thermoviolaceus Nocardiopsis prasina Streptomyces lydicus Streptomyces spp. Actinomadura sp.

Application Detergent, paper and pulp, textile and baking Detergent, paper and pulp, textile Pharmaceutical, leather, detergent and food Textile and leather Textile and beverage Paper and pulp, animal feed

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11 Conclusion Actinomycetes are a group of microorganisms found in soil, water and even air. These have a wide variety of applications in the production of enzymes, nitrogen fixation, etc. These microorganisms are a good option for development in sustainable agriculture. Actinomycetes can enhance the soil fertility by nitrogen fixation, enzyme activities and plant growth promoting role. Besides increase in fertility these can be used to reclaim the polluted environments as they are capable of detoxifying xenobiotics and pollutants and also can degrade polymers to their simpler forms, thus making these a holistic sustainable approach in agricultural sciences.

References Amoroso MJ, Benimeli CS, Cuozzo SA (2013) Actinobacteria: application in bioremediation and production of industrial enzymes. CRC, Boca Raton, p 296 Bhattacharjee R, Dey U (2014) Biofertilizer, a way towards organic agriculture: a review. Afr J Microbiol Res 8(24):2332–2342 Bhatti AA, Haq S, Bhat RA (2017) Actinomycetes benefaction role in soil and plant health. Microb Pathog 111:458–467 Brahmaprakash GP, Sahu PK (2012) Biofertilizers for sustainability. J Indian Inst Sci 92(1):37–62 Dar GH, Mehmood MA, Bhat RA, Hakeem KR (2022) Microbiota and biofertilizers, Vol 2: Ecofriendly tools for reclamation of degraded soil environs. Springer, Singapore. https://doi. org/10.1007/978-­3-­030-­61010-­4 Das S, Lyla PS, Khan SA (2008) Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal. Chin J Oceanol Limnol 26(2):166–177 Del-Pulgar EMG, Saadeddin A (2014) The cellulolytic system of Thermobifida fusca. Crit Rev Microbiol 40(3):236–247 Fett WA, Osman SF, Dunn MF (1987) Auxin production by plant-pathogenic pseudomonads and xanthomonads. Appl Environ Microbiol 53:1839e1845 Fuentes-Ramirez LE, Caballero-Mellado J (2005) Bacterial biofertilizers. In: PGPR: biocontrol and biofertilization. Springer, Dordrecht, pp 143–172 Genilloud O, Gonza’lez I, Salazar O, Martı’n J, Tormo JR, Vicente F (2011) Current approaches to exploit actinomycetes as a source of novel natural products. J Ind Microbiol Biotechnol 38:375–389 Gerretsen FC (1948) The influence of microorganisms on the phosphate intake by the plant. Plant Soil 1:51e81 Ghai R, McMahon KD, Rodriguez-Valera F (2012) Breaking a paradigm: cosmopolitan and abundant freshwater actinobacteria are low GC. Environ Microbiol Rep 4:29–35 Gomez-Escribano JP, Alt S, Bibb MJ (2016) Next generation sequencing of actinobacteria for the discovery of novel natural products. Mar Drugs 14:78. https://doi.org/10.3390/md14040078 Groth I, Schumann P, Rainey FA, Martin K, Schuetze B, Augsten K (1997) Bogoriella caseilytica gen. nov., sp. nov., a new alkaliphilic actinomycete from a soda lake in Africa. Int J Syst Evol Microbiol 47(3):788–794 Hakeem KR, Dar GH, Mehmood MA, Bhat RA (2021) Microbiota and biofertilizers: a sustainable continuum for plant and soil health. Springer, Singapore. https://doi. org/10.1007/978-­3-­030-­48771-­3

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Hsu SC, Lockwood JL (1975) Powdered chitin agar as a selective medium for enumeration of actinomycetes in water and soil. Appl Microbiol 29:422–426 Itelima JU, Bang WJ, Onyimba IA, Oj E (2018) A review: biofertilizer; a key player in enhancing soil fertility and crop productivity. J Microbiol Biotechnol Rep 2:22–28 Jose PA, Jha B (2016) New dimensions of research on Actinomycetes: quest for next generation antibiotics. Front Microbiol 7:1295. https://doi.org/10.3389/fmicb.2016.01295 Katz L, Baltz RH (2016) Natural product discovery: past, present, and future. J Ind Microbiol Biotechnol 43:155e176 Khan W, Rayirath UP, Subramanian S, Jithesh MN, Rayorath P, Hodges DM, Critchley AT, Craigie JS, Norrie J, Prithiviraj B (2009) Seaweed extracts as biostimulants of plant growth and development. J Plant Growth Regul 28(4):386–399 Kumar R, Kumawat N, Sahu YK (2017) Role of biofertilizers in agriculture. Pop Kheti 5(4):63–66 Macaskie LE, Empson RM, Cheetham AK et al (2005) Uranium bioaccumulation by a Citrobacter sp. as a result of enzymatically mediated growth of polycrystalline. Science 257:782–784 Majdah M, Ahmed A (2016) Bioremediation of toxic heavy metals by waste water. Int J Curr Res 8(1):24870–24875 Mohan R, Vijayakumar R (2007) Isolation and characterization of marine antagonistic actinomycetes from west coast of India. Med Biol 15:13e19 Mukhtar S, Zaheer A, Aiysha D, Malik KA, Mehnaz S (2017) Actinomycetes: a source of industrially important enzymes. J Proteom Bioinform 10:316–319. https://doi.org/10.4172/ jpb.1000456 Pepper IL, Gentry TJ (2015) Earth environments. In: Environmental microbiology. Academic Press, Cambridge, pp 59–88 Pogell BM, Zhang HL, Feng YM (1991) Expression of veratryl alcohol oxidase activity and cloned fungal lignin peroxidase in Streptomyces lividans. In: International symposium on biology of actinomycetes. Madison, WI Qin S, Xing K, Jiang JH, Lu IH (2011) Biodiversity, bioactive natural products and biotechnological potential of plant-associated endophytic actinobacteria. Appl Microbiol Biotechnol 89:457–473 Saif S, Khan MS, Zaidi A, Ahmad E (2014) Role of phosphate-solubilizing Actinomycetes in plant growth promotion: current perspective. In: Phosphate solubilizing microorganisms. Springer, Cham, pp 137–156 Singh S, Nain L (2014) Microorganisms in the conversion of agricultural wastes to compost. Proc Indian Natl Sci Acad 80:473e481 Suzuki K, Nagai K, Shimizu Y, Suzuki Y (1994) Search for actinomycetes in screening for new bioactive compounds. Actinomycetologica 8(2):122–127 Takahashi Y, Omura S (2003) Isolation of new actinomycete strains for the screening of new bioactive compounds. J Gen Appl Microbiol 49(3):141–154 Vassilev N, Eichler-Lobermann B, Vassileva M (2012) Stress-tolerant P-solubilizing microorganisms. Appl Microbiol Biotechnol 95:851–859 Veiga M, Esparis A, Fabregas J (1983) Isolation of cellulolytic actinomycetes from marine sediments. Appl Environ Microbiol 46(1):286 Vessey JK (2003) Plant growth promoting rhizobacteria as biofertilizers. Plant Soil 255(2):571–586

Chapter 11

Innovations in Biotechnology: Boons for Agriculture and Soil Fertility Johra Khan

Abstract Increasing population, increasing industrialization, and increasing urbanization are putting pressure on agriculture to increase production to fulfill the increasing food requirements of the world. Using chemical fertilizers and pollutants makes soil infertile and adversely affects the microbes living in it, which ultimately reduces production. However, the use of biotechnology, which is a combination of biology and technology, can overcome these problems. The various innovations in biotechnology help us to maintain soil and its environmental health. In this chapter, some of these innovations are discussed. Keywords  Biotechnology · Biofertilizer · Biochar · Vermicompost · Nanotechnology

1 Introduction The term biotechnology can be defined as the use of technology and living organisms for the sustainable development of humans and the environment (Rittmann and McCarty 2012). Some other definitions of biotechnology associate it with genetic modification (GM). A genetically modified organism (GMO) is an organism that has undergone molecular manipulation or genetic alteration, which is an important aspect of biotechnology (Jacobsen et al. 2013). The use of traditional biotechnology started around 10,000 years ago (Hugenholtz 2013), at or around the same time as the development of agriculture (Wolf and Zilberman 2012), the fermentation of fruit and other foods (Di Berardino et al. 1997), the baking of bread, and the production of cheese and yogurt (Carroll and Hobson 2012). The use of biotechnology can be traced back to Roman farmers, who used to grow leguminous crops to increase soil J. Khan (*) Department of Medical Laboratory Sciences, College of Applied Medical Sciences, Majmaah University, 11952, Majmaah, Kingdom of Saudi Arabia e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_11

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Fig. 11.1  Biotechnology and its application in other aspects of our life

health and fertility (Dodd and Sharpley 2015; Hakeem et al. 2021). Biotechnology has interconnected many areas of life and has greatly affected various technologies based on the application of biological processes in manufacturing, agriculture, food processing, medicine, environmental protection, and resource conservation, as shown in Fig. 11.1 (Chisti and Moo-Young 1999). Soil health or fertility is the most essential factor for the growth of plants and to maintain environmental balance (Nair 2016). Soil forms the most complex biological system on the surface of the Earth; its structure and the communities in it are highly complex and consist of a variety of inhabitants, such as bacteria, fungi, archaea, arthropods, nematodes, protozoa, and many invertebrates (Bardgett 2005). Microorganisms in soil play important roles in matter decomposition, the nutrient cycle, and plant growth. Scientists and researchers around the world are working to develop and innovate different techniques for biotechnology that are used to improve the health and fertility of soil and to maintain the soil ecosystem. Some of these innovations and techniques will be discussed in this chapter.

2 Biofertilizers To promote plant growth, plants need healthy soil and nutrients available in sufficient and balanced amounts. Different natural and human activities destroy soil fertility, which can be restored by using different management strategies: through integrated

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soil fertility management (ISFM) (Chen 2006), encompassing a strategy for nutrient management based on natural resource conservation; through biological nitrogen fixation (BNF); and by increasing the efficiency of the inputs (Shantharam and Mattoo 1997). Most of the techniques for soil health management have been based on chemical fertilizers, which destroy not only the balance of soil components but also the microflora of soil (Giller and Cadisch 1995). Biofertilizers are becoming the best substitute for chemical fertilizers in the growth of crop plants and in maintaining and restoring soil health (Bøckman 1997; Dar et al. 2022). Biofertilizers are also known as microbial inoculants, which are generally preparations of live or latent cells of competent strains of nitrogen-fixing, phosphate-­ solubilizing, or cellulolytic microorganisms used for seeds; soil health, to increase microorganisms; and microbial processes, to speed up some microbial-dependent processes, increasing the availability of nutrients in soil that can not only stimulate plant growth but also maintain soil health (NIIR Board, 2004) (Dhar et al. 2015). There are different sources of biofertilizers, such as bacteria, algae, fungi, and earthworms (Bhardwaj et al. 2014).

2.1 Plant Growth–Promoting Rhizobacteria (PGPR) Biofertilizers help to keep the soil rich in different kinds of macro- and micronutrients through nitrogen fixation (Mahdi et  al. 2010)—by solubilizing or mineralizing phosphate and potassium through the production of plant growth–regulating substances (Suhag 2016), the production of antibiotics, and the biodegradation of organic matter in the soil (Suhag 2016). Plant growth–promoting rhizobacteria (PGPR) are a group of free-living bacteria that were first discovered by Kloepper (Hallmann et al. 1997); they colonize in the roots of plants and stay to seed, thus enhancing the growth of such plants (Suhag 2016). The different bacterial genera among PGPR include Azospirillium, Bacillus, Burkholderia, Klebsiella, Pseudomonas, and many more (Kaymak 2010). PGPR increase plant growth by inducing the production of phytohormones (Arruda et al. 2013), supplying biologically fixed nitrogen (Adesemoye et al. 2008) and increasing the phosphate solubilization and phosphorous uptake (Kennedy et  al. 2004). PGPR not only help in inducing plant growth but also help in the direct or indirect suppression of many infections, such as from bacterial, fungal, viral pathogens and from nematodes (Babalola 2010). Many studies have shown that inoculating PGPR with seeds significantly increases yields in various crops (Mehnaz 2011) and increases the germination of seeds. It also promotes nutrient uptake by roots, increases the total biomass of plants, increases seed weight, induces early flowering, etc. (Gupta et al. 2015). PGPR help to solubilize phosphorous (P), which is an important nutrient in soil that is normally available in large amounts in soil but in its insoluble form. Phosphate-solubilizing bacteria (PSB) are common in the rhizosphere and can be used to overcome this problem (Nadeem et  al. 2014). Some of the

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phosphate-­ solubilizing bacteria include Pantoea agglomerans, strain P5, and Pseudomonas putida, strain P13; they are capable of solubilizing insoluble phosphate from organic and inorganic sources (Chatterjee et al. 2017).

2.2 Algal Biofertilizers Nitrogen gas constitutes 78% of the total gases in the air in our environment, and it is one of the most important nutrients required by plants for their growth. Until the twentieth century, the Haber–Bosch process was used in industries for artificial nitrogen fixing, but this process used to consume more than 12% of the total energy supply on Earth. The use of chemical nitrogen fertilizers was not enough to fulfill the demands for nitrogen in growing crop plants, and these chemical fertilizers were destroying the soil environment, eroding the soil, inhibiting crop production, and increasing the demand for water. Algal biofertilizers such as blue-green algae (BGA) emerged as an alternative that can fix atmospheric nitrogen, supply it to paddy plants, and stabilize soil aggregates (Paudel et al. 2012). Some studies conducted on brown silt loam soil have shown that if BGA inoculum is used, a significant increase in soil subsurface properties, such as soil polysaccharide (Oades 1993), urease (Rillig and Mummey 2006), dehydrogenase, and phosphatase activities, was observed (Rao and Burns 1990). To keep soil fertility stable, soil aggregation is essential, and BGA inoculum has been shown to improve soil aggregation (Burns and Davies 1986). Several studies on algal proteoglycans have shown that they have adhesive properties that help them attach to solid surfaces (Singh 1961) and easily aggregate soil particles, which not only affects the temperature, aeration, and infiltration of soil but also increases the waterholding capacity of soil (Bailey et  al. 1973). Around the world, more than one billion hectares of soil have the problem of salinization and solidification, which affects agricultural productivity (Mulbry et al. 2007). Algalizing soil, especially in paddy crops, has emerged as the best biological remedy to reduce salinization and increase crop production in salinized soil (Whitton 2000). BGA were found to tolerate salinity and easily and fertilely grow in such soil (Roger and Reynaud 1982). Some of the algal species used predominantly on salt-affected soil include Plectonema, Nostoc, Calothrix, Scytonema, Hapalosiphon, Microchaete, and Westiellopsis (Abdel-Raouf et al. 2012). Other than BGA, brown algae have been reported to work as soil conditioners thanks to the activities of alginates, which speed up the decomposition of the organic substances produced by bacteria (Lin et al. 2013) (Table 11.1). Blue-green algae are considered the most successful survivors under abiotic stress conditions (Fogg 2012). Some researchers have modified the genetic structure of BGA to increase their nitrogen-fixing capacity and stress tolerance so that they can help increase the production of paddy crops and practice sustainable agriculture (Reddy et al. 1993; Vahtera et al. 2007). To confer the property of herbicide tolerance, the gene from aerobic diazotrophic Gloeocapsa was introduced into the

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Table 11.1  List of algal species used as biofertilizers in different parts of the world (Chatterjee et al. 2017) Major class of algal biofertilizer Brown macroalgae

Red macroalgae Blue-green algae

Anabaena azollae

Species name Laminaria digitata (Oarweed) Saccharina lastissima (Sugar kelp) Fucus vesiculosus (Bladder wrack) Ascophyllum nodosum (knotted wrack) Ecklonia maxima Stoednospermum marginatum

Phymalolithon calcarcum (Maeri) Lithothamnion coralloides (Maeri) Nostoc, Anabaena, Aulosira, Tolypothrix, Nodularia, Cylindrospermum, Scytonemia, Aphanothece, Calothrix, Anabaenopsis, Mastigocladus, Fischerella, Stigonema, Haplosiphon, Chlorogloeopsis Camptylonema, Gloeotrichia, Nostochopsis, Rivularia, Schytonematopsis, Westiella, Westiellopsis, Wollea, Plectonema, and Chlorogloea Anabaena azollae

Contribution 1. Are rich in nitrogen, potassium, and phosphorous 2. Contain carbohydrates (improve aeration and soil structure, especially in clay soil, and have good moisture-retention properties) 3. Are used as sources of naturally occurring plant growth regulators 4. Enhance plant growth; freezing, drought, and salt tolerances; photosynthesis activity; and resistance to fungi, bacteria, and viruses Contain trace elements 1. Fix 18–45 kg N/ha in submerged rice field 2. Produce growth-­ promoting substances

1. Fix 40–80 kg N/ha 2. Are used as green manure thanks to their large biomass

genome of Nostoc muscorum; similarly, the hetR gene (Vaishampayan 1984), which is responsible for heterocyst differentiation in Anabaena sp., strain PCC7120, enhanced the nitrogenase activity of Nostoc sp., thereby enhancing the production of crops and improving soil fertility (Singh and Singh 1981).

3 Vermicomposting Biotechnology The population, industrialization, and urbanization around the world are increasing day by day and are putting pressure on agriculture; as a result, the accumulation of solid organic waste (SOW) in the environment is increasing (Khalid et al. 2011).

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This SOW is full of nutrients that the soil is losing because of intense agriculture practices. The in situ use of earthworms to degrade SOW not only solves the problem of waste management but at the same time produces manure, which is free from chemical and biological pollutants and whose use improves soil fertility (Taylor et al. 2003). Vermicomposting is a process of using earthworms and microbes to degrade SOW (Gómez-Brandón and Domínguez 2014). In this process, earthworms change the biological activity of SOW through fragmentation and conditioning, whereas the microbes help in the biochemical degradation of the waste. Earthworms eat this SOW, blend it, reduce its C–N ratio, and increase the surface area so that microbes can better work on it (Aalok et  al. 2008). In the gut of earthworms, movement homogenizes the mixture and breaks down complex compounds into simple ones; microbes can then more easily break down these simple compounds. The outcome of this process is known as vermicompost (Dominguez et al. 1997), which is a special type of biofertilizer. The process of degradation by earthworms is environmentally friendly and economical; the vermicompost-producing process is rapid (Aalok et al. 2008) and odorless, and it reduces the quantity of SOW to half in a very short period of time (Suthar 2009). The investment of earthworms in this process is also very cheap. For example, if we start with one million earthworms, then in 2 months, it will double to two million, and this number will increase up to 64 million earthworms by the end of a year. The Eisenia fetida sp. of earthworm can consume SOW equal to its body weight, and for example, 64 million worms can in 1 day consume 64 tons of this waste and produce 30–32 tons of vermicompost, which is a 40–50% conversion rate (Adi and Noor 2009) (Fig. 11.2).

3.1 Procedure for Vermicomposting SOW by Using Earthworms SOWs such as agricultural waste, industrial waste, and household waste are collected and, as per requirements, are sorted, sundried, chopped, and mixed (Suthar 2009). The precompositing period is a period of storage that takes 15 to 30 days (Majlessi et  al. 2012). The precompositing period allows microbes to grow and start the decomposition process. During this period of precomposition, waste becomes soft and easy to digest (Aalok et  al. 2008). After the precomposition process, the earthworms are introduced into the composite bins. These earthworms ingest these wastes and finely grind them into small particles with the help of stones in their muscular gizzards. From here, the 2–3 μm particles are passed on to the intestine for enzymatic digestion (Deka et al. 2011). Once they enter the intestine, they are mixed with various enzymes, such as protease, lipase, amylase, cellulase, and chitinase, to break down complex compounds such as cellulose and proteinaceous substances into simple monomeric forms; they are next mixed with soil and minerals, which are known as vermicasts (Datar et al. 1997).

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Waste material (Domestic waste, agricultural waste and industrial waste)

Mixing with bulking substrate

Direct vermicomposting

Pre treatment (if needed) (sun drying, sorting, chopping and mixing)

Pre-composting (15-30 days) Release of earthworms

Earthworms activities like burrowing, feeding, digesting and casting (GAP)

Organic matter degradation takes place

Release of vermicast

Vermicast to vermicompost (CAP)

Earthworm harvesting

Storage and packaging of vermicompost

Organic agriculture

Fig. 11.2  Flow diagram of vermicomposting procedure (Sharma and Garg 2019)

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The vermicasts are reported to have higher numbers of nutrients in comparison to the surrounding soil (Parthasarathi 2006). Some studies on the microbial communities in urban waste, before and after their conversion to vermicasts, have shown microorganism numbers up to 1.97-fold higher than those in regular soil (Ghilarov 1963). Also, a similar study on potato peel waste and paper industry sludge waste reported a 5–40% increase in bacterial count before and after vermicast formation (Munnoli 1998). By using the E. eugeniae sp. of earthworms, the increase in nutrient values in kitchen waste increased up to 2.12% for nitrogen, increased by 0.7% for phosphorus, and increased by 0.48% for potassium, and the carbon and nitrogen ratio increased up to 32% (Monson et al. 2007). Nitrogen mineralization plays a vital role in restoring soil fertility. Earthworms (Eisenia andrei sp.) are found to increase nitrogen mineralization; some studies using pig manure have shown that during the process of vermicast formation, toward the last stage, when the activity of earthworms are highest, the nitrification rate was the highest, causing the fast conversion of ammonium to nitrate (Dominguez and Edwards 2004). The loss of water from soil owing to transpiration and evaporation makes soil dry, which drives up water demand in crop production (Nobel et  al. 1970). According to several studies, an increase in organic content by using vermicompost increases the water-holding capacity of soil up to 10% (Zablocki et  al. 1999). By adding vermicasts prepared using 200 g of E. fetida, E. eugeniae, and M. megascolex in 3 kg of soil increases the aggregation and water-holding capacity of soil (Nobel et al. 1970), which in response increases crop yields and helps minimize the evaporation of water from soil (Munnoli and Bhosle 2008).

4 Biochar Awareness around the world of the need for sustainable development in agriculture is increasing, which requires identifying new methods, techniques, and substances to enhance soil environments. The use of biochar is one such technique. Biochar is not a new product or substance; it is produced through the thermal degradation of organic matter in the absence of oxygen, in the form of a soil amendment (Lehmann and Joseph 2015a). Its presence in and its introduction into soil around the world are not new given that many natural events, such as forest and grassland fires, already add it to soil (Lehmann et al. 2011). Thanks to the addition of biochar, several biological, physical, and chemical changes have been observed in soil health (Verheijen et al. 2010). Researchers’ interest in biochar developed after others had observed its effects in Amazonian terra preta soils—conferring high fertility in comparison with other soil in areas with no carbon addition (Blackwell et al. 2009). Studies on biochar soil have shown that the addition of it to soil not only increases fertility but also helps in bioenergy production (Woolf et al. 2010), reduces nitrous oxide emissions from agricultural soil (Chan et  al. 2008), helps in the sorption of pesticides, and increases microbe activity in soil.

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4.1 Production of Biochar Biochar can be produced by using different feedstocks, either small-scale units with low-cost modified stoves or large-scale units (a high-cost production method) that use a lot of pyrolysis and a large amount of feedstock. The process starts with cutting feedstocks into small pieces: 3 cm or less. The next step includes burning these feedstocks at a temperature between 350 and 700 °C, in the presence of either little oxygen or no oxygen. A slow pyrolysis takes for 30 min to several hours, whereas the fast pyrolysis takes place within minutes at 500 °C. Fast pyrolysis leads to the generation of bio-oil, which is more valuable than slow biochar (Fig. 11.3).

4.2 Effect of Biochar on Soil Microflora and Microfauna The microbial community in soil keeps changing in response to climate changes (Lehmann et al. 2011). Adding biochar to soil causes changes in both the physical and chemical properties of soil, such as its pH, cation-exchange capacity, soil aggregation, density, pore size, and surface charge (Lehmann and Joseph 2015b). Some studies have shown that the effect of biochar influences not only the properties of soil but also the relationships between soil, microbes, and plants, which ultimately Animal wastes

Industrial waste

Wood chips

Manures

Leaves Different feedstocks

Fast Pyrolysis

High Temperature between 300 to 700°C

Slow Pyrolysis

Low Temperature below 300 °C

Biochar, Gases, Bio-oil (tar) Fig. 11.3  Process of biochar formation

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affects the production of agriculture (Verheijen et al. 2010). Using molecular biology, some researchers have found that biochar has a positive effect on the growth of mycorrhizal fungi (Woolf et al. 2010). Some mycorrhizae are better able to colonize around plant roots in the presence of biochar in soil, and biochar’s effect on plants increases the production of phosphorous (Chan et al. 2008). The processes of forming biochar and the temperature at which it burns affect microbial growth, which has been observed in terra preta soil. Terra preta soil contains woody charcoal, which turns into biochar at low temperatures; this biochar contains an interior layer containing bio-oil, which works like glucose in microbial growth (Thies and Rillig 2012). The mixing of biochar with soil helps to increase soil fertility and also promotes plant growth. The application of biochar in a quantity of 20 t/ha−1 to savanna soil was found to increase the yield of maize by up to 140%, in comparison to the control soil, and for up to 4 years without the further addition of any other fertilizer (Elmer et al. 2010). A similar result was found when 90 g/kg−1 of biochar was mixed with tropical low-fertility soil; it resulted in a great increase in the amount of nitrogen fixed by bean crops (Spokas et al. 2009). As many studies have recorded, adding biochar increases soil fertility and helps to restore the microbial flora of soil, which ultimately helps produce high crop yields (DeLuca et al. 2015). Many studies have found biochar to be effective in controlling pathogens in agricultural land, especially against airborne pathogens, such as powdery mildew and Botrytis cinerea, and soilborne pathogens, such as Rhizoctonia solani, Fusarium, and Phytophthora (Kammann et al. 2016). A bacteria wilt disease in tomatoes can be suppressed by using biochar and biochar composts. Studies have shown that the presence of calcium in soil increases the effect of biochar and helps to improve the physical, chemical, and biological properties of soil (Joseph et al. 2010).

5 Nanotechnology in Soil Development Nanotechnology is the application of humanmade nanoparticles in fields such as biomedical science, bioscience, agriculture, and environmental science (Thomé et al. 2015). The use of nanotechnology in agriculture can help to increase production by controlling nutrients (Fajardo et al. 2012), monitoring water quality (Joo and Cheng 2006), delivering pesticides, and monitoring soil health. In agriculture, the use of nanotechnology has become a key factor in sustainable development thanks to its various applications as nanotubes and biosensors and in the nanofiltration process and a controlled delivery system (Ibrahim et al. 2016).

5.1 Using Nanotechnology in Soil Pollution Control The soil environment is being polluted as the hazardous chemicals from industries— such as the chemical fertilizers from agriculture fields, the heavy metals from mining industries, the pollutants at landfill sites, and municipal wastes—mix

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(Ibrahim et al. 2016). Heavy metal pollutants are the most challenging soil pollutants because of their nondegradable nature (Mura et al. 2013). Heavy metal activity in soil is part of the sorption–desorption process, so they can be immobilized by using different processes, such as through adsorption to metal surfaces, the formation of stable compounds and organic ligands, the surface precipitation method, and the ion-exchange method (Nowack 2008). The use of nanoparticles for heavy metal pollutant removal has been of great interest for the researchers around the world. Several studies have shown that the use of nanotechnology can meet two essential requirements: (1) The nanoparticles must be available and be delivered to the contaminated zone; (2) when the external injection pressure has been removed, the delivered particles should remain in that confined zone only (Bhawana and Fulekar 2012). One of the negative aspects of nanoparticles is their tendency to aggregate at the micrometer and millimeter scales, because of which they lose their distinctive properties—namely their high surface area and their soil deliverability (Rabbani et al. 2016). To overcome this problem, these particles are attached with organic polymers such as carboxymethyl cellulose (CMC) and starch, which prevents nanoparticle agglomeration through steric and electrostatic stabilization and improves nanoparticles’ physical stability and movement in soil (Gutiérrez et  al. 2008). Attaching starch to magnetite nanoparticles enhances sorption and immobilization, and a reduction in toxicity was recorded. The presence of phosphoric acid, phosphate compounds, and natural phosphate immobilizes lead. After attaching a nanoparticle of lead to CMC, the CMC acts as a stabilizer, which increases the rate of phosphate dispersion and immobilizes lead particles in soil (Namdeo and Bajpai 2009). Some studies have suggested that when the carboxyl and hydroxyl groups are in cellulose, they inhibit the agglomeration of nanoparticles and produce stable lead phosphate compounds, known as zero-valent iron (ZVI) and pyromorphite, which are widely used for the in situ immobilization of heavy metal toxins (Konovalova et al. 2016). The process of delivering nanoparticles to soil through in situ methods depends on the permeability of the medium (Ansari and Husain 2012). The soil must be porous, and the area of contamination must be small; in such a medium, nanoparticles can be injected either by installing wells or by using the direct-push technique. There is no standard procedure for it, but the injection pressure should be high, which can cause fractures in the soil (Swarnalatha et al. 2013). The different variables used in field applications are the number of injection wells, the pressure, the concentration of nanoparticles, and the distance of the injection (Soleimani et al. 2012). Because the respective natures of various nanoparticles are not same, conducting an experimental trial on the soil and ground water collected from the site of application is always recommended before carrying out the final application, to assess the different parameters in the procedure and the standardization of the steps in the procedure.

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6 Conclusion Biotechnology and its applications in different aspects of life are the future of sustainable development, and sustainable development is necessary for the wellbeing of humans and the environment around us. Vermicomposting biotechnology, nanotechnology, biofertilizers, and biochar are some of the innovations in soil science that can be used in waste and land management, to improve soil fertility and to promote crop productivity. Finally, the production of valuable bioactive compounds for medicine has grown considerably in recent years.

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Chapter 12

Microbiomes in Climate Smart Agriculture and Sustainability Aadil Farooq War, Iqra Bashir, Rezwana Assad Zafar Ahmad Reshi, and Irfan Rashid

, Iflah Rafiq,

Abstract  The frequency of extreme weather events is projected to increase due to climate change, which will lead to devastating outcomes at vulnerable locations around the world and will lead to decline in overall agricultural productivity. In this context, strategies have been developed to impart abiotic stress tolerance to agricultural plants in order to make global agriculture resilient to climate change. Adaptive symbiotic technology is one such technology that can be exploited to develop climate-­resilient crops by incorporating beneficial plant microbiota into agricultural systems, particularly those involved in enhancing plant growth, nutrient efficiency, abiotic stress tolerance, and disease resistance. This integration requires collaborative effort among researchers, industries, and farmers to understand and effectively manage these interactions in the context of climate-resilient agricultural systems. The adaptive symbiotic technology is an emerging field that provides a well-­ designed solution to this problem by inoculating the microbial inoculant into crop plants that can sustainably improve production and abiotic resistance with the goal of achieving food security. Keywords  Abiotic stress tolerance · Adaptive symbiotic technology · Agricultural productivity · Climate change · Inoculant · Microbiota

1 Introduction Global food sustainability affected by climate change is one of the most serious challenges of the twenty-first century. As anticipated by the International Panel on Climate Change (IPCC), the climate variations over the next three decades could get more serious owing to a number of stresses as a consequence of climate change (Van Aalst 2006). These abiotic stresses will upset agricultural yields in many areas, particularly in developing countries. Under such circumstances feeding a growing A. F. War · I. Bashir · R. Assad (*) · I. Rafiq · Z. A. Reshi · I. Rashid Department of Botany, University of Kashmir, Srinagar, Jammu and Kashmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_12

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world population requires optimizing the reliability and environmental impacts on sustainable agriculture (Scheben et al. 2016). Changes in environmental parameters as a result of climate change, such as temperature, humidity, and salinity, have a huge impact on micro-and macro-organisms, particularly plants, and are a major global concern hampering life on earth (Compant et al. 2010; Sergaki et al. 2018). Because the plants are not locomotive, they have to adjust to an array of habitatimposed stresses such as insufficient nutrition, extreme temperature events, excessive salinity, and precipitation changes (Bartels and Sunkar 2005; Bray 1997; Leone et al. 2003; Redman et al. 2002; Rodriguez et al. 2004). Even a small change in temperature can eventually make many crop varieties unsuitable for a particular region. Although, until recently there have been no commercially developed solutions accessible to efficiently resolve such problems. However, plant-microbiome including mycorrhizae, rhizo-microbiome, and endophytes, have positive effects on agriculture, since agricultural sustainability has been shown to depend on the interaction between these elements. Nevertheless, the range of functions performed by such microbiota is largely underestimated. There are some microbes that can tolerate severe environmental conditions, such as high salinity, low pH and extreme temperatures, and serve as ideal model systems for understanding the fundamental mechanisms behind this extreme stress adaptation (Rodriguez et  al. 2004). It is assumed that plant’s capacity to respond to abiotic stress requires genetic mechanisms, not just confined to the plant genome but also to the genome of associated microbiota (Yin et al. 2004; Schwaegerle 2005; Zhou et al. 2007). Although there are many reports on how plants respond to stress, the underlying mechanisms that allow plants to thrive in high-stress habitats remain unresolved (Bartels and Sunkar 2005; Bray 1997; Leone et al. 2003; Rodriguez et al. 2004). Current views on plant adaptation to stress, assume that plants exist and operate as meta-organisms (host and associated microbiota), that complement each other in numerous functions including resistance in high-stress habitats (Nevo and Chen 2010; Coleman-Derr and Tringe 2014). These microbes and mechanisms could be subsequently engineered to alleviate the stress in crop plants induced by climate change, offering an emerging application which may have a huge impact on agriculture. Instead of developing harder crops through genetic modification and crop breeding, scientists employ adaptive symbiotic technology to manipulate a wide range of symbiotic interactions between plants and microbes in order to develop climate-resilient crop varieties. Conventionally, the integration of a single gene for a desirable trait such as heat tolerance requires long time intervals to integrate into the plant genome, or inclusion requires plasmid stability and survival, which is often difficult to achieve. Despite decades of scientific research, only one drought-­tolerant, genetically modified crop has been developed namely, droughtGard maize, which embodies a bacterial stress-response gene (Adee et  al. 2016). However, researchers with adaptive symbiotic technology use plenty of interactive genes pre-­integrated in a living organism such as symbiotic bacteria or fungi, with the potential to produce powerful results. Hence, adaptive symbiotic technology offers coordinated research initiative, spanning whole microbial diversity for beneficial plant microbes, especially those that confer abiotic stress tolerances and then accelerate their integration into plants

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of agricultural importance facing pressure from global population growth and a changing climate system. This paradigm shows how plants adapt to stress and opens new opportunities to mitigate impacts of climate change in natural and agricultural ecosystems. This review focuses on the importance of mutualistic symbioses with respect to abiotic stress tolerance under natural settings and how these associations could be exploited to achieve climate-resilient crop plants.

2 Plant Microbiome and Tolerance to Climate Change The endophytic bacteria and fungi have been studied widely for their abilities to impart tolerance to various plants facing abiotic and biotic stresses. Recent advances in next-generation sequencing technology have marked the beginning of a new era in gathering information on the genetic repertoires of microbial communities from various hosts. This strategy has offered insights into the relative abundance of different phylogenetic groups in a community and the metabolic and physiological potential of its members. Plant-associated microbes would play an important role in plant stress management and provide excellent templates for understanding the response to plant stress. Symbiotically acquired abiotic stress tolerance involves at least two mechanisms: (i) activation of the host stress response systems soon after stress exposure, enabling plants to avoid or alleviate the impact of stress (Redman et al. 1999), and (ii) biosynthesis of anti-stress biochemicals by endophytes. Diverse plant-associated bacterial and fungal symbionts have been isolated from different sources and their mechanism of action has been summarized in Table 12.1. Thus, plant-associated microbiome may potentially extend plant genomic capabilities, and consequently represent a massive, largely unexplored gene pool for better host function. For these reasons, integrating beneficial microbiomes into agricultural systems holds the potential to greatly improve the efficiency of crop production under anticipated climate adversity.

2.1 Extreme Temperature Stress Plants are adversely affected by high temperature and in response to this stress initiate complex biosynthetic responses involving antioxidant systems, heat shock proteins, phytohormone modulation, adjustments in osmotic potential, and membrane lipids (Iba 2002). Defense mechanism in plants against heat stress not only includes maintenance of membrane stability, scavenging of ROS, and accumulation of antioxidant metabolites, but also involves chaperone signaling, transcriptional modulation, and activation of mitogen-activated protein kinase and calcium-dependent protein kinase (Wahid et al. 2007; Wang and Li 2006). Most of the heat-resistance mechanisms are found to be mediated by plant-associated microbiomes. For example, thermotolerance bestowed by endophytic fungus

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Table 12.1  Plant microbiome mediated abiotic stress tolerance in plants Stress Host Drought Brassica campestris

Symbiotic microbe Strategy against involved stress Piriformospora indica

Increased peroxidases, catalases, and superoxide dismutase levels Reduces ethylene production

Transcriptional changes Upregulation of DREB2A, CBL1, ANAC072 and RD29A Cadhn, VA, sHSP and CaPR-10 cAPX, rbcL, rbcS,

Capsicum annum

Bacillus licheniformis

Cucumis sativus

Bacillus cereus Bacillus subtilis Serratia sp.

Medicago sativa

Sinorhizobium meliloti

Oryza sativa

Upregulation of aquaporin, dehydrin, and malondialdehyde genes Gluconacetobacter IAA and proline Upregulation of diazotrophicus production ERD15 DREBIA/CBF3 and DREBIB/ CBF Upregulation of Trichoderma Delayed hamatum drought-induced DREB2A, CBL1, changes in ANAC072 and stomatal conductance and RD29A, ERD1 net photosynthesis

Saccharum officinarum

Theobroma cacao

Trichoderma harzianum

Temperature Hot Dichanthelium Curvularia lanuginosum protuberata

Triticum aetivum Sorghum sp.

Pseudomonas putida

Increases antioxidative activity, root morphology change Up-regulation of FeSOD and CU/ ZnSOD

Induction of superoxide dismutase genes (sod) Induction of DHN/AQU

Osmoprotectants – trehalose, glycine betaine, and taurine Upregulation of Upregulation of SOD, APX, CAT sod, apx, cat, lipoxygenase genes

Reference Sun et al. (2010)

Lim and Kim (2013) Wang et al. (2012)

Naya et al. (2007)

Pandey et al. (2016)

Vargas et al. (2014)

Bae et al. (2009)

Rodriguez et al. (2004) Morsy et al. (2010) Ali et al. (2011)

(continued)

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12  Microbiomes in Climate Smart Agriculture and Sustainability Table 12.1 (continued) Stress Host Cold Arabidopsis thaliana

Solanum sp. Lycopersicum sp.

Heavy metal As Brassica juncea

Zn, Cd, As, Pb

Prosopis strombulifera

Salinity Oryza sativa

Symbiotic microbe involved Paecilomyces formosus

Pseudomonas vancouverensi Pseudomonas frederiksbergensis

Staphylococcus arlettae

Bacillus sp. Lysinibacillus sp.

Pseudomonas pseudoalcaligenes Bacillus pumilus

Oryza sativa

Achromobacter xylosoxidans

Arabidopsis thaliana

Pseudomonas pseudoalcaligenes

Strategy against stress Accumulation of pigments and induced cold response pathway Codes for proteins that protect cells against cold/ chilling stress. Reduced membrane damage and ROS level. Tomato lipoxygenase

Transcriptional changes Reference Downregulation Su et al. (2015) of RbcLandCOR78 Upregulation of Subramanian CBFs, COR15a, et al. (2015) and COR78 LeCBF1, LeCBF3 and TomLOX gene expression

Arsenic reductase arsC gene activity. Increased soil dehydrogenase, phosphatase, and available phosphorus – Antioxidant enzyme activities, photosynthetic pigments, and low lipid Accumulation of glycine betaine-­ like compounds, decline in proline content Reduced lipid peroxidation and superoxide dismutase activity Regulation of Na+ and K+ homeostasis

Srivastava et al. (2013)

Sgroy et al. (2009)

gbsA and gbsB

Jha et al. (2011)

sod1 downregulated

Jha and Subramanian (2014)

HKT1, KAT1, KAT2 coda (choline dehydrogenase) upregulated

Abdelaziz et al. (2017)

(continued)

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214 Table 12.1 (continued) Stress Host Osmotic stress Capsicum annum

Arabidopsis thaliana Nicotiana tobaccum

Symbiotic microbe Strategy against involved stress Piriformospora indica

Pseudomonas sp.

Transcriptional changes

Gene encodes the CaACCO CaLTPI enzyme ACC oxidase Encodes a lipid transfer protein SEX1 Genes for the starch-degrading enzyme, glucan-water dikinase

Reference Sziderics et al. (2007)

Sarma et al. (2011)

Curvularia protuberata to Dichanthelium lanuginosum in geothermal soils is the product of symbiotic interaction between the two organisms. Studies indicated that this mutualistic association was responsible for the survival of both species in the Yellowstone National Park’s geothermal soils, since they were unable to tolerate the high temperature in isolation (Rodriguez et al. 2004). In addition, Ali et al. (2009) revealed the role of Pseudomonas AKM-P6 strain in boosting sorghum heat stress tolerance due to the activation of unique proteins that improved efficacy of metabolic and physiological processes. Low-temperature distress adversely impacts plant developmental processes thereby limiting the productivity of crops. However, the solution for this issue has been found by scientists in the inoculation of beneficial microbes liable for conferring low-temperature stress resistance. Studies have revealed that inoculation of Burkholderia phytofirmans PsJN bestows grapevine and switchgrass with more effective tolerance against low-freezing temperatures. The inoculation of Burkholderia phytofirmans resulted in better root growth, higher physiological activity, and faster accumulation of stress-related metabolites (proline, phenolics, etc.) at lower temperature, signifying a constructive priming effect on plants (Theocharis et al. 2012; Barka et al. 2006; Kim et al. 2012; Hakeem et al. 2021). Zhang et al. (1996), found that low temperature reduces soybean root nodulation and nitrogen fixation but inoculating soybean with Serratiaproteamaculans and Bradyrhizobium japonicum resulted in higher nitrogen fixation at low temperatures and ultimately faster growth rate. In addition, the wheat seedlings when inoculated with Pseudomonas sp. resulted in higher levels of amino acids, chlorophyll and phenolics, proline, iron, and lower levels of electrolyte leakage and the Na+/K+ ratio, leading to increased cold tolerance (Mishra et al. 2009). It is evident that studies have explored a broad host range of several fungal and bacterial species including grapevines, maize, rice, soybean, sorghum, wheat, and switchgrass with encouraging results under extreme temperature stresses (Selvakumar et al. 2010). Thus, they hold special potential to develop climate-resilient crop varieties to ensure food security under changing climatic conditions.

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2.2 Drought Stress Drought is a multidimensional stress that represents a serious threat to agriculture worldwide, since it influences the water capacity of plants, which is able to change the physiological and morphological characteristics of plants (Rahdari et al. 2012). In addition, drought stress impacts the supply and distribution of plant nutrients, since nutrients are transferred through bulk flow along with water. Drought stress also magnifies ethylene biosynthesis, which prevents plant growth and development through many mechanisms (Ali et al. 2014). It is expected that the water level rise as a consequence of climate change will submerge the part of current agricultural land and there is the need to bring marginal, arid, and semi-arid lands under cultivation to meet the growing food demands (Elsharkawy et al. 2009; Dar et al. 2022). However, the crops that will be raised on these lands will be prone to stresses such as heat and drought. In order to overcome the effects of drought stress, the plants must be resilient to drought or the crop as a whole must be resilient to drought. The plant-associated microbiome has been found to hold the potential to confer drought resistance to plants through the phytohormone, antioxidant, and osmotic adjustments in plants (Boyer et al. 2014). The mechanisms behind microbiome-conferred drought resistance may also involve altered stomatal activity, reduced leaf conductance, and increased solute accumulation in tissues, (Malinowski and Belesky 2000). The endophytic fungus Piriformospora indica is the prime candidate that has been used in climate-resilient sustainable agriculture. This fungus was first isolated from the endemic plants of Thar desert, but later they were found to colonize many plants bestowing them with the drought tolerance (Verma et  al. 1998; Shahollari et al. 2007). Furthermore, studies have reported the role of mutualistic endophytic fungus Colletotrichum magna in providing drought resistance to many crop plants including watermelons, pepper, and tomato (Redman et al. 2002). Sherameti et al. (2008), when working on Arabidopsis, ascertained that inoculating the plant with Piriformospora indica directs the plant shoots to promote the expression of a series of drought-related genes such as MDAR2 and DHAR, which play an important role in their interaction to impart drought resistance. Moreover, it has been found that P. indica has advantages of broad host range and fast propagation, holding strong potential in climate-tolerant agriculture by curbing drought stress. There are lots of examples of bacterial species that help plants to alleviate drought stress. For example, Achromobacter piechaudii confers drought resistance to tomato and pepper by inhibiting ethylene synthesis through the action of 1-­amin ocyclopropane-­1-carboxylate (ACC) deaminase (Glick et al. 2007; Yang et al. 2009; Duan et al. 2009). Although the exact mechanism remains largely elusive, it can be hypothesized that inhibition of ethylene synthesis can reduce stress and contribute to normal development. Also, wheat plants when inoculated with Burkholderia phytofirmans showed improved water use efficiency, increased photosynthetic rate, high chlorophyll pigmentation, and grain yield, than non-inoculated plants when grown under water deficit conditions (Naveed et  al. 2014a). Similar results were shown by maize plants when inoculated with B. phytofirmans and Enterobacter sp.

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(Naveed et al. 2014b). Besides these achievements, there are many other crop plants such as pea, sunflower, sorghum, pepper, tomato, rice, lettuce, and common bean, which have been found to perform better under drought conditions when inoculated with different plant growth-promoting bacteria (Creus et al. 2004; Alami et al. 2000; Dodd et  al. 2005; Mayak et  al. 2004; Cho et  al. 2006; Figueiredo et  al. 2008; Marquez et al. 2007; Arshad et al. 2008; Marasco et al. 2012; Perez-Montano et al. 2014). Such discoveries will result in concrete functional results that will help alleviate the impact of climate change, especially in relation to drought and heat stress, which will lead to increased agricultural production and food security.

2.3 Salt Stress Salt stress is a tough hurdle for improving agricultural plant growth and yield and it is recognized as the second most prevalent soil issue following drought (Golldack et  al. 2014; Wani and Sah 2014). There are two types of salinity, inland salinity attributed to the irrigation practices and coastal salinity attributed to the high oceanic tides. Irrespective of the type, salinity causes osmotic as well as ionic stress which together disturbs the vital process of the plant development at morphological, biochemical, physiological, and molecular levels. Morphologically, it results in a major reduction of plant growth by inducing leaf rolling, leaf burning, and chlorosis. In addition, salinity also causes a build-up of reactive oxygen species (ROS), which tamper the activities of various enzymes and adversely impact the integrity of the membranes, thereby disturbing the vital plant processes such as respiration, photosynthesis, and nutrient acquisition (Kaur et al. 2016; Gupta and Huang 2014). Many approaches, such as soil reclamation and soil management, have been implicated to address the salinity stress; however, all these practices failed to address the salinity issue because they were costly, impractical, and unsustainable. Conversely, the use of symbiotic plant growth-promoting fungi and bacteria as inoculants for crops that grow on salt-affected soils is gaining ground (Shabala et al. 2013; Tiwari et al. 2011; Qin et al. 2014; Paul and Lade 2014; Ruiz et al. 2016). There is considerable amount of research coverage over the role of microbial communities in increasing productivity and improving plant health under salt stress conditions. For instance, Upadhyay et al. (2009) extracted 130 bacterial species while working on wheat grown in saline soil, out of which 24 extracts were found to bestow salinity tolerance to the plant. This tolerance was attributed to the activation of specific genes such as nifH and the production of various proteins and hormones such as gibberellic acid, siderophores, and indole-3-acetic acid (IAA). Halotolerant bacteria thrive under salinity stress and express traits to help plants to survive high salinity. Furthermore, studies have also reported the role of AM fungi in increasing the host tolerance to salt stress. Plants when inoculated with the AMF Glomus resulted in improved growth under saline conditions, probably because of reducing Na+ and increasing phosphate concentrations in shoots (Giri and Mukerji 2004). There are many other studies reporting the role of symbiotic microbes in improving salt stress

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tolerance in agriculturally important crops such as maize, clover, mungbean, cucumber, and tomato (Chinnusamy et al. 2005). The underlying mechanisms behind all these studies were found to be phytohormone production, phosphorus acquisition, improved osmoregulation by reducing salt concentration and proline accumulation (Jindal et al. 1993; Feng et al. 2002; Grover et al. 2010; Ben Khaled et al. 2003; Velazquez-Hernandez et  al. 2011). The above reports indicate that inoculating plants with halotolerant microbial strains may have large positive outcomes for plant growth under salt stress.

2.4 Heavy Metal Stress Global warming and climate change will render traces of chemicals, heavy metals, and domestic chemical compounds more harmful for livestock, agriculture, and eventually for humans. The adverse effects of climate change may alter the property of these chemicals, thereby making them more hazardous for the environment (Moe et al. 2013). The biological and physiochemical strategies to eliminate the chemical contaminants from the soil have failed to deliver, because they are complex, expensive, unsafe for the environment, and publicly unacceptable (Boopathy 2000; Vidali 2001; Doble and Kumar 2005). However, plant microbiome offers promising alternative for this application whereby microbes assist plants to increase metal absorption and decrease their mobility and bioavailability (Ma et  al. 2011; Yang et  al. 2012; Aafi et al. 2012). It is well recognized that heavy metal ions impair enzyme function, damage membrane integrity, impair photosynthesis, induce oxidative stress, and reduce root growth (Nagajyoti et al. 2010; Yadav 2010). These strains in turn increase the plant’s susceptibility to climate change by reducing plant fitness and productivity thereby posing a threat to global food security (Hu et al. 2016). The plant-associated microbiome produces phytohormones (Auxin, Gibberellin, Cytokinin, etc.), siderophores, ACC deaminase, and various enzymes, which enhances plant growth and profitability in polluted heavy metal soils (Waqas et al. 2015; Kukla et al. 2014; Wang et al. 2011; Santoyo et al. 2016). Moreover, such knowledge is a prerequisite for developing management strategies to remove heavy metals from the soil and food chain in order to minimize their effects on agriculture and ultimately humans.

2.5 Water Lodging Flooding has been recognized as a threat to plants in both natural and artificial habitats, as inadequate exchange of gases occurs in water-lodged habitats, affecting plant energy and carbohydrate economies (Voesenek et al. 2006; Bailey-Serres and Voesenek 2008). Most of the crop plants experience extreme growth loss and sometimes death, even if only root system is surrounded by excess water (Jackson 1984).

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Consequently, frequent floods resulting from human-induced climate change can lead to partial or complete plant submergence, with drastic impact on plant productivity (Arnell and Liu 2001; Voesenek et al. 2006). Studies have shown that plant microbiome holds strong potential in addressing the problem of water lodging. Wang et al. (2017), found that Epichloe, a fungal endophyte from Lolium sp. when inoculated into Hordeum brevisubulatum imparts water-logging resistance to the plant by producing osmoprotectant proline and reducing the malondialdehyde concentration and electrolyte leakage. In addition, inoculated plants also showed increased chlorophyll content, increased tillers, and high biomass. Furthermore, inoculating plants with beneficial microbes could decrease leaf width and increase leaf thickness to cope up the water logging stress (Arachevaleta et al. 1989). Taking advantage of such plant-microbe interactions in adaptive symbiotic technology underpins both relief from submergence to plants and increasing crop production in flood-prone environments (Singh et al. 2009).

2.6 Greenhouse Gases The US National Climate Assessment has estimated that as a consequence of Greenhouse gasses (GHGs), weather patterns will continue to become much more erratic and irrational due to climate change, thereby exerting pressure on agriculture and food security. Soil organisms are found to play a pivotal role in climate feedback, since they are mainly responsible for soil organic carbon cycling including greenhouse gas emissions and utilization such as CO2, CH4, and N2O.  Microbial communities may therefore be intimately engaged in reducing greenhouse gas emissions and ultimately climate change. Some microbial communities, such as methanotrophs, have the capacity to use methane as a carbon source to help reduce greenhouse gases in the atmosphere (Singh et al. 2009). There is another group of bacteria called methylotrophs that consume multi-carbon compounds or reduced carbon substrates other than methane as their carbon source, which makes this functional group a frequent participant in the global carbon cycle (Kolb and Stacheter 2013; Iguchi et al. 2015). There is considerable amount of research supporting the role of methanotrophs and methylotrophs in mitigating the atmospheric greenhouse gases. For instance, studies have revealed that methanotrophs act as sink and consume about 5% of atmospheric methane (Hanson and Hanson 1996). In addition, this functional group has been reported to oxidize up to 90% of the methane produced in the soil before it leaks into the atmosphere (Oremland and Culbertson 1992). In view of the climate change, integration of these soil microorganisms into crop plants is therefore a prerequisite for food and the world population to go hand in hand.

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3 Integration of Target Traits into the Crop Plants Through Adaptive Symbiotic Technology The first objective when contemplating inoculation of beneficial microorganisms in crops is to identify the best strain of microbe or a microbial consortium for the intended effect on the target crop. There is an extensive database of microbial cultures accumulated over time from rigorous studies on plants with extreme temperature tolerance http://mbgd.genome.ad.jp/; https://www.ncbi.nlm.nih.gov/genome/ microbes. The next step is to develop a suitable inoculant formulation for the target crop and an effective use methodology, taking into consideration the constraints of the farmers. The formulation chosen and the application method determine the inoculant‘s potential success. Most of the research has been done on explaining microbial inoculation in plants and their possible outcomes, with only a few works focusing on delivery methods. The delivery methods have been divided into development of formulation and inoculating the formulation into plants. In majority of the developing countries, inoculation technology has little influence on crop productivity because formulations are not used or are of poor quality (Bashan 1998). As a result, microbial suspension inoculated in soil or plants has been found to decline rapidly shortly after inoculation and fails to build up a sufficiently large microbial population in the rhizosphere or internal plant tissue due to the inherent heterogeneity of the soil/ plant. These inoculated microbes being unprotected must compete with the often better-adapted native microflora, in order to occupy the niche. Therefore, the target microbial strain must be combined with a carrier in order to maintain their stability in a specified setting which can be achieved by a mechanism called formulation.

3.1 Development and Characteristics of Formulation Formulation applies to the lab or industrial procedure whereby the carrier (abiotic agent used mostly for microbial stabilization) is combined with the microbial inoculum to generate the product called inoculant. Formulation is the art of transforming a carefully cultivated promising microorganism by professional experts in planned and monitored experiments into a commercial product used by traditional growers under unregulated conditions in the field. This method is critical for inoculant commercialization which can decide the success or failure of a biological agent that performs exceptionally well in a research laboratory. The major key characteristics which are must to consider for excellent formulation are: 1. Ideal carrier: The carrier is defined as the abiotic substrate used to mix with biological material such as bacteria or fungi in order to increase its stability in a particular environment. Different types of carriers have been used to enhance inoculants‘survival and biological efficacy by protecting microbes from abiotic

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3.

4.

5.

6.

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and biotic stresses (van Veen et al. 1997). The suitable carrier must be sterile, inexpensive, mixable, and packageable, including high ability to retain water and compliant with most microbial strains. There are range of carriers used in formulations such as peat, sawdust, charcoal, sand, alginate beads, and many more. Although every carrier has its own benefits and flaws, the final carrier selection must be focused on microbial proliferation and survival during storage and irregular agricultural practices. For instance, peat is a widely used carrier as it has the potential to sustain high microbial load, but it has the demerit of universal unavailability. Alternatively, alginate is universally used because of its large-scale industrial production and unique properties such as eco-friendly, dry, synthetic, easy to use, easily biodegradable by soil microbes, and harmless in nature. It supports large and uniform microbial populations and ensures the slow release of bacteria over a long period of time (Bashan 1998). In addition, alginate beads have their own advantage as a carrier, as they hold an efficient microbial population size in a comparatively limited volume over longer periods of time. Therefore, carrier reliability is an absolute requirement for formulation and must be selected with care after considering all the features. Ideal inoculants: Inoculant represents the final prepared product of formulation comprising of carrier and microbial agent or microbial consortium. The role played by the inoculant formulation is to offer appropriate micro-environmental conditions in which the introduced microbial population doesn’t decline rapidly as a consequence of habitat heterogeneity. Ideal inoculants ensure their survival and perseverance in the introduced environment and become available to crops at the time of need (Bashan 1998). This is the main problem with most of the formulations and needs to be addressed at the earliest to increase the efficacy of inoculants. Manufacturing qualities: Inoculants in addition to bearing stability in unknown environments must be bearing properties required in fermentation industry. The manufactured inoculants must have easily adjustable pH, allowing the addition of nutrients for maintaining the viability of microbial agent (Catroux et al. 2001). Farm-handling qualities: Food security is a worldwide problem, but for developing countries it may lead to drastic consequences. Most developing countries especially traditional rural communities are unable to afford specialized machinery that can deliver high-quality inoculant result (Date 2001). Therefore, ideal inoculant must withstand the irregular agricultural practices, allow ease of handling, and should provide controlled but rapid release of microbes into the soil. Eco-friendly: The inoculants used should be non-toxic, biodegradable, leave no carbon footprint, and be non-polluting; in short formulations must be developed in compliance with prevailing environmental considerations about applications of compounds that modify soil characteristics. Long storage quality: Long shelf life is an important attribute of the inoculant. Scientists have postulated that inoculant requires 2 years at room temperature to integrate successfully into the agricultural system (Catroux et al. 2001; Deaker et al. 2004).

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Obviously, it is very difficult to find a single inoculant with all these characters at top-end quality; however, a better inoculant should have as many of these desirable characteristics.

4 Inoculating Microbial Formulation into Plant to Form Meta-organism Once the ideal inoculant has been successfully established it can be inoculated directly on the surface of the seed or into the soil. The application of seed inoculations massively outshines the soil inoculations, and as such it is the most widely used technique for inoculation. Some of the common seed inoculation applications are that it is easy to use and requires lower amount of inoculant in comparison to soil inoculation. The seed inoculation technology starts with the dusting of seeds prior to sowing with inoculant (e.g., peat or alginate inoculant), supplemented with water and bonding agent if needed. However, if the seed size is small dusting is followed by application of fine ground limestone and allowed to air dry. The advantage of using limestone is that it balances the acidic nature of soil, when the seed is sown. The inoculant is either hand mixed with seeds or by spinning drums, broad flour or cement mixers, and automatic tumbling machinery (Schulz and Thelen 2008). In case of the liquid inoculants, seeds are inoculated by spraying inoculant directly onto the seeds, with or without dissolved adhesive and allowed to dry. Furthermore, the motive behind mixing is that every seed must be coated with a threshold number of microbes, in this context bonding agents/adhesives are used. Some of the commercially used adhesives are carboxy methyl cellulose, gum Arabic, vegetable oils, and sucrose solutions (Wani et al. 2007; Viji et al. 2003; Cong et al. 2009; Bashan et  al. 2002). In addition to enhance the seed coating, adhesive also prevents the inoculant from dislodging, while using sowing equipment for seed sowing. There is no consensus about the ideal adhesives, the manufacturers empirically determine the adhesive ideally fit for its formulation (Albareda et al. 2008, 2009). Once inoculated, seeds dry in open air or pressurized air, and they are ready to get sown in the agricultural field. The farmers have already witnessed the effects of adaptive symbiotic technology on agricultural production. However, climate change may reduce yields further in vulnerable areas. These efforts have centered almost exclusively on individual microbial inoculations and have underestimated the importance of microbial communities/consortium inoculation and its potential to interact with the environment under natural settings. Till date studies have focused on inoculation of individual microbes into crops to promote nutrient acquisition and disease protection. However, there is an urgent need to focus on inoculation of individual microbes or microbial consortia into crops that bestow abiotic stress tolerance and mitigate the harmful effects of climate change.

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5 Conclusion Plants in natural ecosystems are in mutualistic relationship with diverse microbes that inhabits every tissue of the plant and this microbiota can have reflective effects on plant stress tolerance. This technology extends the benefits of these mutualistic microbes to unrelated crop plants in order to attain the same benefits that these microbes provide to their original hosts. This technology therefore exploits the symbiotic relationship between plants and beneficial microbiota and directs them to mitigate the impacts of climate change on agricultural crops. Furthermore, it is of great importance to execute research efforts toward the elucidation of molecular mechanisms underlying symbiotic response to abiotic stress. In fact, such research would elaborate the understanding of the implications of plant microbial symbiosis under adverse conditions and would therefore offer new research opportunities aimed at maximizing the benefits of plant microbial symbiosis under circumstances of changing climate.

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Chapter 13

Genetic Engineering Aiming to Improve the Use of Phosphorus in Agriculture Fernanda Maria Policarpo Tonelli, Moline Severino Lemos, and Flávia Cristina Policarpo Tonelli

Abstract  Phosphorus (P) is a crucial element for plants to correctly develop and provide the level of productivity that humans need to feed the growing worldwide population. However, not all forms of P in soil can be taken up and used by vegetal species, so various attempts have been made to provide it artificially, but not all of them have positively affected the sustainability of agriculture (e.g., providing P through fertilizers may not solve the problem and may also cause the eutrophication of water bodies). Among the promising protocols being developed for a more-­ ecofriendly and more-optimized use of P are strategies involving the genetic engineering of plants. This chapter aims to review some important strategies of genetically modifying vegetal species to achieve better P-use efficiency while safeguarding the ecosystem in which these species are inserted. Keywords  Phosphorus uptake · Phosphorus use · Genetically engineered plant · Biotechnology · Optimized use of phosphorus

1 Introduction Phosphorus (P) is a crucial element to life and is required in many processes of living organisms, such as cell replication, energy storage, and protein synthesis. This essential macronutrient is one of the most important for plant development and growth. The agricultural field needs to verify whether the amount of bioaccessible or dissolved P is sufficient to ensure that the growing population will continue to reap the necessary amounts of food from crop yields (Doydora et al. 2020). Food and feed production depends on soil phosphorus availability, and its loss in agricultural systems can severely impact the future of these productions. High F. M. P. Tonelli (*) · F. C. P. Tonelli Federal University of São João del Rei, CCO, Divinópolis, Brazil M. S. Lemos Federal University of Minas Gerais, ICB, Belo Horizonte, Brazil © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_13

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P-depletion rates affect Africa, South America, and Eastern Europe for different reasons, and a global phosphorus shortage is expected to be aggravated by soil erosion (Alewell et al. 2020). Artificially adding P through fertilizers has had different success rates in croplands and in natural terrestrial ecosystems. In croplands, it has offered a much smaller effect. Also, plant responses to the presence of P in soil depend on different factors, such as fertilization regimes (which take into consideration a group of variables such as target yield, fertilizer history in paddocks, soil test results, soil type, and farm financial constraints), the climate, and ecosystem properties (Hou et al. 2020; Hakeem et al. 2021; Dar et al. 2022). Thus, because global P stocks are depleting and because adding this element does not always bring about the desired effect, there is an urgent need to improve the use efficiency of this element in agricultural systems (Bovill et al. 2013).

1.1 Phosphorus’ Bioaccessibility and Use Efficiency in Plants If repeated applications of fertilizers are performed in an attempt to increase phosphorus bioavailability to plants, the expected result will usually not be achieved. It will probably result in an increase in the soil’s P content, but a large fraction will not be available for plant use, and fertilizers also pose risks to the ecosystem by promoting the eutrophication of nearby water bodies (Doydora et al. 2020) (Fig. 13.1). In fact, this is also the final destination of P leaching from urban areas (Yang et al. 2020a). Unfortunately, most of the P applied to soil is immobilized and becomes unavailable to plants because of adsorption, precipitation, or conversion to organic forms (Schachtman et al. 1998). As a result, plants often encounter a shortage of inorganic P in the soils of agricultural and natural systems, even when the total P in soils is abundant (Raghothama 2000). The long-term accumulation of P in soil is undesirable from an agricultural, economical, and environmental point of view because this is an inefficient use of a finite resource. Furthermore, excessive P in the soil controversially ends up resulting in its loss from the soil through leaching and erosion in its surroundings (Doydora et al. 2020).

Fig. 13.1  Attempts to use fertilizer to artificially add P to plants such that they take P up from soil is not an eco-friendly strategy, because the added P after reaching water bodies, causes eutrophication

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In soil, inorganic P is present mainly in its dissolved (and sometimes protonated) forms and as soluble orthophosphate. However, the amount of these forms that is bioaccessible to plants is too low to fulfill their needs (Hinsinger 2001). In acidic soil conditions, for example, phosphorus adsorption to Fe and Al can influence the elements’ availability. Fe:Al-hydroxide mixtures, when containing high-Al ratios, exhibit low phosphate desorption rates. When high-Fe ratios are present in the mixtures, negligible desorption rates are exhibited (Gypser et al. 2018). Organic P (commonly orthophosphate monoesters and diesters) can become accessible to plants only after enzyme-mediated mineralization; their solubilization is not enough to allow them to be used by vegetal species (Cade-Menun et al. 2015). Temperature and pH are known to influence the availability of this form of P. Higher amounts of organic P in soil can be found in temperate sites when compared with those in tropical sites. Also, the proportion of organic P in nonresidual forms decreases with lower latitude and soil pH values (Hou et al. 2018). Phosphorus deficiency is one of the main factors limiting agricultural production in tropical soils such as the brazilian one (Parentoni et al. 2012). The effects of this deficiency in plants are dangerous and threaten their survival. In Citrus grandis, for example, this deficiency impacts nutrient absorption, photosynthetic apparatus performance (CO2 assimilation and chlorophyll are reduced), and antioxidant metabolism (generating oxygen-reactive species and decreasing the content of glutathione and the activity of enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and monodehydroascorbate reductase) (Meng et al. 2021). The process of phosphorus uptake is energy mediated, depending on a proton gradient across the plasma membrane. Transporters involved in the process can be high-affinity ones (impacted by the P concentration being induced in low-P conditions) or low-affinity ones (unaffected by P status). For example, in ryegrass plants, when it comes to the phosphate transporter 1 (PHT1) family of integral membrane proteins that can transport P, the expression level of PHT1.1 is not influenced by the phosphorus supply. However, the expression of PHT1.4 has proven to be largely influenced by the concentration of the element (Parra-Almuna et al. 2020). PHT1 genes are found in several plant species, but they are better characterized in rice—in which the overexpression of PHT1.1 is able to increase the P concentration in sprouts and the number of tillers (Seo et al. 2008; Sun et al. 2012). Nutrient use efficiency is a final product of a combination of parameters, such as nutrient absorption efficiency (related to the acquisition of nutrients from soil) and the capacity to mobilize and apply nutrients; the whole process is coordinated by genes and signaling networks that mediate nutrient uptake, redistribution, assimilation, and storage (Teng et  al. 2017). Therefore, plants commonly modulate their capacity to deal with P according to this element’s presence in soil. Especially in P-deficient soil, some plant species may develop important adaptations to enhance P-acquisition efficiency. Increasing the uptake of P by roots by modulating the expression of transporters is an example. There are plants that enhance the expression of some PHT1 genes under P-deficiency conditions, in an attempt to acquire more P from the environment (Raghothama and Karthikeyan 2005). Root morphological adaptations, for example, are also important for tomato plants in these

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situations; root hair growth, adventitious rooting, and topsoil foraging are interesting examples. The exudation of organic acids and/or reductants by roots to chelate P or mobilize it, the exudation of protons to change soil pH, and symbiosis are relevant strategies that can be naturally adopted (Dixon et al. 2020). Many strategies have been developed to try to artificially optimize soil mobilization for P and to optimize plant acquisition. For example, plants already have a natural strategy to enhance P availability in the rhizosphere, but human beings can also try to artificially increase P availability; organic anions (carboxylates) exogenously added to the root environment can mobilize soil P (Wang and Lambers 2020). In maize/alfalfa polycultures, the pH and organic anions in the rhizosphere contribute more than acid phosphatase does to optimizing phosphorus availability (Sun et al. 2020). Microorganisms are also an interesting tool to be used to achieve this goal; various microorganisms (e.g., bacteria, cyanobacteria, and fungi) have already been reported as able to solubilize P from native soil, making it more accessible and available to be taken up by plant species (Alori et al. 2017). Aspergillus FS9 and Bacillus FS-3 were able to increase the yield of strawberries by 7% and 30%, respectively, in limestone soil (pH 7.6) without the addition of P. Endophytic bacteria could successfully increase nutrient uptake in poplars by influencing the level/activity of proteins related to P solubilization and utilization (Varga et al. 2020). However, studies involving phosphate-solubilizing microorganisms should be performed prior to using them to find the correct microorganism to use in order to obtain the desired result. Bacillus mucilaginosus inoculation in acidic soil (pH 5.2), for example, was not able to improve P uptake by corn (Mercl et al. 2018). Thus, studies involving the inoculation of these organisms should be performed before their use in real situations. Additionally, more studies should conduct molecular investigations to better understand the mechanisms of action in enhancing P availability and use (Doydora et al. 2020). It is also possible to use strategies to select more-suitable genotypes of plant species. Genotypes that are more efficient in general and more responsive to phosphorus could be generated in popcorn hybrids by using parental generation containing organisms for which the merger would result in an accumulation of additive genes that promote popping expansion. Promising crosses could be found to be viable crop options, especially for use in phosphorus-­deficient soils (Gerhardt et al. 2019). In this chapter, however, the strategies that will be highlighted and explored are the ones based on genetic engineering, aiming to improve the use of phosphorus by plants.

2 Genetic Engineering Strategies as Tools to Optimize Agricultural Use of Phosphorus As P-use efficiency is determined not only by P-acquisition efficiency from soils but also by its processing within plants, these processes are the main targets when optimizations will be performed on P usage without enhancing P input through

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fertilizers (Tian et al. 2012). Various phosphorus-related genes have already been identified in major agronomics crops, such as rice (Oryza sativa), corn (Zea mays), and soybeans (Glycine max) (Shimizu et al. 2008; Wissuwa and Ae 2001; Zhu et al. 2005). Among these genes are interesting possible candidates for gene-­ overexpression strategies or transgenesis in a powerful approach to increase nutrient uptake and use, especially when under low-P-availability conditions (Kopriva and Chu 2018). Protocols to increase the absorptive capacity and efficiency of P use are needed especially to be applied in species of economic interest in agriculture. The aim is to achieve more-sustainable and more-ecofriendly agriculture: to improve crop productivity in order to meet worldwide needs while reducing the use of fertilizers (for environmental and economic reasons), practically using the nonrenewable P in soil, and reducing the amount of this element in harvested crops. In the P cycle in nature, a large amount of P in harvested crops impairs the process, which translates into a loss of usable P. The current estimative is that more than 80% of the P from fertilizers ends up on cereal crops eaten by humans and other nonruminants, who excrete the element, causing the eutrophication of waterways (Lott et al. 2009; Rose et al. 2013). To reduce P accumulation in grains, it must be available in soil for other plants to use, and there are already strategies available to do this using tools from molecular biology. The SULTR-like P distribution transporter in rice takes part in the process of controlling the allocation of P to grains. Knocking out this gene reduced P and phytate by about 30% in Oryza sativa grains. The element was redirected to leaves without any significant negative effect on productivity, seed germination, or seedling vigor. This type of protocol maintains productivity, avoiding the removal of P from the field and consequently avoiding the eutrophication of waterways (Yamaji et al. 2017). Genetic engineering can also be used to increase the absorptive capacity and internal use efficiency of legacy soil P in strategies involving the genes of transporters. Studies have shown the possibility of increasing P uptake through the overexpression of P transporters responsible, for example, for root P uptake and transport to sprouts, causing crops to become resilient to P deficiency. The gene expression of phosphorus transporters is regulated by various genes and transcription factors, which are induced especially under a stressful situation involving P-deficiency conditions (Hasan et al. 2016). In Triticum aestivum, the overexpression of the gene that codifies for the transporter PHT1.4 (a high-affinity phosphate transporter) was able to promote the accumulation of P and, consequently, plant growth (Liu et al. 2013). Using genetic engineering to achieve the constitutive expression of the phosphate transporter PHT1.1 in rice, likewise, modulated P homeostasis, directly affecting P absorption (Sun et al. 2012). Phosphate transporter PHT1 from maize (product of the  gene ZmPt9) also plays a role in phosphate uptake. When overexpressed in Arabidopsis, the organism exhibited early flowering, improving not only phosphate uptake but also growth (Xu et al. 2021). The Pht1 gene family in Medicago truncatula contains an important member: the MtPt6 gene. It is a gene whose expression is induced by phosphate starvation. When Arabidopsis knockout mutants of the Pht1.1 and Pht1.4 genes were

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engineered to perform the heterologous expression of this gene (through a transgene received), the phosphate acquisition efficiency of plants improved (Cao et al. 2021). Transporters not only mediate the uptake of P by plant cells but can also influence phosphorus transportation to storage within vacuoles. Vacuolar membranes can contain transporters such as SPX-MFS proteins (from the phosphate transporter 5 family—PHT5) to perform this role. The overexpression of the Pht5.1 gene in Arabidopsis led to the massive sequestration of P within vacuoles and also influenced the regulation of genes responsive to P starvation (Liu et al. 2016). There are also available protocols for DNA manipulation involving genes from transporters that are not mainly involved in P transportation but that can impact its homeostasis (Sun et al. 2014). The overexpression of a nitrate transporter from rice (the Nrt2.3b gene) made it possible to increase the uptake and accumulation of P (through a combination of regulating gene expression, using an advanced root system, and regulating phloem pH) and also increase rice grain yields and nitrogen use efficiency (Feng et al. 2017). The β-expansion gene GmExpB2 (obtained from a Pi-starvation-induced soybean cDNA library) deserves special attention for optimizing P use in plants  (Li et al. 2015). When overexpressed in Arabidopsis, it could enhance P uptake (independent of whether P concentration in the environment was high or low) and increase root cell division and elongation (Guo et al. 2011). In soybean transgenic plants, overexpressing this gene could stimulate leaf expansion and root growth, also improving P efficiency in hydroponic conditions in a P-limited environment (Zhou et al. 2014). In fact, the target of modification can also be the GmPtf1 gene; it consists of a basic helix-loop-helix (bHLH) transcription factor that can regulate GmExpB2 expression by inducing it. Transgenic soybean plants have revealed that changes in GmPtf1 expression modulate GmExpB2 expression and affect not only root growth and biomass but also P uptake (Yang et al. 2021). GmExlB1 gene offers a similar scenario. When overexpressed in Arabidopsis increased biomass and P content. It could improve P acquisition by regulating root elongation and architecture (Kong et al. 2019). The transcription factor gene Ptf1 is also important. It helps rice, maize, and soybeans deal with phosphorus. The factor is a member of the bHLH gene family, and its overexpression in maize induces lateral root development, regulates the genes related to the auxin-signaling pathway, and participates in responses to abiotic stresses such as phosphate starvation and drought (Li et al. 2019a). When the gene of the  transcription factor NIGT1.2 is overexpressed in Arabidopsis thaliana, it increases P uptake and decreases NO3− uptake. The gene of this factor could upregulate the transcription of genes related to P transport (such as Pht1.1 and Pht1.4). A similar regulatory mechanism also exists in Zea mays (Wang et al. 2020). The gene of the protein phosphatase 95 (an enzyme) is another important target. When overexpressed in rice plants, this protein led to a series of signaling events that ended up causing phosphate accumulation. This enzyme positively regulated P

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homeostasis, allowing rice plants to adapt to variable levels of phosphate (Yang et al. 2020b). When the gene of the haloacid dehalogenase (HAD)-like hydrolase 1 from Oryza sativa was overexpressed in rice, it enhanced phosphatase activity, biomass, and the total and soluble P contents. The protein  that  is the final product of this DNA sequence promoted the dephosphorylation of cellular organic P and acted in signaling pathways with kinases to regulate the phosphorylation status of different targets—influencing the homeostasis of phosphorous when under low-P-supply conditions (Pandey et al. 2017). Homologous genes from different species may offer different results when involved in genetic engineering strategies. When the phosphate starvation tolerance (PSTOL) gene in rice was overexpressed, for example, it could not only increase yields but also increased P concentrations in tissues. However, the homologue of this gene in wheat produced a decrease in yield and an increase in P concentration (in grains—which is not a desirable feature, as previously addressed) under P-limiting conditions (Milner et al. 2018). The choline oxidase gene CodA from Arthrobacter globiformis contains the information on the synthesis of an enzyme that catalyzes the oxidative conversion of choline to glycine-betaine. The latter regulated phosphate homeostasis in tomatoes genetically modified to contain the CodA gene, making the plants more resistant to low-phosphate stress. P’s uptake and its translocation were optimized in the same way for plant growth (Li et al. 2019b). There are also strategies applying molecular biology to influence symbioses that can affect P uptake. When overexpressed, the gene responsible for containing the information on the synthesis of the CLE53 protein in Medicago truncatula reduced arbuscular mycorrhizal fungi colonization in the symbioses. However, in mutant plants a higher colonization was observed. Therefore, the disruption of this gene is a viable strategy to enhance phosphorus uptake through mutually beneficial symbiosis, thanks to a reciprocal exchange of nutrients (Karlo et al. 2020).

3 Conclusions It is urgent to dedicate special attention to phosphorous because it is a nonrenewable resource that is important in agriculture: it is essential to normal plant growth and development and to producing sufficient amounts of crops for human needs. P sources may be depleted within the next few decades, so it is necessary to develop sustainable strategies that allow plants, especially crops, to efficiently use P. Genetically engineering vegetable species to optimize P uptake and use is one strategic and elegant solution, offering a wide array of opportunities for more-­ efficient and more-ecofriendly agricultural practices.

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4 Future Perspectives It is expected that even more genes related to improving nutrients will soon be revealed thanks to the fast advance of in silico resources and techniques from molecular biology field. The number of field experiments to verify the impact of genetic engineering protocols on P-use efficiency should also be increased. Advancements in better understanding the molecular mechanisms underlying P homeostasis will probably be crucial to help scientists surpass bottlenecks that limit the success of strategies for optimizing P uptake and use, especially in crops. Studies aiming to verify the effects of using large-scale genetically modified plants on the ecosystem are also expected to increase in number in the near future.

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Hinsinger P (2001) Bioavailability of soil inorganic P in the rhizosphere as affected by root-­ induced chemical changes: a review. Plant Soil 237:173–195 Hou E, Wen D, Kuang Y, Cong J, Chen C, He X, Heenan M, Lu H, Zhang Y (2018) Soil pH predominantly controls the forms of organic phosphorus in topsoils under natural broadleaved forests along a 2500km latitudinal gradient. Geoderma 315:65–74 Hou E, Luo Y, Kuang Y, Chen C, Lu X, Jiang L, Luo X, Wen D (2020) Global meta-analysis shows pervasive phosphorus limitation of aboveground plant production in natural terrestrial ecosystems. Nat Commun 11:637 Karlo M, Boschiero C, Landerslev KG, Blanco GS, Wen J, Mysore KS, Dai X, Zhao PX, de Bang TC (2020) The CLE53–SUNN genetic pathway negatively regulates arbuscular mycorrhiza root colonization in Medicago truncatula. J Exp Bot 71(16):4972–4984 Kong Y, Wang B, Du H, Li W, Li X, Zhang C (2019) GmEXLB1, a soybean expansin-like B gene, alters root architecture to improve phosphorus acquisition in Arabidopsis. Front Plant Sci 10:808 Kopriva S, Chu C (2018) Are we ready to improve phosphorus homeostasis in rice? J Exp Bot 69(15):3515–3522 Li X, Zhao J, Tan Z, Zeng R, Liao H (2015) GmEXPB2, a cell wall beta-expansin, affects soybean nodulation through modifying root architecture and promoting nodule formation and development. Plant Physiol 169:2640–2653 Li Z, Liu C, Zhang Y, Wang B, Ran Q, Zhang J et al (2019a) The bHLH family member ZmPTF1 regulates drought tolerance in maize by promoting root development and abscisic acid synthesis. J Exp Bot 70:5471–5486 Li D, Zhang T, Wang M, Liu Y, Brestic M, Chen THH, Yang X (2019b) Genetic engineering of the biosynthesis of glycine betaine modulates phosphate homeostasis by regulating phosphate acquisition in tomato. Front Plant Sci 9:1995 Liu X, Zhao X, Zhang L, Lu W, Li X, Xiao K (2013) TaPht1;4, a high-affinity phosphate transporter gene in wheat (Triticum aestivum), plays an important role in plant phosphate acquisition under phosphorus deprivation. Funct Plant Biol 40:329–341 Liu TY, Huang TK, Yang SY, Hong YT, Huang SM, Wang FN, Chiang SF, Tsai SY, Lu WC, Chiou TJ (2016) Identification of plant vacuolar transporters mediating phosphate storage. Nat Commun 7:11095 Lott JN, Bojarski M, Kolasa J, Batten GD, Campbell LC (2009) A review of the phosphorus content of dry cereal and legume crops of the world. Int J Agric Resour Gov Ecol 8:351–370 Meng X, Chen WW, Wang YY, Huang ZR, Ye X, Chen LS, Yang LT (2021) Effects of phosphorus deficiency on the absorption of mineral nutrients, photosynthetic system performance and antioxidant metabolism in Citrus grandis. PLoS One 16(2):e0246944 Mercl F, Tejnecký V, Ságová-Marečková M, Dietel K, Kopecký J, Břendová K, Kulhánek M, Košnář Z, Száková J, Tlustoš P (2018) Co-application of wood ash and Paenibacillus mucilaginosus to soil: the effect on maize nutritional status, root exudation and composition of soil solution. Plant Soil 428:105–122 Milner MJ, Howells RM, Craze M, Bowden S, Graham N, Wallington EJ (2018) A PSTOL-like gene, TaPSTOL, controls a number of agronomically important traits in wheat. BMC Plant Biol 18:115 Pandey BK, Mehra P, Verma L, Bhadouria J, Giri J (2017) OsHAD1, a haloacid dehalogenase-like apase, enhances phosphate accumulation. Plant Physiol 174:2316–2332 Parentoni SN, Mendes FF, Guimarães LJM (2012) Breeding for phosphorus use efficiency. In: Fritsche-Neto R, Borém A (eds) Plant breeding for abiotic stress tolerance. Springer, Berlin Heidelberg, pp 67–85 Parra-Almuna L, Pontigo S, Larama G, Cumming JR, Perez-Tienda J, Ferrol N, de la Luz Mora M (2020) Expression analysis and functional characterization of two PHT1 family phosphate transporters in ryegrass. Planta 251:6 Raghothama KG (2000) Phosphate transport and signaling. Curr Opin Plant Biol 3:182–187 Raghothama KG, Karthikeyan AS (2005) Phosphate acquisition. Plant Soil 274:37–49

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Chapter 14

Pseudomonas as Backbone for Environmental Health J. A. Ruley , J. O. Galla, P. Massawe, J. L. C. Ladu, and John Baptist Tumuhairwe

Abstract  Living in a clean and healthy environment is a human right. For this reason, colossal sums of money are budgeted by the state and non-state actors to ensure that environmental health is duly revitalized. A clean and healthy environment presupposes sustainable development as among others; it translates into balance of nature. As eco-engineers, microorganisms are important parts of the environmental health equation and therefore ought to be given adequate consideration in any endeavours aiming at enhancing the environmental health. In this chapter, an extant analysis is made of the contributions of genus Pseudomonas to the different components of the environment, given its ubiquity. The bioremediation roles and potentials of several strains of Pseudomonas are exposited, and case examples of scientific inquiries and experimentations are included to provide a case for Pseudomonas as an environmental bioengineering genus. Keywords  Environmental health · Pseudomonas · Bioremediation · Genus

1 Introduction The root microbiome is home to uncountable numbers of microbes (Bai et al. 2022). These exist as mutualists, pathogens or commensals (Bai et al. 2022; Santoyo 2021). J. A. Ruley (*) · J. O. Galla Department of Agricultural Sciences, University of Juba, Juba, South Sudan P. Massawe Tanzania Commission for Science and Technology, Dar es Salaam, Tanzania J. L. C. Ladu Department of Environmental Sciences, University of Juba, Juba, South Sudan J. B. Tumuhairwe Department of Agricultural Production, College of Agricultural and Environmental Sciences, Kampala, Uganda © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_14

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Praeg et al. (2019) noted the the rizhosphere is highly rich in nutrients that are made available by the root exudates. As a result, the rizhosphere is a hotspot for growth, survival, abundance and diversity of rhizobacteria genera. These genera in the root zones of plants develop synergistic interactions while also offering protection to the plants against any invasive behaviour of soil-borne pathogens such as nematodes by suppressing them (Bhattacharyya et al. 2017). Sutton et al. (2013) reasoned that the abundance and diversity of several bacteria strains in the rhizosphere and the accruing synergy accounts for why the reclamation of soil contaminated through bioremediation has become a possibility at a cheap and affordable cost and in an eco-friendly manner. Indeed, the establishment of plants and promotion of symbiotic interactions between plants and rhizobacteria has led to well-functioning environments due to microecological balance of the ecosystems (Ruley et  al. 2020a, 2022; Hakeem et al. 2021; Dar et al. 2022). Pseudomonas is the most ubiquitous and ecologically significant genus on earth (Marshall et  al. 2019; Nelkner et  al. 2019; Pacheco-Moreno et  al. 2021; Spiers et al. 2000). The reason backing this argument is that the genus is to be found in terrestrial and aquatic environments. In the aquatic environment, Pseudomonas is a universal resident in both freshwater and marine water. In either environment (terrestrial or aquatic), Pseudomonas forms mutual associations with both fauna and flora. Pseudomonas strains are resident in the rhizosphere of most plants (Zhuang et al. 2021) making them the most autochthonous rhizobacteria (Roquigny et al. 2018). The ubiquity of Pseudomonas is related to the high degree of physiologic versatility (Silby et  al. 2011) and genetic makeup (Spiers et  al. 2000) that paves way for their quick adaptability to both terrestrial and aquatic environments (Silby et  al. 2011; Spiers et  al. 2000). This universal distribution suggests a remarkable degree of physiological and genetic adaptability. For this reason, Pseudomonas is an excellent candidate for several biotechnological applications (Azam and Khan 2019; Silby et al. 2011). In the following sections, an analytical review of the influence of Pseudomonas genus is provided. To feed the readers with the critical contributions of Pseudomonas, a disaggregation of the impacts of the genus in the improvement and maintenance of environmental health is provided. The impacts are covered with case examples drawn from terrestrial and aquatic environments.

2 Terrestrial Environmental Degradation and Corrective Potentials of Pseudomonas 2.1 Deleterious Mining Activities Mining activities provide a clear pathway of heavy metals with deleterious effects on soil health (Molina et al. 2020; Palanivel et al. 2020; Ruley et al. 2020a, b, 2022). Worldwide, in all crude oil extracting countries, the quality of soil has declined severely due to PHC contamination (Milala et al. 2016; Shahsavari et al.

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2013; Shukry et  al. 2013). The contaminants have altered soil physicochemical properties and inhibited survival of biodiversity. Crude oil consists of a wide range of PHC and recalcitrant heavy metals such as Cadmium, Chromium, Copper, Nickel and Lead (Ali and Idris 2016) that have carcinogenic, mutagenic and recalcitrant properties when released into the environment (Alexander et  al. 2014; Liu et  al. 2016). Mineral oil and heavy metals are the main contaminants contributing around 60% to soil contamination (Panagos et al. 2013). A combination of these deleterious effects makes crude oil a major contaminant of healthy soils (Arora 2018). Hence, remediation of crude oil contamination is a necessity to reduce the risk of exposure, to restore soil functions and to provide ecosystem services. One of the ways through which soil environmental health is restored is by deploying plants and microorganisms that have potential to biodegrade the PHC contaminants and heavy metals through rhizoremediation (Ruley et al. 2022), Pseudomonas inclusive. The prowess of Pseudomonas in bioremediating PAH-contaminated soils is attributed to its high metabolic diversity, a reason for classing it as a main alkane and PAHs degrader genus (Vidal-Verdú et al. 2022). Rhizoremediation of contaminated soils is greatly supported by inoculation with Pseudomonas (Table 14.1). Silby et al. (2011) mentioned a combination of pseudomonads and biosurfactants that are secreted by Pseudomonas as key cleaning agents of crude oil polluted soils. These compounds detoxify PHC contaminants by mobilizing them into an aqueous state which is less harmful. The potency of several strains of Pseudomonas in the clean-up of hydrocarbon contaminants from terrestrial and aquatic environments is also noted. For example, P. aeruginosa frees soils and groundwater of PHC contaminants (Silby et al. 2011); P. putida biodegrades PAHs (Loh and Cao 2008) by establishing commensal relationships with Table 14.1  Potential of Pseudomonas in clean-up of mining polluted environments Mineral Copper

Strain(s) P. stutzeri

Crude oil

P. aeruginosa, P. putida

Uranium

P. aeruginosa

Fe, Cu, Co, Ni, Cd, Pb, Ag, Au (Arsenic).

P. azotoformans

Role in clean-up Produces extracellular polymeric substances, composed of proteins and carbohydrates that remove Cu from the surrounding environment Enzymatically attack and chelate PAHs, biodegrade PAHs into innocuous compounds that are environmentally harmless; convert the PAHs into food Biomineralization by a metal-resistant. Strain can remove soluble uranium (99%) and sequester it as U oxide and phosphate minerals while maintaining its viability Production of Arsenic-tolerant conditions. Production of siderophores that sustain plant life and increased potential to biodegrade

References Palanivel et al. (2020)

Silby et al. (2011), Molina et al. (2020), Loh and Cao (2008) Choudhary and Sar (2011)

Drewniak and Sklodowska (2013)

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phytoremediation plant species (Molina et  al. 2020; Weimer et  al. 2020) hence, cleansing polluted soils of contaminants. Other Pseudomonas species identified with bioremediation properties include P. fluorescens (Sipahutar et al. 2018).

2.2 Heavy Metal Concentration in Agricultural Lands Microbes are ubiquitous (Ruley et al. 2022). Their main necessities for survival are energy and carbon sources (Kumar et  al. 2018). One of the salient features of microbes is that their biological life processes require heavy metals (Kumar et al. 2018). Thus, Ni, Cr, Cu, Mg, Ca, Mn, Na and Zn are requirements in the metabolic reactions of microorganisms (Kumar et al. 2018). By comparison with bulk soil, the microorganisms living in metal-laden soil are capable of bioaccumulating 50 times more of the heavy metal contaminants in the soil. In non-mining environments where high concentrations of heavy metals have been reported, certain strains of Pseudomonas applied as consortium with other soil fertility additives have reportedly rid the soil of heavy metals (Table 14.2). P. aeruginosa is the most ubiquitous strain of Pseudomonas with greater potential for bioremoval of excess concentration of Cd (Al-Dhabi et al. 2019; Chellaiah 2018). The strain is found everywhere including desert lands, farmlands, grassland areas, forested environments, aquatic zones, human settlements, in plants, utility systems such as hospitals and sewerage, mining areas and riverine ecosystems (Al-Dhabi et  al. 2019; Chellaiah 2018; Li et al. 2018). The dominance of this strain rests on their abilities to resist antibiotics, thrive in stressful environments with heavy metals, adapting and surviving in detergents and persevering in organic solvents (Chellaiah 2018). It produces exopolymers and biosurfactants which offer protection to growing plants against Cd Table 14.2  Heavy metal remediation potentials of Pseudomonas Heavy metal Abundance Cd Soil, rock

Strain(s) P. putida

Action on heavy metal Capable of detoxifying aqueous Cd and significantly decreases the bioavailability of the metal by sequestration. P. aeruginosa, High tolerance to Pb through P. nitroreducens, production of and exopolysaccharides and P. alcaligenes biosorption P. fluorescens Biosorption

Pb

Soil, water, rock

Cr

All environments

Zn

Surface water, P. putida Soil, Rock

Enzymatic attack

Cu

Sludge

Utilization of Cu for biological processes

P. aeruginosa

References Yu et al. (2020)

Kaur et al. (2019)

Kalaimurugan et al. (2020), Yaashikaa et al. (2019). Pardo et al. (2003), Chen et al. (2005) Kaur et al. (2019)

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stressors. Elsewhere, in paddy fields, Li et al. (2018) noted that rice crop is harassed by the scorching effects of high levels of cadmium. A consortium of Pseudomonas and their metabolites as well as several other additives greatly improve the action on contaminants (Attarzadeh et al. 2019; Compant et al. 2019; Tiwari et al. 2018). For example, the application of P. chengduensis strain MBR and palm oil derived biochar chelates Cd by 30%. Furthermore, the presence of Cd in the soil environment creates unhabitable conditions for soil biota. Li et  al. (2018) reiterates that high presence of MBR strains greatly decreases the concentration of Cd hence creating an enabling condition for the survival and multiplication of other necessary soil biota. The MBR strains, therefore, serve as soil cleansers and bioengineers leading to ecological safety (Li et al. 2018).

2.3 Bioremoval of Heavy Metal Concentration from Landfills In the twenty-first century, world’s population has increasingly become urban (Aloo et al. 2021; Mahawar et al. 2020). It is anticipated that by 2050, world waste production might soar to 27 billion tonnes per year (Kumar et al. 2017). The growth in urbanization worldwide has led to a spectacular rise in Anthropocene activities to match the requirements of urban centres. As well, the increase in population has caused a multiplier effect on the growth and development of industries and other socio-economic developments which have led to a massive rise in the quantity of municipal and urban waste produced consequently necessitating creation of landfills. According to Imron et al. (2021), leachate is produced by landfills. One of the key components of leachate is heavy metals such as Hg. The Pseudomonas strains P stutzeri and P. fluorescens are capable of withstanding the scorching effects of Hg in landfill leachate and are excellent removers of Hg.

2.4 Removal of Pesticides In this chapter, the term pesticide is used as an umbrella word to denote the groups of insecticides, fungicides, defoliants, nematicides and anti-rodents (Giri et  al. 2021; Tsaboula et al. 2019). The increase in world population and the anticipated exponential increase by 2050 have necessitated the extensive use of these agrochemicals for purposes of boosting the productivity of arable lands (Tarfeen et al. 2022). The pesticides insert deleterious organic compounds in the environments with about three million people exposed and more than 200,000 people dying of contamination from pesticides annually (Alizadeh et al. 2018; Giri et al. 2021). Environments polluted with pesticides are best bioremediated by microorganisms which convert the toxic compounds into less toxic or non-toxic ones through a process called biorefining (Alizadeh et al. 2018) (See Table 14.3);

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Table 14.3  Potential of Pseudomonas in the remediation of pesticides Pesticide Removal mechanisms Chlorpyrifos Biorefining

Pseudomonas strain P. fluorescens P. aeruginosa

P. putida

Endosulfan Fenvalerate

P. stutzeri Surfactants enhance solubility and P. aeruginosa degradation Biodegradation into intermediates such as P. aeruginosa 4-chloro-α (1-methylethyl) benzene acetic acid that are environmentally friendly

References Yang et al. (2006) Lakshmi et al. (2008, 2009), Sasikala et al. (2012) Sasikala et al. (2012), Pradeep and Subbaiah (2015) Sasikala et al. (2012) Jayashree and Vasudevan (2007) Fulekar (2009)

2.5 Drought-Induced Abiotic Stresses Drought is an indication of disequilibrium in the environment. The impacts of the abiotic stresses ushered in by drought on the environment are well documented worldwide with notable scorching effects reported in several arid and semiarid environments (Kour et al. 2020; Ma et al. 2019). Drastic decline in crop yields due to the perturbations in water and nutrient uptake as well as the ability of the plants to carry out photosynthesis are observed in drought-stricken environments and are manifestations of nature imbalance. As earlier noted, Pseudomonas is a beneficial microorganism. Inoculating crops with strains of P. libanensis EU-LWNA-33 addresses the above pitfalls (Kour et  al. 2020; Ma et  al. 2019). The bacteria strain aids plants growing in drought affected environs to acquire the limiting nutrients while they also  introduces plant growth regulators such as siderophores, IAA and hydrogen cyanide which support vigor and vitality of plants.

2.6 Restoration of Degraded Soils Pseudomonas is a beneficial microorganism (Chandra et al. 2020; Martínez-Hidalgo et al. 2019; Silby et al. 2011). For example, P. aeruginosa is priority rhizobacteria for production of biofertilizers (Chandra et al. 2020) and solubilizes phosphates making them available for use by plants. P. stutzeri is a vital nitrogen-fixing microorganism making it a strategic bioinoculant for deployment to sustain and enhance vitality and vigor in plants (Silby et al. 2011). Among others, they produce siderophores, ammonia, and indole-3-acetic acid (Tao et al. 2020a, b; Qessaoui et al. 2019) antibiotics and several phytohormones (such as auxins, gibberellins, etc.) (Jamil et  al. 2018) while also colonizing rhizosphere of plants leading to nutrient bioavailability and

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bioassimilation (Qessaoui et al. 2019). P. stutzeri inoculum boosts the population of indigenous diazotrophs and ammonia oxidizers in the soil. These are boosters for luxuriant growth and development of plant structures (Ke et al. 2019). Another capability of Pseudomonas to serve as biofertilizers is illustrated by Jamil et al. (2018). Results of their study showed that when plants are inoculated with P. fluorescens in a drought-infested ecological zones, the bacteria strain catalyses the ability of the plants to carry out photosynthesis. The abiotic stresses ushered in by drought are minimalized by improvement of hormonal balance and lessening of the rate at which ethylene is produced. Jamil et al. (2018) profess that the rate of chlorophyll protein breakdown is curtailed by P. fluorescens inoculum. Furthermore, the rhizo exudates serve as osmo-protectants leading to a significant improvement in water regulation and uptake by plants. What is more to say, the rate of intake of toxic ions of essential nutrients such as Na and K are biocontrolled by the inoculum (Jamil et  al. 2018). The inoculation of Pseudomonas in rhizosphere equally suppresses root immunity leading to massive colonization of the zone by beneficial microbes (Yu et  al. 2019). An example of the beneficial microbes is P. simiae, a strain of Pseudomonas that increases the metabolism of carbohydrates, produces coumarins and increases chemical communication in rhizosphere leading to improved environmental conditions for survival and growth of plants as well as beneficial microorganisms (Yu et al. 2019). Together with strigolactones and flavonoids, Stassen et al. (2021) noted that coumarins improve networking and communication between plant root and shoot systems. This encourages vegetative growth of several plant species leading to a symbiotically enhanced environment.

2.7 Cleansing Effect of Pseudomonas on Pathogen-Laden Soils for Plant Growth In pathogen-infested soil environments, the action of P. putida, P. fluorescens, P. syringae pv, P. chlororaphis and P. brassicacearum reduces the abundance of pathogens while also disrupting their patterns of growth (Chiniquy et al. 2021; Kim and Anderson 2018; Tao et al. 2020a, b). This results in natural disease suppressive soils (Dignam et  al. 2019; Vacheron et  al. 2019). These strains are probiotics in plants and animals. Probiotics are health-promoting microbes (Kim and Anderson 2018) which confer systemic immunity to the host plants and animals leading to mitigation of the effects of the pathogens and other non-pathogenic stressors (Pieterse et  al. 2021; Tao et  al. 2020a, b). The probiotic pseudomonads are also known for forming protective biofilms on the root surface of the host plants as well as in secretion of metabolites or enzymes that boost plant health (Kim and Anderson 2018). P. chlororaphis for instance forms butanediol which regulates and moderates stomatal opening and closure leading to protection of plants against drought. In addition, Peptamen secreted by P. chlororaphis enhances collective resistance of plant species against environmental stressors. Pseudomonas henceforth, provides effective biocontrol for suppression of plant diseases induced by soil-borne pathogens (Tao et al. 2020a, b).

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Table 14.4  Roles of Pseudomonas in bioremediation of pesticides Strain(s) Action on waste P. Type of waste: Oily water waste; Bioaugmentation results in aeruginosa utilization of contaminants by the bacterial strain

References Varjani and Upasani (2021), Varjani et al. (2020) P. putida Type of waste: Lignin from paper and pulp industries, tannery, Liu et al. (2022), chemical, paint and dye manufacturing. Adipic acid from Niu et al. (2020), lignin biosynthesized Park et al. (2022) P. luteola Type of waste: Textile effluent. The bacteria strain degrades Jamee and azo dye under anoxic conditions Siddique (2019) P. Type of waste: Dyed textiles Surti and Ansari aeruginosa Remazol Black B is an azo dye which is extensively used in (2021) textile industries. A large amount of this dye is released in the effluent from textile industries, which negatively affects the soil and water environment. Degraded by complete decolouration

2.8 Waste Management and Contributions of Pseudomonas Waste management constitutes another anthropogenic activity that endangers the environment. In the area also, Pseudomonas plays an invaluable role (Annisa et al. 2021) (Table 14.4). For example, the application of Pseudomonas and aquatic plants such as E. crassipes and L. hoffmeisteri provide excellent candidates for the bioremediation of the contaminants in domestic wastewater especially by reducing on the turbidity and chemical concentrations (Sayqal and Ahmed 2021). In relation, Ananya and Apurba (2020) noted that Pseudomonas is a better candidate for bioremediation of p-Nitrophenol (PNP). The phenolic compound is commonly exuded to the environment through industrial waste effluents especially those originating from dye and textile as well as tannery industries. Pseudomonas has a high removal efficiency of more than 90% of the PNP in the environment. This shows how excellent, Pseudomonas is in the biodegradation of phenolic compounds.

3 Aquatic Environment Degradation and Corrective Potentials of Pseudomonas The excellent performance of Pseudomonas is not restricted to only terrestrial environments. The threats to environmental health posed by the natural and anthropogenic activities have equally affected the aquatic environments. This assertion is vindicated by Dar and Bhat (2020) who noted that the burden of aquatic pollutants has increased overtime leading to a manifold rise in the rate of aquatic environment pollution. Aquatic environments are mainly polluted or contaminated by the introduction of heavy metals either through surface run offs or leachate from

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Table 14.5  Roles of Pseudomonas in bioremediation of aquatic environments Degradation Contaminant strain Hg P. putida

Process Secretes enzyme reductase that absorbs 100% of mercury and also reduces toxic Hg(II) to harmless Hg0 P. aeruginosa Secretes merAgene that absorbs Hg ions

Nitrate

P. putida

Cell immobilization

References Zhang et al. (2012)

Joshi et al. (2021), Yin et al. (2016) El-Sesy and Ibrahim (2021)

landfills, excessive nutrient availability especially from pesticides, contact with wastewater and through illicit dumping of industrial and pharmaceutical wastes (Dar and Bhat 2020). Fernandes et al. (2021) and Qi et al. (2019) noted that the increased disposal of pharmaceutical waste has been influenced by the increased use of antibiotics and an assortment of other drugs. Specifically, the dumping of antibiotic residues in the environment for a long period of time introduces antibiotic resistance genes (ARGs) in the environment (Table 14.5) In such polluted environments, Pseudomonas biodegrades the ARGs by hydroxylation, dehydration, deamination, demethylation and decarboxylation (Qi et al. 2019). Dar and Bhat (2020) noted that microorganisms form biofilms in polluted aquatic environments. P. geniculata and P. aeruginosa are prominent biofilm makers (Maes et al. 2019). Much as the biofilms are indicative of the level of pollution, as well, they are better bio-remediators of pollution load in water bodies. This accounts for why biofilm-based bioreactors are increasingly used for purification of polluted water in present time and widely deployed at water treatment points to rid the water of contaminants (Dar and Bhat 2020). Pollution-free water supports human life and aquatic biota. Although nitrate is a major nutrient required by many living organisms, events of high concentrations can be deterrent to the environment (El-Sesy and Ibrahim 2021). With the excessive and recurrent use of inorganic fertilizers and pesticides, the surface water is vulnerable to contamination through seepage of nitrate to ground water. Other sources of nitrate concentration listed by El-Sesy and Ibrahim (2021) include industrial effluent, domestic wastewater, municipal sewage, canals, septic tanks, sewage dumping grounds and animal feedlots. P. putida bioremediates contaminated water by removing the nitrates. When nitrates are not degraded, their continuous accumulation leads to eutrophication of water sources.

4 Conclusion Pseudomonas exhibits several metabolism-dependent and metabolism-independent processes that confer mechanisms for the clean-up of degraded environments. This superiority over most other bacteria strains is attributed to the ubiquity of the genus

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in different environments. The dependent and independent processes enumerated above have made the genus an excellent environmental cleaner which vindicates the beliefs by many environmentalists, microbiologists and soil scientists that the genus Pseudomonas is an environmental engineer and therefore, a backbone for realization of environmental health.

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Chapter 15

Cyanobacteria as Sustainable Microbe for Agricultural Industries Shah Ishfaq, Jeelani Gousia, Syeed Mudasir, and Baba Uqab

Abstract  Cyanobacteria, also known as blue-green algae, have proven to be a potential agent for use in sustainable agricultural practices. It has a wide application in the production of food, bio energy and biofertilizers. Cyanobacteria being adapted to varied soil types are ubiquitous and act as a supplement to soil. They form symbiotic association with several plants and act as plant growth enhancer, nutrient improving and nitrogen fixation agent and thus prove to be a potential biofertilizer. Various strains of Cyanobacteria have the potential to remove pesticides, insecticides and excess nutrients from contaminated soils and wastewater. Moreover, they also pose the tendency to produce biofuels such as hydrogen, ethanol and biodiesel. Cyanobacteria have also been studied for their role in nutrition and health as they are rich in protein, lipids, antioxidants and vitamins. Due to its wide applicability, cost-effective and eco-friendly nature, Cyanobacteria possess a vital status in sustainable agriculture though its mass cultivation requires a lot of expertise and manpower. Keywords  Cyanobacteria · Sustainable agriculture · Bioenergy · Nitrogen fixation · Biofertilizer

S. Ishfaq Department of Environmental Science, University of Kashmir, Srinagar, Jammu & Kashmir, India J. Gousia Centre of Research for Development (CORD), University of Kashmir, Srinagar, Jammu & Kashmir, India S. Mudasir Abdul Ahad Azad Memorial Degree College Bemina, Cluster University Srinagar, Srinagar, Jammu & Kashmir, India B. Uqab (*) Sri Pratap College of Sciences, Cluster University Srinagar, Srinagar, Jammu & Kashmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_15

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1 Introduction Soil fertility is based on many variables mainly environmental, physical and biological. Although multiple studies have addressed physical and chemical causes, inadequate attention has been given to biological causes. Soil respiration, phosphorus and mineralization are essential variables that play a major role in assessing the soil’s biological well-being. Current soil management strategies rely primarily on inorganic chemical fertilizers that present a significant threat to human health and the environment (Williams and Laurens 2010; Hakeem et al. 2021). Specifically in developed nations, the indiscriminate usage of industrial fertilizers has undeniably improved production and has had negative consequences. Organic fertilizers are also a healthier choice and not only a cost-effective but also a sustainable and renewable supply. Soil degradation, indiscriminate usage of pesticides, insecticides, road building, power plants, landslides and deforestation contribute to a decline in soil quality which can be recovered by adopting soil conversation methods such as afforestation, biomining, usage of biofertilizers and bio pesticides and promotion of biodegradable goods (Singh et al. 2016). Chemical fertilizers, because of their continuous and long-term usage, result in deteriorating the soil quality in all terms whether physical, chemical or biological and they have direct impact on crop production. Biofertilizers are needed to reestablish soil fertility. These biofertilizers have the capacity to boost the water, retain water and important nutrients such as calcium, vitamins and proteins (Rai et al. 2000; Dar et al. 2022).

2 Biofertilizers Biofertilizers are substances comprising microorganisms or microbes that enhance their productivity when added to seeds, plant surfaces or soil, colonize the rhizosphere or inside the plant and foster plant growth by increasing the supply of critical nutrients to plants as a consequence of their biological activity and increasing crop yields (Issa et al. 2001). These microorganisms absorb atmospheric nitrogen and make it accessible to plants in the form of nitrates and nitrites. These often transform insoluble phosphates to the types the plants need. Thus, biofertilizers act as interactions between living beings and plants (Malik et al. 2001). Biofertilizers primary reservoirs include mycorrhizal mushrooms, blue-green algae (BGA) or sand bacteria from cyanobacteria. A few microorganisms used as biofertilizers include Rhizobium, Azotobacter and Azospirillum. These are the natural source of fertilizers, and are thus commonly used in farming.

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3 Classification of Biofertilizers Biofertilizers are categorized mainly on the basis of employed microorganisms or on the basis of their activity type. Biofertilizers when classified on the basis of microorganisms are classified as follows: 1. Bacterial biofertilizers which mainly include biological nitrogen-fixing (Symbiotic), Non-symbiotic, free-living nitrogen fixers. 2. Cyanobacteria (BGA, blue-green algae) which again may be symbiotic or free-living. 3. Fungal biofertilizers which include ectomycorrhizal fungi, endomycorrhizal fungi and vesicular arbuscular mycorrhiza (VAM). On the other hand, when categorized according to their activity, biofertilizers can have the following forms 1. Nitrogen-fixing biofertilizers 2. Phosphate-solubilizing biofertilizers (PSB) 3. Plant growth-promoting biofertilizers.

3.1 Nitrogen-Fixing Biofertilizers Nitrogen as needed by crops in large quantities is the most important priority for the plant production. Nitrogen in the crops is principally derived from soil sources, fertilizers and manures applied to soil accretion by precipitation and irrigation water and bio-nitrogen fixation (BNF) involving a wide range of different species (Rosenberg et al. 2008). Biological nitrogen fixation is a significant source of earthly nitrogen production. The essential raw material for nitrogen is fixation, be it biological or chemical, and soil, of which 79% is nitrogen. It is clearly evident that industrially fixing nitrogen cannot satisfy the world’s cumulative nitrogen needs, particularly in countries with increasing population and ever-rising demands for food and fibre. The generally recognized approach is to maximize the accessible supply of plant nutrients in an optimized manner effectively and efficiently. Agricultural nitrogen requirements would also need to be fulfilled through fertilizers, sustainable manures, effective recycling and biofertilizers. Biological nitrogen fixation is an economically beneficial and ecologically advantageous route for increased nutrient availability. It is pertinent to mention that certain biological nitrogen-fixing bacteria perform a prominent role in agriculture and agricultural products and those include blue-green algae, Azolla, Azotobacter and Azospirillum. The biofertilizers with nitrogen addition improve nitrogen by applying atmospheric nitrogen to the field plant network.

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3.2 Phosphate Biofertilizers Phosphorus is an essential nutrient, just next to nitrogen, and is graded as a major nutrient factor along with nitrogen and potassium. Phosphate fertilizers are of a separate class because they tend to improve the solubility/availability of phosphorus of sparsely soluble types already found in the soil. Phosphorous-solubilizing biofertilizers can play a significant role in improving the productivity of the residual phosphorous compounds in the field. It has been confirmed that 140 million tons of low-grade phosphate have been deposited in the soil, which cannot be accessed directly by plants. Just by adding phosphorous-solubilizing bacteria into the soil will make the plants to utilize it. As a function secreting organic acids by bacteria particularly Pseudomonas, Bacillus, Penicillium and Aspergillus, the pH in their proximity helps in the solubilization of attached soil phosphates.

3.3 Plant Growth-Promoting Biofertilizers Under the common general category Pseudomonas sp. has been granted the priority for plant growth promoter of rhizobacteria (PGPR) which indirectly means rhizobacteria with plant health promoter qualities (PHPR) (Singh et al. 2017a, b). Since the bacteria pseudomonas fluorescens have property to under go fluorescence under UV LIGHT. They compete for the exclusion of substrate and niche and the development of siderophores and antibiotics. Furthermore, for biological control, more than one pathway may be used. Pseudomonas sp. has the property to “scoop up” rhizospheric nutrients due to their versatility in the growth and absorption of nutrients. These bacteria usually enhance plant growth by generating plant growth promoters by improving the supply and absorption of mineral nutrients, and by eliminating soil-borne pathogens or other deleterious microorganisms in the rhizosphere. The inhibition of soil-borne plant pathogens by rhizosphere microorganisms is called bio-control. It is a well-known fact that biofertilizers play a significant role in supplementing essential plant nutrients for sustainable agriculture, the environment and the climate. The utilization of biofertilizers in agricultural practices was advocated taking into consideration an appropriate dose and a beneficial response to plant growth and crop yield.

4 Types of Biofertilizers The foregoing are essential categories of biofertilizers: • Symbiotic (Nitrogen-Fixing Bacteria) Rhizobium is among the most essential symbiotic (nitrogen-fixing bacteria). Thus, the bacteria want refuge and get nutrition from the seeds. In exchange, they aid by supplying the plants with set nitrogen (Lipok et al. 2009).

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• Root Association of Nitrogen-Fixing Bacteria (Associative Mutualism) Azospirillum is a nitrogen-fixing bacteria that tends to live near to the roots of higher plants but does not need to establish a particular relationship with plants. This activity is generally referred to as activity with the rhizosphere. This definition is called associative mutualism, in ecological terms. • Symbiotic (Nitrogen-Fixing Cyanobacteria) Blue-green algae (BGA) or cyanobacteria establish a symbiotic relationship with a variety of plants. Liverworts, ferns and even lichens are also classified among the nitrogen-fixing cyanobacteria. Anabaena is considered responsible for the fixation of nitrogen, and its origin is typically in the fern’s leaf nodules. The fern plants die and unlock the same for the usage of the rice plants. Azolla pinnate associated with rice plant is also a fern but does not influence plant growth. • Free-Living Nitrogen-Fixing Bacteria Free-living soil bacteria are mostly associated with nitrogen fixation being mostly saprotrophic anaerobic organisms in nature. The examples of such bacteria include Clostridium, Beijerinckii, Azotobacter and Bacillus polymyxin. Rhizobium and Azospirillum are perhaps the most commonly used of all forms of Biofertilizers.

5 Components of Biofertilizers Most significant ingredients of biofertilizers that play a key role and give them a special position are as follows:

5.1 Bio Compost Bio compost is an eco-friendly item made up of surplus materials extracted from the decomposed sugar industry. This is compounded by the human friendly bacteria, fungi and other plants (Nisha et al. 2007).

5.2 Tricho-Card This is another eco-friendly and non-pathogenic ingredient utilized in number of crops including horticultural and ornamental plants, such as paddy, apple, sugar cane, brinjal, maize, cotton, tomatoes and citrus. It functions as an efficient destroyer and antagonistic hyperparasitic to many boron larvae, shoots, berries, leaves, flower eaters as well as other pathogens in the region.

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5.3 Azotobacter This defends the plants from bacteria found in the soil and performs a vital function in the determination of ambient nitrogen. For plants, nitrogen is a very critical fertilizer, and approximately 78% is nitrogen in the overall atmosphere (Nisha et al. 2007).

5.4 Phosphorus Phosphorous-based fertilizers are being utilized to assess soil amount of nitrogen. Any soil requires more nitrogen, whereas others require less nitrogen. Insoluble phosphorus is introduced into the soil to replace phosphate in clay minerals.

6 Role of Cyanobacteria and Sustainable Agriculture Study in recent years has contributed to cyanobacteria being used as a possible agent for sustainable farming practices (Singh et al. 2016). Rich in protein, carbohydrates and lipids, these can be employed for organic food and non-food processing, as well as for chemicals and bioenergy (Wase and Wright 2008; Sarsekeyeva et al. 2015; Rajneesh et al. 2017). Cyanobacteria are adopted to survive in wet soils affecting their structural stability, nutritional status and productivity (Nisha et  al. 2007). In addition, about 25% of the total cyanobacterial biomass is comprised of exopolysaccharides (EPS) (Nisha et al. 2007). The EPS leads to soil aggregation by holding the soil particles together and helps increase organic content, water-holding capacity and support growth of plant-growth promoting rhizobacteria (PGPR). The PGPR and cyanobacteria improve the fertility of soil and nutrient utilization leading to increase in plant growth and enhance tolerance against environmental stresses such as salinity and drought (Singh et al. 2011; Prasanna et al. 2012; Singh 2014). Sustainably, Cyanobacteria can be beneficial in agricultural systems as they have wide applicability in Bioremediation and pollution abatement, Bioenergy, nutrition and health.

6.1 Cyanobacteria as Biofertilizer Cyanobacteria are commonly called as blue-green algae that possess the characteristics of both gliding bacteria as well as higher plants. Capability to fix nitrogen and ability to photosynthesize determine their adaptability to various types of soils hence making them ubiquitous and supplement the soil. This capability of nitrogen fixation make cyanobacteria a potential biofertilizer (Song et  al. 2005;

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Prasanna et al. 2013). They have the capability to increase the productivity under varied agro-­environments, that is, they thrive both on surface as well as below the surface. Improved output utilizing cyanobacteria is accomplished by the following: 1. Increased pore size 2. Excretion of Growth promoting hormones such as auxins and gibberellins (Rodriguez et al. 2006) 3. Enhancing the water-holding capacity (Roger and Reynaud 1982) 4. Increased soil biomass after their death (Saadatnia and Riahi 2009) Cyanobacteria possess an economic importance due to its agronomic value to be used as biofertilizer. They can produce natural biologically active products (Ördög et al. 2004; Gademan and Portman 2008; Sielaff et al. 2008; Wase and Wright 2008; Rosenberg et al. 2008; Tan 2010). For example, Aulosira fertilisima, Calothrix sp., Scytonema sp., Nostoc linckia, Tolypothrix sp., and Anabaena variabilis have been utilized for the production of rice. Cyanobacteria like Diazotrophes are used to produce cost-effective biofertilizers that are easily available. They have the tendency to aerate soil, increase water-holding capacity, add vitamin B12 and control the deficiency of nitrogen in soil (Song et al. 2005; Hall et al. 1995; Paumann et al. 2005; Malik et al. 2001). Nostoc and Anabaena surviving on the rocks and soil surface can fix up to 20–25  kg/ha atmospheric nitrogen. Seasonally, Anabaena can fix up to 60 kg/ha/season thus enriching the soil with organic matter (Moore 1969). Anabaena variabilis have also been found capable of accumulating the inorganic Carbon (Kaplan et  al. 1980). In addition, Cyanobacteria showing symbiosis with plants, fungi, bryophytes, pteridophytes, gymnosperms, angiosperms and animals have been found to be enhancing the N2-fixing capability. For example, Azolla commonly called as water fern form symbiotic relation with Anabaena azollae to be used as a major biofertilizer. Green algae when dried contain higher percentage of macro and micronutrients and amino acids as well (El-Fouly et al. 1992; Mahmoud 2001).

6.2 Role in Bioremediation Rapid urbanization and industrialization has disrupted the steady state between different components of earth’s environment. Bioremediation has proven to be a combating solution to the global pollution problems. Cyanobacteria can act as a bioremediating agent for a variety of contaminants such as pesticides, phenol, xenobiotics and heavy metals (Kesaano and Sims 2014; Kumar et al. 2016; Hamouda et al. 2016; Singh et al. 2016). Persistent toxins such as organochlorine and organo-­ phosphorus insecticides have also been eliminated effectively by strains such as Anacystis nidulans, Microcystis aeruginosa and Synechococcus elongatus (Vijayakumar 2012). Similarly Nostoc, Nodularia, Anabaena, Oscillatoria, Microcystis and Synechococcus are bioremediators of lindane (El-Bestawy et  al. 2007). Few species of Nostoc, Anabaena, Lyngbya, Spirulina and Microcystis remove herbicides from soils by utilizing glycophosphate as nutrient source for

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phosphorus (Forlani et al. 2008; Lipok et al. 2009). Nostoc linckia and Oscillatoria rubescens are able to degrade chemical dyes through their enzyme systems (El-Sheekh et al. 2009). Besides strains of cyanobacteria have proven efficient in removal of heavy metals from contaminated environments.

6.3 Role in Wastewater Treatment Use of Cyanobacteria provides a time-intensive, cost-effective, clean and interesting method in treating wastewaters. Wastewaters are rich in nutrients such as nitrogen and phosphorus; using cyanobacteria act as a promising method for the removal of these nutrients. Besides nutrients, Cyanobacteria are capable of remediating heavy metals as well through the process of biosorption.

6.4 Role in Bioenergy Global energy consumption is likely to increase to 681 trillion MJ in 2025 (Otero et al. 2007). This increase demands shift towards the eco-friendly, renewable sources of energy. This renewable energy is referred to as bioenergy which is based on the conversion of biomass into biofuels and biodiesel (FAO 2006). The bioenergy production involves conversion of biomolecules into ethanol. Cyanobacteria are a viable alternative for production of biofuels due to their easy genetic manipulation and simple growth (Angermayr et al. 2009). Cyanobacteria can be genetically manipulated to produce ethanol (e.g. Trichodesmium, Synechocystis and Synechococcus) and hydrogen (about 14 cyanobacterial genera are reported to produce hydrogen gas) (Dutta et al. 2005). Biodiesel production can be achieved with regard to the high lipid content for which diatoms are more suitable in addition to Cyanobacteria (Chisti 2007). However, there is a limitation in the application of cyanobacteria in biofuel production due to its low commercially viable application.

6.5 Role in Nutrition and Health Cyanobacteria might be used as supplemental sources of food as these are a good source of proteins, lipids, minerals, vitamins and antioxidants (Rosenberg et  al. 2008). Spirulina has been named as magic agent due to its usage as food supplement, feedstock, cosmetics and anticancer agent (Vonshak 1996). It has the highest protein about 70% and fatty acid 70–80%. Carbohydrate amounts for 15–20% while nucleic acid amount for 5% only (Santillan 1982). Besides nutrition, Spirulina can induce egg production in hens, increase body weight in shrimps and fish fry. It can also reduce cholesterol in animals and humans and can enhance immune responses against various diseases.

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General representation of Cyanobacteria, its applications and constraints in its cultivation with possible solutions

7 Mass Cultivation of Cyanobacteria Cyanobacteria are a good agricultural complement for production of fuel, feed, food and chemicals. However, its production on large scale requires a lot of resources and expertise. Some of the microalgae and Cyanobacteria can be cultivated on large scale such as, Dunaliella, Haematococcus, Chlorella and Arthrospira (Rosenberg et  al. 2008). Cultivation of Cyanobacteria requires minerals and water, light and essential nutrients Commercially Cyanobacteria can be cultivated in the following ways: • Cultivation using sunlight in open systems • Cultivation using sunlight in closed systems • Cultivation using artificial light in closed systems

8 Cultivation Using Sunlight in Open Systems In this design, cyanobacteria are mass cultivated in shallow and open ponds (Cañedo and Lizárraga 2016) using sunlight as the source of energy. The advantage of this system of cultivation is that the energy source, that is, sunlight is free of cost and produce specific biomaterials and tons of dried biomass (Lee 1997). However, there are certain limitations in this method of cultivation such as contamination by algae, microbes and grazers is unpreventable. In addition, the open systems show diurnal

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fluctuations in response to environmental conditions such as light, temperature, evaporation and precipitation that determine the survival and productivity of the systems, for example, Spirulina (Li and Qi 1997; Vonshak 1996).

8.1 Closed System Cultivation Using Sunlight This type of system is designed to utilize solar radiation as energy source (Grima et al. 1999). This system uses transparent material to make vessels that are placed outside under natural light (Khatoon and Pal 2015). This system is costlier due to cost of transparent materials. This system is similar to open system as this system also uses sunlight as source of energy. The advantage of this system over open system is that contamination of grazers and other competitors is prevented.

8.2 Cultivation Using Artificial Light in Closed System This system uses vessels with artificial light source for cultivation of photosynthetic microbes (Lee and Palsson 1994). These vessels are same as conventional fermenters called as photobioreactors as these are driven by light. Softwares are used to control and optimize the culture parameters. This system is costlier than outdoor systems of cultivations. This system has an advantage of producing the high quality and quantity of biomass with high-value production like stable isotopes (Apt and Behrens 1999). These systems are feasible to be used for genetically modified organisms as the parameters are controlled.

9 Advantages of Biofertilizers • • • • • • • • • • •

Reduction in use of chemical fertilizers. Secrete plant growth hormones which help in plant growth. Biofertilizers improve soil texture and yield of plants. They do not allow pathogens to flourish. Eco-friendly and cost-effective. Biofertilizers protect the environment from pollutants since they are natural fertilizers. They destroy many harmful substances present in the soil that can cause plant diseases. Biofertilizers are proved to be effective even under semi-arid conditions. Can be produced easily on a large scale. No special care is necessary while using biofertilizers. Farmers may grow (e.g. Azolla) in their own fields.

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10 Conclusion Cyanobacteria in today’s world have emerged as a biofertilizer with full potential; their ability to use water, carbon dioxide and nutrients especially has given them a special status. Agricultural practices around the world have become sustainable with efficient use of Cyanobacteria. These practices have not only reduced the global warming but also have resulted in sustainable and eco-friendly agricultural practices. Thus, it would not be wrong to say that Cyanobacteria can be used for improving the quality of food, quality of soil and overall quality of environment.

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Chapter 16

Functional Diversity of Endophytic Microbiota in Crop Management of Cucumis sativus L. Showkat Hamid Mir, Aadil Farooq War, Rezwana Assad

, and Irfan Rashid

Abstract  Cucumis sativus L. (Cucumber) is a widely grown species of the plants belonging to family cucurbitaceae. It is a vine, bearing cylindrical fruit and is eaten as a culinary vegetable all over the world. To prevent pathogens, which adversely affect cucumber production and cause severe economic loss to farmers, cucumbers are often sprayed with pesticides. However, keeping in view the adverse effects of pesticides on humans and the environment, researchers were looking for alternate management options. The most effective and sustainable strategy employed in the management of cucumber crop is the use of allied endophytic microbiota, which not only act as biocontrol agents against many pathogens, but also assist in mineral uptake and utilization in cucumber crops. Several endophytes colonize cucumber plants that facilitate plant growth by different mechanisms, including the increase in the bioavailability of essential minerals, release of certain chemicals such as phytohormones, biomass production, disease control, and other activation mechanisms. Keeping these facts in view, this chapter is designed to highlight the updated scenario of functional diversity of endophytic microbiota associated with cucumbers in cucumber crop management. Keywords  Biocontrol · Biofertilizer · Crop management · Cucumis sativus · Endophytes · Stress tolerance

1 Introduction Cucumber (Cucumis sativus L.) is the world’s fourth most indispensable vegetable (Tatlioglu 1993). Its economic importance varies across different regions of the world, being most popular in Europe, the USA, USSR, and Asia. Cucumber is S. H. Mir Julius Maximilian University of Würzburg, Würzburg, Germany A. F. War · R. Assad (*) · I. Rashid Department of Botany, University of Kashmir, Srinagar, Jammu and Kashmir, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_16

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native to India (Sebastian et al. 2010), where it has been grown for food from past 3000 years. Due to its small number of genes, rich diversity of sexual expression, suitability for vascular biology studies, short life cycle (3  months from seed to seed), and accumulation of genetic and genomic resources, cucumber is being developed as a new model species in plant biology (Ren et al. 2009; Han et al. 2009; Huang et al. 2009; Guo et al. 2010). In the last decade, more genomic resources became available for cucumber including de novo sequenced genomes, a re-­ sequenced core collection of germplasm, and multiple global expression datasets (Huang et al. 2009; Qi et al. 2013; Wang et al. 2018). Despite recent advances in molecular studies related to disease resistance, several diseases attack this cultivated species and cause huge losses annually (Al-Sadi et al. 2011; Al-Balushi et al. 2018). In so many cases, these diseases are caused by viruses or some other microbe infections. For example, fungal pathogen Pythium aphanidermatum, which causes damping off disease in cucumbers and results in 75% mortality in young seedlings thus causing severe loss to the cucumber crop (Al-Sadi et al. 2011). Farmers generally resort to monoculturing of cucumber crops which tends to increase soil-borne plant pathogens such as Pythium and Fusarium (Hakeem et al. 2021). Although various measures have been attempted to control pests, none have yet proved to be entirely successful. The repeated use of pesticides, which are highly hazardous to health and result in several environmental issues, has necessitated the exploration for alternate disease resistance mechanisms and potential biocontrol agents. A number of recent studies have shown that non-pathogenic microbes within the plant microbiome, that is, endophytes (endo means within and phyte means plant), can dramatically modify the expression of resistance to host against many plant diseases, yet their participation in plant defense is undervalued hitherto (Busby et  al. 2016). Endophyte-mediated biocontrol is centered on a direct pathogenic strain activity via parasitism and antibiosis, or by competition for nutrients or root niches, or the indirect plant-mediated response prompted by certain endophytes, called endophyte-mediated resistance. Endophytes are the microbes that colonize plant internal tissues and mostly occur inside cells or the vascular system and establish symbiotic relationships without having any profound negative effects on the host. These biological interactions have reflective effects on plants growth, health, development, production and on soil quality, which may trigger many constructive impacts on the reliability and sustainability of agro-ecosystems. However, the proper recognizing of the underlying mechanisms utilized by the endophytes in fostering plant growth remains rather elusive, thus making it difficult to fully exploit these growth-­promoting interactions to improve the plant growth in applied settings (Hardoim et al. 2008; Marasco et al. 2012; Rashid et al. 2012). The capability of endophytes, either bacterial or fungal endophytes to promote growth and development of host, is generated either through direct or indirect mechanisms. The direct mechanisms of plant growth promotion by endophytes entail the acquirement of mineral nutrients and regulation of phytohormone levels. On the other hand, indirect mechanism involves reduction in the damage caused by infection of phytopathogens, that is, biocontrol (Khan and Doty 2009; Luo et al. 2012;

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Fig. 16.1  Functional diversity of endophytic microbiota of Cucumis sativus

Mitter et al. 2013). Furthermore, the role of endophytes has been highly acknowledged for producing a range of secondary metabolites, which fortify the crop defense systems and help them in coping several environmental stresses such as temperature, drought, heavy metal toxicity, flooding, and salinity. The establishment of symbiotic interactions between the host and the endophyte significantly enhance growth, yield, and influence soil enzymatic activities by triggering the release of certain extracellular enzymes such as lipases, cellulases, phosphatase, protease, and amylases and growth regulators (gibberellic acid, indole-3-acetic acid), while in return, host provides them shelter (Dar et al. 2022). Numerous studies have demonstrated the potential of cultured endophytes to their hosts in several economically important cucurbits for their nutrient procurement and growth promotion activities. Thus, this chapter focuses on the functional diversity such as disease control and other beneficial functions of endophytic microbiota in the cucumber crop management (Fig. 16.1).

2 Cucumber Plant Growth Promotion by Endophytes as Biofertilizers Endophytes promote plant growth directly by either facilitating the acquisition of essential nutrients such as nitrogen, iron, and phosphorus or by synthesizing the phytohormones such as auxins, gibberellins, and cytokinins. A few endophytes have been found to support plant growth by means of lowering the levels of

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phytohormones such as ethylene by synthesizing the ACC deaminase enzyme, which prevents ethylene synthesis by cleaving the 1-aminocyclopropane-1-carboxylate (ACC) ethylene precursor.

2.1 Direct Enhancing of Plant Growth 2.1.1 Nitrogen Fixation Nitrogen is an important component of almost all biomolecules mainly including proteins, enzymes, nucleic acids, and chlorophyll (Leghari et al. 2016). Although nitrogen being the most abundant element in the earth’s atmosphere, that is, dinitrogen (N2), its utilization by the plants is limited. The plants can only use this N2 when it gets fixed into usable forms such as ammonia (NH4+) and nitrate (NO3−). The ability to fix atmospheric nitrogen requires the nitrogenase enzyme, which is restricted to certain bacteria and archaea (Galloway et al. 2008). The only bacteria that are able to fix nitrogen are called diazotrophs and may live either freely in soils or in symbiotic association within the rhizosphere, phyllosphere, and internal tissues of leguminous and other terrestrial plant (Young 1992). For the first time, Cavalcante and Dobereiner (1988) isolated an endophytic diazotroph (Gluconacetobacter diazotrophicus) from tissues of non-leguminous plant (sugarcane) and postulated that this diazotroph satisfies every nitrogen requirement of sugarcane (Boddey et  al. 1991; Stephan et  al. 1991). Since this discovery, many other crop plants such as corn, wheat, cucumber, rice, canola, and kallar grass have been found to harbor nitrogen-fixing organisms (Hao and Chen 2017). Furthermore, studies have found that inoculating agriculturally important plants with consortium of bacteria such as Gluconobacter, Herbaspirillum, Burkholderia, and Paenibacillus increased stalk yield, comparable to chemical fertilization (Schultz et al. 2014). Cucumber, a popular vegetable among cucurbits, is widely cultivated in the world and one of the key features of cucumber growth is that vegetative growth and reproductive growth simultaneously proceed over an extended period of time. It has been observed that at its first stage of fruit harvesting, the stems and leaves continue to grow together at the same time as the fruit is enlarged. Therefore, supply of nitrogen supply is necessary throughout the fruit harvesting period (Miyazaki 2000; Noda 2001). C. Sativus is inhabited by a variety of endophytes, which are extremely important for mineral need, particularly nitrogen, at different growth stages. Several studies have revealed that the most common nitrogen-fixing endophytic bacteria colonized by the cucumbers are Paenibacillus polymyxa, Burkholderia cepacia, and some Bacillus species, which were found to increase the availability of nitrogen for plants, and thus contribute to plant growth and development (Hao and Chen 2017). Researchers now focus on the plant growth promoting attributes of endophytic diazotrophs other than nitrogen fixation, so that single microbial inoculant can boost plant growth through different mechanisms, thereby decreasing the dependence on detrimental synthetic fertilizers. Therefore, application of endophytic bacteria as a

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potential biofertilizer is the most cost-­effective and eco-friendly approach for promoting the growth of this plant. 2.1.2 Phosphate Solubilization Phosphorus constitutes an indispensable macronutrient necessary for plant growth and development (Bieleski and Ferguson 1983). As a result of weathering and regular applications of phosphorus fertilizers, the agricultural soils have accumulated large quantity of phosphorus (Richardson 1994). However, soon after application, majority of inorganic soluble phosphate added as chemical fertilizers to the soil get speedily immobilized thus becoming unavailable to plants (Dey 1988). Several studies have revealed the potential of different fungi and bacteria to solubilize inorganic insoluble phosphates such as dicalcium phosphate, hydroxyapatite, tricalcium phosphate, and rock phosphate (Goldstein 1986). Most common bacterial strains found to solubilize phosphate are Bacillus, Pseudomonas, Burkholderia, Rhizobium, Achromobacter, Microccocus, Erwinia, Agrobacterium, and Flavobacterium. Among fungi, the potential phosphate solubilizers include Aspergillus tubingensis, Aspergillus fumigatus, Aspergillus terreus, Penicillium rugulosum, Penicillium radicum, Fusarium oxysporum, and Curvularia lunata. A lot of studies have been identified that inoculating the cucumber seeds with phosphate solubilizing bacteria such as Gluconacetobacter liquefaciens, Azospirillum lipoferum, Burkholderia cepacia resulted in considerable increase in phosphate ion concentration, root length, plant biomass (Wang et al. 2017). It has been reported that the inoculation of bacterial strain Burkholderia cepacia with potential phosphate solubilizing and phosphatase activity improves the production of cucumbers and is now being used as commercial biofertilizer (Wang et al. 2012, 2017; Hao and Chen 2017). Therefore, phosphate-­solubilizing microbes act as potential biofertilizers and play a central role in the acquisition of nutrients in cucumbers by facilitating the uptake of phosphorus. However, further research is desirable to genetically manipulate the phosphate-­solubilizing microbes, in order to introduce this trait in strains having other growth-promoting properties to gain maximum beneficial effects. 2.1.3 Phytohormone Production Phytohormone production is one of the key attributes of endophytes to improve plant growth and strengthen the stress tolerance of plants (Pieterse et al. 2009). A number of genes responsible for the production of indole acetic acid, gibberellins, and cytokinins have been found to be present in metagenome of endophytic microbial communities colonizing plants (Bhore et al. 2010; Zúñiga et al. 2013; Shahzad et  al. 2016). The bacterial species such as Azospirillum sp., Acinetobacter sp., Pseudomonas sp., Azotobacter sp., and Bacillus sp. have been found to synthesize phytohormones such as indolebutyric acid, indoleacetic acid, cytokinins,

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gibberellins, octadecanoids, and other compounds that mimic the role of phytohormones and support the plants in their survival. The endophytes may either produce or suppress phytohormone biosynthesis in order to benefit the host plants. For instance, Sphingomonas sp. promotes the growth of tomato plants by facilitating phytohormone synthesis, such as gibberellic acid and auxins (Khan et  al. 2014). Furthermore, endophytes may also promote the growth of the plants by suppressing the production of phytohormone like ethylene and protect the plant from inhibitory levels of ethylene. For instance, nine different types of gibberellic acids were developed by Cladosporium sp. in cucumber, which considerably enhanced the growth characteristics of cucumber plants. Furthermore, among the 24 enterobacteriaceae strains isolated from the seed of cucumber, 21 strains were auxin producers. While among the 56 Bacillus strains that were isolated from the cucumber seed endophytes, only 20 strains showed auxin production. In addition to auxin and gibberellin producing endophytes, the cucumber seed also colonize several endophytes which are responsible for cytokinin production. For example, the inoculation of cytokinin producing endophytic bacterial species such as Bacillus megaterium, Bacillus subtilis, Azotobacter chroococcum, Klebsiella pneumonia, and Proteus vulgaris were found to enhance cell division, cotyledon size, and biomass production in cucumber, thereby promoting plant growth and development (Hussain and Hasnain 2009). Even though most of the phytohormones secreted by bacteria proved to be beneficial on plant growth, the elevated levels of ethylene and abscisic acid produced by some bacteria have adverse effects and may inhibit seed germination and cause abnormal root growth, which seriously reduces the plant growth and production. Despite the fact about the negative role of ethylene, there are studies which demonstrate the positive role of ethylene in countering certain biotic/abiotic stresses (de Garcia Salamone et al. 2006). For instance, the ethylene synthesis by some microbes residing inside plant tissues encourages leaf abscission, opening of flowers and ripening of fruits. However, the beneficial or inhibitory effects of ethylene depend on its optimal or suboptimal levels. For instance, ethylene at lower concentrations increases the leaf area of mustard thereby increasing photosynthetic ability and plant growth (Khan 2005). Studies have revealed that plant growth-promoting rhizobacteria (PGPR) promote plant growth by producing 1-amino cyclopropane1-carboxylate (ACC) deaminase that helps in amending the levels of ethylene by converting the ACC into α-Ketobutyrate and ammonia (Glick et al. 1998; MarquezSantacruz et al. 2010). As a result, the presence of bacteria with ACC deaminase activity helps to protect the plants exposed to stress from inhibitory ethylene levels by making ACC inaccessible for transformation into ethylene. Evidence of the positive role of ACC deaminase synthesized by endophytic bacteria is provided from one of the study of Gamalero et al. (2008) on cucumber plants, who demonstrated that inoculating cucumber seeds with Pseudomonas putida and Gigaspora rosea protect these plants from abiotic and biotic stresses. In addition to stress tolerance, these strains promote overall root length, plant biomass and total projected leaf area of cucumber plants.

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2.1.4 Endophytes Promoted Siderophore Production Iron, an essential element for all life forms, acts as a cofactor for diverse enzymes and proteins (Leghari et al. 2016). It is widespread in earth’s crust, but its bioavailability is limited for the plants. Siderophores are the molecules produced by microbes that act to solubilize this unavailable iron because of having high iron affinity and capability to absorb it. The siderophores produced by endophytic microbes chelate the iron and convert it into the plant usable soluble complexes in the soil, and thus act as the means for plant to access this nutrient. It has been found that endophyte-assisted siderophore production helps plants to flourish well in soils that are low in iron and the plants lacking siderophore-producing microbes have been found to suffer from deficiency of the iron (Carvalhais et al. 2013). Researchers have postulated that rice microbiome offers the goldmine, full of genes encoding proteins responsible for siderophore production, siderophore reception and storage of iron, thus offering great potential for genetic engineering in sustainable agriculture (Sessitsch et al. 2012). Several siderophores producing endophytes have been reported to be in symbiotic association with the cucumber plants such as Pseudomonas putida and Azospirillum brasilense (Walter et al. 1994; Pii et al. 2015). Pii et al. (2015) revealed the presence of siderophore producing bacteria Azospirillum brasilense in cucumber, which helps cucumber plants to recover from iron deficiency. In addition, it was reported that Azospirillum that produced siderophores also serves to protect cucumber plants from phytopathogens by depriving them of iron, since they themselves bind to the bio-available iron and thereby end up in making iron unavailable for pathogens (Aznar et al. 2015; Pii et al. 2015). Khalaf and Raizada (2016) evaluated different strains of bacteria for siderophore activity and they found that most of the strains isolated from seed endophytes of cucumber which showed siderophore activity belong to enterobacteriaceae. However, Bacillus and Paenibacillus showed maximum siderophore activity among the isolated strains of cucumber seed endophytes.

2.2 Indirect Plant Growth Promotion The endophytes provide the indirect benefits to the colonizing plant mainly through their antagonistic effects toward plant pathogens, that is, biological control. 2.2.1 Biological Control The fungi and bacteria, the primary agents of the most plant diseases which cause substantial yield loss (Chakraborty and Newton 2011; Lo Presti et al. 2015), were originally controlled by chemicals that proved expensive and negatively affected both human health and the functioning of ecosystem (Anderson et  al. 2004;

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Suryanarayanan et al. 2016). However, the endophytes of the plant possess strong antagonistic properties against phytopathogens mediated by the cell-­wall degrading enzyme production, reducing stress levels of ethylene through ACC deaminase, siderophores, induction of plant-induced systemic resistance, antibiotic production and niche and resource competition (Compant et al. 2010; Santoyo et al. 2016). Endophytes can also trigger induced systemic resistance (ISR) that is recognized as a promising biological control tool leading to greater pathogenic tolerance. The interactions involving plants and beneficial microorganisms elicit an immune response in plants that look similar to the one caused by pathogens. Studies have reported that activating the plants immune response like ISR is the regular property of Pseudomonas and Bacillus species, although these groups do not possess them exclusively (Yi et al. 2013). Endophytes are often found to induce systemic resistance acquired (SAR) similar to that induced by necrotrophic pathogens that protect the plant against a wide range of phytopathogens (Tuzun 1991; Hammerschmidt 2009). Recently, agricultural research mainly focused on approaches wherein endophytes could be exploited as biocontrol agents in order to avoid the hazardous effect to the environment caused by the continuous application of pesticides. Several endophytes have been found to successfully emerge for the management of a broad range of plant pathogens and are known to produce numerous secondary metabolites. This chapter aims to highlight the importance of many endophytes as biological control agents to contain many plant pathogens for the sustainable crop management. Endophytic bacteria colonized in the endosphere and rhizosphere as well as in vascular tissues of the cucumber have been to be effective against many pathogens such as Fusarium oxysporum and Verticillium sp. Fusarium wilt induced by the fungal pathogen Fusarium oxysporum is among the serious constraints on the production of cucumber worldwide. A few strategies were used to control the wilt causing pathogenic fungi Fusarium oxysporum, including soil solarization, fungicide treatment as well as biocontrol agents. Studies have demonstrated that cucumber plants when inoculated with Bacillus subtilis and Paenibacillus polymyxa showed resistance against Fusarium oxysporum wilt disease (Zhang et al. 2008). In another study, it was found that the fusarium wilt was significantly reduced (49%) after cucumbers were inoculated with Bacillus subtilis SQR 9.This strain of Bacillus was able to sustain well in the rhizosphere of cucumber and decreased the expansion of F. oxysporum in the rhizosphere of cucumber, thus protecting the host from this pathogen. Another worst disease, which remarkably reduces the yield of the cucumbers, is the damping off caused by Pythium aphanidermatum. Priyanka et al. (2019) found that Pseudomonas aeruginosa and Achromobacter denitrificans significantly reduced the growth of pathogen. However, Pseudomonas aeruginosa not only caused inhibition of the pathogen, but also increased the yield significantly and thus could be employed as potential endophytic bio-inoculant with adequate biosafety measures. Within greenhouse conditions where cucumber seeds were inoculated with entophytic fungi, galls produced by the pathogen Meloidogyne incognita were significantly reduced and thus proved to be an efficient method for the control of

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plant parasite nematode. The most effective strains against galls were Fusarium, Paecilomyces, Chaetomium, Trichoderma, Acremonium, and Phyllosticta. The colonization of these strains was also found to be localized to both lower as well as upper parts of the plants (Yan et al. 2011). Based on the results, they concluded that Chaetomium Ch1001 have the highest potential to reduce galls and thus could be considered as an important biocontrol for M. incognita, which is the causative agents of galls in cucumber plants. Furthermore, the volatile antimicrobial compounds produced by endophytes also act as resistance means against many fungal pathogens. For instance, cucumber plants when inoculated with bacterial inoculum able to produce VOCs such as 3-pentanol and 2-butanone develops resistance against pathogens Pseudomonas syringae (causative agent for bacterial angular leaf spot) and Myzus persicae (phloem sucking aphid). Despite having huge potential and impact on agriculture, the actual mechanisms behind such biocontrol traits of microbes are yet to be identified. Some endophytic bacteria that have been isolated from Cucumis sativus are shown in Table 16.1.

3 Endophyte-Assisted Phytoremediation The increased industrialization lead to extensive chemical load on environment, by adding harmful organic and inorganic chemicals such as pesticides, heavy metals, petroleum hydrocarbons, polycyclic aromatic hydrocarbons (Meagher 2000; Ma et  al. 2011). To overcome these environmental complications, cost-efficient and reliable approaches are essential for removing such chemicals from the environment, especially soil. The biological method such as endophyte-assisted phytoremediation offers the feasible way for soil remediation by in situ degradation or immobilization of these chemicals in the soil or accumulating them into plant tissues. Endophytes enhance phytoremediation through the production of functional proteins and enzymes such as catalases, dehalogenases, glutathione S-transferases, cytochrome P450 monooxygenases, hydrolases, peroxidases, laccases, and polyphenol peroxidases that directly participate in the detoxification, degradation, deposition, and stabilization of mixed pollutants (Schwitzguébel 2017; Ali et al. 2019). The bacterial endophytes are believed to be the main participants in the degradation of organic pollutants (Etesami 2018). Studies have revealed the presence of phe, tol, and alk gene cassettes in Aureobasidium pullulans, which is an important colonizer in cucumbers. This gene cassette has a role in cucumber tolerance to lead and cadmium toxicity by regulating ROS systems, phytohormone, and enzyme production. Moreover, there are enough number of studies reporting the existence of refined system in cucumber plants for detoxification, tolerance, and phytoremediation of heavy metals. Studies have reported that endophytes assist cucumber plant survival under heavy metal toxicity by activating plasma membrane ATPase activity, H+/Pb2+, H+/Ni2+, H+/Mn2+

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Table 16.1  Endophytic bacteria isolated from Cucumis sativus Group Firmicutes

Isolated from plant part Seed

Bacteria

Seed

Enterobacteria

Seed

Proteobacteria

Seed

Actinobacteria Bacteroidetes

Seed Leaf

Actinobacteria

Leaf

Firmicutes

Leaf

Proteobacteria

Leaf

Dothideomycetes Stem

Endophyte Bacillus sp. Paenibacillus sp. Pediococcus sp. Ochrobactrum pseudintermedium Pseudomonas putida Serratia marcescens Pseudomonas sp. Pantoea agglomerans Microbacterium sp. Hymenobacter sp. Nocardioides sp. Flavobacterium sp. Deinococcus sp. Deinococcus thermus Pseudoclavibacter sp. Phycicoccus sp. Nocardioides sp. Microbacterium sp. Frigoribacterium sp. Lysinimonas sp. Curtobacterium sp. Brachybacterium sp. Arthrobacter sp. Aeromicrobium sp. Paenibacillus sp. Bacillus sp. Variovorax sp. Sphingomonas sp. Rhizobium sp. Xanthomonas sp. Pseudomonas sp. Methylobacterium sp. Massilia sp. Aureimonas sp. Agrobacterium sp. Aureobasidium pullulans

Reference Yan et al. (2011) Khalaf and Raizada (2016)

Mahmood et al. (2019)

Ali et al. (2019) (continued)

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Table 16.1 (continued) Group Ascomycetes

Ascomycetes

Isolated from plant part Roots

Endophyte Fusarium oxysporum Chaetomium sp. Coniochaeta lignaria Penicillium sp. Talaromyces sp. .Colletotrichum sp. Root, stem, and leaf Acremonium sp. Actinomucor sp. Aureobasidium sp. Aspergillus sp. Cercospora sp. Chaetomium sp. Cladosporium sp. Colletotrichum sp. Curvularia sp. Fusarium sp. Humicola sp. Paecilomyces sp. Phyllosticta sp. Stagonospora sp. Trichoderma sp. Aureobasidium sp.

Reference Kim et al. (2006)

Yan et al. (2011)

antiporters, and heat shock proteins (HSPs) (Migocka and Klobus 2007; JanickaRussak et al. 2012; Jia-Wen et al. 2013). Taking in view the above fact, it can be concluded that endophyte-assisted phytoremediation offers promising technology to diminish pollutant residues in mixed pollutant soils.

4 Endophyte-Conferred Abiotic Stress Tolerance Plants being static cannot escape from wide range of environmental stresses to which they get exposed. Extreme conditions sidetracked from the optimum levels such as low or high temperature, drought, salt stress and acidic conditions, nutrient stress, heavy metal stress, and starvation are the chief abiotic stresses that restrict plant growth and development (Chaves and Oliveira 2004). All these abiotic stresses in one way or the other interfere with the normal physiological pattern of plants by causing inhibition of photosynthesis, decrease in germination rates, loss of membrane integrity, increased generation of reactive oxygen species, suppresses root growth, extensive denaturation, and aggregation of cellular proteins, inhibition of enzymatic reactions, which if left unchecked, lead to plant death (Greenberg et al. 2008; Munns and Tester 2008; Xu et al. 2016). The plant endophytes come up with the symbiotically conferred stress tolerance by either activating stress response

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systems of the hosts soon after exposure to stress or by avoiding the impacts of the stress impact by directing the plants to synthesize anti-stress biochemicals (Waqas et al. 2012). The cucumber plants in the presence of endophytes were able to survive cold stress by increasing antioxidant activity and decreasing lipid damage by negotiating the reduced glutathione, catalase, peroxidase, and polyphenol oxidase activities (Waqas et al. 2012). Furthermore, inoculating cucumber plants with Phoma glomerata sp. and Penicillium sp. increase their tolerance to NaCl and PEG induced salt toxicity and drought compared to the control plants. Endophyte-inoculated cucumber plants were found to adjust stress levels by controlling the proportions of stress hormones such as abscisic acid, salicylic acid, and jasmonic acid compared to non-­ inoculated plants. Also, these inoculants were able to increase the acquisition of essential nutrients such as calcium, potassium, magnesium, thereby increasing the plant biomass and other growth parameters (Waqas et al. 2012). Thus, endophytes have the potential to act as protecting agents in agro-ecosystems under extreme abiotic stress environments. Although the mechanisms underlying endophyte conferred abiotic stress resistance have been explicitly elucidated, it is not clear that how endophytes sense physiological changes, regulate the gene expression, and help the plants to adapt to the new environment.

5 Conclusions Cucumber endophytes can be explored as potential bio-inoculants that could provide an eco-friendly approach to improve plant growth and yield and concurrently circumvent the excessive use of hazardous fungicides and chemical fertilizers. In near future, beneficial effects of cucumber endophytic associations are expected to elevate with subsequent advancement in recombinant technology, which can decipher the molecular mechanisms directing functional diversity of endophytic microbiota and assist apprehending its full potential in enriching the cucumber crop.

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Chapter 17

Nanoscience in Agricultural Steadiness Atin Kumar , Satendra Kumar, Rachna Juyal, Himani Sharma, and Mamta Bisht

Abstract Nanoscience is a potential area of multidisciplinary research and enormous activities are carried out in industries, including medical, pharmaceuticals, technology, and farming sector. Nanotechnology has a broad range of possible applications in varied fields for the betterment of humans. Due to increasing environmental effects, a significant section of the population in emerging nations experience daily food insecurity, in contrast to the industrialized world where there is an abundance of food. A key agricultural management process is overseen by nanotechnology, primarily due to its microscopic size. Additionally, there are a large number of potential advantages such as enhancement in food quality and its assurance reducing the need of inputs for crop production, and improving the absorption of nutrients taken from the soil in the range of nanoscale, which has created the usage of nanotechnology a very cumbersome process. Natural resources employed in agriculture and food processing industries face difficulties related to vulnerability, stability, public health, and standard of living. Nanomaterials in agriculture sector are intended to lower down the amount of chemicals distributed in soil particles, reduce losses of beneficial nutrients from fertilizers given to crops, and boost output by preventing pest attack and increase nutrient uptake capacity of crops from the soil. With revolutionary nano tools for the control of quick diagnostic techniques, boosting plant nutrient absorption, and other uses, nanotechnology has the potential to completely reform the agriculture sector on a large scale. Specific usage of nanoparticles are made in the form of nanofertilizers and nanopesticides to check the quality of final product obtained and also to determine the quantity of nutrients already present in the soil in order to raise the productivity levels without causing A. Kumar (*) · R. Juyal · H. Sharma School of Agriculture, Uttaranchal University, Dehradun, Uttarakhand, India S. Kumar Department of Soil Science & Agricultural Chemistry, Sardar Vallabhbhai Patel University of Agriculture & Technology, Meerut, Uttar Pradesh, India M. Bisht Department of Chemistry, School of Applied and Life Sciences, Uttaranchal University, Dehradun, Uttarakhand, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_17

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any harmful effect on the soil, water, and to safeguard agricultural crops from a diversity of insect pests that attack on the crops and to reduce the losses caused by biotic factors are among the considerable objectives of using nanotechnology in agriculture. Nanotechnology may operate as sensing devices to check the condition of the soil in agricultural fields, ensuring the health of the crops. Presenlty, consideration has been paid to how nanotechnology is being applied to the food and agricultural industries. This chapter highlights numerous “nano-enabled agricultural” fields, their applicability, and possible future study domains in light of the advantages mentioned earlier. Keywords  Nanotechnology · Agriculture · Fertilizers · Management · Bio-remediation

1 Introduction Agriculture has always been the most significant and reliable sector because it produces and supplies the necessary constituents for food and feed sector. Population of world is increasing at a steady rate with the simultaneous increase in availability of natural resources (such as production land, water, and soil), so it is necessary for agriculture to develop in a way that is economically sustainable, environmentally friendly, and profitable. This amendment is a pre-requisite for accomplishing many targets in the agriculture sector in the coming future (Johnston and Mellor 1961; Mukhopadhyay 2014). Economic expansion has a noticeable impact on agricultural nutrient balances, and because of this assumption, emerging countries should place a high priority on improving soil fertility (Campbell et al. 2014; Hakeem et al. 2021; Dar et al. 2022). The technical advancement in agriculture sector is a major need in the present time to get rid of rising hunger and food scarcity of the ever increasing population. Therefore, in order to advance agriculture, we should make one brave move. In this planet, the majority of people live in rural areas where agriculture expansion has not been very successful and are dispersed throughout the world. The most important concern nowadays is to build in order to combat poverty in agriculture and the food-acquiring nutritional process. Therefore, new technology that is specifically focused on improving agricultural production should be embraced (Yunlong and Smit 1994). Stability of food and nutrition has recently become an integral part of new knowledge. In order to achieve certain target-oriented goals, it is necessary to record how the development of farming sector is dependent on various conditions such as social integration, soil-health conditions, energy requirements, climate changes, and various natural resources. As a result, sustainable agriculture improves people’s ability to actually minimize food insecurity and malnutrition. To recover the damage caused by faulty agricultural practices, environmental sustainability is critical (Thornhill et al. 2016).

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The boundless branches of nanotechnology in this twenty-first century are making a marked influence on the global financial system and various socioeconomic units. It addresses the material’s physical, chemical, and biological aspects. Nanomaterial, as stated by US EPA (US Environmental Protection Agency), is a material that constitutes particles which have, at minimum, one of its elements in the size scale from 1 to 100 nm. Its capacity to generate and/or manipulate particles at this scale leads to the formation of inventive and original properties that can be used to avoid a wide range of technical and socioeconomic inequalities. Developing nations like China have hurriedly completed their research on the delivery of agricultural pesticides using nanotechnology, and in the following 5–10 years, field applications are anticipated. However, a number of elements, including market requirements, profitability, environmental advantages, risk analysis, and organization structure in the context of other alternative ones, are vital to their success. Nanotechnology will have a prosperous and hopeful future if emphasis will be given on latest research and innovations that are required in agriculture. It provides a wide range of opportunities in different disciplines such as health and pharmaceutical departments, electronic department and agriculture sector. The potential exploitation and advantages derived by using nanotechnology are immeasurable. The current global population is nearly seven billion and 50% of that population resides in Asian countries only. A relatively large proportion of this population that live in developing countries suffers from daily food scarcities which can lead to various environmental consequences or political disturbances, while in the developed and underdeveloped countries world, there is abundant food production. The aim of various nanoscience-based technologies in numerous developing countries is to breed the crops for drought and pest resistance, which also amplify the productivity. It has been widely reported that nanotechnology has the power to transform the fields of medical services, textile products, materials, ICT, and energy. Nanotechnology in food and agriculture sector is gaining importance now a days. While most of the fund is invested in rich countries, scientific research have been given an importance at potential agricultural, food, and water safety implementations that have created a dynamic impression on rural regions of under-developed countries (Campbell et al. 2014). By 2050, expected world’s population is about ten billion, and the demand for food is expected to rise by 50%, primarily in low-income nations. These projections are from the Food and Agricultural Organization (FAO). Currently, there are 815 million impoverished people, and by 2050, two billion more people will be added in the category of mal nutrition. Due to population explosion, climate variability, environmental damage, and requirement of clean water and renewable energy sources, global production and supply of food are in extreme danger. The global food production systems must make thoughtful reforms in light of this circumstance. The current agricultural system consumes an excessive amount of resources. More than three billion tonnes of crops are produced annually, needing 187 million tonnes of fertilizer, four million tonnes of insecticides, 2.7 trillion cubic meters water (which accounts for 70% of all freshwater use throughout the world), and higher than two quadrillion BTU of energy range. As a result, the current agricultural farming

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practices are ineffective for reaching the SDGs. Because of this, sustainable agriculture is a crucial industry for reaching SDG 02, “zero hunger,” which is one of the United Nations’ 17 sustainable development goals. Agrochemicals of many kinds, including fungicides, insecticides, herbicides, rodenticides, fertilizers, and plant growth regulators, are employed in farming to boost crop yield, quality, and productivity. Agrochemicals also reduce crop damage and protect plants from diseases (Aktar et al. 2009). However, only 0.1% of the distributed agrochemicals reaches the relevant plant portions and are effective against the intended disease. This is a very low bioavailability (Camara et al. 2019) and the majority stays in the environments and plants nonspecific target sites. Agrochemicals frequently endanger living creatures through degrading, volatilizing, photolyzing, and absorbing through residual effects. As a result, using nanotechnology to agriculture opens up new opportunities for lowering the toxicity of agrochemicals to human health by reducing their aftereffects and reducing environmental pollution by decreasing their loss that occur in various forms such as volatilization loss, leaching of toxic agrochemicals, and some drainage problems. These nano-agrochemicals also enhance nutrient absorption capacity of crops, their solubility, and viscosity, and are an effective substitute for managing pests and diseases that leads to various impacts on crops. However, depending on the particle’s chemical characteristics, its size, shape, and dose, metal nanoparticles may have either beneficial or harmful effects on plants (Sangeetha et al. 2017). Moreover, such nanoparticles get interacted with plants, soil, and air. These nanoparticles are released into the environment due to their static nature which ultimately causes negative impacts on public health; thus, the only alternative to combat these negative impacts is by controlling and managing inputs precisely. Therefore, biocompatibility, environmental friendliness, and adaptability in the biological system should be met by nanomaterials for agricultural purpose before their utilization. The expansion of nanomaterial engineering employing eco-friendly materials and environmentally acceptable green synthesis techniques provides a vast area necessary for the viability of agricultural development (Pandey 2018; Sangeetha et al. 2017). The current state of agriculture is beset by a number of peculiar problems, including chronic illnesses, elevated temperature, high salinities, heavy metal contamination, nutrient imbalances, and environmental degradation. Sustainable eco-friendly smart agriculture has been promoted by the use of nanotechnology. Increasing the productivity of agricultural farms will be made possible. When wireless networking and sensor-based disease or insect tracking systems along with irrigation monitoring systems are employed in the fields, the overall productivity of agricultural farms is definitely increased. The most important priority nowadays is to reduce agricultural hardship and also making it possible for everyone to get quality and nutritious food. As a result, it should be mandatory to implement new technology that firmly focuses on improving agricultural production (Yunlong and Smit 1994). Food and nutritional security have recently become an integral part of the emerging knowledge. Crops produced in agriculture depend on different factors such as social inclusion, health of soil, global climate changes, energy, different ecosystem processes, various natural resources, and good

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sovereignty and must also be able to meet specific target-oriented objectives. Adopting sustainable agriculture practices is crucial to raise the possibility that people will be able to end poverty and food insecurity. Agriculture is reviving day by day by implementation of eco-friendly practices, hence environmental sustainability and involvement in the food chain ecosystem should always be kept in mind for better agricultural food production (Thornhill et al. 2016). In modern agriculture, sustainable production and increased efficiency are impossible without using various agrochemicals such as pesticides and fertilizers. However, each agrochemical being used faces some difficulties such as increased levels of impurities in water or harmful left-overs of food products that poses danger to human beings and creates disturbances in environmental systems; thus, the precise management and self-regulation of inputs required helps to lower down these negative consequences (Kah 2015). Applications of high-tech technologies in agriculture with engineered nano tools have proved to be an excellent strategy for bringing a transformation in traditionally used agricultural methods of crop production, and therefore minimize or completely eradicate the negative impacts of modern agricultural techniques on the ecology as well as to intensify both the quality and quantity of produce thus obtained (Sekhon 2014; Liu and Lal 2015).

2 Applications of Nanotechnology in Agriculture Different applications of nanotechnology in agriculture sector are the foundation stones for providing food, feed, fiber, fire, and fuels (4 Fs). In the coming future, need for food will increase considerably while natural resources such as land, water, and soil fertility are limited up to a certain level. The cost of production by using chemical-based inputs like fertilizers and pesticides is foreseen to be increased at an alleviating pace due to only few sources of fuels such as natural gas and petroleum. To overcome these hindrances, precision farming is a better alternative to decrease production costs and to boost agricultural production. Through betterment in nanotechnologies, various state-of-the-art approaches are accessible for upgrading precision farming techniques that will allow take into consideration the precise control at nanometer scale. Agri-nanotechnology has the competency to modify the agricultural practices. Nanoparticles of your own needs are developed by using different physical and chemical procedures. The biogenetic manufacturing of nanoparticles is gaining huge attentiveness due to easy processes of manufacturing and their originality. Biodiversity of bacterium and autotrophic organisms (plants) have the power to manufacture nanoparticles or aid in the process of manufacturing of nanoparticles. Execution of smart delivery system based on nanoparticles and nanosensors controls the discharge of agrochemicals and helps in site-specific distribution of different macromolecules required for maintaining plant disease resistance, efficient nutrient performance and make the plant to develop defense strategy without disturbing the natural conditions. Nanoparticle-based plant alteration has the capability

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for alteration at genetic levels of plant development. Nanotechnology has the ability to transform the agriculture and food sectors with latest techniques at the molecular level for the control of diseases, faster disease diagnosis, enhancing the efficiency of plants to uptake nutrients from the soil, etc. Otherwise, nanobiotechnology can increase our knowledge of the life cycle of different crops and hence can dramatically increase productions or nutritional contents, as well as creating improved techniques to keep an eye on the varied weather conditions (Raliya et al. 2013). Latest developments in technologies for agriculture have been the most important contributor in bringing a change in conventional agriculture. Among all recent technological inventions, nanotechnology has a pronounced place in reshaping the agricultural practices. The development of nanoparticles can open a gateway for improvements in plant biotechnology. For obtaining agricultural sustainability, nanotechnology has a considerable impact as it raises the overall productivity by proper nutrient management and assessment of water quality available to plants (Gruere 2012; Mukhopadhyay 2014; Prasad et al. 2014). Following are the major implications of nanotechnology for sustainable agriculture:

2.1 Nanofertilizers Although agricultural fertilizers are still not developed by the big chemical corporations, nanofertilizers have been widely accessible on the market for the past 10 years. Nanofertilizers may include nanoscale amounts of titanium dioxide, silica, iron, Zn, Cd, Se, and Zn. They should also provide controlled release and enhance the quality of their product. For agricultural productivity, extensive research on the absorption, biological function, and toxicity of a few metal oxide nanoparticles (NPs), including Al2O3, TiO2, CeO2, FeO, and ZnONPs, has been conducted in the last 10 years (Dimkpa 2014; Zhang et al. 2016). Given the alkaline character of the soils, a zinc deficit has been identified as one of the major constraints restricting agricultural productivity. Smart agriculture is a way to highlight short- and long-­ term modifications in the phase of climate change in the twenty-first century and acts as a connecting link to others (Helar and Chavan 2015). It aims to assist the nations and other operational elements in shielding the important and only required agricultural management practices (Kandasamy and Prema 2015). Research on the growth of resources to a nanometric scale and their innate characteristics has received a lot of attention recently. Due to their low toxicity, bioactivity, and distinctive visual features, these NPs have also drawn interest in biological investigations. When nanoscale particles are combined, physiological tests assessing the presence or activity of particular chemicals become easy to understand, more precise, and have wide range of adaptability (Vidotti et al. 2011; Kandasamy and Prema 2015). Thus, using nanoscale particles has many benefits over using conventional methods.

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2.2 Nanopesticides Future research is needed in the use of nanoparticles for food production and plant protection. Dominance of insect pests is the major problem in agricultural fields, NPs has a crucial role in the management of both insect pests and host infections (Khot et  al. 2012). A new pesticide formulation with nanoencapsulation offers improved absorption, selectivity, transparency, and persistence with progressive release characteristics (Bhattacharyya et al. 2016). These advantages are primarily accomplished by either preventing the encapsulated active components from deterioration losses or extending the duration of their pest control efficiency. Pesticide dose and their toxicological effects on humans have decreased as a result of the development of nano-encapsulated pesticides, which is environmentally friendly for precision farming (Nuruzzaman et  al. 2016) Therefore, developing nontoxic and effective pesticide functionality to boost the world’s food supply while minimizing adverse environmental effects on ecosystems is necessary (De Oliveira et al. 2014; Kah and Hofmann 2014; Bhattacharyya et al. 2016; Grillo et al. 2016).

2.3 Systems for Delivering Nutrients and Plant Hormones Using Nanotechnology It is indeed easier to use agricultural resources such as water, fertilizers, and other chemicals at the nanoscale level. It uses nanomaterials, global positioning systems (GPS), and satellite photography of fields to identify crop pests and other conditions like famine. Nanosensors that are established in the agricultural fields can possibly identify the presence of any particular plant virus and the concentration of nutrients present in the soil. Additionally, they reduce environmental degradation caused by excessive fertilizer use. Thus, widespread usage of nanofertilizers has been noticed these days. Nano-processing and nano-barcoding may be utilized to determine the quality of agricultural produce. The control of plant hormones such as auxin, which has a role in proper root development and seedling morphology, is studied by nanotechnocrates. There now exist many nanosensors which respond to the activity of auxin. This advance in auxin research will enable researchers to better understand how plant roots adapt according to the microclimate, especially in poor soils (McLamore et al. 2010).

2.4 Nanotechnology for Organic Farming Increasing productivity (i.e., crop yields) without using much input (i.e., fertilizers, pesticides, herbicides, and many other factors) via environmental monitoring systems and targeted intervention strategies has been a long-term objective of organic

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farming. Computers, GPS, and latest remote sensing technologies are used in organic farming to assess geographically limited climatic conditions, identifying if crops are growing as efficiently as possible or precisely pinpointing both type and extent of troubles faced by the crops. It is possible to fine-tune sowing, fertilizer, chemical, and water use to reduce production costs and maybe enhance productivity, all of which are advantageous to the farmer. Collected data can be used to evaluate soil characteristics and crop growth. Additionally, precision farming can assist in minimizing environmental pollution by limiting agricultural waste.

2.5 Nanoherbicides The simplest method for getting rid of weeds is to remove their seed banks from the soil and preventing their growth when the soil and weather conditions are conducive for their establishment. Nanoherbicides, which are exceptionally small, are capable of being mixed in with the soil, eliminate weeds without leaving behind any hazardous effects, and restrict the growth of weeds that have eventually become resistant to many traditional herbicides. Weeds are able to persist and reproduce through deep roots and tubers in the ground. Hand-pulling of weeds from diseased fields can cause them to spread to unaffected areas. The usage of nano application is same whether it results from a nano-sized active ingredient or from the synthesis of a nano-sized formulation by affixing an additive. Herbicide will only be used when necessary in accordance with the conditions of the agricultural field and the efficiency of herbicides is increased when active ingredient is supplemented with a smart delivery system. In agricultural fields where there is enormous weed population, total production is actually reduced to a greater extent. The use of nanotechnology to increase herbicide effectiveness could lead to increased crop output without having any negative impact on agricultural laborers who are required to physically remove weeds if herbicide spraying is avoided.

3 Future Advantages of Using Nanotechnology in Agriculture There is currently a research and development pathway that could improve agriculture’s productivity, boost yields and quality of product, and consequently enhance nutritional content. In particular, the development of novel nanopesticides and nanofertilizers has drawn significant attention to the uses and advantages of nanotechnology in the agricultural industry. Nanosensors, nano-chemicals, soilcleaning nanoparticles, etc., are all being utilized and evaluated in advanced countries. Nanosensors, which are able to detect toxic compounds, viruses, and bacteria, and nano-delivery systems, which helps in precisely supplying

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micronutrients at the appropriate time and to the appropriate plant part, are just a few of the applications that are anticipated for use in food and agriculture. The enormous potential of agricultural and food nanotechnology in underdeveloped nations has been the subject of numerous reports. Rising nanotechnology applications indicates the low input utilization efficiency in agriculture as well as the stress caused by drought and increased soil temperatures. Nanoscale agrochemicals can boost productivity and decrease waste by reducing it. Increased yields as well as water conservation may also be achieved by using nanoporous materials that can absorb water and gradually release it when needed. The application of nanotechnology in agriculture has enormously increased in recent years. According to Barik et  al. (2008), more demanding applications for nanoparticles include bio-remediation of polluted soil and water, and antifungals on textiles. Another domain where nanomaterials can be very useful in agriculture is photocatalysis. Numerous studies have been conducted on various nanostructures of zinc oxide (ZnO) and titanium dioxide (TiO2) as photocatalysts. Nanopesticides contain many toxic chemicals that are converted into comparatively nontoxic components such as CO2, N2, and H2O.

4 Conclusion The sole industry that produces food for people using proven technologies is agriculture. Therefore, having current agricultural knowledge is required. Despite having certain relative advantages in the agricultural industry, developing nations continue to face challenges due to the low priority placed on food goods. Although there is a wealth of information regarding specific nanoparticles, the toxic effect of many NPs is still not well understood, which limits the applications of these materials owing to the unavailability of understanding of risk evaluations and impacts on human health. The utilization of this technology requires the creation of a comprehensive database and international cooperation for its regulation and legislation. Nanotechnology applications have the potential to transform agriculture by better management of inputs for plant production. Researchers in nanotechnology can provide a lot of advantage to society through different applications in agriculture and food systems. Introduction of any new technology always has an ethical responsibility to make people aware about the unforeseen risks that may come along with the tremendous positive potential. Spreading awareness among the people about benefits and challenges of nanotechnology will lead to better acceptance among the public for this emerging technology. In the coming years, nanotechnology applications will be made possible by quick testing of technologies and biosensors relating to the management of pest infestations and prevent contamination of agricultural goods. The use of nanotechnology in agriculture is still at its initial stage, and many more opportunities are anticipated in the forthcoming decades. For a wide variety of biological applications, nanoparticles offer an incredibly beautiful framework. It encourages more investigators to work on future breakthroughs in the fields of

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electrochemical sensing applications, bioimaging devices, medicine, healthcare, and agriculture since this gives a straightforward strategy for the manufacture of nanoparticles. Additionally, recent analysis seeks to improve the effectiveness, with which plants use water, pesticides, and fertilizers, as well as to minimize pollution and enhance the agriculture’s long-term sustainability. Some applications of nanotechnology are almost ready for commercial production, including nanosensors and nanoscale varnishes to remove relatively thick, more inefficient polymer coatings that minimize corrosion, nanosensors for aquatic toxin sensing, nanoscale biopolymers for enhanced detoxification and reprocessing of heavy metals, nanostructured metals that deteriorate potentially dangerous hydrocarbons at room temperature, smart particles for environmental monitoring systems and purification, and nanoparticles as an innovative photocatalytic activity. Thus, agriculture and pest management will soon undergo a revolution, thanks to nanotechnology. The green revolution will be accelerated over the following two decades. Insecticides, pesticides, and insect repellents are made possible by nanoparticles. As it can be applied to areas such as sustainable and highquality agriculture and the improved and nutrient-dense food for people, nanotechnology has a significant opportunity in the agricultural sector. This can improve the overall quality of people. This technology is now considered to be the future of every nation around the globe. Any new technology that is implemented must be carefully evaluated for any potential unexpected circumstances that might arise from its bright prospective. However, developing skilled future labor for this new innovation is also crucial for a state’s economy. As a result, it is crucial to educate the general public about its advantages as soon as possible, as this will greatly enhance awareness and spur the development of new technologies in all fields. For several reasons, including the unfavorable public perception of genetically modified (GM) crops, the need for highly skilled personnel in government agricultural research and technology divisions, and the absence of a robust framework, digital equipment, and reducing advancements in technology, the bigger picture of nanoscience in agriculture is undecided. A very bright and successful future will be right over the horizon if we can significantly eliminate the uneven barrier that persists today within society, the general public, and the advancement of scientific concepts. The public’s reaction to genetically modified crops, the lack of many of the required skills in awareness raising research groups, and other factors make the future of nanotechnology questionable. The strong barrier between the social and natural sciences must be destroyed, and if we are successful in doing so, we may be able to create a socio-technological future that is more acceptable and equitable.

References Aktar MW, Sengupta D, Chowdhury A (2009) Impact of pesticides use in agriculture: their benefits hazards. Interdiscip Toxicol 2(1):1–12

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Barik TK, Sahu B, Swain V (2008) Nanosilica-from medicine to pest control. Parasitol Res 103:253–258 Bhattacharyya A, Duraisamy P, Govindarajan M, Buhroo AA, Prasad R (2016) Nano-biofungicides: emerging trend in insect pest control. In: Prasad R (ed) Advances and applications through fungal nanobiotechnology. Springer International Publishing, Cham, pp 307–319 Camara M, Jamil NR, Abdullah AFB (2019) Impact of land uses on water quality in Malaysia: a review. Ecol Process 8(10) Campbell BM, Thornton P, Zougmoré R, van Asten P, Lipper L (2014) Sustainable intensification: what is its role in climate smart agriculture? Curr Opin Environ Sustain 8:39–43 Dar GH, Mehmood MA, Bhat RA, Hakeem KR (2022) Microbiota and biofertilizers, Vol 2: Ecofriendly tools for reclamation of degraded soil environs. Springer, Singapore. https://doi. org/10.1007/978-­3-­030-­61010-­4 De Oliveira JL, Campos EV, Bakshi M, Abhilash PC, Fraceto LF (2014) Application of nanotechnology for the encapsulation of botanical insecticides for sustainable agriculture: prospects and promises. Biotechnol Adv 32:1550–1561 Dimkpa CO (2014) Can nanotechnology deliver the promised benefits without negatively impacting soil microbial life? J Basic Microbiol 54:889–904 Grillo R, Abhilash PC, Fraceto LF (2016) Nanotechnology applied to bio-encapsulation of pesticides. J Nanosci Nanotechnol 16:1231–1234 Gruere GP (2012) Implications of nanotechnology growth in food and agriculture in OECD countries. Food Policy 37:191–198 Hakeem KR, Dar GH, Mehmood MA, Bhat RA (2021) Microbiota and biofertilizers: a sustainable continuum for plant and soil health. Springer, Singapore. https://doi. org/10.1007/978-­3-­030-­48771-­3 Helar G, Chavan A (2015) Synthesis, characterization and stability of gold nanoparticles using the fungus Fusarium oxysporum and its impact on seed. Int J Recent Sci Res 6:3181–3318 Johnston BF, Mellor JW (1961) The role of agriculture in economic development. Am Econ Rev 51:566–593 Kah M (2015) Nanopesticides and nanofertilizers: emerging contaminants or opportunities for risk mitigation? Front Chem 3:64 Kah M, Hofmann T (2014) Nanopesticides research: current trends and future priorities. Environ Int 63:224–235 Kandasamy S, Prema RS (2015) Methods of synthesis of nano particles and its applications. J Chem Pharm Res 7:278–285 Khot LR, Sankaran S, Maja JM, Ehsani R, Schuster EW (2012) Applications of nanomaterials in agricultural production and crop protection: a review. Crop Prot 35:64–70 Liu R, Lal R (2015) Potentials of engineered nanoparticles as fertilizers for increasing agronomic productions. Sci Total Environ 514:131–139 McLamore ES, Mohanty S, Shi J, Claussen J, Jedlicka SS, Rickus JL, Porterfield DM (2010) A self-referencing glutamate biosensor for measuring real time neuronal glutamate flux. J Neurosci Methods 189:14–22 Mukhopadhyay SS (2014) Nanotechnology in agriculture: prospects and constraints. Nanotechnol Sci Appl 7:63–71 Nuruzzaman M, Rahman MM, Liu Y, Naidu R (2016) Nanoencapsulation, nano-huard for pesticides: a new window for safe application. J Agric Food Chem 64:1447–1483 Pandey G (2018) Challenges and future prospects of agri-nanotechnology for sustainable agriculture in India. Environ Technol Innov 11:299–307 Prasad R, Kumar V, Prasad KS (2014) Nanotechnology in sustainable agriculture: present concerns and future aspects. Afr J Biotechnol 13(6):705 Raliya R, Tarafdar JC, Gulecha K, Choudhary K, Ram R, Mal P et al (2013) Scope of nanoscience and nanotechnology in agriculture. J Appl Biol Biotechnol 1(3):041–044

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Sangeetha J, Thangadurai D, Hospet R, Purushotham P, Karekalammanavar G, Mundaragi AC, David M, Shinge MR, Thimmappa SC, Prasad R, Harish ER (2017) Agricultural nanotechnology: concepts, benefits, and risks. Nanotechnology:1–17 Sekhon BS (2014) Nanotechnology in agri-food production: an overview. Nanotechnol Sci Appl 7:31–53 Thornhill S, Vargyas E, Fitzgerald T, Chisholm N (2016) Household food security and biofuel feedstock production in rural Mozambique and Tanzania. Food Secur 8:953–971 Vidotti M, Carvalhal RF, Mendes RK, Ferreira DCM, Kubota LT (2011) Biosensors based on gold nanostructures. J Braz Chem Soc 22:3–20 Zhang Q, Han L, Jing H, Blom DA, Lin Y, Xin HL et al (2016) Facet Control of Gold Nanorods. ACS Nano 10(2):2960–2974

Chapter 18

Carbon and Silver Nanoparticles for Applications in Agriculture Samiran Upadhyaya, Madhabi Devi, and Neelotpal Sen Sarma

Abstract  Carbon and silver are considered to be miraculous nanomaterials. They find enormous applications due to their low toxicity, high stability, and exceptional optical and electrical property. One of the highly growing demands of silver and carbon-based nanomaterials is their potential application in agriculture. With the rise in population, global food demand is increasing rapidly. The emergence of carbon and silver nanomaterials has opened up the doors towards advanced and sustainable farming to cope up with the increasing food demand. Carbon and silver nanoparticles have exclusive characteristics that can influence the metabolic activities of plants for their growth, thus leading to higher yields. Both silver and carbon-­ based nanomaterials are essential for enhanced seed germination, enhanced photosynthetic activity, pest control, and targeted drug delivery, leading to large-­ scale production. This chapter focuses on the various aspects and applications of silver and carbon-based nanomaterials in agriculture for precise and sustainable farming to meet the world’s food demand. Keywords  Nanoparticles · Sustainable farming · Carbon-based nanomaterials · Phytopathogens · Seed germination

S. Upadhyaya (*) Department of Chemistry, Gauhati University, Jalukbari, Guwahati, Assam, India Advanced Materials Laboratory, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati, Assam, India M. Devi Department of Physics, Majuli College, Kamalabari, Majuli, Assam, India N. S. Sarma Advanced Materials Laboratory, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati, Assam, India © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_18

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1 Introduction Agriculture is regarded as one of the most critical sectors globally, as it produces food to the growing population, and the by-products serve as raw materials for industrial applications. The population of the world, with the present growth rate, is expected to reach 9.7 billion in 2050, which may cause a severe threat to agriculture (Ioannou et al. 2020). Climate change is another factor which may further worsen agricultural productivity and food security. Increasing temperature and the level of carbon dioxide change in frequency and intensity of extreme weather conditions, changes in drought, and rain patterns have negatively impacted agriculture (Zandalinas et  al. 2018). The effect of climate change on the ecological balance includes abiotic stress on plant growth, such as high salinity, irregular availability of heat or water supply, fluctuating temperature and light, and unavailability of nutrients (Suzuki et al. 2014). The combined effect of these stresses leads to the hindered growth of many plant species. As per the data revealed by the Ministry of Finance, Government of India, the agricultural growth rate was 3.6% in 2004–2014, against 4%. The agricultural growth has further seen a dip in 2020, with a growth rate of 3% due to the COVID-19 pandemic. Also, as per the statistics provided by the ministry of Agriculture, the per capita food grains production was in 2014–2017 was only 179  kg, compared to 207  kg in 1991–1995. This decline raises serious concern about the food availability and security (Pramanik et al. 2020). The declining agricultural productivity with an increasing population causes a severe threat to the generations to come. The availability of water and land resources is limited in the present scenario. In such a case, the targeted agricultural goals can only be achieved by increasing the productivity per unit natural resources; and hence the income. In the modern era of development, increased agricultural income can be generated by the sustainable use of advanced technology. The present time is a difficult situation in the farm sector, which is further deteriorated by increasing soil pollution and climate change, especially in a country like India, where 60% of the population depends on agriculture. To overcome the situation of ‘technology fatigue’, we must focus on technologies, which can use the available resources judiciously, thus leading to enhanced agricultural productivity. With the advancement in material science, advanced materials such as polymers, nanomaterials, bio-conjugates, and composites can be a boon for various applications. Among all, nanomaterials, due to their excellent features, reflecting various physio-chemical aspects, are widely used in multiple fields. Agriculture is of no exception. Nanomaterials are frequently used in the present era for various techniques, redefining the agricultural sector. Many advanced methods, such as hybrid varieties, priming, and mutation breeding, are used for a good yield of agro-products. Priming is a necessary procedure, which readily activates the defence mechanism of plants, by control over reactive oxygen species (ROS) and gene expression that contributes to stress (Balmer et  al. 2015). Nanomaterials are the most widely as well as

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conveniently used agents for priming, reducing abiotic stress for plant growth. The nanomaterials are used in low quantities, thus being economical overall. In recent times, various nanomaterials, are employed for their potential ability to enhance growth factors in plants. Nanotechnology can be regarded as one of the best technological advancements for reviving agricultural productivity (Kuzma and VerHage 2006). The use of nanotechnology in agriculture has been recently realised, although the research was started almost 50 years back (Mukhopadhyay 2014). Nanomaterials are vital for plant growth under a stable and stressed condition. They can be useful to increase fertiliser efficiency and yields, early detection of pathogens, smart drug and nutrient delivery to the plants, processing, packaging of food, etc. (Moraru et al. 2003; Chau et al. 2007). Nanomaterials-derived genetically hybrid crops and nanocatalysts are useful to reduce pollution, improve soil fertility, water purification, water retention, and precision farming (Kuzma 2007; McMurray et  al. 2006; Kalpana-Sastry et al. 2009; Hakeem et al. 2021; Dar et al. 2022). Nanotechnology offers a more significant potential of enhancing agricultural productivity efficiently, with the involvement of low cost and minimal waste (Kah 2015). Thus, a second green revolution is probably possible with the use of nanotechnology. Among all the metallic and non-metallic nanomaterials, particular focus has been on carbon-based nanomaterials (CBN) and silver nanoparticles (AgN) in modern times. Considering the wide range of applications, Ag and carbon can be arguably regarded as the primary precursors to nanomaterials synthesis to enhance agricultural productivity. CBN, such as graphene oxide (GO), reduced graphene oxide (RGO), single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and fullerene (C60), because of their superior physico-­ chemical properties and exceptionally high mechanical strength, are exciting candidates in agricultural research. In contrast, AgN is enriched with antimicrobial and antioxidant properties to safeguard crops from phytopathogens (Chen et al. 2013, 2014). The demand for CBN and AgN has been rising tremendously with each

Fig. 18.1  Year-wise publications related to applications of (a) carbon-based nanomaterials, and (b) silver nanoparticles in agriculture

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passing year in agricultural applications, as evident from Fig. 18.1. (Data obtained from Pubmed.gov). Interestingly, in 1996 only one research article was published about the utility of CBN in agriculture, whereas in 2019, total publications in this field were 292. Similarly, only two publications reporting the application of AgN in agriculture were published in 2006, whereas the number went up to 178 in 2019. Both the nanomaterials together can enhance agricultural productivity, thus helping to grow the agro-economy of the nation. In fact, SWCNT, MWCNT, fullerene (C60), graphene, and silver are among the nanoparticles featuring in the priority list of the Organization for Economic Cooperation and Development (OECD) due to their various interesting as well as tunable properties (Servin and White 2016). The cost and environmental compatibility are additional benefits that CBN and AgN provide. Although few negative impacts of CBN and AgN have been reported, these are much fewer in counts compared to the beneficial aspects. In this chapter, an attempt has been made to analyse the impacts of CBN and AgN for agricultural applications.

2 Applications of Carbon-Based Nanomaterials in Agriculture CBN can be easily considered as the most widely used nanomaterials of the decade, for their enormous applicabilities in nanocatalysts, nanosensors, nano-barcodes, and DNA sequencing. Although the allotropes of carbon were discovered, the chapter of carbon nanomaterials started with the discovery of fullerene C60  in 1985, followed by CNT in 1991 and graphene in 2004 (Hong et al. 2015). Presently, carbon nanomaterials family includes CNT, graphene, nano-horns, nano-cones, nano-­ onions, carbon dots, nano-fibres, and nanobeads. The most commonly used members are CDs, CNT, and graphene (Sharon 2010; Cha et al. 2013; Baptista et al. 2015). Due to their exciting physio-chemical properties, CBN is widely used in agriculture, starting from germination and growth to efficient packaging. Carbon content, pH, texture, clay, etc., are the primary factors that affect the movement of CBNs in the environment (Avanasi et al. 2014), depending on the colloidal stability. CBNs can be used for the detection and diagnosis of antibodies, antigens, and bio-molecules acting as markers for certain plant diseases from the germination to the growth stage (Rosi and Mirkin 2005). Among different nanomaterials, CBN, such as SWCNTs, MWCNTs, graphenes, buckyballs, and carbon dots,, occupy a superior position in various agricultural applications (Mukherjee et al. 2016). The importance of different CBNs in agriculture has been described in detail. Figure  18.2 shows the scheme representing the complete range of applications of CBN.

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Fig. 18.2  Applications of carbon-based nanomaterials in agriculture

2.1 Carbon Nanotubes CNTs can be sub-categorised as SWCNT and MWCNT, based on the surface (walls/ layers). SWCNT requires careful experimentation and rectification, making them costlier than MWCNT. CNTs exist in three forms based on chirality, armchair, chiral, and zigzag (Ibrahim 2013). CNT has been reported to be an efficient material for the enhancement of agricultural productivity. Many notable pieces of research have been done showing the utilities of CNT in agriculture. It was reported by Remya et al. that SWCNT, MWCNT, and C60 were highly significant for seed germination of rice plants, with no side effects. Enriched shoot and root development were prominent in the SWCNT-enriched plant as per the findings (Nair et al. 2012). CNT may be used at the time of seed germination to protect a plant from diseases and promote growth. It serves as a vehicle to carry the desired organic and inorganic nutrients into the plant seeds. Lin and Xing observed an increase of 17% in the root length of ryegrass (Lolium perenne) upon exposure of LMWCNT (Ling and Xing 2007; Khodakovskaya et al. 2009). CNTs could also be used as transport channels mimicking aquaporins, as suggested by some computational analysis (Liu et al. 2009), due to minimum friction and maximum smoothness at the CNT surface (Duan and Wang 2010). CNT plays a vital role in transporting dye molecules and DNA to the plants. It also enhances the uptake of Fe, Ca (calcium), and water, resulting in efficient root and stem growth by accumulating in the root and inducing gene expression (Siddiqui et al. 2015). Recent reports also suggest

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that under salt stress conditions, CNT regulates the composition of essential oils (Gohari et al. 2020). There have been many notable pieces of research presenting the evidence of CNT as a useful material for agriculture. Tripathi et  al. in 2011 observed that water-soluble, citrate-coated CNTs led to the formation of the aligned network, which helped in the efficient water uptake, leading to the enhancement in plant growth (Tripathi et  al. 2011). Khodakovskaya et  al. observed an enhanced growth rate of 55–64% in tobacco plants on the exposure of 5–500  μl MWCNT (Khodakovskaya et al. 2012). Wang et al. reported 40–160 μl MWCNT exposure to wheat seedlings resulted in a 50% increase in root length (Wang et  al. 2012). Lahaina et al. found a 50% and 90% increase in the rate of germination of barley/ soybean and corn, respectively, on the exposure of MWCNT at 50–200 μl (Lahiani et al. 2013). Similarly, Tiwari and group reported that an exposure of 60 mg/L of MWCNT led to an increase in both nutrient uptake (1.6 × Fe, 2 × Ca) and plant biomass (43%). There is a lot more research on CNT for agricultural enhancements carried out and is still in progress. CNT, due to its exciting properties, is expected to be further used for agriculture in the future, and a lot more research is to be done in the days to come.

2.2 Carbon Dots Carbon nanoparticle (CNP), also known as carbon dot (CD), an essential class of CBN, is used as a material of choice for food packaging and transportation. Fluorescent CNPs can also be useful to analyse and track the quality of the products by studying the barcode on the products by observing under UV light. CNPs can be of great use for fluorescent labelling of vaccines for in vivo imaging. Following the vaccine pathway would certainly provide us the detailed information on the mechanism of treatment of the plant pathogens. The low toxicity of CNPs adds further to the utility. Due to their strong photoluminescence, low cost, tunability, water dispersibility, and biocompatibility, CDs are among the most used nanomaterials and are suitable alternatives to metal-based quantum dots (Shojaei et al. 2019). A study by Li et al. shows the abrupt growth of mung bean plant by the uptake of CD derived from phenylenediamine. The CD imposed no cytotoxicity and induced seed germination (Li et al. 2016). A report by Tripathi and Sarkar showed enhanced growth (10×) of wheat root on the exposure of water-soluble CDs for 10 days with a concentration of 150 mg/L (Tripathi and Sarkar 2015). Another interesting study reveals the use of the aqueous solution of carbon nano-onions (WsCNO) for the enhanced growth of gram plants. The WsCNO, synthesised by wood wool pyrolysis, was absorbed by the plant via uptake through the xylem and phloem (Sonkar et al. 2012). A recent study from China showed that rapeseed pollen-derived CD increased plant biomass by 48%, compared to the controlled one. The efficient absorption of nutrients was observed in Brassica parachinensis L. It is also important to note that the addition of CD in this study did not affect the overall composition of vitamins, proteins, and soluble sugar (Zheng et al. 2017).

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Many more productive works of CD have been reported. With the development of technology, CDs will find a crucial position as a candidate in agriculture applications.

2.3 Graphene And Derivatives Graphene, a honeycomb lattice with a two-dimensional arrangement of carbon and single-atom thickness, has been in wide use high value and easy functionalisation with polymers, DNA, and other nanomaterials. The other functionalised classes of graphene, such as GO, RGO, and carbon nano-horns (CHNs), have been proven to be suitable materials for agricultural productivity. Graphene and their derivatives can also be easily functionalised with other molecules and ions, making them candidates of choice for advanced agriculture. Many notable applications of graphene-­ based materials have been available in the literature, which include tissue engineering, diagnostic, genes/drug delivery, and bio-sensing (Hu et al. 2010; Liu et al. 2008; Wang et al. 2010). Zhang et al. reported that treatment of tomato seeds with 40 μg/ml of graphene increased the germination rate up to 43%, due to penetration of graphene through the seed husk, facilitating efficient water transport (Zhang et  al. 2015). Another study revealed the utility of graphene quantum dot (GQD), a nano-sized derivative of graphene, as growth regulators. The enhanced growth of coriander and garlic plants was reported on exposure with GQD. The length of the roots and flowers was largely enhanced in the presence of GQD (Chakravarty et al. 2015). A complex with iron (Fe), GO-Fe (III) composite, developed by Andelkovic et al., was used as fertiliser, with a slow release of potassium (K), thus minimising the probability of leaching. The K release rate was much slower than commercially used fertilisers. It was found that more than 99% of the P released from the composite was absorbed. The process thus provided an efficient K transport system without affecting the environment (Andelkovic et  al. 2018). GO-based highly sensitive soil moisture micro-sensor was developed by Palaparthy et  al., with a sensitivity of 370% and 340% for red soil and black soil, respectively. The stability of the sensor was more than 4 months, with the response time of 100–120  s (Palaparthy et  al. 2018). In another notable work, gold (Au) nanoparticle deposited RGO was utilised for hydrazine determination in agricultural wastewater via the electrochemical pathway. The designed sensor was also used to test real samples from agricultural sites (Lu et al. 2016). A new class of CBN of the graphene family, CNHs have been found to show a positive impact on the terrestrial plants’ growth. CHNs are the disordered graphene sheets, with lateral size up to 10  nm, and 4–5 A of inter-layer distance approximately (Xu et al. 2011). An exposure of CNHs (100 μL for 24 h) to tobacco cells led to an increase of growth rate up to78%, as reported by Lahiani et  al. (Lahiani et al. 2015).

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Graphene can be modified and functionalised easily, apart from being environment friendly, making them an essential candidate for agricultural applications. Going by the present scenario, graphene-based materials will be tremendously used for different agricultural applications.

2.4 Fullerenes Fullerenes are an important class of CBN, with many exciting properties that enable them to be used in different sectors, including agriculture. Fullerenes and their derivatives are useful as neuro-protecting and antioxidant agents, with minimum toxicity. Water retaining ability and increase in fruit yield and biomass are the most critical functions of fullerenes. Ma and Wang reported the dependence of fullerene in the uptake of trichloroethylene (TCE) by eastern cottonwood (Populus deltoides). In the presence of fullerene, the uptake was increased by 22% at 2 mg/L and 82% at 15 mg/L of fullerene (Ma and Wang 2010). The effects of C60 fullerene on the bio-accumulation of p,p′-DDE on different plants was investigated by De La Torre-Roche et  al. In soybean, p,p′-DDE was decreased by 48%, whereas in zucchini 29% increase in the p,p′-DDE uptake was observed on the exposure of fullerene. No effect was observed in tomato (De La Torre-Roche et al. 2013). Another vital water-soluble CBN, called fullerols, a fullerene derivative [C60(OH)20], is an important candidate for the growth and development of agricultural plants. It is also an anticancer agent. As reported by Kole et al., fullerol was found to enhance the phytomedicinal and biomass content of bitter melon, which is one of the major sources of AIDS, cancer, and diabetes treatment. The exposure of fullerol led to increase in anticancer agents, cucurbitacin-­B by 74% and lycopene by 82%. Fullerol exposure was also found to increase insulin (91%) and charantin (20%) contents, both of which are anti-diabetic molecules. The seed yield was found to increase from 112% to 128% (Kole et al. 2013). The applications of fullerene in agriculture are yet to be explored, and can just be considered the initial stage, with lot more to be investigated for agriculture applications.

2.5 Negative Effects of Carbon-Based Nanomaterials in Agriculture Despite different applications of CBN in agriculture, demonstrated by different groups, certain limiting factors resist their practical field applicability in agriculture. First, although CBNs are found to be non-toxic in genetic and physiological levels in most cases, their chronic phytotoxicity study in environmental conditions is minimal. Second, only limited studies on the potential damages and transgenerational

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impacts of plants exposed to CBN (Husen and Siddiqi 2014; Ghosh et al. 2015). The third factor is the lack of understanding of the stability of CBN in a medium comprising other contaminants, leading to possible leaching (Douterelo et  al. 2013). And finally, the mechanism of transfer of CBN to plants from soil and then to higher levels of herbivores and carnivores is still not understood. Many adverse effects of CBNs in agriculture have been reported in the literature by different research groups, which must be taken into consideration before using CBN in agriculture. The use of CNT has been reported to have a few adverse effects in agricultural fields. In a study by Jackson et al., it was evident that the Interaction between CNTs and cell membranes is of strong electrostatic nature, which results in oxidative stress and cell puncture, ultimately leading to disruption of the cell membrane. CNTs may induce reactive oxygen species (ROS), which may interact with organelles, inducing protein inactivation, or DNA damage, resulting in apoptosis (Jackson et al. 2013). Commercially available CNTs contain metal particle, such as iron (Fe), nickel (Ni), and Cobalt (Co) up to 45–15%, used during preparation, which may have toxic effects on essential plant microbes (Kang et al. 2007; Zhang et al. 2013). Stampoulis et al. found that an exposure of MWCNT for 15 days (1000 mg/L) led to a decrease in the biomass of zucchini by 60% (Stampoulis et al. 2009). As per a report, functionalised MWCNT at high concentration (around 5000 μg/g) led to a decrease in soil pH, thus affecting the bacterial diversity of the soil (Kerfahi et al. 2015). Another report suggested a decline in enzyme activity up to 50%, along with microbial biomass (Chung et al. 2011). Similar toxicological effects of CNTs in plants have been shown by many researchers, including retarded growth, decreased plant microbes, loss of soil fertility, and decrease in plant biomass (Jin et al. 2014; Rodrigues et al. 2013). SWCNT may induce cell apoptosis and lead to the proliferation of kidney cells by hindering the adhesive ability of the cells. They may also cause lung inflammation. SWCNT, along with bronchial and keratinocytes epithelial cells, leads to an increase in oxidative stress markers. MWCNT, via inhalation, may remain persistent deep in the lungs and induce fibrotic as well as inflammatory reactions. MWCNTs also cause protein alterations, leading to cell cycle inhibition, vesicular exocytosis alterations, and down-regulation of proteins (Agrawal and Rathore 2014). Although few negative impacts of CNT in plants were reported, most of these findings are based on laboratory experiments. A clear picture of the results is necessary for a more complex but relevant condition, where we can assess the actual impact of CNT in a plant. Although very useful in agriculture, fullerene and graphene are also known to impact plant growth negatively. In a study, it was found that the exposure of C60 fullerene at 0–50 mg/kg of dry soil led to a threefold decrease in the population of fast-growing bacteria, while showed no significant effect on protozoa (Johansen et  al. 2008). Certain photosensitive fullerene, when exposed to light, binds with DNA and cause deformations, leading to cleavage of DNA strands (Takenaka et al. 1999). Cheng et al. reported that the exposure of GO at 0.5–1 mg/kg for 21 days led to a 50% decrease in soil enzymes, such as phosphate and xylosidase (Chung et al. 2015). CBN can bind strongly with persistent pesticides, which may minimise the

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residue uptake by damaging the root membranes; CBN may also bind to the pest control agrichemicals. So, considering the above aspects, the direct applications of CBN in agriculture is still in the initial ‘toddler’ phase. Interestingly, despite the negative factors, carbon is among the top nanomaterials used in agriculture. CBN may have long-­term adverse effects on the environment as per the reported works. However, there is still a wide research gap, and the mechanistic details have not been understood completely. There is a lack of precise overt mechanism and phytotoxicity of CBN; there is a need for researchers to refocus on the development of a subtle system under actual environmental conditions.

3 Applications of Silver Nanoparticles in Agriculture AgN is the most widely used metal nanoparticles by many industries and researchers due to their excellent antimicrobial properties. Since the ancient period, Ag has been used as a therapeutic agent in Ayurveda for disinfectant water and food (Mishra and Singh 2015). In the present era of nanotechnology, Ag has caught special attention due to its enhanced properties, compared to bulk Ag. A report in 2009 suggests that more than 800 megatons of AgN were used globally every year, which has been increasing exponentially (Wijnhoven et al. 2009). It is used by various industries, such as textiles, healthcare, IT (Information & Technology), beauty, and electronics. As per the Global Market Insight, the current market size of AgN is 1.1 billion (as of 2016) and is expected to cross 3 billion in 2021 (Trends 2017). It is quite astonishing to know that AgNs in just 30 min could kill around 650 types of pathogens, including bacteria, yeast, fungi, and viruses (Shahrokh and Emtiazi 2009). The beneficial aspects of AgN have not yet been fully explored in agricultural sectors. Out of the partial literature available, most of the findings have been obtained in experimental laboratory conditions. The exciting characteristics of AgN enable it to be used in various applications, which has been summarised schematically in Fig. 18.3. To fully understand the utilities and the toxicity profile of AgN based on the available literature, a detailed analysis is essential, which has been put forward in this section. AgNs have high antimicrobial properties in very low concentrations (1–10 μM) with negligible toxicity. Hence, they are widely used in many pharmaceutical and biological processes, orthopaedics, dental care, wound repair, and water sanitisation, among others. But the applicability of AgN in the treatment of plant diseases has been relatively less explored. The high surface area of AgN and the surface plasmon resonance are often considered an asset for bio-sensing applications. During the photosynthetic reaction, the chlorophyll binds with AgN and forms a hybrid complex and produces excited electrons, which is almost ten times more. The electron-hole separation and the surface plasmon resonance of AgN induces the generation excited electrons in chlorophyll, leading to an enhanced artificial light-­ harvesting system (Siddiqui et al. 2015). In addition, AgN enhances the antioxidant

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Fig. 18.3  Applications of silver nanoparticles in agriculture

enzymatic activities and production of proline, soluble sugar, and amino acids, leading to overall protection against factors inducing abiotic stress (Mehrian et al. 2015; Mohamed et al. 2017). AgN is also responsible for the production of ATP by inhibiting the expression of the associated protein (Yamanaka et al. 2005). AgN has been reported to be predominantly crucial in controlling plant pathogens, such as B. sorokiniana and M. Grisea and also against Cladosporium fulvum, which are responsible for plant diseases, such as tomato leaf mould (Jo et  al. 2009). Graphene oxide-supported AgN has been proven to be an effective antibacterial agent against Xanthomonas perforans (Ocsoy et  al. 2013). AgN is also used for antimicrobial food packaging for the protection and preservation of food. The packagings, in most cases, are such that they release antioxidants and antimicrobial agents, thereby improving shelf life, quality, and safety, leading to less food wastage (Chaudhry et al. 2018). AgN is known to be effective in treating a wide range of plant diseases caused by fungal pathogens. Using AgNs prior to the plant-fungal colonisation is effective in controlling powdery mildew. Further, AgNs have also shown to extend the life span of flowers, protect flowers from vascular blockage by minimising microbial growth. AgN, often used as a substitute to pesticides, is also used to control sclerotium, which forms phytopathogenic fungi by the collapse of hyphae. AgN also causes the damage of fungus of Raffaelea class, leading to the death of an oak tree. The effects of AgN were also observed on conidial germination (Nair et al. 2010). AgN is found to be safe for the environment at optimum conditions, which supports the candidature of AgN in agriculture. AgN may have toxic effects only at very high concentrations, although the actual mechanism of interaction with plants is still unknown. Some interesting findings make the research related to AgN towards soil microbes challenging, astonishing, and refreshing at the same time.

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Yang et al. studied the effect of Ag+ and AgN towards various vital bacteria in the soil, such as Pseudomonas stutzeri (denitrifying bacteria), Nitrosomonas europaea (nitrifying bacteria), and Azotobacter vinelandii (nitrogen fixer). As evident from the study, Ag+ is toxic to the soil, negatively impacting the denitrifying bacteria. In response to this, AgN was 20–48 times less toxic than Ag+ ions, thus causing no impact towards the soil bacteria (Yang et al. 2013). This study was again supported by Shahrokh et  al., showing that a low dose of AgN did not affect Rhizobium. Interestingly, 0.2 ppm of AgN enhanced the activity of the Azotobacter (Shahrokh et al. 2014). Interestingly, the size dependence of AgN was found to be prominent, with particles of size less than 5 nm were reported to be more toxic towards nitrifying bacteria (Choi and Hu 2008). Salama observed a positive effect of AgN on the growth of Phaseolus vulgaris and Zea mays, leading to enhancement of carbohydrate, protein, and chlorophyll contents of the leaves, increase in shoot/root length and increase in leaf surface area (Salama 2012). The positive, dose-dependent impact of AgN on the vigour index and growth of Brassica juncea, in addition to inducing antioxidant enzyme activity was revealed by Sharma et  al. (2012). The findings stated above clearly show that an optimum dose of AgN could be beneficial to the microbial processes, leading to high agricultural productivity, without compromising with the environmental safety concerns. Previous studies rose concerns about the toxicity of Ag towards soil health at higher concentrations. AgN accumulation in plant biomass is dependent on the size and concentration, which in turn is responsible for the cytotoxicity. The faster movement of small-sized nanoparticles was noticed in Populus deltoides x nigra (Wang et al. 2013) and the Oryza sativa root cells (Mazumdar and Ahmed 2011), as reported by Wang et al. and Mazumdar et al. respectively. In contrast to that, a study by Haverkamp and Marshall found no evidence of larger-sized Ag+ accumulation in Brassica juncea (Haverkamp and Marshall 2009). This leads to the lesser bioavailability of Ag+ derived from AgN in soil, which are mostly absorbed by the plants compared to larger-sized Ag+ ions (Lee et al. 2012). The more sorption of AgN by plants leads to lesser mobility into the soil, thus causing minimum impact to the soil compared to the larger-sized Ag. Apart from the utilities of pristine form, AgN can be functionalised with different materials to obtain materials of choice for agriculture. In an exciting study, a hybrid form of AgN and CBN, an AgN-GO composite was reported by Juanni Chen et al., which was found to be an exciting candidate for antifungal and sporicidal activity. A high rate of inactivation of conidia of F. graminearum was observed on exposure to AgN-GO. F. graminearum is responsible for Fusarium head blight (FHB) in wheat plants. The observations were recorded in practical wheat leaves, along with laboratory testing. Further, the ROS production was induced by the composite, also leading to the death of fungal spores (Chen et al. 2016). AgN application in agro-growth is an important finding by the agro-scientists, which is applicable widely from plant growth to soil enhancement and crop protection. It can be inferred from the above discussions, the significant role of AgN in agriculture is the protection against the plant pathogens, although other roles cannot

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18  Carbon and Silver Nanoparticles for Applications in Agriculture Table 18.1  Few notable reports on the application of AgN against plant pathogens Sl No. Reported research 1 High voltage arc discharge synthesised AgN 2 Nano-sized Ag-silica composite prepared by γ-irradiation 3 Ag-chitosan nano-composite 4 Pine cone mediated AgN

6 7

8

9 10 11 12

13

14 15

AgN synthesised from Piper nigrum Gossypium hirsutum derived AgN Bio-synthesised AgNs by Stenotrophomonas sp. BHU-S7 AgN in plant protection: Chapter Calothrix elenkinii supported AgN Endophytic bacteria derived AgN Bio-synthesised AgN from Phyllanthus emblica fruit extract AgN synthesised from garlic derived endophytic bacteria Pseudomonas fluorescens fabricated AgN Cellulose decorated AgN

Applications Treatment of Fusarium culmorum Treatment of Pseudomonas syringae in potato Treatment of grey mould in strawberry

Reference Kasprowicz et al. (2010) Chu et al. (2012) Moussa et al. (2013) Velmurugan et al. (2013)

Antibacterial activity against Bacillus thuringiensis, Pseudomonas syringae, Burkholderia glumae, Bacillus megaterium, and Xanthomonas oryzae Antifungal activities against phyopathogens Paulkumar et al. (2014) Treatment against Xanthomonas axopodis Vanti et al. pv. malvacearum and Xanthomonas (2019) campestris pv. campestris Treatment against Xanthomonas oryzae pv. Mishra et al. oryzae (Xoo) that causes sheath blight (2020) disease in rice Use of AgN in protection of plants from Gupta et al. pathogens and in crop development (2018) Treatment of Alternaria blight effected Mahawar et al. tomato plants (2020) Inhibition of pathogenic bacteria and Ibrahim et al. growth of rice plant (2019) Treatment of pathogen Acidovorax oryzae Masum et al. Strain RS-2 in rice (2019) Treatment of Fusarium graminearum, a wheat Fusarium head blight pathogen

Ibrahim et al. (2020)

Tobacco mosaic virus control

Ahsan (2020)

Eco-nematicide for root-knot nematode

Fouda et al. (2020)

be ignored. Table 18.1 shows the crucial functions of AgN, prepared by different means, against plant pathogens, apart from the ones discussed above. The table will go on unfinished if we mention all the anti-pathogen activities of AgN. The value of AgN is very high in agriculture and agricultural product developments, which is growing with every passing day. Interestingly, due to the phytopathogenic property, there are around 250 varieties of consumer products based on AgNs, ranging from surgical products, cosmetics, and textiles. Hence, AgN can undoubtedly be called precious material for agriculture and crop development.

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3.1 Negative Effects of Silver Nanomaterials in Agriculture Although beneficial material for agriculture, there are few ill effects of AgN towards the soil health, plants, and environment. Long-term impact of AgN in human beings and the environment is an essential topic of discussion, which is often not given due importance. As per the study by Morones et al., AgN alters the membrane properties by adhering to the surface of the cell, which in turn affects the respiration and permeability of the cells. The release of AgN may cause DNA damage (Morones et al. 2005). AgN changes membrane permeability by degrading lipopolysaccharide molecules. Some reports also suggest that AgN damages enzymes responsible for transporting cell nutrients, thus causing weakening of the cell membrane (Phogat et al. 2016). Further, AgN interacts with thiol groups of proteins, leading to the inactivation of necessary enzymes (Feng et al. 2000). AgN has also been known to destroy the DNA replication of plants. The use of AgN also causes detrimental effects to the denitrifying bacteria in the soil. Most of the processes for the synthesis of AgN involve toxic reagents and expensive energy consumption procedures, such as laser pyrolysis, reverse precipitation, chemical vapour deposition, arc discharge, and micro-emulsion. However, since the last decade, particular focus has been given to the use of bioreagents for the synthesis of AgN, such as various microbes and plant extracts. The bio-agents, which are low cost, negligibly toxic, and environment friendly, could lead to biocompatible AgN nano-sized particles for their effective use in agriculture, thus leading to better agronomics.

4 Conclusion and Future Prospects Advanced technologies, such as nanomaterials, are necessary to increase food production. CBN and AgN are of utmost importance in agriculture. In fact, they are among the few nanomaterials present in the priority list of the Organization for Economic Cooperation and Development. Due to various exciting properties of CBN and AgN, they are extensively used in agriculture for the enhancement in crop growth, which would undoubtedly help meet the world food demand. The most crucial factor to note while using CBN and AgN is the optimum dose. In some conditions, the use of a higher concentration of these nanomaterials may cause adverse effects on plant life. Important factors, such as the use of robust experimental designs and advanced analytical methods for characterisation and cautious handling to avoid impurities, are essential for efficient research to significantly advance the current study of CBN and AgN in agricultural sectors. The confounding factors that may arise need to be considered. From the literature survey, it can be ascertained that the toxic effects of CBN and AgN on plant growth are primarily due to the irregular doses, which can probably be controlled with extensive experiments.

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Furthermore, in the current era of technological development, compact and handy technology is required for the upliftment in the agricultural sector. A broader approach of research is necessary with relevance in the ecological system that might include time-consuming study and experiments under a realistic environment, along with sensitive endpoints. Nevertheless, we can come to an end, hoping to see an expansive growth in agriculture in the near future by the judicial use of carbon and silver nanomaterials. Acknowledgements  The authors would like to thank Department of Science and Technology, Government of India for providing financial support. The authors would also like to thank Knowledge Resource Centre, IASST, for their help in anti-plagiarism test. Conflict of Interest  The authors declare no conflict of interest.

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Correction to: Microbiota in Sustainable Degradation of Organic Waste and Its Utilisation in Agricultural Industry Murugaiyan Sinduja, Joseph Ezra John, R. Suganthi, S. Ragul, B. Balaganesh, K. Mathiyarasi, P. Kalpana, and V. Sathya

Correction to: Chapter 2 in: G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-­3-­031-­32967-­8_2 The first author name of Chapter 2 was unfortunately published with an error. The initially published version has now been corrected.

The updated original version of this chapter can be found at https://doi.org/10.1007/978-­3-­031-­32967-­8_2 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8_19

C1

Index

A Abiotic stress tolerances, 210–214, 221, 279–280 Actinomycetes, 35, 66, 172, 185–191 Adaptive symbiotic technology, 210, 218–221 Agricultural productivity, 3, 4, 6, 7, 74, 96, 97, 109, 114, 172, 196, 290, 298–301, 303, 308 Agriculture, 3, 30, 60, 80, 96, 115, 146, 168, 184, 193, 210, 233, 257, 277, 286, 298 Agriculture waste, 60–66, 198 B Beneficial microorganisms, 118–121, 124, 138, 146, 184, 219, 244, 245, 276 Biochar, 11, 12, 200–202, 204, 243 Biocontrol, 74, 76, 102, 126, 137, 138, 245, 270, 276, 277 Bioconversion, 39, 62–63, 66 Bioenergy, 32, 33, 47–49, 61, 62, 200, 260, 262 Biofertilizers, 61, 63, 66, 72–84, 108, 114–127, 134–141, 146–162, 167–178, 194–198, 204, 244, 245, 256–261, 264, 265, 271–277 Biopesticides, 8, 43, 96–108, 134, 137, 139, 141, 256 Bioremediation, 17, 61, 75, 125, 137, 189, 190, 240, 241, 246, 247, 260–262, 293 Biostimulants, 138–140 Biotechnology, 3, 9, 10, 60–66, 104, 127, 193–204, 290

C Carbon-based nanomaterials, 15, 18, 299–306 Chemical, 4–12, 14, 15, 17, 30, 31, 44, 45, 49, 60, 61, 65, 66, 72, 73, 75, 78–80, 96, 97, 100–103, 105–108, 115, 123–127, 134, 136, 138–141, 146, 149, 152, 155, 157, 168, 171, 177, 184, 188, 195, 196, 198, 200–202, 217, 245, 246, 256, 257, 260, 262–264, 272, 273, 275, 277, 280, 287–293, 310 Climate change, 2, 20, 33, 97–99, 115, 188, 201, 209–218, 221, 222, 286, 288, 290, 298 Crop management, 3, 269–271, 276 Crop yield, 3, 7, 9, 14, 41, 43, 47, 61, 72–74, 76, 80, 82, 84, 101, 146, 148, 184, 185, 200, 202, 244, 256, 258, 288, 291 Cucumis sativus, 8, 212, 269, 271, 272, 277–279 Cyanobacteria, 39, 73, 77, 78, 81, 83, 134–136, 140, 146, 148, 170, 232, 256–265, 269–280 D Degradation, 2, 7, 8, 15, 17, 30–51, 59–66, 97, 114, 115, 120, 124, 198, 200, 240–247, 256, 277, 288, 291 Demand, 2, 3, 6, 7, 21, 32, 61, 63, 66, 72, 73, 84, 96, 97, 100, 116, 134, 141, 146, 161, 178, 184, 188, 196, 200, 215, 257, 262, 287, 299, 310

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 G. H. Dar et al. (eds.), Microbiomes for the Management of Agricultural Sustainability, https://doi.org/10.1007/978-3-031-32967-8

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318 E Endophytes, 210, 211, 218, 270–280 Enhanced phosphorus uptake, 235 Environment, 1, 3, 5–9, 17–20, 30–35, 41, 47, 48, 50, 51, 60–63, 65, 66, 73, 75, 77, 96, 98–101, 103–106, 108, 114, 118–120, 122, 124–126, 135, 170–173, 175–177, 187, 189, 191, 193, 196, 197, 200, 202, 204, 217–221, 231, 232, 234, 240–248, 256, 258, 261, 262, 264, 265, 276, 277, 280, 288, 300, 303, 304, 306, 307, 310, 311 Environmental health, 19, 32, 239–248 Essential nutrients, 122, 170, 245, 258, 263, 271, 280 F Fertilizers, 6, 60, 72, 126, 134, 146, 168, 195, 230, 247, 256, 272, 287 Food, 1–18, 20, 21, 31, 32, 34, 39–41, 44, 45, 59–61, 63, 66, 72–74, 84, 96–98, 100, 101, 104, 108, 114, 116, 123, 124, 127, 134, 141, 146, 167, 170, 171, 190, 209, 214–218, 220, 229, 242, 257, 260, 262, 263, 265, 270, 286–291, 293, 294, 298, 299, 302, 306, 307, 310 Food processing, 12–13, 134, 194 Fruits, 10, 12, 14, 34, 43, 45, 46, 84, 146–162, 193, 272, 274, 304, 309 G Genetic engineered plant, 232–236 Genus, 240, 241, 247, 248 Growth, 3, 4, 6–8, 13, 21, 30, 31, 39, 42–44, 49, 50, 60, 61, 64, 72–82, 96, 99, 100, 102, 103, 105, 107, 115, 117–124, 126, 133, 134, 137, 138, 140, 146–151, 159, 160, 167, 168, 170–177, 183–185, 187, 189–191, 194–197, 202, 211, 214–217, 229, 232–235, 240, 243–245, 256, 258–262, 264, 270–277, 279, 280, 288, 290, 292, 298–305, 307–311 H Health, 3, 6, 8, 12, 14, 17–19, 31–33, 41, 43, 49, 60, 65, 66, 79, 96, 97, 99, 104, 106–108, 114–121, 124–126, 133, 134, 146, 148, 156, 161, 168, 170, 172, 175, 185, 194, 195, 200, 202, 216, 240, 245,

Index 256, 258, 260, 262–263, 270, 275, 287, 288, 293, 308, 310 I Immobilization, 137–138, 203, 247, 277 Improved phosphorus use, 229–236 Inoculant, 39, 42, 50, 51, 72, 77, 83, 108, 116–118, 120, 123–125, 161, 184, 185, 195, 216, 219–221, 272, 280 Integrated pest management (IPM), 96, 104, 106, 175 M Macrophytic biofertilizer, 136–141 Management, 3, 30, 60, 61, 76, 105, 126, 133, 161, 172, 188, 194, 211, 246, 256, 276, 289 Microbes, 15, 35, 37–42, 46, 50, 51, 72, 73, 76–83, 101, 102, 117, 120–122, 134, 136–139, 141, 146, 148, 150, 160, 172, 175, 185, 187, 188, 198, 200, 201, 210–212, 214, 216–222, 239, 241, 245, 256–265, 270, 273–275, 277, 305, 307, 310 Microbiota, 29–51, 134, 135, 139, 168, 172, 210, 222, 269–271, 280 N Nano fertilizer, 7, 8, 18, 116 Nanoparticles (NPs), 9, 10, 13, 17, 18, 20, 149, 154, 202, 203, 288–294, 298–311 Nanotechnology, 2–22, 202–204, 287–294, 299, 306 Nitrogen fixation, 41, 73, 76–80, 96, 118, 135, 140, 147, 172, 173, 185, 187–189, 191, 195, 214, 257, 259, 260, 272–273 O Optimized agricultural phosphorus utilization, 232 Organic waste, 31–42, 45, 47–48, 50, 60, 62, 65, 66, 125, 197–200 P Pests, 6, 8–10, 12, 43, 66, 73, 97, 100–106, 115, 139, 141, 270, 287, 288, 291, 293, 294, 306

Index Phytopathogens, 74, 75, 140, 172–174, 270, 275, 276, 299 Populations, 2, 20, 32, 36, 41, 43, 60, 72, 75, 84, 96, 97, 100, 101, 108, 114, 115, 123, 127, 134, 146, 167, 168, 178, 184, 186, 187, 197, 210, 211, 218–220, 229, 243, 245, 257, 286, 287, 292, 298, 305 Pseudomonas, 39–41, 43, 46, 74–76, 79–83, 107, 121–123, 125, 147, 148, 153, 172, 176, 186, 190, 195, 212–214, 240–248, 258, 273–278, 308, 309 Q Quality, 11, 12, 14–16, 21, 31, 32, 60, 61, 72, 81, 84, 96–99, 108, 109, 115, 124–126, 134–136, 146, 151–153, 158, 160, 178, 185, 202, 219–221, 240, 256, 258, 264, 265, 270, 288–292, 294, 302, 307 R Regulation, 20, 50, 213, 234, 245, 270, 293 Restoration, 115, 116, 119, 120, 125–127, 244–245 S Seed germination, 74–76, 81, 150, 233, 274, 301, 302 Soil, 3, 6, 7, 9, 17–18, 20, 30–32, 34, 41–43, 45, 47–49, 51, 60, 61, 63, 65–66, 72, 73, 75–84, 96–98, 106–109, 114–127, 134–141, 146–149, 152, 156–158, 160, 161, 168–177, 184–188, 190, 191, 193–198, 200–204, 213, 214, 216–221, 229–233, 240–246, 248, 256–261, 264, 265, 270–273, 275–277, 279, 286, 288, 290–293, 298, 303, 305, 307, 308, 310 Soil fertility, 7, 14, 17, 31, 72, 96, 97, 106–109, 114, 115, 118–120, 123,

319 125–127, 140, 146, 148, 157, 168, 184, 185, 191, 194–198, 200, 202, 204, 241, 256, 286, 289, 299, 305 Solid state fermentation (SSF), 137, 138 Stress tolerance, 73–76, 138, 196, 214, 217, 222, 273, 274, 280 Sustainable agriculture, 6, 7, 21, 30, 41, 48, 51, 72, 79, 84, 96, 98–101, 108, 119, 141, 169–171, 176, 178, 183–191, 196, 210, 215, 256–265, 275, 286, 288–290 Sustainable farming, 134, 138, 260 Sustainable management, 8 U Uptake, 43, 73, 74, 76, 82, 84, 120, 122, 123, 140, 146, 147, 154–156, 169, 173, 184, 185, 195, 231–236, 244, 245, 273, 290, 301, 302, 304, 306 V Vermicompost, 123, 149, 150, 152–157, 198, 200 W Waste management, 11, 30, 33, 50, 51, 60–62, 65, 198, 246 Y Yield, 3, 6, 7, 9, 10, 20, 32, 42, 43, 45, 47, 64, 65, 72, 76, 81, 82, 84, 97, 101, 105–107, 115, 122, 124, 137, 139, 153–154, 159, 175, 176, 184, 195, 209, 215, 216, 221, 230, 232, 234, 235, 264, 271, 272, 275, 276, 280, 292, 293, 298, 299, 304