[1st Edition] 9780128124246, 9780128124239

Table of contents :
Content:
Series PagePage ii
CopyrightPage iv
ContributorsPages vii-viii
PrefacePage ixDonald L. Sparks
Chapter One - Long-Term Aging of Biochar: A Molecular Understanding With Agricultural and Environmental ImplicationsPages 1-51S. Mia, F.A. Dijkstra, B. Singh
Chapter Two - Brazilian Agriculture in Perspective: Great Expectations vs RealityPages 53-114F.A.O. Camargo, L.S. Silva, G.H. Merten, F.S. Carlos, P.C. Baveye, E.W. Triplett
Chapter Three - Bio-Intervention of Naturally Occurring Silicate Minerals for Alternative Source of Potassium: Challenges and OpportunitiesPages 115-145B.B. Basak, B. Sarkar, D.R. Biswas, S. Sarkar, P. Sanderson, R. Naidu
Chapter Four - Livestock Production and Its Impact on Nutrient Pollution and Greenhouse Gas EmissionsPages 147-184K. Sakadevan, M.-L. Nguyen
Chapter Five - Mineral Nutrition of Cocoa: A ReviewPages 185-270J.A. van Vliet, K.E. Giller
IndexPages 271-276

Citation preview

ADVANCES IN AGRONOMY Advisory Board

PAUL M. BERTSCH

RONALD L. PHILLIPS

KATE M. SCOW

ALFRED E. HARTEMINK

University of Kentucky

University of California, Davis

University of Minnesota

University of Wisconsin - Madison

Emeritus Advisory Board Members

JOHN S. BOYER

MARTIN ALEXANDER

EUGENE J. KAMPRATH

LARRY P. WILDING

University of Delaware North Carolina State University

Cornell University

Texas A&M University

Academic Press is an imprint of Elsevier 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States 525 B Street, Suite 1800, San Diego, CA 92101–4495, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 125 London Wall, London, EC2Y 5AS, United Kingdom First edition 2017 Copyright © 2017 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-12-812423-9 ISSN: 0065-2113 For information on all Academic Press publications visit our website at https://www.elsevier.com/

Publisher: Zoe Kruze Acquisition Editor: Alex White Editorial Project Manager: Helene Kabes Production Project Manager: Magesh Kumar Mahalingam Cover Designer: Greg Harris Typeset by SPi Global, India

CONTRIBUTORS B.B. Basak ICAR-Directorate of Medicinal and Aromatic Plants Research, Anand, India P.C. Baveye Unite EcoSys, AgroParisTech, Universite Paris-Saclay, Thiverval-Grignon, France D.R. Biswas Indian Agricultural Research Institute (IARI), New Delhi, India F.A.O. Camargo Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil F.S. Carlos Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil F.A. Dijkstra Center for Carbon, Water and Food, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, Australia K.E. Giller Wageningen University and Research, Wageningen, The Netherlands G.H. Merten Large Lakes Observatory, Swenson College of Sciences and Engineering, Duluth, MN, United States S. Mia Center for Carbon, Water and Food, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, Australia R. Naidu Global Centre for Environmental Remediation; Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, University of Newcastle, Callaghan, NSW, Australia M.-L. Nguyen Soil and Water Management & Crop Nutrition Section, International Atomic Energy Agency, Vienna, Austria K. Sakadevan Soil and Water Management & Crop Nutrition Section, International Atomic Energy Agency, Vienna, Austria P. Sanderson Global Centre for Environmental Remediation, University of Newcastle, Callaghan, NSW, Australia

vii

viii

Contributors

B. Sarkar Future Industries Institute, University of South Australia, Mawson Lakes Campus, SA, Australia S. Sarkar Central Institute for Fresh Water Aquaculture, RRC Anand, Anand, India L.S. Silva Federal University of Santa Maria, Santa Maria, RS, Brazil B. Singh Center for Carbon, Water and Food, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, Australia E.W. Triplett University of Florida, Gainesville, FL, United States J.A. van Vliet Wageningen University and Research, Wageningen, The Netherlands

PREFACE Volume 141 contains five comprehensive chapters on the crop and soil sciences. Chapter 1 is a review on the molecular understanding of longterm aging of biochar, with particular emphasis on agriculture and the environment. Chapter 2 is an interesting commentary on the status of Brazilian agriculture, including a historical perspective, as well as the present and future outlook. Chapter 3 deals with naturally occurring silicate minerals as an alternative source of potassium, with emphasis on both challenges and opportunities. Chapter 4 is a timely review on livestock production and its impact on nutrient pollution and greenhouse gas emissions. Chapter 5 is a comprehensive review on cocoa. I am grateful to the authors for their fine reviews. Donald L. Sparks Newark, DE, USA

ix

CHAPTER ONE

Long-Term Aging of Biochar: A Molecular Understanding With Agricultural and Environmental Implications S. Mia1, F.A. Dijkstra, B. Singh Center for Carbon, Water and Food, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW, Australia 1 Corresponding author: e-mail address: [email protected]

Contents 1. Introduction 2. Biochar and Its Aging 2.1 Decomposition of Aliphatic and Volatile Carbons 2.2 Breaking Down of Aromatic Moieties 3. Accelerated Methods of Biochar Aging 3.1 Biochar Aging With Chemical Agents 3.2 Microbial Aging of Biochar Supplemented With Fresh Biomass Under Favorable Environmental Conditions 3.3 Physical Aging of Biochar 4. Properties of Biochar and Biochar-Derived Organic Matter 4.1 Structural and Functional Composition 4.2 Elemental Composition and Polarity 4.3 Specific Surface Area 4.4 Surface Charge Characteristics 5. Biochar Aging Impacts on Agriculture and Environment 6. Conclusions Acknowledgments References

2 4 5 7 8 8 13 13 14 14 21 24 24 32 38 38 38

Abstract Biochar has unveiled a new avenue for carbon (C) sequestration and has shown the potential to increase agricultural productivity. Although there is still debate about the mineralization rate of biochar and its role in sustaining soil fertility after fresh biochar amendment, oxidized or aged biochar has shown strong positive effects on crop productivity. Aging of biochar changes its physiochemical properties, while a range of biochar-derived organic materials (BDOMs) can be formed. These changes have significant consequences for the bioavailability and transport of nutrients and contaminants. Advances in Agronomy, Volume 141 ISSN 0065-2113 http://dx.doi.org/10.1016/bs.agron.2016.10.001

#

2017 Elsevier Inc. All rights reserved.

1

2

S. Mia et al.

In this review, we provide an overview of biochar aging, focusing on its change in structure, surface chemical properties, and the interactions of biochar and BDOMs with nutrients and contaminants in the soil. Synthesis of spectroscopic data from nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and near edge X-ray fine structure (NEXAFS) showed that with progressive aging, either artificially or naturally, biochar undergoes structural and chemical changes leading to progressive formation of surface functional groups such as carboxyl, phenolic, and carbonyl groups. As a result, the O:C ratio, negative surface charge, and cation exchange capacity increase with increased level of aging. The surface oxidized biochar and BDOMs may interact with soil minerals, nutrients, and contaminants resulting in increased mineral-stabilized organic matter, cation retention, anion bioavailability, and reduced organic contaminants’ sorption. Therefore, application of aged biochar could potentially increase agricultural productivity with increased capacities to retain nutrients while serving the role of C sequestration.

1. INTRODUCTION Soils are the largest terrestrial carbon (C) pool and contain more C than the combined amount present in the vegetation and in the atmosphere (Lehmann and Kleber, 2015). A significant part of the soil C is pyrogenic that has resulted from wildfires, deliberate burning, or from anthropogenic additions as (bio)char (Bird et al., 2015; Brodowski et al., 2007; Dai et al., 2005; Masiello, 2004; Schmidt and Noack, 2000). Additionally, each year a considerable amount of pyrogenic C (PyC) accumulates with a global annual contribution estimated at 116–385 Tg C (Santı´n et al., 2015). Being rich in aromatic C, the retention time of PyC in soil is usually long, ranging from decadal (Bird et al., 1999) to centennial (Knicker et al., 2013; Kuzyakov et al., 2009; Zimmerman, 2010) to millennial timescales (Eusterhues et al., 2005; Watanabe and Takada, 2006). Therefore, addition of PyC as biochar has opened a new window for long-term C storage in soil and climate change mitigation. Fresh biochar addition to soils showed an increased crop yield through increased nutrient retention and bioavailability or intrinsic nutrient addition (Jeffery et al., 2011), although negative and neutral effects have also been found (Liang et al., 2014). A pronounced yield increase was observed with aged biochar (Crane-Droesch et al., 2013; Major et al., 2010). For instance, Terra Preta soils and other anthropogenic soils amended with PyC as char that has aged with time have shown a high capacity of nutrient retention and crop productivity (Cheng et al., 2008; Liang et al., 2006). One of the possible mechanisms is an increase in the cation exchange capacity (CEC) through surface oxidation of the PyC.

3

A Molecular Insight Into Biochar Aging

Amendments of fresh biochar to soil can undergo similar aging processes with important consequences for nutrient retention and crop production. Biochar, a continuum of PyC, possesses a range of physiochemical properties. Biochar properties influence the biogeochemical process of bioavailability, mobility and transport of nutrients (Glaser et al., 2000; Hiemstra et al., 2013; Lehmann et al., 2001), and contaminants (Lou et al., 2013). With aging, the physicochemical properties of biochar also change and result in the release of a range of biochar-derived organic materials (BDOMs) (definitions of terms can be found in Box 1). Therefore, an understanding of biochar aging along with physicochemical properties is important for nutrients and contaminants management. A large number of reviews have been published on different aspects of biochar and PyC in general, and several of them focused on biochar mineralization and C stability in soils. For example, the soil microbial role on biochar stability has been reviewed, illustrating the different mechanisms of mineralization through biotic and abiotic processes (Ameloot et al., 2013). In other reviews, factors controlling the stabilization and transport of PyC have been described (Czimczik and Masiello, 2007; Knicker, 2011). To date, a comprehensive assessment of the biochar aging process has not been undertaken. Here, we review studies where the physiochemical properties of biochar and BDOMs were examined at different stages of aging, caused either by natural aging in the soil or by chemical treatment. We will then discuss the potential impacts of biochar aging on agriculture and environment.

BOX 1 Definition of Terms Biochar—Pyrolyzed biomass that is produced with limited or no oxygen for soil application, targeted to achieve agricultural or environmental benefits (Sohi et al., 2010). Char(coal)—Partially burned biomass produced during wild fire or any other fires (Schmidt et al., 1999). Aromatic moieties—A plane of C formed with a variable number of fused benzene rings (Laine, 2012; Schmidt and Noack, 2000). Volatile organic carbon (VOCs)—The intermediate products of pyrolysis, such as pyrazines, pyridines, pyrroles, and furans, which are entrapped in between planes of biochar or char. This fraction of C is usually removed at high temperature, i.e., 950°C within a short period of time (10 min) (Keiluweit et al., 2010; Spokas et al., 2011). Continued

4

S. Mia et al.

BOX 1 Definition of Terms—cont’d Biochar-derived organic materials (BDOMs)—On aging, biochar undergoes physiochemical changes and different organic materials are produced ranging from surface oxidized biochar to molecular benzene polycarboxylic acids. All together, these materials can be treated as BDOMs. Following the protocol of International Humic Acid Society (IHAS), BDOMs can be separated into four different fractions. These are (a) surface oxidized char, neither dissolve in acid nor alkali or water, (b) humic acids (HAs), dissolve in alkali but not in acid, (c) fulvic acids (FAs), dissolve in both acid and alkali, and (d) dissolved organic carbon (DOC), soluble in water (Abiven et al., 2011; Hiemstra et al., 2013; Trompowsky et al., 2005). Artificially aged biochar—Biochar can be aged using accelerated aging methods, for instance, physical methods including drying or wetting and chemical methods such as HNO3, H2O2, K2Cr2O7, KMnO4, RuO4, (NH4)2S2O8, and O3 treatment (Hiemstra et al., 2013; Jimenez-cordero et al., 2015; Liu et al., 2013; Smith et al., 2015; Sultana et al., 2011). The derived surface oxidized biochar is considered as artificially aged biochar or oxidized biochar, which is soluble to neither acid nor alkali or water. Biochar-derived humic acids (BDHAs)—The alkali-soluble fractions but acidinsoluble fractions collected after aging process (Trompowsky et al., 2005). Naturally aged char—The char that has been aged in soil with natural soil processes such as physical breakdown, chemical action of temperature, photo-oxidation, or by microbial degradation or combinations of several processes (Chughtai et al., 1991; Cohen-Ofri et al., 2006; Hockaday et al., 2007; Sutherland, 1992). This fraction only includes surface oxidized char but dissolves neither in acid nor alkali or water.

2. BIOCHAR AND ITS AGING Biochar is charred biomass rich in aromatic C, produced under limited oxygen supply or in the absence of oxygen. During pyrolysis, aliphatic chains of C in the feedstock are converted to aromatic C (Baldock and Smernik, 2002; Chen and Ho, 1998; Demirbas¸, 2000; Zeng et al., 2011) via a range of intermediate products, generally called polyaromatic hydrocarbons (PAHs), such as acetone, benzene, and toluene (Braadbaart and Poole, 2008; Spokas et al., 2011). The aromatic C condenses further with increasing temperature (>270°C) and pyrolysis residence time (Braadbaart et al., 2009), leading to the formation of aromatic moieties or planes. The aromatic moieties of variable sizes are connected to each other or with aliphatic chains (Laine, 2012; Schmidt and Noack, 2000) forming interconnected C planes, which is known as fixed C (Baldock and Smernik, 2002;

A Molecular Insight Into Biochar Aging

5

Keiluweit et al., 2010). Some of the intermediate products are entrapped between planes of fixed C and known as volatile organic compounds (VOCs) (Braadbaart et al., 2009). VOCs are considered to be labile (Yargicoglu et al., 2014). The proportion of fixed C and VOCs depends on pyrolysis conditions, such as heating rate, pyrolysis temperature (Wiedner et al., 2013), residence time, and feedstock’s quality (Baldock and Smernik, 2002). In general, biochars produced at high temperature contain a low proportion of aliphatic C, VOCs, and a high proportion of aromatic C (Baldock and Smernik, 2002; Knicker et al., 2005). Biochar with a mixture of highly heterogeneous biomacromolecules can be produced by changing any of the variables, i.e., pyrolysis temperature and duration or feedstock quality (Knicker et al., 2008a; Masiello, 2004). Therefore, biochar for specific target bound applications such as C sequestration or agricultural amendment can be produced. Biochar structure, especially the fixed C, has been described in detail elsewhere (Preston and Schmidt, 2006). Here, we have redrawn a model of biochar from the published literature (Fig. 1). It has been perceived that biochar or PyC is mostly inert (Preston and Schmidt, 2006) and ubiquitous in the environment (Bird et al., 2002; Foereid et al., 2011; Schmid et al., 2002). However, a number of studies showed that biochar applied to soil undergoes changes due to activities of soil biological, chemical, and physical agents (Cheng and Lehmann, 2009; Fang et al., 2014a,b, 2015; Hockaday et al., 2006, 2007; Sutherland, 1992). The changes in biochar with the aging process are discussed under two subheadings in the following sections.

2.1 Decomposition of Aliphatic and Volatile Carbons Depending on the production conditions and feedstock, biochar may contain variable proportions of aliphatic C and VOCs. When biochar is applied to soil, aliphatic C and VOCs are mineralized by soil microorganisms as evidenced from the reduction of aliphatic C with aging (Braadbaart et al., 2009; Hockaday et al., 2006; Kuzyakov et al., 2014). For example, Kuzyakov et al. (2014) found direct evidence of microbial decomposition of biochar using a 14C tracer study. In biochar, the aliphatic parts connect the aromatic moieties or are present as side branches of the aromatic layers (Fig. 1). Therefore, microbial decomposition of aliphatic C results in the release of disconnected aromatic moieties. These aromatic moieties thus oxidize and develop functional groups, e.g., carboxylic groups at the breaking points. Due to development of functional groups, the oxidized biochar can interact with soil minerals, nutrients, and contaminants. The

O

• Layer of aromatic moieties connected with aliphatic chains or aromatic rings N

• Volatile organic carbon (VOC) entrapped within interconnected layer

O

O

N

CH2-CH2-CH2

O+

N

N

O+

VOC

o

O+ +

• Release of surface oxidized aromatic moieties • Release of VOC and mineralization or interaction with soil minerals or ions

Medium-term aging (25–1 kyears)

• Breaking down of aromatic moieties into smaller sizes with surface oxidation • Release of BPCAs from the surface of aromatic moieties • Physical stabilization of oxidized biochar and BPCAs due to interaction with minerals • Transport of BPCAs • Mineralization continued with the release of progressively smaller sized biochar

Long-term aging (1–100 kyears)

Molecular BPCAs and loss of BPCAs

Depolymerization or mineralization by biotic or abiotic processes

Early aging (0–25 years)

• Mineralization of aliphatic interlinking chains

N

O+

O+

O

O+

O

N N

CH-n(CH)2-CH2-

O

Model biochar O

OH O

O

HO

O OH

O O HO

OH O

O

OH O H

OH

O OH

OH O

H

OH HO

O

O

O

OH

OH

OH

Surface oxidized biochar

HO

O

OH O

B3CA

H H HO

O H HO

O OH

O

Surface oxidized biochar with ~6 benzene rings

OH O

O

OH O O HO

Carbon loss as CO2

N

N

HO

Benzene polycarboxylic acids = BPCAs

o

HO

O+

CH n(CH)2-CH2- CH2-

O

OH

B6CA

Fig. 1 Schematic presentation of biochar aging and the production of biochar-derived organic materials (BDOMs) including benzene polycarboxylic acids (BPCAs). Biochar structure is redrawn with adoption after Goldberg (1985), Fakoussa and Hofrichter (1999), and Knicker et al. (2008a). Surface oxidized biochar is adopted after Kamegawa et al. (2002) and Mao et al. (2012) while BPCAs are adopted after Hammes et al. (2008). Curved arrow indicates breaking point.

A Molecular Insight Into Biochar Aging

7

decomposition rate of the aliphatic part of biochar might take place at similar timescales as decomposition of normal soil organic matter (SOM), although a faster decomposition was suggested for comineralization with labile organic matter (Hamer et al., 2004; Keith et al., 2011; Pietik€ainen et al., 2000) in natural ecosystems. Therefore, labile or aliphatic C of biochar can turn over within a short period of time (0–25 years) leaving oxidized, but otherwise intact, aromatic moieties behind (Hilscher et al., 2009).

2.2 Breaking Down of Aromatic Moieties With progressive aging, the large aromatic moieties, either disconnected or intact, will undergo physical, chemical, microbial (Chughtai et al., 1991; Cohen-Ofri et al., 2006; Hockaday et al., 2007; Hofrichter et al., 1999; Sutherland, 1992), and possibly photochemical degradation (Bird et al., 1999). Basically, aromatic moieties of biochar consist of benzene rings. The benzene rings at the edges of biochar have a lower number of bonds with which they are connected to the larger aromatic moieties compared to the rings in the core of the moieties. Therefore, decomposition of biochar occurs first at the edges leading to the release of some of the aromatic rings from the biochar edges, and forming functional groups at the breaking points. As a result, surface oxidized biochar and benzene polycarboxylic acids (BPCAs) are formed. The surface oxidized biochar becomes progressively more resistant to further decomposition due to the loss of the more labile part (Bird et al., 1999) and its interactions with soil minerals (Bird et al., 2002). However, with further progressive aging, biochar will continue to break down and lead to increasingly smaller sized aromatic moieties. With this process, the size of aromatic moieties might reach to a stage of few conjugated benzene rings with a high number of surface functional groups. The transformation from large size aromatic moieties to several few fused rings in soil could take place within a time frame of hundreds to thousands of years. For example, small-sized aromatic moieties that have resulted from thousands year of aging can be identified in Terra Preta and other anthropogenic soils as well as in marine sediments (Mao et al., 2012; Schmid et al., 2002). The timescale might be even longer for very condensed biochar. Conversely, biochar with low aromatization may reach at this stage within a short timescale of 25–100 years. The smaller aromatic moieties consisting of few benzene rings may even undergo further breakdown, and in extreme cases, it may lead to the formation of molecular benzene with six carboxylic acid groups (B6CAs). The formation of molecular B6CAs may take a very long time of over 1000 years.

8

S. Mia et al.

The released benzene rings from aromatic moieties may contain a variable number of carboxylic acids, ranging from 2 to 6. The level of carboxylation depends on the number of bonds involved that were connected to other aromatic rings in the aromatic moieties. During the initial stages of aging, the aromatic moieties will release benzene rings with a low number of carboxylic groups (3–4) as these benzene rings were connected to aromatic moieties at the edges with only a few bonds and therefore relatively easy to break down. At advanced stages of biochar aging, the benzene rings will contain a larger number of carboxylic functional groups (5–6) as these benzene rings are released from the core. Therefore, the BPCA release pattern can be in the order of B2CA > B3CA > B4CA > B5CA > B6CA, suggesting an indication for the degree of aging. For example, in a field study, Hammes et al. (2008) claimed a loss of 25% of BPCAs over 100 years, mostly as B3CA and B4CA, with no loss of B5CA and B6CA. The BPCAs, thus produced with aging, are very reactive and interact with soil minerals, nutrients, and contaminants. When bound to soil minerals, physically protected BPCAs might escape from further degradation and can remain in the soil for a longtime estimated to be millions of years (Eusterhues et al., 2005). However, BPCAs can also be leached and transported from soils due to increase in solubility (Kalbitz et al., 2000). Additionally, a part of BPCAs may also be chemically sorbed to both biochar and SOM. With progressive aging, the number of functional groups on the oxidized biochar surface, particularly carboxylic and phenolic, increases, and simultaneously the BPCAs released from progressively aged biochar contain a high number of carboxylic groups. Therefore, the negative surface charge at aged biochar and BDOMs will increase with the advancement of the aging process.

3. ACCELERATED METHODS OF BIOCHAR AGING Biochar ages in the environment with natural oxidizing agents as well as with soil microbial agents. However, biochar aging can be accelerated following several methods, which are described in the next section.

3.1 Biochar Aging With Chemical Agents Biochar or PyC is usually oxidized with several chemical oxidizing agents targeting different fractions, i.e., oxidized (bio)char fraction, acid-soluble fraction (fulvic acids, FAs), and acid-insoluble fraction (humic acids, HAs) (Table 1). A number of oxidizing agents, such as H2O2, H2SO4, HNO3,

Table 1 Biochar Aging With Different Chemical Agents Oxidation

Targeted Materials

Oxidizing Agent Pyrogenic (OA) Material (POM)

POM: OA Temperature Duration Oxidized (w/v) (°C) (h) Biochar

FAs HAs References

H2O2 (1–30%)

Biochar

20

25

2

+







Huff and Lee (2016)

H2O2 (1–30%)

Biochar

33.3

25

24

+







Sun et al. (2016)

HNO3 and H2SO4 (1:3)

Biochar

80

70

6

+







Ghaffar et al. (2015), Qian and Chen (2014) and Qian et al. (2015)

HNO3

Biochar

45

100

4







+

Guimara˜es et al. (2015)

KOH

Biochar

–

100

2

+







Yakout (2015)

HNO3 (65%)

Biochar

1

100

3

+







Yakout (2015)

H2SO4 (2%)

Biochar

–

150

24

+







Yakout (2015)

H2O2 (15–30%) Biochar

10

25–30

100

+







Yakout (2015) and Wang et al. (2015)

Na2S2O8 and H2O2

Biochar

10

60

4

+







Khalid and Klarup (2015)

H2O2 (0–30%)

Biochar

400

60

24–240

+







Guo and Chen (2014)

HNO3 (25%)

Biochar

30

90

4







+

Hiemstra et al. (2013)

H2O2

Biochar

70

80

2

+







Cross and Sohi (2013)

HNO3 (65%)

Biochar

10

80

48

+







Liu et al. (2013)

H2O2

Biochar

6.3

22

2

+







Xue et al. (2012) Continued

Table 1 Biochar Aging With Different Chemical Agents—cont’d Oxidation

Targeted Materials

Oxidizing Agent Pyrogenic (OA) Material (POM)

POM: OA Temperature Duration Oxidized (w/v) (°C) (h) Biochar

FAs HAs References

HNO3

Char

50

104

4

+




+

Sultana et al. (2011)

H2O2 (7%)

Char

50

30

336

+




+

Sultana et al. (2011)

RuO4

Char

134

25

16

+




+

Sultana et al. (2011)

HNO3

Biochar

170

8

+

+

Schneider et al. (2011)

K2Cr2O7 in H2SO4

Biochar

400–267 60

+







Ascough et al. (2011)

HNO3 (65%)

Charcoal

–

170

8




+

+

Wiedemeier et al. (2015)

HNO3 (65%)

Biochar

–

170

8




+

+

Schneider et al. (2010)

HNO3 (65%)

Black carbon

180

8







+

Ziolkowski and Druffel (2009)

HNO3 (65%)

Charcoal

–

170

8







+

Kaal et al. (2008)

HNO3 (65%)

Charcoal

–

170

8







+

Hammes et al. (2008)

RuO4

HA acids

67–133

25

24

+




+

Ikeya et al. (2007)

HNO3 (65%)

Black carbon and charcoal

20

170

8

+







Brodowski et al. (2005, 2007)

HNO3 (25%)

Biochar

60

100

4

+

+

+

Trompowsky et al. (2005)

H2O2 (0–7%)

Char

50

30

168–672 +




+

Shindo et al. (2004)

HNO3 (61%)

Black carbon

33.3, 16.7

100

1000

+




+

Kamegawa et al. (1998, 2002)

RuO4

Coal

0.1

40

24–48

+




+

Murata et al. (2001)

H2O2 (30%)

Black carbon

10

60

2

+

+

+

Wu et al. (1999)

HNO3

Char

50

200

1

+




+

Shindo and Honma (1998)

25

24

+







Moreno-Castilla et al. (1997)

Saturated Activated carbon 10 (NH4)2S2O8 in H2SO4 HNO3

Char

4

–

4

+




+

Haumaier and Zech (1995)

H2O2

Char

15.4

–

96







+

Haumaier and Zech (1995)

HNO3 (65% M)

Activated carbon 10

80

48

+







Moreno-Castilla et al. (1995)

H2O2 (30%)

Activated carbon 10

25

48

+







Moreno-Castilla et al. (1995)

(NH4)2S2O8

Activated carbon 10

25

48

+







Moreno-Castilla et al. (1995)

HNO3 (65%)

Black carbon

20

170

8

+







Glaser et al. (1998)

KMnO4 (4%)

Soil HAs

250

–

2

+

+

+

Schnitzer and Calderoni (1985)

H2O2 (30%)

Anthracite (coal) 6

25

308

+







Heard and Senftle (1984)

KMnO4 (4%)

Biochar

90

32







+

Shafizadeh and Sekiguchi (1983)

100

12

S. Mia et al.

and (NH4)S2O8, have been used in the oxidation process. Additionally, variable biochar to oxidant ratios, oxidation temperature, and period of exposure have been used. There is variability in the strength among the oxidizing agents, where HNO3 has shown to be one of the stronger oxidizing agents (Sultana et al., 2011; Yakout, 2015). A progressively increased concentration of oxidizing agent and duration of oxidation can cause a greater magnitude of biochar oxidation, but can also result in increased weight loss of biochar (Ascough et al., 2011; Cross and Sohi, 2013; Wang et al., 2015). The fraction of HAs and FAs also depend on particular oxidizing agents, strength, and duration of oxidation (Shindo and Honma, 1998; Sultana et al., 2011). Sultana et al. (2011) found the highest HA yield (299 mg g
1 biochar C) after oxidation of a Japanese cedar wood biochar (pyrolyzed at 400°C) with HNO3 (1:50, w/v) at 104°C for 4 h in comparison to oxidation with H2O2 (2.5 M, 1:50, w/v) at 30°C for 336 h and with RuO4 (1:134, w/v) at 25° C for 16 h. Additionally, new functional groups might be introduced while oxidizing. For instance, introduction of dNO2 was identified when biochar was oxidized with HNO3 (Trompowsky et al., 2005). Biochar properties also determine the production of oxidized biochar, HAs and FAs (Ascough et al., 2011; Cross and Sohi, 2013; Trompowsky et al., 2005). In general, highly aromatic biochars are very resistant to oxidation (Ascough et al., 2011; Cross and Sohi, 2013). Trompowsky et al. (2005) oxidized eucalyptus wood biochar with HNO3 (25%, 1:60 w/w) at 100°C and reported the highest HAs production (450 mg g
1 biochar) from the biochar produced at 450°C, while the production of FAs was the highest from the biochar produced at 300°C (310 mg g
1). The lower production of HAs and FAs from biochar, produced at higher temperature (>500°C), may be due to oxidation resistance of the highly condensed aromatic moieties. Therefore, biochar intrinsic chemical properties such as aromaticity, strength of the oxidizing agent, biochar to oxidizing agent ratio, oxidation temperature and duration can determine the magnitude of oxidation and production of oxidized biochar, HAs and FAs. However, it is not clear which parts of biochar, either aliphatic or aromatic, are oxidized with a particular type of chemical. For a targeted bound application, such as for agricultural use, it is needed to investigate which of the chemical oxidizing agents or their combination can sufficiently increase CEC without incurring a significant weight loss of the original biochar. A challenge will further be to find cost-effective ways to purify the oxidized materials for agricultural use, and to minimize harmful effects of residual oxidizing agents in the biochar on the environment and human health.

A Molecular Insight Into Biochar Aging

13

3.2 Microbial Aging of Biochar Supplemented With Fresh Biomass Under Favorable Environmental Conditions Aging of biochar can be accelerated with the aid of microorganisms whose activity can be enhanced through supplementation of labile organic compounds such as glucose or fresh biomass (Hamer et al., 2004; Keith et al., 2011; Pietik€ainen et al., 2000). Recently, biochar has been used as an animal feed and a bulking agent for compost and in these systems biochar was found to be oxidized or aged (Dias et al., 2010; Joseph et al., 2015). During the composting process, microbial degradation of both composting materials and biochar, particularly the aliphatic part, may accelerate biochar aging for several reasons. These are (a) a high temperature (70°C) during the bio-oxidation phase of composting that stimulates the oxidation of biochar (Dias et al., 2010), (b) refugee sites inside biochar that support the growth of microorganisms (Jindo et al., 2012), (c) increased comineralization of biochar labile fractions due to adsorption of organic material in the biochar surfaces (Deluca et al., 2006), and (d) increased aeration within the compost pile (Steiner et al., 2010) that boosts microbial activity (Khan et al., 2014; Wei et al., 2014). Co-composting of biochar is also found to retain nutrients from mineralizing biomass. For example, mineralization of organic N from fresh biomass can increase inorganic N concentration and such released N can be retained as NO3

N and NH4 +
N on the ion exchange sites of biochar (Kammann et al., 2015; Mizuta et al., 2004). Consequently, N losses during composting can be reduced (Li et al., 2015). As a result, the labile C:N ratio reduces, which may further accelerate the composting process. Therefore, biochar blended composting can reduce N loss while contributing to the aging of biochar. With a similar approach, biochar can be aged with glucose supplementation when exposed to a relatively high temperature (50–70°C). Feeding of biochar to animals can also result in oxidation while providing benefits to animals (Joseph et al., 2015). While passing through the animal digestive system, the biochar experiences both acidic and alkaline environments. In addition, biotic agents in the rumen of animals can also play important roles in oxidation of biochar. Joseph et al. (2015) reported that biochar fed to animals was more oxidized and contained more nutrients on its surface compared to a fresh biochar.

3.3 Physical Aging of Biochar Biochar can be aged through physical breakdown, although this form of aging may not be as effective as chemical and microbial aging in terms of

14

S. Mia et al.

the chemical reactivity of biochar. For example, biochar was aged with alternate wetting–drying methods at different levels of moisture content in a number of studies (Liu et al., 2013; Mohanty and Boehm, 2015; Naisse et al., 2015; Zhang et al., 2016). Freezing and thawing have also been practiced for biochar aging (Mohanty and Boehm, 2015; Naisse et al., 2015). Additionally, partial surface oxidation of biochar was proposed by Lee et al. (2013) with an oxygen plasma treatment and air treatment directly after pyrolysis (at hot conditions).

4. PROPERTIES OF BIOCHAR AND BIOCHAR-DERIVED ORGANIC MATTER Changes in the structure and surface properties of biochar and BDOMs are usually determined using spectroscopic techniques, such as NMR, FTIR, XPS, NEXAFS, and chemical analyses (e.g., surface charge and CEC determination). To explore the changes in biochar properties with aging, the properties of fresh biochar, artificially aged biochar, biocharderived humic acids (BDHAs), naturally aged char (ranging in age between 100 and >1000 years), and HAs from char received soils are compared to reference SOM and HAs in the following sections.

4.1 Structural and Functional Composition 13

C NMR has been used in many studies to characterize different proportions of C species such aliphatic, aromatic, and carboxylic or carbonyl in PyC. Fig. 2 shows some examples of 13C NMR spectra from different studies of fresh biochar, artificially aged biochar, BDHAs, naturally aged char, HAs collected from char received soils, SOM, and HAs from a soil without (bio)char. The NMR signal at 0–45 ppm has been assigned to aliphatic (CHx), 45–110 ppm to O-alkyl (OCH3), 110–160 ppm to aromatic, and 160–220 ppm to carboxyl and carbonyl C species (Hilscher et al., 2009; Knicker et al., 2007). There was a high signal intensity in the aromatic region (130 ppm) for all biochar-related materials, except for the SOM and soil HAs, suggesting a higher fraction of aromatic C content in (bio)char and BDHAs. The artificially aged biochar and biochar-derived HAs showed an indication of carboxylation with a stretching signal at 165 ppm (Baldock and Smernik, 2002; Hilscher et al., 2009; Knicker et al., 2007; Shindo et al., 2004; Sultana et al., 2011). Similarly, a dominant signal at 165 ppm in the naturally aged char and HAs collected from char received soils suggests carboxylation with aging (Golchin et al., 1997a,b; Ikeya et al.,

15

A Molecular Insight Into Biochar Aging

Carboxyl/carbonyl C Aromatic C

Aliphatic C

Fresh biochar Artificially aged biochar Biochar-derived HAs Naturally aged biochar HAs from char received soil SOM Soil HAs 300

200 100 Chemical shift (ppm)

0

Fig. 2 13C NMR spectra of fresh biochar (produced at 400°C, BC400), artificially aged biochar (oxidation of BC400 with HNO3) and biochar-derived HAs from BC400 (Sultana et al., 2011), naturally aged char (Schmid et al., 2002), HAs collected from char received soils (Shindo et al., 2004), a soil organic matter (SOM) (Kiem et al., 2000) and a soil HA without bio(char) (Ikeya et al., 2004).

2004; Rumpel et al., 2006; Schmidt et al., 1999; Skjemstad et al., 2002). These findings suggest a greater extent aging of the naturally aged char than the artificially aged biochar materials. In contrast, there was a high signal intensity at 20–40 ppm and at 70 ppm in the SOM and soil HAs, indicating that they had a high fraction of aliphatic and O-alkyl C (Ikeya et al., 2004). Additionally, both SOM and soil HAs contained carboxyl C species. In a number of studies, the fraction of different C species has been quantified by deconvolution of signal intensities of C species in the NMR spectra. To understand the extent of carboxylation, we synthesized the data for fractions of C species obtained from 13C NMR spectra from different studies (Fig. 3). The fraction of aromatic C content (%) indicates the degree of aromaticity, while the fraction of carboxyl and carbonyl C species (%) indicates the level of oxidation or aging of biochar. The SOM and HAs in soils without (bio) char contained comparatively low proportion of aromatic C (23% and 26%), while naturally aged chars and HAs collected from char received

16

S. Mia et al.

n = 72

20

Fresh biochars Artificially aged biochars Biochar HAs Char received SOM Natually aged chars HAs from char received soil SOM Soil HAs

n = 15

18 n = 23 n = 37 n = 130

16 14

n = 124

12 10

Biochar aging

Carboxyl + cabonyl C content (%)

22

n = 13

n=9

8 6 10

20

30 40 50 60 Aromatic C content (%)

70

80

Fig. 3 Relationship between aromaticity (% aromatic C) and carboxylation (percentage of carboxyl + carbonyl C) in fresh biochars, artificially aged biochars, biochar-derived HAs, naturally aged chars, and HAs collected from char received soils. The error bar indicates standard error for the number of observations as indicated in the graph. Data are taken from Arai et al. (1996), Dieckow et al. (2005), D€ umig et al. (2009), Duarte et al. (2013), Golchin et al. (1997a,b), Hatcher et al. (1989), Hilscher et al. (2009), Hiradate et al. (2004), Ikeya et al. (2004), Kaal et al. (2008), Khan et al. (2006), Kiem et al. (2000), Kleber et al. (2003), Knicker et al. (2006, 2007, 2008b, 2013), Liang et al. (2008), Maie et al. (2002), Mastrolonardo et al. (2015), Mo€ller et al. (2000), Novotny et al. (2007), Rodionov et al. (2006), Rumpel et al. (2006), Schmidt et al. (1999), Shindo et al. (2004), Skjemstad et al. (1996, 2002), Solomon et al. (2007), Suárez-Abelenda et al. (2014), Sultana et al. (2011), Tate et al. (1990), Tinoco et al. (2006) and Trompowsky et al. (2005).

soils had a higher content of aromatic C (33% and 40%). The proportions of aromatic C in fresh biochars, artificially aged biochars, and biochar HAs were the highest (>60%) which is likely due to the presence of a considerable fraction of aromatic C in pyrogenic materials. Fresh biochars had the lowest fractions of carboxyl and carbonyl C (8.7%) which increased to 10.4% after they were artificially aged, suggesting that artificial aging causes carboxylation. The fraction of carboxyl and carbonyl C was the highest (19.3%) in HAs collected from char received soils, while a similar carboxylation (17.9% of carboxyl and carbonyl C) was found for HAs derived from artificially aged biochars. Moreover, the carboxylation of naturally aged chars was significantly higher (a 48% greater carboxyl and carbonyl C) than artificially aged biochars, suggesting a higher degree of aging. As compared to soil HAs, both HAs, either derived through artificial aging or collected from char received soils, had a greater level of carboxylation, suggesting that

17

A Molecular Insight Into Biochar Aging

HAs from PyC have a higher capacity for carboxylation compared to HAs from non-PyC. A possible explanation for this difference may be due to the presence of a relatively larger number of carboxyl or carbonyl groups in small aromatic moieties compared to SOM, which predominantly consists of macromolecules with aggregation of long-chain aliphatic and aromatic C species. FTIR spectroscopy is usually used to identify different functional groups present in organic compounds. FTIR spectra of fresh biochar, artificially aged biochar, biochar-derived HAs, and naturally aged char from different studies were compared to understand the changes in functional groups with aging of biochar (Fig. 4). The assignment of signal stretching for different functional groups is presented in Table 2. Consistent with other pyrogenic materials, all four biochars or BDHAs showed a clear stretching signal for aromatic C]C at 1600 cm
1 and aromatic CdH at 3200 cm
1 (Ascough et al., 2011; Cheng et al., 2008; Ghaffar et al., 2015; Jimenezcordero et al., 2015; Liu et al., 2013; Qian and Chen, 2014; Qian et al., 2015; Singh et al., 2016; Yakout, 2015). For the artificially aged biochar, stretching signal was observed at 1700 and 1210 cm
1, suggesting the –COOH CKC

–OH Fresh biochar

–OH

Artificially aged biochar

Naturally aged char

Biochar-derived HAs

4000

3500

3000

2500

2000

1500

1000

Wavenumber (cm−1)

Fig. 4 FTIR spectra of fresh and artificially aged biochars (adapted from Liu et al., 2013), Terra Preta char (from Archanjo et al., 2014) and biochar-derived HAs (from Trompowsky et al., 2005). The dotted lines represent the bands for different functional groups.

18

S. Mia et al.

Table 2 Assignment of FTIR Spectral Stretching to Different Functional Groups Signal Stretching (Wavenumber References Functional Group cm21)

Kaolinite bound to aged 3695 biochar with (dOH)

Singh et al. (2016)

Phenolic dOH

3400

Liu et al. (2013), Shindo et al. (1986a,b) and Trompowsky et al. (2005)

Oxides sorbed to aged biochar with (dOH)

3395

Singh et al. (2016)

Aromatic CdH

3050, 3200

Kamegawa et al. (2002) and Singh et al. (2016)

Aliphatic CdH

2620, 2850, 2920, 2965

Kamegawa et al. (2002), Lehmann et al. (2005) and Singh et al. (2016)

Carboxylic and ketones C]O

1690, 1720

Ascough et al. (2011), Kamegawa et al. (2002), Lehmann et al. (2005), Liu et al. (2013) and Singh et al. (2016)

Aromatic C]C and C]O of quinone

1600

Ascough et al. (2011), Kamegawa et al. (2002), Lehmann et al. (2005), Liu et al. (2013) and Singh et al. (2016)

NdH bonded amide and heterocyclic N

1534, 1346

Qian et al. (2015) and Trompowsky et al. (2005)

Aliphatic CdH

1450

Ascough et al. (2011)

CadCdO

1415

Archanjo et al. (2014)

Phenolic dOH

1200

Ascough et al. (2011), Kamegawa et al. (2002), Lehmann et al. (2005) and Liu et al. (2013)

PO4 3-

1100

Archanjo et al. (2014)

CadPO4

960

Archanjo et al. (2014)

presence of carboxylic or ketone (C]O) and phenol groups, respectively (Ascough et al., 2011; Cheng et al., 2008; Ghaffar et al., 2015; Jimenezcordero et al., 2015; Liu et al., 2013; Qian & Chen, 2014; Qian et al., 2015; Trigo et al., 2014; Uchimiya et al., 2012; Yakout, 2015). In addition, there was an increase in the intensity of dOH stretching band at 3400 cm
1 for aged biochar or biochar-derived HAs (Cheng et al., 2008;

A Molecular Insight Into Biochar Aging

19

Ghaffar et al., 2015; Liu et al., 2013; Shindo et al., 1986a; Trompowsky et al., 2005). Biochar HAs, derived with artificial aging, showed stretching bands for carboxyl or ketone (1710 cm
1) and hydroxyl (1250 cm
1), but with a greater intensity suggesting a higher content of these functional groups (Ghaffar et al., 2015; Shindo et al., 2004; Trompowsky et al., 2005). Chemical oxidation of biochar with HNO3 introduced a nitro (
NO2) group at around 1540 and 1346 cm
1 (Qian and Chen, 2014; Qian et al., 2015; Trompowsky et al., 2005), indicating a change in chemical properties during oxidation with HNO3. Natural aging of biochar also caused functionalization, showing absorption bands at 1700 cm
1 for carboxylic and at 1210 cm
1 for hydroxyl groups (Ascough et al., 2011; Cheng et al., 2008; Lehmann et al., 2005; LinChao et al., 2009; Nishimura et al., 2012; Rebollo et al., 2008; Shindo et al., 1986a,b; Trigo et al., 2014). In natural environments, due to interactions between aged (bio)char and ions or molecules in soil solutions, the position of participating functional groups may be shifted. For example, the carboxyl signal at 1700 cm
1 shifted to 1400 cm
1 due to the formation of CadPdO (Archanjo et al., 2014). Singh et al. (2016) recently found absorption bands of SOM (2850 and 2965 cm
1 for aliphatic CdH of SOM) and minerals (3695 cm
1 for dOH of kaolinite, 3395 cm
1 for dOH of oxides) in the light fraction (density C]O), and at 288.8–288.9 eV to carboxyl, ester, and lactones (Singh et al., 2014; Yao et al., 2010). With aging, either artificially or naturally, increased absorption of the binding energy at 285–289 eV was observed in many studies suggesting an increased existence of hydroxyl, carbonyl, and carboxyl functional groups (Cheng and Lehmann, 2009; Ghaffar et al., 2015; Lin et al., 2012; Pereira et al., 2014; Yao et al., 2010). When biochars were artificially aged, the fractions of C forming hydroxyl, carbonyl, and carboxylic functional groups were

20

S. Mia et al.

A

80

Fraction of carbon species (%)

Fresh biochars Artificially aged biochars

60 Naturally aged chars

40

20

0 Carboxyl group –COOR

Carbonyl –CKO

B 0.8

Ether or hydroxyl –COR

Aliphatic or aromatic C–C, CHx,CKC

C –OH

n = 16

CKC–COOH Naturally aged char Absorption (a.u.)

OC/C

0.6

0.4 n = 16

0.2

Artificially aged biochar Fresh biochar

n=6

0.0 Fresh biochars

Artificially aged biochars

Naturally aged chars

280

285

290

295 300 305 Energy (eV)

310

315

320

Fig. 5 Comparison of surface functionality of fresh biochars with artificially or naturally aged (bio)chars. (A) Proportion (%) of different functional groups as identified in XPS C1s. (B) Proportion of oxygen-containing carbon species to the total carbon at (bio)chars surface as analysed with XPS C1s. (C) NEXAFS spectra of fresh, artificially aged biochar (adopted from Singh et al., 2014) and Terra Preta char (adopted from Lehmann et al., 2005). Error bar indicates standard error for number of observations. The number of observations for Panel B is indicated in the figure while for Panel A it is 14, 24, and 14, respectively for fresh biochars, artificially aged biochars, and naturally aged chars. The dotted lines in Panel C represent the bands for different functional groups. For Panel A, the data are collected from Cheng et al. (2006, 2008), Nguyen et al. (2008), LeCroy et al. (2013), Liu et al. (2013), Sorrenti et al. (2016), Singh et al. (2014) and Yang et al. (2016) while the Panel B is derived with data from Cheng et al. (2006, 2008), Nguyen et al. (2008), LeCroy et al. (2013), Liu et al. (2013) and Singh et al. (2014).

increased by 14.2%, 50.8%, and 66.6%, respectively. In comparison to fresh biochars, the increment for naturally aged chars was 37.1%, 189.3%, and 21.5% in hydroxyl, carbonyl, and carboxylic C, respectively. It is noticeable that the change in carbonyl C fraction was much higher in the naturally aged chars compared to both fresh and artificially aged biochars, but the fraction of carboxyl C was lower than artificially aged biochars. It is not clear why the fraction of carboxyl C species is lower in the naturally aged chars than

A Molecular Insight Into Biochar Aging

21

artificially aged biochars. However, the oxygen-containing C species to total C at the surfaces in the naturally aged chars was much higher, respectively by 113% and 257% than both artificially aged and fresh biochars (Fig. 5B). Surface properties of biochar after aging have also been studied with NEXAFS. In Fig. 5C, NEXAFS spectra from different studies were compared. The NEXAFS peak at 283.0–284.5 eV can be assigned to quinone; 284.0–258.5 eV to aromatic C]C, CdH; 286.0–287.4 eV to CdOH, C]O, RdC]O, CdN, C]N; 287.0–287.8 eV to aliphatic CdH; 288.0–288.8 eV to COOH, C]O; 289.0–289.5 eV to CdO; and 290.0–290.5 eV to C]O (Singh et al., 2014). Singh et al. (2014) aged biochar with soils at elevated temperature (40°C and 60°C) and found an increased intensity of stretching bands at carboxyl groups (288.5 eV) in the light density fraction (1000 years)

C+

C+

C+

A−

H OH

C+

A−

OH

O

C+

A−

Oxidized biochar

O

(iii)

C+

C+

C+

OH

C+

OH O H

O

O

C+

A−

Medium-term aging (25–1k years)

C+ C+ (ii) O + C+ OH C+ C OH

O

C+

Early aging (0–25 years)

− − + + + + + + + + − − − − − (iv) −

Surface negative charge (CEC) of biochar derived humic materials

Mineral surface

A Molecular Insight Into Biochar Aging

Free solution

Fig. 10 A model representation of interactions among soil minerals, cations, anions, biochar, and biochar-derived humic materials at different degrees of aging. C+ indicates cations, while A
represents anions. The interactions are (i) biochar positive surface and anion interactions, (ii) biochar negative surface charge and cation interactions, (iii) positive mineral surface–negative biochar surface–anion interactions, and (iv) negative mineral surface–cation–negative biochar surface interactions.

minerals, BDOMs, and nutrients (cations and anions) along the aging process are illustrated in Fig. 10. When fresh biochar is applied to soil, fresh biochar may adsorb a considerable amount of anions (Zheng et al., 2013) as it possesses a high SSA and little negative charge, or sometimes positive charge in the low pH range (1.000 ha) and claimed

Brazilian Agriculture in Perspective

93

that this was the great catalyzer of deforestation, but it was probably due to a decrease of 2.6% of farms with between 100 and 1000 ha in the same period. The survey of deforestation in 2013 demonstrated that the settlements were mainly responsible for the total deforestation in the period (29% of the total), representing 140,000 ha of the total 584,000 ha reported as deforested (IPAM, 2014). It is also proven that, apart from the settlements, deforestation is driven by the expansion of beef cattle and timber trade (Barona et al., 2010). According to the International Tropical Timber Organization, Brazil exported 236 million m3 of wood in 2014 and ranks fourth in timber trade in the world, behind China (284 million m3), India (296 million m3), and the United States (481 million m3). There were two major peaks of deforestation in 1995 and 2004, which are now under control, despite the 28% increase in 2013 over 2012, when annual deforestation was one of the lowest of the monitored period (MCTI, 2014). The impacts of deforestation and agriculture on the balance in greenhouse gas emissions (in CO2-equivalent units) over the past 20 years are evident (Fig. 3). The share of GHG emissions from land use and forestry

Fig. 3 Brazilian greenhouse gas emissions equivalent to CO2 in the period 1990–2012. Data from Brazilian Ministry of Science, Technology and Innovation, MCTI (Minist
erio da Ci^encia Tecnologia e Inovac¸ão), 2014. Estimativas anuais de emissões de gasesde efeito estufa no Brasil, second ed. MCTI/SEPED, Brasília, p. 168 (in Portuguese).

94

F.A.O. Camargo et al.

(land-use changes—LUCs) in the total emissions in the country varied most in this period. The LUC shows the peaks of deforestation in 1995 and 2004 and a downward trend in recent years to less than 15% of the national emissions in 2012. In these 20 years, gas emissions from farming have been growing slowly and steadily, most of them resulting from beef cattle production (44% of total emissions). In 2010, agriculture along with the energy sector accounted for most GHG emissions in the country (MCTI, 2014). In 2012, the estimated emissions of the country (including land-use change and forest—LUCF) were 4% of the total issued in the world, whereas China, the United States, and the European Union accounted for 46% of the emissions, including LUCF. Another advantage of the agricultural sector of the country for the world and the environment is the use of renewable energy. While most developed countries of the OECD (the United States, Canada, England, Germany, Japan, and Australia, among others) use 93% of nonrenewable energy, Brazil used only 46% in 2007. Energy from sugarcane has become the second largest energy source in the country. The surpluses of Brazilian GHG emissions and political initiatives in the country have been traded in carbon credits, and Sao Paulo, of all Brazilian states, ranks first in shares from Clean Development Mechanism (CDM) projects. To understand the international pressure on Brazil to preserve the Brazilian Amazon and Cerrado territories, it is worth remembering that some sectors of the international community are intentionally manipulating the international public opinion in favor of the preservation of natural resources of these territories. Underlying the intentions of some sectors of the international community are certainly economic interests, in particular the goal of weakening competition for commodities on the markets. The Brazilian public opinion and the press, in general, have assimilated the international environmental discourse. A critical point in this whole situation is that most areas with agricultural potential in Brazil lie in the Cerrado region. A part of these areas is covered by native vegetation and another significant portion is used for pasture (110 million ha), which is partially degraded (about 27 million ha). Especially from the degraded pasture areas, high amounts of sediments were transported to the Pantanal region, causing negative impacts in that environment (Merten and Minella, 2013). A strategy of preventing the conversion of native vegetation areas due to the expansion of agricultural activity in the region would be to impose conditions of recovering degraded pastures for agricultural use of Cerrado areas. The expansion of livestock farming in the Amazon region could be reduced if there were a political

Brazilian Agriculture in Perspective

95

orientation to invest efforts (through credit, research, and extension) in the improvement of the current conditions of beef cattle management, with a view to raise the stocking density, so that the same amount of beef Brazil has been producing could be raised on a smaller area with lower environmental costs for the country. 5.2.3 Economic Aspects With regard to the economic aspects that affect agriculture, we highlight the international barriers that interfere with the marketing of agricultural products, financing of agricultural activities in the country, our infrastructure, and the so-called Brazil cost. Although agriculture lost ground to industry in the composition of the Brazilian GDP in recent years, the activity accounts for a third of the GDP when including related sectors of the economy called agribusiness (corporate/commercial farming). This performance could be better, mainly if there were no trade barriers set by the European market, which absorbs 24% of Brazilian exports. In 2000, this market consumed 41% of agricultural exports, but it is currently the second largest food exporter after the United States. The drop from 41% to 24% is explained by the protectionist trade barriers, mainly the nontariff and CAP of the EU, which ensure artificial competitiveness with products outside the EU. The CAP is the root of European protectionism and was created as a system of agricultural subsidies to ensure better conditions for EU farmers by investments of US$ 126 billion in subsidies in 2011. Nontariff barriers resulted from the low competitiveness of European agricultural products and are the main obstacle against the trade of Brazilian agricultural products with the EU. These protectionist measures consist of import quotas and red tape, technical, ecological, sanitary, and phytosanitary barriers. Similar to the CAP in the EU, the United States has the Farm Bill that defines protectionist measures; both markets together import 50% of our agricultural products. A major part of these barriers is not up to international benchmarks and only intended to control imports and ensure internal and external price competitiveness of national agricultural products. Cotton is an example, into which the American government invests huge subsidies to maintain this totally uneconomic crop for the country. All countries have their forms of protection, and as the Brazilian agricultural products have characteristics that make them more competitive, they must be introduced according to the requirements of the international market. In this case, Brazil is not prepared either with proper representations abroad. The proof is that countries that produce much less agricultural

96

F.A.O. Camargo et al.

goods, e.g., France, Belgium, and Holland, export a volume that is twice as high as that of Brazil. In fact, Brazilian diplomacy has not trained thinktanks to discuss and defend the country’s agricultural markets, and in the emerging countries, which are major shoppers, the Brazilian trade representation is marginal. Aside from the trade barriers and subsidies that affect the foreign trade of the Brazilian agricultural market, there are also countless internal structural problems that hamper the process economically. Among these logistical problems, the most critical are related to the flow, e.g., transport (road, rail, and water ways), storage (distribution location and ports), and port services. The flow from the Cerrado or from more distant places has the most expensive logistics on the planet and depends on road transport and highways in disrepair. Due to the decayed state of the federal highway system in Brazil in 2013, fuel costs increased by BRL 1.4 billion. The construction and rehabilitation of transport routes require licensing, the overcoming of other technical and bureaucratic obstacles, and the goodwill of the government. In terms of storage, the country has a capacity of only 125 million tons of grain, which is limiting for a harvest of nearly 200 million tons. The national port services are insufficient and unsatisfactory, with sluggish loading/ unloading of ships, insufficient cargo handling capacity, lacking piers, and deficient basic logistics, requiring excessive labor for cargo handling, which is unionized and inefficient labor, compared to ports in other countries of South America. The attempts of the past governments to improve logistics infrastructure with the creation of programs such as PAC (Growth Acceleration Program) were lost by administrative interference, high internal corruption, and the inefficiency of the Brazilian government. Beneath these problems is the possibility of widespread power blackouts, since the current energy matrix was constructed during the military government and no investments were made by the civil governments since then to meet the requests of a population that has doubled in size and demand. Investing in logistics has apparently been the chief government investment in response to political demands of farmers and companies ever since the values of funding and costs of agricultural activity decreased in the country. With the saturation of the port capacity in the South and Southeast, the obvious alternative was the North and Northeast, using mainly rail and waterways instead of roads (Frederico, 2013). In this setting, the private companies (trading companies, banks, input companies, etc.) began to provide not only production but also monopolization of the flow, assuming storage, transport systems, and ports,

Brazilian Agriculture in Perspective

97

and maintaining an image of success of an activity over which the country has lost control. Another economic factor affecting agricultural production is the so-called Brazil cost. This expression is a term in the economic and political jargon of the country and is a generalization of a set of difficulties, such as poor infrastructure, excessive bureaucracy, administrative corruption, immoderate labor costs and high taxation, legal uncertainty, unskilled labor, expensive and inefficient logistics, etc., that stall the national development by increasing unemployment, informal labor, tax evasion, and foreign currency fraud. In a comparison of agricultural goods produced in the country (e.g., tractors, implements, and agricultural inputs), considering only eight items, it was found that in 2010 the price of the Brazilian product was on average 36.27% higher because of the “Brazil cost” than the price of an equivalent agricultural product from Germany or the United States. The infrastructure logistics to transport grain alone causes an estimated loss of US$ 4 billion per harvest—although the tax rate, one of the highest on the planet, is not even included in this Brazil cost. Due to the critical situation in the country, Brazil has been falling successively every year in competitiveness ranking (GCI—http://reports.weforum.org/globalcompetitiveness-index/; accessed November 17, 2016) and in 2013–2014 was ranked 56th due to the depreciation of subassets such as macroeconomic indicators (75th position), functioning of institutions (80th), government efficiency (124th), corruption (114th), and lacking trust in politicians (136th). Furthermore, the lack of quality of overall infrastructure (114th) and education (121st), along with an economy rather barred against foreign competition (144th), accounts for the low competitiveness of the country. In terms of financing of agriculture, farmers can get loans from a number of formal and informal funds, reaching BRL 20 billion in 2006 (IBGE, 2006). Banks account for over 80% of this amount and credit cooperatives for almost 5%. Classes A/B described in Table 8 account for 65% of the loans and class C for about 15% of the total financing. The historical series of rural credit in Brazil can be viewed on the website (www.bcb.gov.br/htms/ creditorural) and shows far higher values than those disclosed in the period by farmers for the 2006 Census. In 2012, the direct credit taken up by producers was BRL 114 billion, 68% of which was allocated to agriculture and the rest to animal husbandry. Federal banks accounted for 54% of this funding, followed by private banks (33%), credit unions (10%), and state banks (3%). Around 55% of this sum was spent on costs, 31% on investment and the rest for marketing. Cooperatives financed 4.6 million, of which 88% was

98

F.A.O. Camargo et al.

destined for agriculture. Small properties were financed (PRONAF) with BRL 16.3 billion, of which 49% was spent on agriculture (35%) and livestock production (14%) and the remaining 51% on investment in agriculture (25%) and livestock (26%). The direct credit for producers financed 2.6 million contracts for production on 13.7 million ha, while PRONAF funded 1.8 million contracts and the cooperatives 7.9 million contracts on 25,000 ha. Another crucial aspect of the economy of Brazilian agriculture is the lack of integration between public policies and the production chains. With the deregulation of markets, the adoption of liberal policies, and the globalization of the economy in the 1990s, the government decided to fragment the ministries directly involved with agricultural activities. At the apex of the bidirectional development of Brazilian agriculture, there are on the one hand the Ministry of Agriculture that deals with credit and income security of large and medium farmers and on the other hand the Ministry of Agrarian Development that addresses the interests of smallholders. In addition, the Ministry of Social Development and Fight Against Hunger deals with food distribution to the most needy. The Ministries of Planning and of Treasury, as well as the Chief of Staff Ministry, among others have an indirect effect on agriculture. The lack of integration between agricultural policies and the uninterrupted competition for resources and assignments among ministries creates a totally unproductive administrative chaos. As a result, the country’s agricultural sector, although one of the largest, is also one of the most vulnerable commodity producers. The direct support in the form of tariff protection is almost totally nullified by the high fees charged by banks. This, together with the ministries, agencies, entities, and councils of interest and representation, only worsens disintegration and dilutes the efficiency of the activity (Scolari, 2006). Apart from this lack of integration in the higher spheres of power, integration strategies and actions involved in the agricultural sector and production chains are also missing, due to the conservative view of the sector as a supplier of raw materials and not as a part of a larger chain that could add more value to its products. 5.2.4 Technical Aspects In technical terms, the actual Brazilian agriculture is still haunted by problems with rural technical assistance that tends to be available only in the southern states of Brazil, with the high levels of agrochemicals, lack of development of more efficient irrigation technologies, the need for innovation in research to meet the new challenges related to climate change, and the

Brazilian Agriculture in Perspective

99

demand to produce more with less negative environmental impact. The extension service in Brazil is represented in all 27 states of the Federation, with state and mixed state-federal institutions that reach about 1.7 million farmers and their families. They are based in 4200 offices in rural areas of 94% of the Brazilian municipalities and employ a technical staff of 15,000 extension workers with the most varied backgrounds (agronomists, veterinarians, animal scientists, sociologists, economists, agricultural experts, etc.). Despite these figures, the 2006 Census revealed that only 20% of all small farms (up to 500 ha) received technical assistance. Part of this deficiency is associated with budget cuts and extension workers engrossed in bureaucratic functions (related to regional programs and credit) that have impaired the quality of service in rural areas, especially in regions where challenges are more complex, as in northern and northeastern Brazil. Highly skilled and continuous assistance by motivated staff is required in these regions. The inputs were a driving force of the evolution of Brazilian agriculture in the 1960s, but can now limit crop production due to the economic conditions and availability in the country. Nation-wide, fertilizer use has increased significantly (Table 1) and in 2012, 30 million tons were used mainly in the states of Mato Grosso, Sa˜o Paulo, and Parana´ (44% of Brazilian consumption). Brazil is currently the fourth largest consumer of nutrients for fertilizer mixtures, representing about 5.9% of the global consumption, after China, India, and the United States. Despite this volume, the quantities are still far below those used in countries with a more developed agriculture and the demand is expected to increase with the increasing domestic production. The intensified productivity of Brazilian agriculture has been largely a result of fertilizer application, which means greater land-use efficiency and use of less land, with an estimated contraction of land requirement of 80 million ha. Currently, agricultural growth may be restricted by fertilizers, with a demand that is greater than the domestic production, as well as by international prices, poor logistics, agricultural costs, etc. This is the case of phosphorus and potassium, with dwindling local and global reserves, which in the near future may restrict all agricultural activities, with a serious and irreversible impact for the entire world population. Another intensely used group of materials in agriculture are the agrochemicals, which has raised concerns about food safety and environmental contamination. Brazil consumes 20% of the agrochemicals sold in the world and ranked first with applications of nearly 1 million tons of agrotoxins in 2013. The export monocultures such as soybean, cotton, sugarcane, and corn consume 80% of this volume, whereas a high quantity of fungicide

100

F.A.O. Camargo et al.

is being used for vegetables. According to the IBGE, about 70 million Brazilians are exposed to agrotoxins, since much of the food, especially for fresh consumption, was treated with an application at some point. One possibility to reduce pesticide consumption in the country is the use of transgenic seeds. In the case of transgenic soybean (growing season 2003/2004), an additional gain of BRL 2.3 billion was reported, resulting from reduced production costs and increased yields (Rodrigues, 2012). However, a detailed comparative analysis of the costs of the growing season 2013/2014 revealed that the production of conventional was cheaper than that of genetically modified (GM) soybean, in spite of the suspension of some governmental taxes (technology fee) and reduction in herbicide requirement (Richetti, 2013). The estimated savings in water, fuel, and pesticides as well as improved management and higher yield potential were cited to justify the adoption of this biotechnology. However, the lower production costs do not compensate for the differentiated management, the cost of transgenic seed is not worth the possible cost reduction with herbicides, and the higher value of conventional grain eliminates the possible higher gain with transgenic seed. The results demonstrate that the potential of this technique is not optimized yet, because so far the only segment with effective participation in profits is seed production, selling GM for twice (over 100%) the price of conventional seed. Although monocultures are extremely unstable in terms of plant health and commercial crops depend on the use of agrochemicals for the control of competitors, more efficient and less toxic products must be adopted in the production system, since the food and environmental insecurity is already present in the food consumed and in contaminated soil and water. Water is another important component of agricultural production and, although 13% of the world’s freshwater reserves lie in Brazil (70% in the Amazon basin), water can be a limiting factor for crops. Nation-wide, the use of drinking water for irrigation has been reduced, especially in southern Brazil, where rice is being grown in a flooded system. Recent technologies, developed by agricultural research with rice (SOSBAI, 2012) to reduce water consumption for irrigation, have been widely adopted by farmers, with very positive results. But much remains to be done regarding the role of irrigation in Brazilian agriculture, both with respect to an increase in irrigated agriculture as well as in improved efficiency of irrigation practices. The use of 54% of the total water consumption in agriculture (Table 1) to irrigate less than 10% of the cultivated area is presently a risk, and in the future, climate change can aggravate this situation, when consumption by the

Brazilian Agriculture in Perspective

101

population will be higher and the water availability decreased by contamination or other factors aside from climate. Probably, the use of GM crops with high drought resistance can be a solution. Maize varieties with this trait are being released in the United States and will likely be planted in Africa by 2017 (Rech and Lopes, 2012). Another important aspect is the need for a more efficient management system of the country’s water bodies, to evaluate the impact of agriculture on water resources more effectively. Currently, the National Agency of Waters has focused more on measuring the water quantity and quality in large basins through a monitoring network, while less attention has been paid to aspects related to the water quality of, particularly, small rural basins (Merten and Minella, 2013). In relation to research in agricultural sciences, the intensification of Brazilian science in terms of publications does not necessarily have a strong impact on technological growth, but the application in and contribution to innovation have generally been rather restricted. The current trend of Brazilian agriculture, specifically in terms of commodities, tends to an intensified use of Genetically Modified Organisms (GMO) and of the whole agronomic management associated with this system. However, this production model has not prevented Brazil from continuing as the largest consumer of agrochemicals in the world, which is obviously neither sustainable nor environmentally safe, in particular with regard to the water quality. The search for sustainable agriculture must be accompanied by an enormous effort of agricultural research to address issues related to soil management (improvement of soil quality and efficient fertilizer use), irrigation (improved use efficiency of irrigation water), plant health (resume biological control programs), and weed control (by the use of not only herbicides but also management practices such as crop rotation, associated with a combination of mechanical and cultural practices already studied in detail in the past). In this context, the development of organic agriculture also becomes highly desirable, especially to meet the demand for the production of safer food. With regard to the low innovation capacity of Brazil, the global innovation index (http://globalinnovationindex.org) began to be calculated from 2007, when Brazil ranked 40th. This position was the best the country has ever reached and has since slid back to the 64th position in 2013. Although Brazil is in 13th place in the ranking of publications, Switzerland (18th) and Sweden (21st) ranked 1st and 2nd in innovation rate in 2013. This paradox can be explained by the fact that applied research generates development, whereas innovation occurs in the function of a business demand in

102

F.A.O. Camargo et al.

companies. Since our companies are not prepared to innovate owing to constraints in terms of structure and of the proper culture, it is once again the role of universities to promote innovation. This applies to Agricultural Sciences, which should be less specific, more focused, and more pragmatic in relation to the real problems of society, with a clear understanding that the production of knowledge in itself generates no value, unlike the use made of this knowledge. By science-related marketing in Brazil, science has been featured as responsible for generating knowledge, products, and processes that ensure increased productivity and hence the profitability of agricultural activities. Some authors claim that science allows a greater control of the conditions of the production process, with an expanded scope to dominate the natural resources, and especially a more effective exploitation of the biological potential of plants and animals for higher gains with the activity. With the greater control of nature, the agriculture and mainly agribusiness have become dependent on industry-oriented scientific processes. Owing to science, agriculture ceased to be an uncertainty in terms of environmental factors to become a certainty in terms of economic profitability (Elias, 2006), and much of the agricultural activity evolved to an undertaking characterized by the rationality of the technical–scientific–informational period (Santos, 2000). The elevation of science to this level can be questioned with the recent example of the lower production cost of soybean, Brazil’s main commodity, as a factor of efficiency and international competitiveness. In a comparison of the costs with the main competitor, American soybean, it is evident that the only and most important factor of competitiveness is the cost of Brazilian land. While 1 ha for soybean cultivation costs little more than US$ 200 in the state of Maranha˜o, it would cost US$ 25,000 in Iowa. If this item were removed from the calculation, Brazilian soybean would be the most expensive on the planet and would be commercially completely uninteresting. Obviously, raising the productivity with maximum exploitation of the physiological potential of a crop does not completely solve the competitiveness issue. The efficient and effective use of materials and equipment, management, and resource administration must be improved to actually make the crop viable, as is the case with other crops in the country. Currently, basic and applied research generated at universities and by public institutions of agricultural research (OEPAS and Embrapa) lay the scientific basis required for the expansion and consolidation of Brazilian agriculture. In this scenario, the direction of research conducted by Embrapa

Brazilian Agriculture in Perspective

103

and its creation itself are evidently part of governmental policy actions for the expansion of commercial agriculture and export. Embrapa was reorganized to operate the public research system in closer cooperation with multinational companies (as in the case of transgenics) and agribusiness (Delgado, 2012). Both Embrapa and the graduate programs are supported by the Brazilian society as a whole, and both have the responsibility of a commitment to do less biased and socially more equitable agricultural research, which goes beyond the discourse of business, marketing, and the “Brazilian agricultures.” 5.2.5 Media Aspects Brazilian agriculture, in particular commercial farming, has come under fire from the scientific and journalistic media in the country and the world. The interests behind this pressure seem clear and are generally associated with deforestation, greenhouse gas emissions, the agrarian question, and the export-focused model, among others. Journalists often use some scientifically whitewashed data to give their reports credit and, based thereon, affix the labels that suit them. Moreover, the vast majority of research results, especially those related to the Amazon, are produced by foreign scientists who get to publish issues of this nature without difficulty in high-impact journals with wide circulation. As if this were not enough, the few scientific papers produced in the country in this regard are clearly ideologicallydriven and the discussion is focused exclusively on the possible problems. When a problem ceases to exist, as in the case of the slowdown of deforestation since 2006, the focus shifts to the agrarian question or whatever else seems easier to attack. In this context, one can cite the case of the NGOs that operate as private research institutes and are sponsored by major international competitors of the Brazilian agriculture and those interested in the maintenance of our biological and mineral resources in the Amazon. These researchers must produce something that can justify the existence of the research structure and of their proper wages. Only to exemplify the claim of discrepancies in deforestation rates in the country, there are institutes overestimating deforestation, by up to 200% of the estimates made by public bodies internationally recognized for their quality of research and monitoring, as in the case of INPE and Amazon Deforestation Monitoring Project (Projeto do Desflorestamento na Amaz^ onia Legal—PRODES) of the Ministry of Science, Technology and Innovation (MCTI). Another situation is that of the international correspondents in the country, who write anything that can make news, with a concept of publication that associates scientific

104

F.A.O. Camargo et al.

illiteracy with journalistic presumption and ideological biasedness to produce anything but the truth, as long as it publishable. Obviously, the ideological and speculative patrolling in the country should monitor areas where problems and limitations are far greater, as in the case of education, health, safety, etc., with development rates that are among the lowest of the world. It also seems evident that the achievements of Brazilian agriculture and the expectations generated for the future of the country and the world resulting from this activity should be acknowledged and respected. The limitations of the Brazilian agricultural model can be used as a starting point to establish a fairer collective discussion, committed to the development of the country and useful primarily for the Brazilian society. 5.2.6 Strategic Aspects The most likely future scenarios into which the Brazilian agriculture will be inserted must be projected, and this exercise is part of the strategic planning for an essential sector for the Brazilian economy. The sustainable intensification of agricultural activity is already a reality in the country, but needs to be expanded and consolidated as a new process of transformation and procedure in agriculture, featuring a new paradigm, to meet former and future demands of Brazilian society. The challenge is to retrieve more food from the same area with the technology available, warranting food and environmental quality and safety, based on an efficient and intensive use of available resources, the restoration of degraded environments, protection of natural resources, and improved environmental services, while productivity is being increased (Godfray et al., 2010). The FAO defines this as the optimization of production per unit area, taking into account the sustainability of integrated components (social, economic, political, and environmental) of the production system. In fact, many of the practices of sustainable intensification are already being applied, but there is still a large yield gap (i.e., difference between the actual yield and the yield obtained with appropriate technologies and inputs) to be filled, which are the goals to be pursued. Furthermore, the productivity barriers can be overcome by increasing potential yields with innovative strategies (Lal, 2013). Other possible upcoming technological innovations are associated with a better understanding of the rhizosphere processes and the feasibility of their use in production processes, e.g., of suppressive soils, soilless agriculture (aeroponics, hydroponics, aquaponics, space agriculture), automation and seamless integration into the industrial sector, etc. In fact, Brazilian agriculture has to get ready for the next 50 years,

Brazilian Agriculture in Perspective

105

since the changes and transformations will be greater and more challenging than any faced so far in the history of mankind. Based on the normative scenarios (expected future reality) of the Brazilian agriculture, described earlier in the text, one can briefly state that despite the increase in the number of inhabitants, the population growth rates of the planet will decline and quality of life as a whole is expected to improve and, consequently, social and environmental development, with greater demand and higher standards of markets and products. Climate change and limited resources, for example, of water and fertilizer, should influence the productivity and technologies to be adopted. The country’s economy will continue depending on macrocommercial farming and increase the importance of microfamily business with great prospects for the development of an agriculture focused on the production of organic foods since these systems are more labor intensive. Small farmers and microfarming business will develop faster toward a further diversification of activities and products and increased participation in markets, with a declining number of jobs, and a rise in automation and demand for activity-specific technologies. However, the gap between regions and between land and income distribution will continuously increase, and so will the social problems arising from these disparities. The domestic market will grow and boost competition in the international market. In general, macrocommercial agribusiness will grow steadily, but challenges lie ahead due to the poor economic performance of the country and the effects and problems arising from this underperformance (return to high inflation, drop in investment, strengthening of American Chinese economies, devaluation of the Brazilian real, higher domestic interest rates, reduced funding and budget scope, harvest limitations by logistical problems, etc.). For the trend and exploratory scenarios (that tend to happen and may happen, respectively), the possibilities of direct and indirect effects on agriculture are countless. The model of rural development is expected to be restructured, to meet the demands of a consolidated macro commercial agriculture and of a continuously growing microfarming business, harvest after harvest. The Brazil cost must be curtailed and exports of current and new products should be solidified and increased, improving the international competitiveness of our agriculture. With regard to the environment, the trend is to promote intensive sustainability, systemic and integrated use of natural resources (soil, water, forests), and food production with less environmental impacts, among others, independent of the preexisting social pressure. Food safety has always been imperative, but as incomes rise, the

106

F.A.O. Camargo et al.

population will demand new products with certified quality and production processes. Many of these new requirements will depend on support from a more focused and realistic research, with a strong characteristic of innovation, targeted to more specific sectors, such as subsistence, organic, and regionalized commercial agriculture, agroforestry systems, among others. In terms of application, our biodiversity and the possibility of using biotechnology, bioinformatics, automation, and other technologies should be exploited in a more sustainable way, aiming above all to equalize the differences in Brazilian society (general socialization of welfare).

6. CONCLUDING REMARKS In the history of Brazil, no economic sector has been as important for the country as agriculture. Ever since colonial times up to the present, agricultural activity has been primarily responsible for the maintenance of the economic health and trade balance in a nation whose industry is not adequately prepared to assume its role on the national scene. Agriculture has undergone several transformations, resulting in a bidirectional model of development that emphasized discrepancies among all elements involved in the process (Table 9). The origins of this model date back to colonial times, when the rural oligarchy was established on the basis of slave workforce with sufficient efficiency to meet the demands for export of products such as sugarcane, coffee, and cotton, in a low-technology world. In this setting, the gap between the large and the small, the rich and the poor, and the young and the old, among other dichotomies, began to appear more clearly. The dependence on monocultures for export at the expense of the polyculture production for internal consumption consolidated the differences, and this model continued to develop until the mid-20th century. In the intervening years, the economic support of the country consisted of a few crops, which by themselves could not feed the nation. Changes in the scenario of Brazilians’ diet set in with changes resulting from the green revolution, in which the State chose to side with the largeand medium-scale farmers as the drivers of change. Incentives and subsidies of all kinds were available for the new production model, and artificial inputs (chemical and mechanical) replaced the traditional, more natural ones. The industry and agroindustry complexes took charge of the production process and established a new production standard based on capital accumulation. In this context, Brazilian science, generated by public universities and research institutions, provided the conditions for technological adaptation, an

Table 9 Phases of Brazilian Agriculture, Its Main Characteristics, and Indicators of Bidirectional Development Bidirectional Characteristics of Brazilian Agriculture Phases of Agriculture

Processes

Products

Producers

Land Ownership

Purpose

Preindustrialization (1500–1950)

Conservative and subsistence

Mono- and polycultures

Oligarchy and proletariat

Latifundium and minifundium

Dominance and subsistence

Green revolution (1950–1990)

Technological and empirical

Raw material and Small and large scale food

Intensive and extensive

Productivity and food

Global scientific (1990–present)

Agribusiness and family farming

Commodities and Entrepreneur and products family farmer

Corporate and family

Profit and products

108

F.A.O. Camargo et al.

expansion of the agricultural area, and productivity increases. Developing in this direction, Brazil stopped depending on foreign technology and imports to feed its population, but became a commodity exporter and assigned again the primary role to agriculture in domestic economy and foreign trade. In return, a side effect of the transformation was a widening of the income gap in rural areas, leading to a concentration of land ownership, unemployment, abandonment of polyculture, and increased urbanization. The economic crisis in Brazil in the 1980s and 1990s caused corporate agriculture and its production model to cease being fully subsidized by the State. It emerged from this condition under the name of “agribusiness” and restored its old production model, under the auspices of science, which ensured greater control of nature, certainty of gains, and the status of modernity. Large corporations of global commodities assumed the role of the State not only in financing but also in logistics at all production stages. They ensured the dependence of the rural areas by buying out the production of rural entrepreneurs in advance and thereby the control and dependence of the activity, as well as sovereignty over food production and the economy. Currently, “agribusiness” is the only growing sector of the Brazilian economy that maintains the trade balance with foreign countries and causes GDP to grow. Primary surpluses resulting from this sector have been the only justification for the use of Brazilian territory by rural entrepreneurs at the demands of corporations and have helped associate a general success story to an activity the Brazilian public no longer controls. In fact, this performance is only possible thanks to the local conditions of cheap land, as well as abundant sun light and water, since all other production inputs supplied by corporations are extremely expensive, compared to the markets of key competitors (the United States and European Union). Without these prerequisites, the country would not have become the second largest producer of meat and the third largest producer of agricultural goods, especially for crops such as soybean. The concentration of arable land and its expansion into tropical biomes such as the Amazon and the Pantanal have fueled intense national and international debates. Land use for agricultural activity in the country has released an alarming amount of sediments and pollutants into major river basins of the country, impairing the water quality and availability, and leading to the irreversible loss of elements needed for the maintenance of the future production system. In the global setting, the pressure is great to withdraw the only advantage and winning margin in production of the Brazilian agriculture, which is the abundant and low-cost land, and thus eliminate the only factor of international competitiveness. In this particular

Brazilian Agriculture in Perspective

109

case, it seems that the intention is just to relieve the pressure on the American and European markets that are saturated in terms of land availability and have reached the physiological limits of crops and production technology. From the standpoint of these markets, deforestation allowed only the expansion of farming and logging at low production costs, representing an expansion of the production of commodities and a competitive disadvantage for American and European products. International campaigns against deforestation in the Amazon (i.e., the Brazilian Amazon) stem from incentives for agricultural markets of developed countries, using an environmental pretense to back up their particular interests. It has been estimated that the American investment in reducing tropical deforestation through climatic and environmental policies and offsets and by the international political pressure would yield revenues of about US$ 300 billion between 2012 and 2030 for American producers of soybeans, vegetable oil, meat, and raw wood. The hypocrisy of agricultural markets and international media in taking on the environmental cant does not authorize Brazilians to cut down forests or to use their resources unsustainably. However, it is worth remembering that the sovereign decision about the management of the territory for the benefit of the society belongs one and only to Brazil itself. While the macrobusiness activity of the Brazilian agriculture has to balance the burden of global competition, plus its own problems, to stay in the market, generating profits and justifying its existence, agricultural microenterprises are still affected by a legacy of 300 years of policies and decisions driving in the opposite direction of the whole process. Keeping up or widening the gap between the "Brazilian agricultures" would trim and cut any possibility of maintaining economic, environmental, and food sovereignty. This is a situation the Brazilian government is aware of and has been trying to amend over the last 50 years. Similarly, as the government invested in large and medium-scale farms during the green revolution, it has been trying to streamline the smallholders’ reality by distributing 88 million ha of farmland through the agrarian reform. The issue of land reform in the country also deserves attention since the distribution of land for the sake of ownership alone proved to be an inefficient strategy when no support was provided at the same time, based on credit, technical assistance, and organization of the producers. Of the total land earmarked for rural settlements, 76% are in the northern region and 12% in the Northeast, mostly on poor soils and far away from consumer markets (in the case of settlements in the Amazon region) and with little water availability (settlements in the Northeast).

110

F.A.O. Camargo et al.

The policies, funding, and assistance programs created in the last 20 years and Brazilian science were not efficient enough to fully unlock the potential of the social group of subsistence farmers. It is extremely desirable to eradicate the polarization of the "Brazilian agricultures" (agribusiness and family farming) with the understanding that these are unique, complementary, necessary, limited, and have an equally essential purpose. Brazil today and tomorrow cannot exist sovereignly without both converging in a single direction. This should be the basic principle underlying an NAP that harmonizes both forms of agriculture.

7. PLEA FOR AN NATIONAL AGRICULTURAL POLICY (NAP) In the history of Brazil, agriculture has generated two distinct groups of performers and performances, resulting from the differentiated actions and attitudes of the parties and the governmental support. The development in opposite directions gave rise to groups with proper identity, concepts, niche, elements, and models of validation. Both groups are unique in their definitions, fallible in their concepts, indispensable in their functions, and complementary in their primary goal (agriculture). The basic principle of formulating an NAP is acceptance of these groups, understanding of their characteristics, recognition of their importance, and search for the convergence of outlooks and of results for the benefit of the Brazilian society. The elaboration of an NAP and its stages (formulation, implementation, and evaluation) should be based on the principle of duality, with a pluralistic view as orientation, equality as form of organization of interests and incrementalism as the decision-making model. In the pluralistic view of policy formulation, the interests should be organized in egalitarian groups, tackling the problems free of ideological influences, with multiple definitions of values, impacts, and rights. Information must be questioned and discussed, but not manipulated. The formulation is worked out collectively by the concerned parties and strategically planned to be incremental, checked, and adjusted according to the decision-making process. The implementation should be founded on the satisfaction of the pivotal interest groups with plenty of room for decision making among organizations, with consensus building and shared goals. The initial reconciliation between the different natures of the organizations involved will be the key point to establish a dialectic of convergence from the specific to a single interest: the Brazilian agriculture.

Brazilian Agriculture in Perspective

111

The primary objective of NAP must be the food sovereignty of the country. For practical purposes, duality may be considered in the layout, but this perception must be overcome, with regard to the need for a single agriculture that meets the interests of Brazilian society. Agriculture will be founded on the basic principle of sustainability and safety of all components of the actuation system, directed toward the pursuit of intensification with low environmental impact, neutrality of natural resource degradation, and increasing climate resilience. It will be based on pillars that characteristically reflect concomitant interests, sectors, and actions such as production and conservation, funding and trade, research and innovation, assistance and rural extension, infrastructure and logistics, employment and income, rural cooperatives, and education, among others. The NAP must involve a clear compensation for the private use of the Brazilian territory and assign these compensations for social, environmental, and economic convergence provided by the NAP. It is up to the Brazilian government, while abstaining from partiality or interference with the decisions of the interest groups, to implement, evaluate, and increment the development in small steps in line with the primary objective and ends to be defined by stakeholders and the Brazilian society. Even if the unification of Brazilian agricultures may seem utopian and beyond reach, it is time to start managing the country’s interests independently and remember that only competitors have an interest in splitting things up (“divide and conquer”). Only through multiplication and balance will Brazilians get to reap the harvest they are expecting after these 500 years of history of the country and its agriculture.

REFERENCES Alves, E., Oliveira, A.J., 2005. O orc¸amento da Embrapa. Rev. Pol. Agric. 4, 73–85 (in Portuguese). Ayer, H.W., Such, G.E., 1971. Social rates of return and aspects of agricultural research: the case of cotton research in Sa˜o Paulo. Brazil. Am. J. Agric. Econ. 54, 557–569. Barona, E., Ramankutty, N., Hyman, G., Coomes, O.T., 2010. The role of pasture and soybean in deforestation of the Brazilian Amazon. Environ. Res. Lett. 5, 1–9. Battelle, 2013. 2014 global R&D funding forecast. Battelle Mag, 33. Beintema, N., Avila, F., Fachini, C., 2010. Brazil: new developments in the organization and funding of public agricultural research. ASTI Country Note Washington, DC/Brasilia: International Food Policy Research Institute (IFPRI)/Brazilian Agricultural Research Corporation, p. 8. Bollinger, A., Magid, J., Amado, T.J.C., Skora Neto, F., de Fatima dos Santos Ribeiro, M., Calegari, A., Ralisch, R., de Neergaard, A., 2006. Taking stock of the Brazilian ‘ZeroTill Revolution’: a review of landmark research and Farmers’ practice. Adv. Agron. 91, 1–64. Brasil-Empresa de Pesquisa Energ
etica, 2013. Balanc¸o Energ
etico Nacional 2013. EPE, Rio de Janeiro, p. 55 (in Portuguese).

112

F.A.O. Camargo et al.

Bruinsma, J., 2009. The Resource Outlook to 2050. By how much do land, water and crop yields need to increase by 2050? In: Expert Meeting on How to Feed the World in 2050. Food and Agriculture Organization of the United Nations. Economic and Social Development Department, p. 33. Camargo, F.A.O., Venegas, V.H.A., Baveye, P., 2010. Brazilian soil science: from its inception to the future, and beyond. R. Bras. Ci. Solo 34, 589–599. CGEE (Centro de Gesta˜o e Estudos Estrat
egicos), 2013. Ci^encia para o desenvolvimento sustenta´vel global: contribuic¸a˜o do Brasil. Sı´ntese dos Encontros Preparato´rios ao FMC 2013. Centro de Gesta˜o e Estudos Estrat
egicos, Brasilia, p. 114 (in Portuguese). CONAB (Companhia Nacional de Abastecimento), 2016a. Acompanhamento da Safra Brasileira de gra˜os. V.3—Safra 2015/16—N.8—Oitavo Levantamento, Brası´lia, 178 pp, May 2016 (in Portuguese). CONAB (Companhia Nacional de Abastecimento), 2016b. Acompanhamento da Safra Brasileira de Cana-de-Ac¸u´car, Brası´lia. V.3—Safra 2016/17—N.1—Primeiro Levantamento. 66 pp (in Portuguese). De La Mata, G.C., Riega-Campos, S., 2014. An analysis of international conservation funding in the Amazon. https://www.moore.org/programs/environmental-conservation/andesamazon-initiative/learn-more-about-the-andes-amazon-initiative. Delgado, N.G., 2012. Agronego´cio e agricultura familiar no Brasil: desafios para a transformac¸a˜o democra´tica do meio rural. Nov. Cad. NAEA 15 85–129 (in Portuguese with English abstract). Elias, D., 2006. Globalizac¸a˜o e fragmentac¸a˜o do espac¸o agrı´cola do Brasil. Scr. Nova 1, 59–81 (in Portuguese with English abstract). FAO (Food and Agriculture Organization), 2007. The state of food and agriculture. http:// www.fao.org/docrep/010/a1200e/a1200e00.htm. Franc¸a, C.G., Del Grossi, M.E., Vicente, P.M., 2009. O censo agropecua´rio 2006 e a agricultura familiar no Brasil. MDA, Brası´lia, p. 96 (in Portuguese). Frederico, S., 2013. Agricultura cientı´fica globalizada e fronteira agrı´cola no Brasil. Confins (Paris) 17, 1–17 (in Portuguese). Friedman, S., 2012. Farms here, forest there: tropical deforestation and US competitiveness in agriculture and timber. http://assets.usw.org/our-union/pulp-paper-forestry/farmshere-forests-there-report-5-26-10.pdf. Godfray, H.C.J., Beddington, J.R., Crute, I.R., Haddad, L., Lawrence, D., Muir, J.F., Pretty, J., Robinson, S., Thomas, S.M., Toulmin, C., 2010. Food security: the challenge of feeding 9 billion people. Science 327, 812–818. Gomez, G.G., 2014. General comments to the AAA El Dorado task force. http:// anthroniche.com/darkness_documents/0103.htm. Hansen, M.C., Potapov, P.V., Moore, R., Hancher, M., Turubanova, S.A., Tyukavina, A., Thau, D., Stehman, S.V., Goetz, S.J., Loveland, T.R., Kommareddy, A., Egorov, A., Chini, L., Justice, C.O., Townshend, J.R.G., 2013. High-resolution global maps of 21st-century forest cover change. Science 342, 850–853. IBGE (Instituto Brasileiro de Geografia e Estatı´stica), 2006. Censo Agropecua´rio 2006— Agricultura familiar—primeiros resultados. IBGE, CDCI, Rio de Janeiro, p. 267 (in Portuguese). IBGE (Instituto Brasileiro de Geografia e Estatı´stica), 2010. Pesquisa nacional por amostra de domicı´lio—seguranc¸a alimentar, 2004–2009. IBGE, CDCI. IBGE, CDCI, Rio de Janeiro, p. 183 (in Portuguese). IPAM, O., 2014. Aumento no Desmatamento na Amaz^ onia em 2013: um ponto fora da curva ou fora de controle? Relato´rio de 07 de Janeiro de 2014. 8 pp. Lagi, M., Bertrand, K.Z., Bar-Yam, Y., 2011. The food crises and political instability in North Africa and the Middle East. arXiv:1108.2455 15. Lal, R., 2013. Food security in a changing climate. Ec. Hydr. 13, 8–21.

Brazilian Agriculture in Perspective

113

Lapola, D.M., Martinelli, L.A., Peres, C.A., Ometto, J.H.B., Ferreira, M.E., Nobre, C.A., Aguiar, A.P.D., Bustamante, M.M.C., Cardoso, M.F., Costa, M.H., Joly, C.A., Leite, C.C., Moutinho, P., Sampaio, G., Strassburg, B.B.N., Vieira, I.C.G., 2014. Pervasive transition of the Brazilian land-use system. Nat. Clim. Change 4, 27–35. Leisher, C., Touval, J., Hess, S.M., Boucher, T.M., Reymondin, L., 2013. Land and forest degradation inside protected areas in Latin America. Diversity 5, 779–795. Lopes, A.S., Guimara˜es Guilherme, L.R., 2016. A career perspective on soil management in the Cerrado region of Brazil. Adv. Agron. V 137, 1–72. Lopes, I.V., Rocha, D.P., Lopes, M.R., Bomfim, R.C., 2012. Perfis das classes de renda rural no Brasil. Rev. Pol. Agri. 2, 21–27 (in Portuguese with English abstract). Martha Jr., G.B., Contini, E., Alves, A., 2012. Embrapa: its origins and changes. In: Baer, W. (Ed.), The Regional Impact of National Policies: The Case of Brazil. Edward Elgar, Cheltenham, pp. 204–226. Martinelli, L.A., Naylor, R., Vitousek, P.M., Moutinho, P., 2010. Agriculture in Brazil: impacts, costs, and opportunities for a sustainable future. Curr. Opin. Environ. Sustain. 2, 431–458. Matos, P.F., Salazar, V.L.P., 2011. A modernizac¸a˜o da agricultura no Brasil e os novos usos do territo´rio. Geo UERJ 22, 290–322 (in Portuguese with English abstract). Matthey, H., Fabiosa, J.F., Fuller, F.H., 2004. Brazil: the future of modern agriculture? MATRIC Briefing Paper 04-MBP 6, p. 25. MCTI (Minist
erio da Ci^encia Tecnologia e Inovac¸a˜o), 2014. Estimativas anuais de emisso˜es de gasesde efeito estufa no Brasil, second ed. MCTI/SEPED, Brası´lia, p. 168 (in Portuguese). Merten, G.H., Minella, J.P.G., 2013. The expansion of Brazilian agriculture: soil erosion scenarios. Int. Soil Water Cons. Res. 1, 37–48. Nicholls, W.H., 1970. The transformation of agriculture in a semi-industrialized country: the case of Brazil. In: Thorbecke, E. (Ed.), The Role of Agriculture in Economic Development. NBER Books (The National Bureau of Economic Research), Cambridge, pp. 311–386. Orsini, F., Kahane, R., Nono-Wondin, R., Gianquinto, G., 2013. Urban agriculture in the developing world: a review. Agron. Sust. Dev. 33, 695–720. Pereira, M.F., 1999. Evoluc¸a˜o da fronteira tecnolo´gica mu´ltipla e da produtividade total dos fatores do setor Agropecua´rio brasileiro de 1970 a 1996. Tese, PPG Engenharia de Produc¸a˜o, UFSC, p. 144 (in Portuguese with English abstract). Pereira, P.A.A., Martha Jr., G.B., Santana, C.A.M., Alves, E., 2012. The development of Brazilian agriculture: future technological challenges and opportunities. Agric. Food Sec. 1, 1–4. Prado, R.M., 2008. Diagnosis about the knowledge in soil science in Brazil: the scientific production of journals from 1988 to 2007. Rev. Bras. Po´s-Graduac¸a˜o 5, 303–321. Rada, N., Valdes, C., 2012. Policy, technology and efficiency of Brazilian agriculture. ERR-137, U.S. Department of Agriculture. Econ. Res. Rep., 137, p. 43. Radulovich, R., 1990. A view on tropical deforestation. Nature 346, 6281. Rech, E.L., Lopes, M.R., 2012. Insights into Brazilian agriculture structure and sustainable intensification of food production. Food Energ. Sec. 1, 77–80. Richetti, A., 2013. Viabilidade econ^ omica da cultura da soja na safra 2013/2014, em Mato Grosso do Sul. Dourados: Embrapa Agropecua´ria Oeste. Comun. T
ecn., 187, p. 10 (in Portuguese). Rodrigues, R., 2012. A evoluc¸a˜o da transgenia. Esp. Citr. 7, 50–52 (in Portuguese). Salles-Filho, S., Bonacelli, M.B., 2007. Em busca de um novo modelo para as organizac¸o˜es pu´blicas de pesquisa no Brasil. Ci. Cult. 59, 28–32 (in Portuguese).

114

F.A.O. Camargo et al.

Salles-Filho, S., Albuquerque, R., Szmercsa´nyi, T., Bonacelli, M.B.M., Paulino, S., Bruno, M., Mello, D., Corazza, R., Carvalho, S.M.P., Corder, S., Ferreira, C., 2000. Ci^encia, tecnologia e inovac¸a˜o—a reorganizac¸a˜o da pesquisa pu´blica no Brasil. Editora Komedi, Campinas (in Portuguese). Santos, R.F., 1988. Ana´lise crı´tica da interpretac¸a˜o neocla´ssica do processo de modernizac¸a˜o da agricultura brasileira. Rev. Econ. Pol. 8, 131–148 (in Portuguese). Santos, M., 2000. Por uma outra globalizac¸a˜o: do pensamento u´nico à consci^encia universal, p. 174, Rio de Janeiro, Record (in Portuguese). Scolari, D.D.G., 2006. Produc¸a˜o agrı´cola mundial: o potencial do Brasil. Ver. Fund. Milton Campos. No. 25, Brası´lia, DF, 86 pp. SOSBAI (Sociedade Sul-Brasileira de Arroz Irrigado), 2012. Arroz irrigado: recomendac¸o˜es t
ecnicas da pesquisa para o Sul do Brasil. SOSBAI, Porto Alegre, p. 176 (in Portuguese). Sparovek, G., Barreto, A., Klug, I., Papp, L., Lino, J., 2011. Revisa˜o do Co´digo Florestal brasileiro. Novos estudos—CEBRAP 89, 111–135 (in Portuguese). Spolador, H.F.S., Roe, T.L., 2013. The role of agriculture on recent Brazilian economic growth: how agriculture competes for resources. Dev. Econ. 51, 333–359. TCU (Tribunal de Contas da Unia˜o), 2004. Levantamento de auditoria operacional. Minist
erio da Agricultura, Pecua´ria e Abastecimento, Minist
erio do Meio Ambiente, Minist
erio do Desenvolvimento Agra´rio, Brasilia (in Portuguese). Tollefson, G., 2010. Food: the global farm. Nature 466, 554–556. Vogt, K.A., Gara, R.I., Honea, J.M., Vogt, D.J., Weynand, T.P., Roads, P.A., Fanzeres, A., Sigurdardottir, R., 2007. Historical perception and uses of forests. In: Vogt, K.A., Honea, J.M., Vogt, D.J., Andreu, M., Edmonds, R., Sigurdardottir, R., Weynand, T.P. (Eds.), Forest and Society. Sustainability and Life Cycles of Forests in Human Landscapes. CABI Books, Cambridge, pp. 1–28. Walker, R., Moorea, N.J., Arimab, E., Perzc, S., Simmonsa, C., Caldasd, M., Vergara, D., Bohrere, C., 2009. Protecting the Amazon with protected areas. Proc. Nat. Acad. Sci. U.S.A. 106, 10582–10586. Webb, P., Block, S., 2012. Support for agriculture during economic transformation: impacts on poverty and undernutrition. Proc. Nat. Acad. Sci. U.S.A. 109, 12309–12314.

CHAPTER THREE

Bio-Intervention of Naturally Occurring Silicate Minerals for Alternative Source of Potassium: Challenges and Opportunities B.B. Basak*,1, B. Sarkar†, D.R. Biswas{, S. Sarkar§, P. Sanderson¶, R. Naidu¶,||,1 *ICAR-Directorate of Medicinal and Aromatic Plants Research, Anand, India † Future Industries Institute, University of South Australia, Mawson Lakes Campus, SA, Australia { Indian Agricultural Research Institute (IARI), New Delhi, India § Central Institute for Fresh Water Aquaculture, RRC Anand, Anand, India ¶ Global Centre for Environmental Remediation, University of Newcastle, Callaghan, NSW, Australia jj Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, University of Newcastle, Callaghan, NSW, Australia 1 Corresponding author: e-mail address: [email protected]; [email protected]

Contents 1. Introduction 2. Potassium Dynamics in Soil 3. Potassium-Bearing Minerals in Soil Environment 3.1 Silicate Minerals as a Source of Potassium 4. Bio-Intervention of Silicate Minerals and K Availability 5. Mechanisms of Potassium Mobilization From Silicate Minerals 5.1 Dissolution by Organic Acids 5.2 Metal-Complexing Ligands 5.3 Formation of Biofilm 6. Bio-Approaches for K Mobilization From Silicate Minerals 6.1 Microbial Intervention 6.2 Composting 7. Structural Changes of Silicate Minerals Due To Bio-Intervention 8. Plant Growth and K Nutrition on Bio-Intervened Silicate Minerals 8.1 Pot Trials 8.2 Field Trials 9. Conclusions and Future Prospects Acknowledgments References

Advances in Agronomy, Volume 141 ISSN 0065-2113 http://dx.doi.org/10.1016/bs.agron.2016.10.016

#

2017 Elsevier Inc. All rights reserved.

116 119 120 121 124 126 126 127 128 129 129 132 133 134 134 137 139 140 140

115

116

B.B. Basak et al.

Abstract Soil needs simultaneous replenishment of various nutrients to maintain its inherent fertility status under extensive cropping systems. Replenishing soil nutrients with commercial fertilizer is costly. Among various fertilizers, deposits of potassium (K) ore suitable for the production of commercial K fertilizer (KCl) are distributed in few northern hemisphere countries (Canada, Russia, Belarus, and Germany) which control more than 70% of the world’s potash market. Naturally occurring minerals, particularly silicate minerals, could be used as a source of K, but not as satisfactorily as commercial K fertilizers. In this context, bio-intervention (in combination with microorganisms and/or composting) of silicate minerals has been found quite promising to improve plant K availability and assimilation. This is an energy efficient and environmentally friendly approach. Here we present a critical review of existing literature on direct application of silicate minerals as a source of K for plant nutrition as well as soil fertility enhancement by underpinning the bio-intervention strategies and related K solubilization mechanisms. An advancement of knowledge in this field will not only contribute to a better understanding of the complex natural processes of soil K fertility, but also help to develop a new approach to utilize natural mineral resources for sustainable and environmental friendly agricultural practices.

1. INTRODUCTION Potassium (K) ranks third among the essential plant nutrients after nitrogen and phosphorus and seventh among all the elements in the Earth’s crust. Modern intensive agriculture leads to a decline in soil nutrient levels due to mining through crop uptake and other losses. The issue of K is more pronounced in the developing countries as most of the farmers have mainly focused on the application of nitrogen and phosphorus for crop production neglecting K and micronutrients. Such an imbalanced nutrient management practice has badly impaired the productivity of soil. According to an estimate by the Food and Agriculture Organization (FAO) of the United Nations, the global demand of potash fertilizer was likely to increase annually by 2.6% over 2014 and the supply would balance the demand. Of the overall increase in demand for 3400,000 tons of potash between 2014 and 2018, 56% would be in Asia, 27% in the America, 11% in Europe, 6% in Africa, and 0.4% in Oceania (FAO, 2015). Most of these have to be imported to respective continents (FAO, 2015). Most importantly, K fertilizers make up only 10% or less of the total fertilizer inputs despite the fact that K undergoes the highest nutrient depletion rates in developing countries, especially in African countries. These countries do not have any suitable K-bearing mineral ores from which commercial K fertilizers

117

Bio-Intervention of Naturally Occurring Silicate Minerals

Global potash production 20,000 Others 18%

Canada 26%

15,000

Thousand Mt (K2O)

Germany 9%

10,000

China 11%

Russia 19% Belarus 17%

5000

0 st

Ea

tin

La

a

ic er

ia

As

e

an

e

e

op ur

ia

As

Am

h

lE

ia

tra

a

ut

So

en

C

ric

a

op ur

tE

an

es si

a

ic er

p ro

Eu

Am

tA

es

st

ce

Af

O

W

W

Ea

th or

N

−5000

d a

si

lA

tra

en

C

−10,000

Fig. 1 Projection of regional potash balance according to FAO for 2018 in thousand metric tons K2O equivalent. World fertilizer outlook (FAO (Food and Agricultural Organization), 2015. Current World Fertilizer Trends and Outlook to 2014–18, Food and Agriculture Organization of the United Nations, Rome).

can be produced. Potash ores have a rather limited distribution globally (Moores, 2009; Rittenhouse, 1979), with the bulk of the world’s K mined in Canada, Europe, and the Middle East (Fig. 1). Most of the K ores suitable for commercial K fertilizer production are distributed in few countries in the northern hemisphere (Canada, Russia, Belarus, and Germany), which controls more than 70% of the existing potash market. In terms of the consumption patterns, it is in the order of East Asia > Latin America > South Asia > Africa (Fig. 1) where no significant K ore deposit is available for commercial K fertilizer production. Thus, there is a very little scope for many developing countries to be self-sufficient in K nutrition by using conventional fertilizers. On global basis, the supply of K experiences an annual deficit of 20 kg K ha1 (Sheldrick et al., 2002). In African countries and China, the total annual K deficits reach up to 4.1 and 8.3 million tons, respectively, which correspond to a respective estimate of 20 and 60 kg K ha1 year1 in these regions (FAO, 2015). The K deficit in East Asia is in excess of 9 million tons per year, mostly dominated by China

118

B.B. Basak et al.

(FAO, 2015). India and other developing countries are having almost a similar situation. The extent of K fertilizer deficit in these areas is increasing over the years. On the other hand, removal of K from soil in comparison to N and P is remarkably higher in different copping systems particularly in those involving cereal and fodder crops. A huge gap between K removal and replenishment has been found in various cropping systems (Yadav et al., 1998). For example, the gap between soil K removal and replenishment in India was estimated as high as 196, 170, and 255 kg ha1 in the rice– wheat, soybean–wheat, and rice–wheat–green gram cropping systems, respectively (Yadav et al., 1998). Potassium-bearing minerals are limited and finite resources in few selected countries. Therefore, to satisfy the K demand for world crop production, the amount of additional potash required is more than the current global production. The requirements of potash fertilizers in developing countries are so substantial that production must be more than double to sustain the soil K stocks (Manning, 2010). The cost of K fertilizers increased tremendously throughout the world. The situation in Southeast Asia, Africa, and Oceania is alarming because there is no reserve of K-bearing minerals. The whole consumption of K fertilizers is imported in these regions. Thus, there is an urgent need to find alternative K sources to mitigate plant needs and thereby to reduce the dependency on costly K fertilizers. To address the problem, it is necessary to consider the unconventional sources of K like naturally occurring rocks and minerals, particularly the silicate minerals. Despite silicate minerals are not as effective as commercial K fertilizers, novel approaches may speed up K release from the mineral structures, which is appropriate in circumstances where farmers are presently deprived of the global K fertilizer market. This review aims to demonstrate the importance of alternative K sources for plant nutrition since commercial K fertilizers are under shortage, particularly in developing countries. Critically, the review focuses on the K dynamics in soil, K-bearing minerals, approaches of K mobilization from different K-bearing minerals, evidence of use of K-bearing minerals as K fertilizers, and the effect of modification, especially microbial inoculation and composting, on K mobilization in soils. By critically analyzing the K nutrition results from existing published trials, this review also discusses whether K-bearing minerals with suitable modification can be considered as an alternative to conventional K fertilizers for sustainable crop production.

Bio-Intervention of Naturally Occurring Silicate Minerals

119

2. POTASSIUM DYNAMICS IN SOIL Potassium exists in soil in different forms, which are in quasiequilibrium with each other. Based on the availability to plants and microbes, forms of soil K are categorized into four groups: water-soluble (solution-K), exchangeable, nonexchangeable, and structural or mineral-K. Exchangeable K or available K is held by negatively charged clay minerals and organic matter in soils, while nonexchangeable K is consisted predominantly of interlayer K of nonexpandable clay minerals such as illite and lattice K in K-minerals such as K-feldspars (Sparks, 1987). The major portion of the total soil K exists in the mineral fraction. Total soil K reserves are large in most of the soils, but the distribution of different K forms differs from soil to soil as a function of the dominant soil minerals present (Jiyun, 1993; Shanwal and Dahiya, 2006; Steingrobe and Claassen, 2000). It is reported that about 92–98% of the total soil K exists as part of mineral or structural-K in a fixed or nonexchangeable form. The sum of solution and exchangeable forms of K is considered as the “readily available form” which constitutes about 1–2% of the total K in soil. Further, the share of the readily available forms is 98% in exchangeable and 2% in solution. However, all these forms exist in dynamic equilibrium with each other (Subba Rao and Brar, 2002; Tripler et al., 2006). It is evident that nonexchangeable K (also called as “slowly available K”) is released and become available to plant uptake when solution and exchangeable K are depleted (Sharpley, 1989). The various K forms in soils and their transformation into soil solution through various pools and pathways are represented schematically in Fig. 2. The exchangeable K tends to attain equilibrium with solution K rapidly, but only slowly with

Fig. 2 Scope of bio-intervention for direct mobilization of potassium from mineral under dynamic pools of soil potassium.

120

B.B. Basak et al.

nonexchangeable K. Because of the crop removal, soil solution K gets depleted. The replacement of the K-depleted soil solution is then affected primarily by the release of exchangeable K from mineral-K (clay minerals). As and when the exchangeable K fraction is depleted substantially or exhausted by crop uptake, the nonexchangeable K replenishes the exchangeable form, thus the K supply is maintained.

3. POTASSIUM-BEARING MINERALS IN SOIL ENVIRONMENT Potassium in soil is mainly present as K-bearing minerals. The K-supplying power of a soil depends on the content and the nature of K-bearing minerals as well as on the rate at which structural and fixed-K become available to plants. More than 90% of the total K in soils is found in mineral form or as structural-K. Mineral-K is generally assumed to be only slowly available to plants; however, the availability is dependent on the level of K in other forms, and the degree of weathering of the mineral-K fractions (Jiyun, 1993; Sparks, 1987; Sparks and Huang, 1985; Tripler et al., 2006). The major rock-forming minerals of almost all igneous and metamorphic rocks are silicates. Similarly, the dominant rock-forming minerals in sediments are also usually silicates. The mineralogy of sedimentary rocks is very important as many nutrients are associated with the layer silicate clay minerals. However, both igneous and metamorphic rocks consist of mixtures of the four major rock-forming mineral groups: quartz, feldspar, mica, and ferromagnesian minerals (Harley and Gilkes, 2000; Manning, 2010; Steingrobe and Claassen, 2000). The primary sources of K-bearing minerals in soils are feldspars, micas (e.g., muscovite—white mica; biotite—black mica; and phlogopite), zeolite, glauconite, potassium-taranakite, illite, vermiculite, and chlorite. Mica-group minerals are of special interest for plant nutrition as they may be a major source of K, Mg, Zn, and Mn. It may be either muscovite (white mica), biotite (black mica) or phlogopite. Muscovite is dioctahedral mica, while biotite and phlogopite are trioctahedral micas which exhibit greater repulsion, and thus weather more easily and release K. Another important mineral is glauconite which is essentially a hydrated-iron– magnesium–potassium–aluminum-silicate (hydrated-Fe-Mg-K-Al-silicate). It contains about 5–6% K2O and can be used as a source of K. Potassium is also present in the form of secondary or clay minerals like illite or hydrous mica, vermiculite, chlorite, and interstratified minerals (Jiyun, 1993; Mengel and Rahmatullah, 1994). Owing to advanced weathering process, the K in these

121

Bio-Intervention of Naturally Occurring Silicate Minerals

Table 1 Chemical Formula and Potassium Contents (Expressed as Element and Oxide) for Potash Ore/Minerals and for Common Potassium Silicate Rock-Forming Minerals Mineral Formula Weight % K Weight % K2O Potash ore/minerals

Sylvite

KCl

52.35

63.09

Carnallite

MgCl2, KCl, 6H2O

14.05

16.94

Kainite

KMgSO4Cl, 3H2O

15.69

18.91

Langbeinite

2MgSO4, K2SO4

18.84

22.71

Potassium feldspar

KAlSi3O8

14.03

16.91

Leucite

KAlSi2O6

17.89

21.56

Nepheline

(Na, K)AlSiO4

13.00

15.67

Kalsilite

KAlSiO2

24.68

29.75

Muscovite

KAl3Si3O10(OH)2

9.03

10.88

Biotite

K2Fe6Si6Al2O20(OH)2

7.62

9.18

Phlogopite

K2Mg6Si6Al2O20(OH)4

9.39

11.30

Silicate minerals

From Manning, D.A.C., 2010. Mineral sources of potassium for plant nutrition. A review. Agron. Sustain. Dev. 30, 281–294.

secondary or clay minerals are relatively easily available to plants than primary minerals. The main K fertilizer ore minerals together with the dominant rockforming K silicate minerals are listed in Table 1.

3.1 Silicate Minerals as a Source of Potassium A number of studies have presented the ability of different K-bearing silicate minerals to yield nutrients under laboratory, pot, and field trial conditions (Table 2). These trials include pot (green house) and field experiments using a range of crops, different time scales, and under different climates. The most commonly trialed minerals include granite, glauconite, phlogopite, biotite, gneiss, feldspar, etc. The agronomic effectiveness of K-bearing minerals is largely determined by their mineralogy and chemical composition. A consistent set of trials were carried out in Western Australia, in which granite was used in pot trials on wheat, clover, and ryegrass (Bolland and Baker, 2000; Coreonos et al., 1996; Hinsinger et al., 1996). The application of granite (2.29% K2O) significantly

122

B.B. Basak et al.

Table 2 Summary of Crop Trials With Direct Application of Silicate Minerals Used as K Fertilizer Crop Minerals Trial Type Agronomic Benefit References

Legume

Feldspar

Field

Insignificant

SanzScovino and Rowell (1988)

Rice

Phlogopite

Pot culture

Increased grain yield Weerasuriya et al. (1993)

Wheat

Granite

Pot culture

Increased biomass and grain yield

Hinsinger et al. (1996)

Wheat

Diorite

Pot culture

Insignificant

Hinsinger et al. (1996)

Ryegrass Granite

Pot culture

Increased in biomass Coreonos et al. yield and K uptake (1996)

Pearl millet

Glauconitic sandstone

Rao and Subba Sand culture Dry matter yield Rao (1999) K content significantly increased

Alfalfa

Gneiss

Pot culture

Insignificant

Italian ryegrass

Gneiss

Pot culture

Significant increase in Wang et al. K content in biomass (2000)

Perennial Gneiss ryegrass

Pot culture

Significant increase in Wang et al. K content in biomass (2000)

Maize

Gneiss

Pot culture

Significant increase in Wang et al. K content in biomass (2000)

Clover

Granite

Pot/field

Insignificant

Chinese cabbage

Fused potassium Sand and soil Significant increase in Yao et al. (2003) silicate culture K uptake

Tomato

Feldspar

Field

Increased biomass and fruit yield

Badr (2006)

Okra

Feldspar

Field

Increased pod yield

Abdel-Mouty and El-Greadly (2008)

Grape

Biotite

Field

Increase berry yield and K content

Stamford et al. (2011)

Wang et al. (2000)

Bolland and Baker (2000)

123

Bio-Intervention of Naturally Occurring Silicate Minerals

Table 2 Summary of Crop Trials With Direct Application of Silicate Minerals Used as K Fertilizer—cont’d Crop Minerals Trial Type Agronomic Benefit References

Olive

Glauconitic sandstone

Hydroponics Effect as slow release Karimi et al. K fertilizer (2012)

Italian ryegrass

Granite powder Green house Significant increase in Silva et al. plant biomass yield (2013)

Spring barley

Madaras Sand culture Plant biomass and Zinnwalidite, K uptake increased et al. (2013) waste mica, and in the order of orthoclase Zinnwalidite > waste mica > orthoclase

Leek

Pot culture Biotite, microcline, and nepheline synite

Biotite found most Mohammed effective and readily et al. (2014) available source of K

Arabica coffee

Phonolite

Increased fruit yield similar to KCl application

Field

Mancuso et al. (2014)

increased biomass yield (10–20%) in wheat, whereas ground diorite (0.3% K2O) did not show any significant response. Pot trials conducted with clover and ryegrass (Coreonos et al., 1996; Silva et al., 2013; Wang et al., 2000) also showed that application of granite powder enhanced both yield and shoot K content significantly compared to the control. Agronomic effectiveness is also greatly influenced by the plant species and soil types. Among several plant species investigated, the utilization of K from gneiss followed the order: maize > ryegrass > alfalfa, and a greater uptake was possible from finer-sized particles (Wang et al., 2000). So, type of plants and their root architecture played a vital role in releasing K from minerals. In another study, phlogopite mica and K-feldspars significantly improved the yield and K uptake by rice grown in a sandy soil having very low exchangeable K (Weerasuriya et al., 1993). These minerals might be effective K suppliers in highly weathered soils where use efficiency of chemical fertilizer is very low. For example, application of K-feldspar served as an alternative to KCl in Colombia, where economic and agricultural conditions, including the occurrence of Oxisol exerted problems with KCl use (SanzScovino and Rowell, 1988; Wang et al., 2000). Initial soil K status also influenced the effectiveness of the minerals and their application is quite effective particularly in K deficient soils.

124

B.B. Basak et al.

Few field trials were also conducted in order to work out the efficiency of minerals as the source of K for crop growth. For example, feldspar was tested as a source of K using okra (Abdel-Mouty and El-Greadly, 2008), legumes (SanzScovino and Rowell, 1988), and tomato (Badr, 2006) cultivation. These studies showed that okra and tomato yield increased by 39.3% and 40%, respectively, with feldspar application, whereas legumes did not show any response. Application of K-bearing minerals like biotite, microcline, orthoclase, and waste mica increased plant biomass yield and K uptake in spring barley (Madaras et al., 2013) and leek (Mohammed et al., 2014) as well. The mineral source of K was effective in some long duration crops like grape, coffee, and olive. Berry yield K content in grape increased when biotite was used as a source of K in vineyard (Stamford et al., 2011), while phonolite was as effective as KCl in increasing fruit yield in coffee (Mancuso et al., 2014). These studies indicated that plant species along with their growth pattern also could facilitate the release of K from K-bearing minerals. Although crushed rock materials were promoted as nutrient sources for some time, this was largely confined in alternative or organic farming sectors (Lisle, 1994; Walters, 1975). The use of K-bearing minerals as such or silicate rock fertilizers in traditional agricultural practices was found poor because of low solubility of silicate rocks, subsequent low availability of nutrients to plants, and the practicality of applying large amounts of ground rock to agricultural land (Bolland and Baker, 2000; Harley and Gilkes, 2000; Hinsinger et al., 1996). So, only crushed rock materials as such were not sufficient to supply K to plant as compared with conventional soluble K sources. However, several biological means, particularly the use of K mobilizing microorganisms, can mobilize K from rocks and minerals and thus can increase K availability to plants. So, the use of rock powders in combination with some suitable biological modification can be an alternative source of K for crop production, especially with the gradual growth in popularity of organic farming.

4. BIO-INTERVENTION OF SILICATE MINERALS AND K AVAILABILITY Applications of silicate minerals as such are not as effective as commercial K fertilizers. So, some interventions are needed to speed up the K release rate. Release of K in soil from K-bearing minerals is influenced

Bio-Intervention of Naturally Occurring Silicate Minerals

125

by many factors, especially by the microbial activity in the rhizosphere region. Microbial activity releases K directly from the mineral structure as well as from the nonexchangeable reserve. Many microorganisms hold a primary catabolic role in the degradation of silicate mineral structure, which contributes to the release of K in soils. These microorganisms are able to solubilize the unavailable forms of K from K-bearing minerals, such as micas, illite, and orthoclase, by excreting organic acids which either directly dissolve the rock K or chelate the silicon ions to bring the K into solution (Bennett et al., 1998; Biswas and Basak, 2013; Friedrich et al., 1991; Ullman et al., 1996; Vandevivere et al., 1994). These microorganisms are commonly known as K solubilizing microorganisms (KSM). In China and South Korea, the K-dissolving bacteria are known as “biological K fertilizer” (BPF) and used for bio-activation of soil K reserves so as to alleviate the shortage of K fertilizers (Basak and Biswas, 2012; Han and Lee, 2005; Han et al., 2006; Lin et al., 2002; Sheng et al., 2002). On the other hand, blending of K-bearing minerals during composting is an alternative and viable technology to release K from minerals (Badr, 2006; Nishanth and Biswas, 2008; Zhu et al., 2013). Therefore, biological modification or bio-intervention (microbial intervention and composting) can turn out to be an important and effective means to mobilize K from K-bearing minerals for plant nutrition. Such bio-intervention strategies (Fig. 3) provide fewer chances for pollution and consume less energy in improving available K assimilation by plants.

Fig. 3 Brief mechanisms of potassium mobilization from silicate minerals through biointerventions.

126

B.B. Basak et al.

5. MECHANISMS OF POTASSIUM MOBILIZATION FROM SILICATE MINERALS 5.1 Dissolution by Organic Acids The principal mechanism of K solubilization from K-bearing minerals is the action of organic acids synthesized by the soil microorganisms (Table 3) (Huang and Keller, 1972; Huang and Kiang, 1972; Leyval and Berthelin, 1989). The protons associated with the organic acid molecules decrease the pH of the solution, and therefore, induce the releasing capacity of cations such as Fe, K, and Mg. Microbial respiration and degradation of particulate and dissolved organic carbon can elevate the carbonic acid concentration at mineral surfaces, in soils and in ground water (Barker et al., 1998; Calvaruso et al., 2006), which can lead to an increase in the rates of mineral weathering by a proton-promoted dissolution mechanism. Experiments revealed that Table 3 Potassium Solubilizing Microbes (KSMs) Involved in Solubilization of K From Minerals Microbes Predominant Acid Produced References Bacteria

Bacillus mucilaginsus

Oxalic and citric

Liu et al. (2006)

Bacillus edaphicus

Oxalic and tartaric

Sheng and He (2006)

Bacillus globiospora

Gluconic, acetic, and tartaric

Sheng et al. (2008)

Paenibacillus mucilaginosus

Tartaric, citric, and oxalic

Liu et al. (2012) and Hu et al. (2006)

Aspergillus niger

Citric, glycolic, and succinic

Sperberg (1958)

Torulaspora globosa

Acetic acid

Vora and Shelat (1998)

Aspergillus terreus

Itaconic

Magnuson and Lasure (2004)

Aspergillus fumigatus

Succinic and acetic

Song et al. (2014)

Penicillium purpurogenum

Oxalic

Song et al. (2014)

Glomus mosseae

Citric, malic, and oxalic

Yousefi et al. (2011)

Glomus intraradices

Citric, malic, and oxalic

Yousefi et al. (2011)

Fungi

AMF

Bio-Intervention of Naturally Occurring Silicate Minerals

127

species of Bacillus increased the soluble K content in the culture medium (Han et al., 2006; Sheng et al., 2002). It was also proposed that Bacillus mucilaginosus increased the dissolution rate of silicate and aluminosilicate minerals and released the K+ and SiO2 from the crystal lattice primarily by generating organic acids like oxalic, citric, tartaric, fumaric, glycolic acids, etc. Among these acids, oxalic and citric acids were the most common and present in a relatively larger quantities. In addition to production of carboxylic acids (citric, tartaric, and oxalic acids), microorganisms could also produce some intermediate and high-molecular-weight organic molecules like mannuronic and guluronic acids. Like the low-molecular-weight organic acids, the high-molecular-weight acids could also increase the extent of mineral weathering presumably by complexing with the ions in solution, thereby lowering the solution saturation state (Welch and Vandevivere, 1994; Welch et al., 2002). It was found that the exopolysaccharides produced by microorganisms strongly adsorbed to organic acids and thus assisted in their attachment to the mineral surface, resulting in an area of high concentration of organic acids near the mineral (Liu et al., 2006). The extracellular polysaccharides (EPS) adsorbed SiO2 and thus affected the equilibrium between the mineral and fluid phases and directed the reaction toward SiO2 and K solubilization. Bacteria might also increase the release rates by creating and maintaining microenvironments where metabolite concentrations, such as extracellular polymer, primarily proteins, and polysaccharides, were higher than in the bulk solution (Malinovskaya et al., 1990; Ullman et al., 1996). Organic acid molecules have a triple action on mineral weathering: (i) they adhere to the mineral surface and extract nutrients from the mineral particles by electron transfer reaction; (ii) they break the oxygen links; and (iii) they chelate ions present in solution through their carboxyl and hydroxyl groups. The third mechanism indirectly accelerates the dissolution rate by creating gradient between cation and anion concentrations in the solution (Welch et al., 2002).

5.2 Metal-Complexing Ligands Another possible mechanism of K mobilization by microorganisms is the production of metal-complexing ligands. In addition to producing a variety of organic acids, microbes also produce high-molecular-weight polymers and organic ligands (mannuronic acid, guluronic acid, and alginates). Ligands can complex with ions on the mineral surface and can weaken the metal– oxygen bonds. Alternatively, ligands can directly affect the reactions by

128

B.B. Basak et al.

forming complexes with ions in the solution, thereby decreasing the solution saturation state. The high-molecular-weight polymers can accelerate the ions diffusion away from the mineral surface by producing slime layers around the mineral surface, which increases the contact time between water and the mineral (Banfield et al., 1999). For example, the production of capsular polysaccharide or EPS and enzymes by KSMs’ viz., B. mucilaginosus and Bacillus edaphicus (Banfield et al., 1999; Lin et al., 2002; Richards and Bates, 1989) may accelerate the dissolution of a variety of silicates. The capsular polysaccharide produced by B. edaphicus contained functional groups (–COO–) that complexed with mineral ions, lowering the solution saturation state, and thereby enhanced dissolution (Sheng et al., 2002). In addition to many simple and complex organic acids, microbially produced organic ligands might include metabolic by-products, extracellular enzymes, and chelates, which would help in the dissolution of K-minerals by decreasing the pH of the environment. Chelating molecules might increase the dissolution rates of cations by forming strong bonds with them or with mineral surfaces (Welch et al., 2002). Mixture of polymers and lowmolecular-weight ligands produced by B. mucilaginosus had a beneficial effect on silicate mineral (biotite and muscovite) weathering (Malinovskaya et al., 1990). Bacteria might also increase the release rate of K by creating and maintaining microenvironments where metabolite concentrations are higher than in the bulk solution (Ullman et al., 1996). Thus, the production and release of extracellular polymers, primarily proteins, and polysaccharides into the surrounding environment increase the release of K from silicate mineral structures.

5.3 Formation of Biofilm An additional hypothesized mechanism of mobilization of mineral-K is by the formation of biofilm on the rhizospheric mineral surfaces by certain bacterial strains (Balogh-Brunstad et al., 2008). Biofilm is defined as a microbial community concentrated on the root–hypha–mineral interface and is protected by extracellular polymers produced by themselves utilizing plant and fungal exudates in soils (Banfield et al., 1999; Gadd, 2007). These bacteria were remarkable for their tremendous phylogenetic and metabolic diversity and for their ability to adapt and colonize extreme environments which were not tolerated by other organisms. In such a microenvironment, bacteria extracted inorganic nutrients and energy directly from the mineral matrix and thereby helped in mineral weathering. Extracellular polymers,

Bio-Intervention of Naturally Occurring Silicate Minerals

129

primarily proteins, and polysaccharides produced by the microorganism served as a catalyst and thereby induced the K release from silicate mineral structure. It was also reported that ectomycorrhizal hyphal networks and root hairs of nonectomycorrhizal trees could embed in biofilms and transfer nutrients to the host. It suggested that the presence of biofilms accelerated the weathering of biotite and anorthite, and thereby increased the mineral uptake by plants (Adey et al., 1993; Shi et al., 2014).

6. BIO-APPROACHES FOR K MOBILIZATION FROM SILICATE MINERALS 6.1 Microbial Intervention KSM include mainly bacteria and some fungi, but bacteria are the most dominant members. They are also known as potassium solubilizing bacteria (KSB) or potassium-dissolving bacteria or silicate-dissolving bacteria (SDB). A wide range of KSMs including bacteria (B. mucilaginosus, B. edaphicus, Bacillus circulans, Acidithiobacillus ferrooxidans), fungi (Aspergillus niger, Aspergillus fumigatus, Aspergillus terreus), and some arbuscular mycorrhizal fungi (AMF) were reported to release K from K-bearing minerals in plant available form (Biswas and Basak, 2013; Lian et al., 2002; Liu et al., 2011; Prajapati et al., 2012; Rajawat et al., 2012; Sheng et al., 2008; Singh et al., 2010; Wu et al., 2005). Apart from the above-mentioned microorganisms, some rhizospheric microorganisms were also reported as K solubilizers. These include Enterobacter hormaechei (KSB-8) (Prajapati et al., 2012), Arthrobacter sp. (Zarjani et al., 2013), Paenibacillus mucilaginosus (Hu et al., 2006; Liu et al., 2011), Penicillium frequentans, Cladosporium (Argelis et al., 1993), Aminobacter, Sphingomonas, Burkholderia (Uroz et al., 2007), Paenibacillus glucanolyticus (Sangeeth et al., 2012), etc. But the strains like B. mucilaginosus and B. edaphicus were the most efficient in their action (Li, 2003; Li et al., 2006; Lian et al., 2002; Sheng, 2005; Zhao et al., 2008). Table 4 summarizes several examples where K-release from minerals was augmented by bio-intervention (microbial and composting). 6.1.1 Potassium Solubilizing Bacteria KSB, particularly the genus Bacillus, enhance K availability through solubilization of the insoluble K from silicate minerals during the process of biodegradation of silicate minerals (Han et al., 2006; Liu et al., 2006). The results of such activity involve both geochemical and structural changes

Table 4 Summary of Experiments of Mobilization of K From Silicate Minerals Through Bio-Intervention Type of Experiment/ Condition Mineral Microbial Strain/Bioagent Outcome

References

Laboratory study/ Muscovite and biotite in vitro

Local rhizobacterial strain (K-31, K-81)

Significantly improved K release from minerals

Mikhailouskaya and Tchernysh (2005)

Laboratory study

Feldspar

Bacillus cereus

Increased K release from feldspar

Badr et al. (2006)

Composting

Feldspar

Bacillus cereus

Significant K mobilization from feldspar Badr (2006)

Laboratory study

Mica and feldspar

Bacillus mucilaginsus

K release increased by 66% from mica

Laboratory study

Bacillus mucilaginsus Muscovite mica, microcline, and orthoclase

Laboratory study

Mica and feldspar

Bacillus strain

Increased soluble K content

Laboratory study

Feldspar and illite

Aspergillus fumigatus

Drastically increased K release from the Lian et al. (2008) K-minerals

Composting

Waste mica

Aspergillus awamori

Sharp increase in water soluble K after 120 days

Nishanth and Biswas (2008)

Laboratory study

Feldspar and potassium aluminum silicate

Aspergillus terreus and Aspergillus niger

Higher K released by A. terreus from both the minerals

Prajapati et al. (2012)

Composting

Quartz powder

Earthworm (Eisenia fetida)

Significantly increased available K content

Zhu et al. (2013)

Laboratory study

Alkaline ultramafic rock powder

Yeast (Torulaspora globosa)

38% of total K released from rock powder

Rosa-Magri et al. (2012)

Laboratory study

Waste mica

Bacillus mucilaginsus

About 34% increase in available K content after 28 days

Biswas and Basak (2014)

Laboratory study

Muscovite

Penicillium purpurogenum

30% K dissolved from muscovite

Song et al. (2014)

Liu et al. (2006)

Significant amount of potassium released Sugumaran and from different minerals Janarthanam (2007) Grigis et al. (2008)

Bio-Intervention of Naturally Occurring Silicate Minerals

131

in the rocks and silicate minerals. The metabolic diversity of Bacillus spp., i.e., the various types of Bacillus strains and their mutants, has led to the fact that many representatives of this group are being used as K biofertilizers (Sheng and He, 2006; Sheng et al., 2003). It was found in several experiments that species of KSB increased the soluble K+ content when cultured with media containing K-bearing minerals under in vitro laboratory conditions (Han et al., 2006; Sheng et al., 2002). The K solubilization capacity was also governed by the type of bacterial strains. For example, local bacterial strain (K-81) solubilized 2.6, 2.0, and 4.6 times more K from biotite, muscovite, and hydromuscovite, respectively, than K-31 strain under same laboratory conditions (Mikhailouskaya and Tchernysh, 2005). On the other hand, the amount of K solubilization was found to differ from mineral to mineral by the same bacterial strain (Liu et al., 2006; Sheng and He, 2006). K released by B. mucilaginosus was observed as 4.29, 1.26, and 0.85 mg L1 from mica, microcline, and orthoclase, respectively (Sugumaran and Janarthanam, 2007). Thus, both the types of silicate minerals and the associated bacterial strains could play an equally significant role in K solubilization. 6.1.2 Potassium Solubilizing Fungi Like KSB, some fungi (A. niger, A. fumigatus, A. awamori, Penicillium sp.) and yeast (Torulaspora globosa) could release K from K-bearing minerals (Lian et al., 2008; Prajapati et al., 2012; Song et al., 2014), and they are known as potassium solubilizing fungi (KSF). Among the KSF, A. niger, A. fumigatus, and A. terreus were able to release significant amount of K from insoluble source of K under laboratory conditions within a short period of time (Lian et al., 2008; Prajapati et al., 2012). Penicillium purpurogenum and T. globosa were able to release 30% and 38% of the total K, respectively, from a silicate rock powder within 15 days under laboratory conditions. So, KSF could be a potential bio-agent for improving K release from silicate minerals as well as a promising K biofertilizer. 6.1.3 Arbuscular mycorrhizal Fungi AMF could also release nutrient elements including K from the mineral structure by releasing protons, CO2, and organic acids in surrounding environment (Jones et al., 2009; Veresoglou et al., 2011; Yousefi et al., 2011). The AMF, which are well known to improve P nutrition of plants (Bolan, 1991), were also able to solubilize K, Fe, Mg, and Al from apatite, phlogopite, biotite, feldspars and other silicates rock powders, and promote plant

132

B.B. Basak et al.

growth under nutrient-limiting conditions (Balogh-Brunstad et al., 2008; Hoffland et al., 2003; Jongmans et al., 1997; Leyval and Berthelin, 1989, 1991; Paris et al., 1995; Wallander and Wickman, 1999). But the K release rate was very slow and only occurred when surrounding environment was deficient in K. So, the AMF could be a promising K biofertilizer for long duration crops (plantation and fruit) where slow but continuous supply of the nutrient is required.

6.2 Composting Composting of organic matter with K-minerals can release K and improve the K availability in the system. The silicate structure of K-minerals could be disintegrated during the composting process because of the production of organic acids and CO2, which rendered low pH environment in the system. Carbonic acid produced from CO2 is assumed to play an important role in weathering of minerals through suppression of pH and the known impact of increased proton activity to accelerate the weathering of primary silicate minerals (Banwart and Berg, 1999). This mode of action is similar to low-molecular-weight organic acid produced by the microorganisms. Similarly, vermicomposting (with the introduction of earthworms) accelerated the K release from silicate minerals due to the low pH, high microbial population, and improved enzymatic action in the earthworm intestine (Liu et al., 2011). There are only few evidences available in the literature which demonstrated enhanced K release from silicate minerals through composting process (Badr, 2006; Biswas et al., 2009; Nishanth and Biswas, 2008). For example, concentration of available K releasing from feldspar increased markedly through composting process and the maximum increase was observed with 40% feldspar addition in the total compost dry weight (w/w) (Badr, 2006). In another study, a significant amount of K released from waste mica when composted with rice straw and cow dung slurry for 120 days (Nishanth and Biswas, 2008). Addition of low-grade rock phosphate along with waste mica to crop residue during composting improved the quality of the compost in terms of its total N, P, and K contents which helped to enhance the mobilization of unavailable K in waste mica into plant available forms (Biswas et al., 2009). Significant release of K was observed when K-bearing mineral powder (PBMP) was composted in the presence of earthworm (Eisenia fetida), which increased the available and effective K content in the final compost (Zhu et al., 2013). The amount of acids which are produced during the composting process is presumably much

Bio-Intervention of Naturally Occurring Silicate Minerals

133

higher than an individual microorganism because composting often involves a heterogeneous microbial strain. In case of vermicomposting, the K release from silicate minerals might be accelerated by both the chemical and the physical actions of earthworms. These actions come from the enhanced enzymatic activities and the grinding of minerals within the earthworm’s gut. Hence, composting process could significantly contribute to the K mobilization from rocks and minerals and become available option for the production of K-enriched organic fertilizer.

7. STRUCTURAL CHANGES OF SILICATE MINERALS DUE TO BIO-INTERVENTION Bio-intervention of silicate minerals leads to the release of K either by direct K dissolution from the mineral structure or by chelation of Si and Al ions with organic molecules. Both the processes might lead to some structural alternation of the mineral species. As the Si and Al ions are the main structural framework of silicate minerals, there is a significant possibility of their structural change or breakdown. For example, soil microorganisms were able to transform biotite minerals following the release of K and other ions (Boyle and Voigt, 1973). Microbial destruction of feldspar was evident due to an accelerated weathering by ligand excretion and release of limiting nutrient from the mineral structure (Bennett et al., 1998). The structural degradation of silicate minerals (e.g., mica and feldspar) by B. mucilaginosus occurred as a result of the release of K+ and SiO2 under laboratory conditions (Liu et al., 2006). Significant changes of full-width at half maximum (FWHM) in the X-ray diffraction (XRD) reflection of mica were observed when inoculated with B. mucilaginosus under both the laboratory and the pot culture conditions (Basak and Biswas, 2009; Biswas and Basak, 2014). The same bacterial strain was found to alter a montmorillonite structure under laboratory conditions (Yang et al., 2016). These alterations also led to the structural degradation of the mineral and reduced the water retention capacity of montmorillonite, which might raise a question about the long-term sustainability of the technology (Yang et al., 2016). However, further research is needed in order to unravel the microstructural changes of minerals due to bio-intervention and its possible environmental impacts. Advanced instrumental techniques like scanning electron microscopy (SEM), transmission electron microscopy (TEM), XRD, neutron scattering, and also synchrotron-based methods could be used to pin point the specific change or alteration of minerals occurred due to the microbial intervention.

134

B.B. Basak et al.

8. PLANT GROWTH AND K NUTRITION ON BIO-INTERVENED SILICATE MINERALS Application of silicate rocks alone as the source of K has yielded varying results, and sometimes it was not very effective in increasing the crop growth and nutrition. But an integrated application of silicate minerals with K mobilizing microorganisms was found promising in increasing the crop growth and yield under both pot culture and field experiments using a range of K-bearing silicate minerals in combination with either different species of KSM or composting.

8.1 Pot Trials Reports on the bio-intervention of silicate minerals as a source of K under pot culture experiments are listed in Table 5. Significant amount of K uptake was reported from biotite and microcline by Pinus sylvestris colonized by two ectomycorrhizal fungi, Paxillus involutus and Suillus variegatus (Wallander and Wickman, 1999). Slime-forming bacteria (B. mucilaginosus, B. edaphicus, and Bacillus cereus) isolated from soils, rock surface, and earthworm intestine could dissolve silicate minerals. This helped in improving yield and K uptake in tomato, cotton, rape, mustard, groundnut, wheat, sorghum, and sudan grass by supplying K to K-deficient soils (Badr et al., 2006; Basak and Biswas, 2009; Lin et al., 2002; Sheng, 2005; Sheng and He, 2006; Sugumaran and Janarthanam, 2007). Inoculation of these bacterial strains could improve the yield by 21% in rape, 24% in cotton, 125% in tomato, 58% in sorghum, and 125% in groundnut, while K uptake increased by 31% in rape, 34% cotton, and 71% in sorghum (Badr et al., 2006; Lin et al., 2002; Sheng, 2005; Sugumaran and Janarthanam, 2007). Application of enriched vermicompost prepared from gneiss and steatite powder also resulted in a higher growth and yield than plants grown in Oxisol with nonenriched vermicompost. Further, vermicompost enriched with steatite powder increased the dry matter yield of maize by 21.5% in comparison to applying nonenriched vermicompost and steatite alone to the soil (de Souza et al., 2013). Apart from improving plant growth parameters, soil K content was also improved by inoculation of bacterial strain. The available K content increased from 3.63 mg kg1 in nonrhizosphere soil to 5.73 mg kg1 in rhizosphere soil when plant root was inoculated with B. mucilaginosus strain (Lin et al., 2002).

Table 5 Summary of Pot Experiments: Improved Plant Nutrition Through Bio-Intervention of Silicate Minerals Rock/Mineral

Bio-Intervention (KSMs and Composting) Crop/Plant

Biotite and microcline Paxillus involutus and Suillus variegatus

Salient Outcomes

References

Pine

Mycorrhizal fungi improved K uptake by releasing K from mineral structure

Wallander and Wickman (1999) Sheng (2005)

Illite powder

Bacillus edaphicus NBT

Cotton and rape

Dry matter yield and K content increased

Illite and rock phosphate power

Coinoculation of Bacillus mucilaginsus (KSB) and Bacillus megaterium (PSB)

Eggplant

Enhanced plant growth and NPK uptake as well Han and Lee (2005) as soil availability of P & K

Feldspar

Bacillus cereus

Sorghum

Yield and K uptake increased while K status in soil improved

Badr et al. (2006)

Feldspar and illite

Bacillus edaphicus wild strain (MPs series) Wheat

Crop growth and K content increased

Sheng and He (2006)

Illite and rock phosphate powder

Coinoculation of Bacillus mucilaginsus (KSB) and Bacillus megaterium var phosphaticum (PSB)

Pepper and cucumber

Increased availability of P & K in soil and uptake Han et al. (2006) by plants

Microcline, orthoclase, Bacillus mucilaginsus and muscovite mica

Groundnut

Yield and oil content increased while K status in soil improved

Waste mica

Bacillus mucilaginsus

Sudan grass

Improved biomass yield and K uptake by sudan Basak and Biswas grass as well as soil K status (2009)

Waste mica

Coinoculation of Bacillus mucilaginsus (KSB) and Azotobacterchrooccum (N-fixer)

Sudan grass

Biomass yield, K, and N uptake increased

Basak and Biswas (2010)

Feldspar

Bacillus mucilaginsus

Maize

Plant growth and K uptake increased

Abou-el-Seoud and Abdel-Megeed (2012)

Gneiss and steatite

Earthworms (Eisenia andrei)

Maize

Steatite charged vermicompost increased 21.5% de Souza et al. (2013) dry matter yield over nonenriched vermicompost

Sugumaran and Janarthanam (2007)

136

B.B. Basak et al.

Sometime coinoculation with other bacteria like plant growth promoting rhizobacteria (PGPR), phosphate solubilizing bacteria (PSB), and N-fixing bacteria may improve the performance of individual inoculants due to synergistic effects on each other. The use of PGPR including PSB and KSB as biofertilizers was suggested as a sustainable solution to improve plant nutrition and production (Alexander, 1977; Park et al., 2003; Vassy, 2003). Synergistic effects of soil fertilization with rock P and K materials and coinoculation with PSB Bacillus megaterium and KSB B. mucilaginosus KCTC 3870 on the improvement of P and K uptake by eggplant (Solanum torvum L. NIVOT) grown under limited P and K soil in green house was reported (Han and Lee, 2005). Although individual inoculation did not increase the yield and uptake of N, P, and K by eggplant, coinoculation with both bacteria and fertilized with rock P and K materials increased the yield as well as N, P, and K uptake by shoot (14%, 22%, and 14%, respectively) and roots (11%, 14%, and 21%) (Han and Lee, 2005). Similarly coinoculation of biofertilizer containing N-fixer (Azotobacter chroococcum), P-solubilizer (B. megaterium), and K-solubilizer (B. mucilaginosus) and AMF (Glomus mosseae and Glomus intraradices) had beneficial effect on soil properties and maize growth. The study also indicated that half the amount of biofertilizer applications had similar effects when compared with organic fertilizer or chemical fertilizer treatments. Microbial inoculums not only increased the nutritional assimilation of total N, P, and K in plants, but also improved soil properties (Wu et al., 2005). The potential of coinoculation with PSB B. megaterium var. phosphaticum and KSB B. mucilaginosus on mobilization of P and K from rock minerals and their effect on nutrient uptake and growth of pepper and cucumber was also studied in Korea (Han et al., 2006). The integrated use of coinoculation with two bacterial strains and insoluble rock P and K materials resulted in higher yield and nutrient uptake by pepper and cucumber as well as 36% and 31% increase in P and K availability in soils, respectively, as compared to the control (Han et al., 2006). Similarly waste mica (K source) coinoculated with K solubilizing (B. mucilaginosus) and nitrogen fixing (A. chroococcum A-41) bacteria was found to be effective in increasing the biomass yield and N and K uptake in Sudan grass grown under K limiting soil (Basak and Biswas, 2010). Soil fertilization with apatite (P source), feldspar, and illite powders in combination with PSB and KSB (B. megaterium var. phosphaticum) and KDB (B. mucilaginosus and B. subtilis) significantly improved P and K uptake, P and K availability and growth of maize plant grown under P and K limited calcareous soil (Abou-el-Seoud and Abdel-Megeed, 2012).

Bio-Intervention of Naturally Occurring Silicate Minerals

137

Therefore, bio-intervention of silicate minerals was found to be effective as a source of K and could be an alternative to commercial K fertilizer. These results of pot and green house studies are quite promising, but still need to be replicated the success under field conditions for better acceptance of this technology in sustainable faming system.

8.2 Field Trials The effectiveness of integrated application of K-bearing minerals and KSMs have already been established, but through a fewer number of field trials (Table 6). Application of K-bearing minerals (feldspar, illite, muscovite, and biotite) inoculated with KSB strains (B. cereus, B. mucilaginosus, and Bacillus pasteurii) significantly improved the yield and K uptake in wheat, tomato, hot pepper, peanut, and sesame under field conditions (Badr, 2006; Mikhailouskaya and Tchernysh, 2005; Supanjani et al., 2006; Youssef et al., 2010). Soil inoculated with KSF (Pseudomonas putida) was found quite effective in plantation crops like tea and tobacco, and could supplement 25% of the chemical fertilizers (Bagyalakshmi et al., 2012; Subhashini, 2015). Similarly, potassium enriched compost prepared from waste mica was quite effective as the source of K in potato-soybean cropping system (Biswas, 2011). However, other mineral ions such as Si and Mg contained in the rock powder might have also contributed toward the yield. Application of enriched compost to the first crop resulted in a significant increase in soybean yield grown on residual fertility which could supplement 50% of the total K requirement of soybean crop (Meena and Biswas, 2013). The application of bacterial strains (K-31 and K-81) with K-mineral (hydromuscovite, muscovite, and biotite) effectively improved the available K content in sandy loam soil (Luvisol) and indicated the effectiveness of K mobilizing bacteria in a K deficient situation (Mikhailouskaya and Tchernysh, 2005). These results clearly indicated that both the microbes and composting process mobilized K from K-bearing minerals which acted as a continuous source of K throughout the cropping system. The result of field studies indicated that bio-intervention of silicate minerals could be a viable option of crop growth in place of costly commercial K fertilizers. In most of the cases, this technology performed better than control as well as application of silicate mineral alone. In some cases, bio-intervention of silicate minerals was as effective as commercial K fertilizers or even better than that. So, more systematic study is needed to standardize this technology in large scale which can effectively supplement the costly K fertilizers while maintaining yield and quality of crops.

138

B.B. Basak et al.

Table 6 Summary of Field Experiments: Improved Plant Nutrition Through Bio-Intervention of Silicate Minerals Bio-Intervention (KSMs and Rock/Mineral Composting) Crop/Plant Salient Outcomes References

Muscovite and biotite

Local rhizobacterial strain (K-31, K-81)

Wheat

Improved grain yield Mikhailouskaya and K status of soil and Tchernysh (2005)

Feldspar

Bacillus cereus

Tomato

More fruit yield and Badr (2006) potassium use efficiency (KUE) as compared to K2SO4

Potassium rock (illite) powder

Bacillus mucilaginosus strain (KCTC 3870)

Hot pepper

Supanjani et al. Improved biomass and fruit yield as well (2006) as K availability in soil

Waste mica

Potato– Composting with Aspergillus soybean awamori

Biswas (2011) Mica enriched compost significantly increased yield K uptake by both the crops

Feldspar

Bacillus pasteurii Peanut (Biopotash) and sesame

Increased K uptake Youssef et al. by maize and wheat (2010)

Muriate of potash

Pseudomonas putida

Improved leaf yield Bagyalakshmi and quality as well as et al. (2012) nutrient uptake

Waste mica

Soybean Composting with Aspergillus awamori

Mica charged compost improved Soybean yield and K uptake as compared to ordinary compost

Sulfate of potash

Frateuria aurantia Tobacco

Potassium content in Subhashini (2015) tobacco leaf increased 39% when soil inoculated with bacterial strain

Tea

Meena and Biswas (2013)

Bio-Intervention of Naturally Occurring Silicate Minerals

139

9. CONCLUSIONS AND FUTURE PROSPECTS This review highlighted the contribution of bio-intervention of naturally available K-bearing minerals as a possible alternative of K fertilizer for sustaining crop production and maintaining soil K level. Investigations on the possible use of silicate rocks for K supply through bio-intervention (K mobilizing microbes and composting) yielded promising results. The benefit of this approach was, however, confined mostly within laboratory or green house scale studies. The validity and possibility of sustaining agronomic performance and reduce the cost of cultivation through the use of cheap natural sources is highly important. Thus, combined application of different kinds of bio-agents like KSB, KSF, AMF, yeast, and earthworm in different combinations could provide a faster and continuous supply of K from low cost mineral powders. Currently, there is a lack of consistency in terms of the design of individual trials, limiting comparison, and extrapolation. Performance of this technology under different soil types and properties is rarely reported. The relative impact of this technology on the mineral-weathering process is still poorly understood. Further research is highly justified due to a continuously increasing price of conventional K fertilizers worldwide. In further study, emphasis should be given to find out the best combination of different factors which can be suitable alternative of conventional potash fertilizers. There is a huge scope for careful selection of the silicate rock as K sources. On the basis of dissolution rate, priority should be given to rocks that are enriched with bioavailable K. It is appropriate to consider the use of commonly abundant K-bearing minerals such as feldspars and mica (muscovite, biotite, etc.) for field crop trials. The best KSM strain can be selected on the basis of their ability to dissolve silicate minerals or release K from the minerals. There is also an opportunity to isolate indigenous KSM strains which may be more suitable in local argo-ecological conditions in comparison to an alien species. Composting process would enhance the dissolution of K from indigenous mineral which is very promising, but more systematic approaches are needed in order to explore their efficacy. It is essential that scientists from both biology and mineralogy disciplines effectively collaborate in conducting this research. Future studies should more concentrate to test this potential technology under field conditions.

140

B.B. Basak et al.

ACKNOWLEDGMENTS This work was made possible by an Endeavour Research Fellowship awarded to senior author by the Australian Federal Government. It was also supported by the Indian Council of Agricultural Research (ICAR), New Delhi.

REFERENCES Abdel-Mouty, M.M., El-Greadly, N.H.M., 2008. The productivity of two okra cultivars as affected by gibberilic acid, organic N, rock phosphate and feldspar applications. J. Appl. Sci. Res. 4, 627–636. Abou-el-Seoud, I.I., Abdel-Megeed, A., 2012. Impact of rock materials and biofertilizations on P and K availability for maize (Zea maize) under calcareous soil conditions. Saudi J. Biol. Sci. 19, 55–63. Adey, W., Luckett, C., Jensen, K., 1993. Phosphorus removal from natural waters using control algal production. Restor. Ecol. 1, 29–39. Alexander, M., 1977. Introduction to Soil Microbiology. John Wiley and Sons, New York. Argelis, D.T., Gonzala, D.A., Vizcaino, C., Gartia, M.T., 1993. Biochemical mechanism of stone alteration carried out by filamentous fungi living in monuments. Biogeochemistry 19, 129–147. Badr, M.A., 2006. Efficiency of K-feldspar combined with organic materials and silicate dissolving bacteria on tomato yield. J. Appl. Sci. Res. 2, 1191–1198. Badr, A.M., Shafei, M.A., Sharaf El-Deen, S.H., 2006. The dissolution of K and P-bearing minerals by silicate dissolving bacteria and their effect on sorghum growth. Res. J. Agric. Biol. Sci. 2, 5–11. Bagyalakshmi, B., Ponmurugan, P., Marimuthu, S., 2012. Influence of potassium solubilizing bacteria on crop productivity and quality of tea (Camellia sinensis). Afr. J. Agric. Res. 7, 4250–4259. Balogh-Brunstad, Z., Keller, C.K., Gill, R.A., Bormann, B.T., Li, C.Y., 2008. The effect of bacteria and fungi on chemical weathering and chemical denudation fluxes in pine growth experiments. Biogeochemistry 88, 153–167. Banfield, J.F., Barker, W.W., Welch, S.A., Taunton, A., 1999. Biological impact on mineral dissolution: application of the lichen model to understanding mineral weathering in the rhizosphere. Proc. Natl. Acad. Sci. U.S.A. 96, 3404–3411. Banwart, S.A., Berg, A., 1999. Accelerated weathering of feldspar under elevated PCO2 (g) at 25°C and 1 Atm. In: Ninth Annual VM Goldschmidt Conference, vol. 1, p. 7240. Barker, W.W., Welch, S.A., Chu, S., Banfield, J.F., 1998. Experimental observations of the effects of bacteria on aluminosilicate weathering. Am. Mineral. 83, 1551–1563. Basak, B.B., Biswas, D.R., 2009. Influence of potassium solubilising microorganism (Bacillus mucilaginosus) and waste mica on potassium uptake dynamics by sudan grass (Sorghum vulgare Pers.) grown under two Alfisols. Plant Soil 317, 235–255. Basak, B.B., Biswas, D.R., 2010. Co-inoculation of potassium solubilizing and nitrogen fixing bacteria on solubilization of waste mica and their effect on growth promotion and nutrient acquisition by a forage crop. Biol. Fertil. Soils 46, 641–648. Basak, B.B., Biswas, D.R., 2012. Modification of Waste Mica for Alternative Source of Potassium: Evaluation of Potassium Release in Soil from Waste Mica Treated with Potassium Solubilizing Bacteria (KSB). Lambert Academic Publishing, Saarbr€ ucken, Germany, ISBN: 978-3-659-29842-4, 80 pp. Bennett, P.C., Choi, W.J., Rogera, J.R., 1998. Microbial destruction of feldspars. Miner. Manag. 8, 149–150.

Bio-Intervention of Naturally Occurring Silicate Minerals

141

Biswas, D.R., 2011. Nutrient recycling potential of rock phosphate and waste mica enriched compost on crop productivity and changes in soil fertility under potato–soybean cropping sequence in an Inceptisol of Indo-Gangetic Plains of India. Nutr. Cycl. Agroecosyst. 89, 15–30. Biswas, D.R., Basak, B.B., 2013. Potassium solubilizing microorganisms; their mechanisms, potentialities and challenges as potassium biofertilizer. Indian J. Fert. 9, 102–116. Biswas, D.R., Basak, B.B., 2014. Mobilization of potassium from waste mica by potassium solubilizing bacteria (Bacillus mucilaginosus) as influenced by temperature and incubation period under in-vitro laboratory condition. Agrochimica 38, 309–320. Biswas, D.R., Narayanasamy, G., Datta, S.C., Singh, G., Begum, M., Maiti, D., Mishra, A., Basak, B.B., 2009. Changes in nutrient status during preparation of enriched organomineral fertilizers using rice straw, low-grade rock phosphate, waste mica, and phosphate solubilizing microorganism. Commun. Soil Sci. Plant Anal. 40, 2285–2307. Bolan, N.S., 1991. A critical review on the role of mycorrhizal fungi in the uptake of phosphorus by plants. Plant Soil 134 (2), 189–207. Bolland, M.D.A., Baker, M.J., 2000. Powdered granite is not an effective fertilizer for clover and wheat in sandy soils from Western Australia. Nutr. Cycl. Agroecosyst. 56, 59–68. Boyle, J.R., Voigt, G.K., 1973. Biological weathering of silicate minerals. Plant Soil 38, 191–201. Calvaruso, C., Turpault, M.P., Frey-Klett, P., 2006. Root-associated bacteria contribute to mineral weathering and to mineral nutrition in trees: a budgeting analysis. Appl. Environ. Microbiol. 72, 1258–1266. Coreonos, C., Hinsinger, P., Gilkes, R.J., 1996. Granite powder as a source of potassium for plants: a glasshouse bioassay comparing two pasture species. Fertil. Res. 45, 143–152. de Souza, M.E.P., de Carvalho, A.M.X., de Ca´ssia Deliberali, D., Jucksch, I., Brown, G.G., Mendonc¸a, E.S., Cardoso, I.M., 2013. Vermicomposting with rock powder increases plant growth. Appl. Soil Ecol. 69, 56–60. FAO (Food and Agricultural Organization), 2015. Current World Fertilizer Trends and Outlook to 2014–18. Food and Agriculture Organization of the United Nations, Rome. Friedrich, S., Platonova, N.P., Karavaiko, G.I., Stichel, E., Glombitza, F., 1991. Chemical and microbiological solubilization of silicates. Acta Biotechnol. 11, 187–196. Gadd, G.M., 2007. Geomycology: biogeochemical transformations of rocks, minerals, metals and radionuclides by fungi, bioweathering and bioremediation. Mycol. Res. 111, 3–49. Grigis, M.G.Z., Khalil, H.M., Sharaf, M.A., 2008. In-vitro evaluation of rock phosphate and potassium solubilizing potential of some Bacillus strains. Aust. J. Basic Appl. Sci. 2, 68–81. Han, H.S., Lee, K.D., 2005. Phosphate and potassium solubilizing bacteria effect on mineral uptake, soil availability and growth of eggplant. Res. J. Agric. Biol. Sci. 1, 176–180. Han, H.S., Supanjani, Lee, K.D., 2006. Effect of co-inoculation with phosphate and potassium solubilizing bacteria on mineral uptake and growth of pepper and cucumber. Plant Soil Environ. 52, 130–136. Harley, A.D., Gilkes, R.J., 2000. Factors influencing the release of plant nutrients from silicate rock powders: a geochemical overview. Nutr. Cycl. Agroecosyst. 56, 11–36. Hinsinger, P., Bolland, M.D.A., Gilkes, R.J., 1996. Silicate rock powder: effect on selected chemical properties of a range of soils from Western Australia and on plant growth assessed in a glasshouse experiment. Fertil. Res. 45, 69–79. Hoffland, E., Giesler, R., Jongmans, A.G., van Breemen, N., 2003. Feldspar tunneling by fungi along natural productivity gradients. Ecosystems 6, 739–746. Hu, X., Chen, J., Guo, J., 2006. Two phosphate- and potassium-solubilizing bacteria isolated from Tianmu Mountain, Zhejiang, China. World J. Microbiol. Biotechnol. 22, 983–990.

142

B.B. Basak et al.

Huang, W.H., Keller, W.D., 1972. Organic acids as agents of chemical weathering of silicate minerals. Nat. Phys. Sci. 239, 149–151. Huang, W.H., Kiang, W.C., 1972. Laboratory dissolution of plagioclase feldspars in water and organic acids at room temperature. Am. Mineral. 57, 1849–1859. Jiyun, J., 1993. Advances in soil potassium research. Acta Pedol. Sin. 1, 11. Jones, D.L., Nguyen, C., Finlay, R.D., 2009. Carbon flow in the rhizosphere: carbon trading at the soil-root interface. Plant Soil 321, 5–33. Jongmans, A.G., van Breemen, N., Lundstr€ om, U., van Hees, P.A.W., Finlay, R.D., Srinivasan, M., Unestam, T., Giesler, R., Melkerud, P.A., Olsson, M., 1997. Rock eating fungi. Nature 389, 682–683. Karimi, E., Abdolzadeh, A., Sadeghipour, H.R., Aminei, A., 2012. The potential of glauconitic sandstone as a potassium fertilizer for olive plants. Arch. Agron. Soil Sci. 9, 983–993. Leyval, C., Berthelin, J., 1989. Interaction between Laccaria laccata, Agrobacterium radiobacter and beech roots: influence on P, K, Mg and Fe mobilization from minerals and plant growth. Plant Soil 117, 103–110. Leyval, C., Berthelin, J., 1991. Weathering of a mica by roots and rhizospheric microorganisms of pine. Soil Sci. Soc. Am. J. 55, 1009–1016. Li, D.X., 2003. Study on the effects of silicate bacteria on the growth and fruit quality of apples. J. Fruit Sci. 20, 64–66. Li, F.C., Li, S., Yang, Y.Z., Cheng, L.J., 2006. Advances in the study of weathering products of primary silicate minerals, exemplified by mica and feldspar. Acta Petrol. Mineral. 25, 440–448. Lian, B., Fu, P.Q., Mo, D.M., Liu, C.Q., 2002. A comprehensive review of the mechanism of potassium release by silicate bacteria. Acta Mineral. Sin. 22, 179. Lian, B., Wang, B., Pan, M., Liu, C., Teng, H.H., 2008. Microbial release of potassium from K-bearing minerals by thermophilic fungus Aspergillus fumigatus. Geochim. Cosmochim. Acta 72, 87–98. Lin, Q.M., Rao, Z.H., Sun, Y.X., Yao, J., Xing, L.J., 2002. Identification and practical application of silicate-dissolving bacteria. Agric. Sci. China 1, 81–85. Lisle, H., 1994. The Enlivened Rock Powders. Acres USA, Louisiana, ISBN: 0-911311-48-3, 194 pp. Liu, D., Lian, B., Dong, H., 2012. Isolation of Paenibacillus sp. and assessment of its potential for enhancing mineral weathering. Geomicrobiol. J. 29, 413–421. Liu, W., Xu, X., Wu, X., Yang, Q., Luo, Y., Christie, P., 2006. Decomposition of silicate minerals by Bacillus mucilaginosus in liquid culture. Environ. Geochem. Health 28, 123–130. Liu, D.F., Lian, B., Wang, B., Jiang, G., 2011. Degradation of potassium rock by earthworms and responses of bacterial communities in its gut and surrounding substrates after being fed with mineral. PLoS One 6, e28803. Madaras, M., Mayerova´, M., Kulha´nek, M., Koubova´, M., Faltus, M., 2013. Waste silicate minerals as potassium sources: a greenhouse study on spring barley. Arch. Agron. Soil Sci. 59, 671–683. Magnuson, J.K., Lasure, L.L., 2004. Organic acid production by filamentous fungi. In: Advances in Fungal Biotechnology for Industry, Agriculture, and Medicine. Springer, USA, pp. 307–340. Malinovskaya, I.M., Kosenko, L.V., Votselko, S.K., Podgorskii, V.S., 1990. Role of Bacillus mucilaginosus polysaccharide in degradation of silicate minerals. Mikrobiologiya 59, 49–55. Mancuso, M.A.C., Soratto, R.P., Crusciol, C.A.C., Castro, G.S.A., 2014. Effect of potassium sources and rates on Arabica Coffee yield, nutrition and macronutrient export. Rev. Bras. Ci^enc. Solo 38, 1448–1456.

Bio-Intervention of Naturally Occurring Silicate Minerals

143

Manning, D.A.C., 2010. Mineral sources of potassium for plant nutrition. A review. Agron. Sustain. Dev. 30, 281–294. Meena, M.D., Biswas, D.R., 2013. Residual effect of rock phosphate and waste mica enriched compost on yield and nutrient uptake by soybean. Legum. Res. 36, 406–413. Mengel, K., Rahmatullah, 1994. Exploitation of potassium by various crop species from primary minerals in soils rich in micas. Biol. Fertil. Soils 17, 75–79. Mikhailouskaya, N., Tchernysh, A., 2005. K-mobilizing bacteria and their effect on wheat yield. Latv. J. Agron. 8, 154–157. Mohammed, S.M.O., Brandt, K., Gray, N.D., White, M.L., Manning, D.A.C., 2014. Comparison of silicate minerals as sources of potassium for plant nutrition in sandy soil. Eur. J. Soil Sci. 65, 653–662. Moores, S., 2009. Potash tunnel vision. Ind. Miner, 19, 56–62. Nishanth, D., Biswas, D.R., 2008. Kinetics of phosphorus and potassium release from rock phosphate and waste mica enriched compost and their effect on yield and nutrient uptake by wheat (Triticum aestivum). Bioresour. Technol. 99, 3342–3353. Paris, F., Bonnaud, P., Ranger, J., Lapeyrie, F., 1995. In vitro weathering of phlogopite by ectomycorrhizal fungi. I. Effect of K+ and Mg2+ deficiency on phyllosilicate evolution. Plant Soil 177, 191–201. Park, M., Singvilay, O., Seok, Y., Chung, J., Ahn, K., Sa, T.M., 2003. Effect of phosphate solubilizing fungi on P uptake and growth to tobacco in rock phosphate applied soil. Korean J. Soil Sci. Fertil. 36, 233–238. Prajapati, K., Sharma, M.C., Modi, H.A., 2012. Isolation of two potassium solubilizing fungi fromceramic industry soils. Life Sci. Leafl. 5, 71–75. Rajawat, M.V.S., Singh, S., Singh, G., Saxena, A.K., 2012. Isolation and characterization of K-solubilizing bacteria isolated from different rhizospheric soil. In: Proceeding of 53rd Annual Conference of Association of Microbiologists of India, p. 124. Rao, C.S., Subba Rao, A., 1999. Characterization of indigenous glauconitic sandstone for its potassium supplying potential by chemical, biological and electro ultrafiltration methods. Commun. Soil Sci. Plant Anal. 30, 1105–1117. Richards, J.E., Bates, T.E., 1989. Studies on the potassium-supplying capacities of southern Ontario soils. III. Measurement of available K. Can. J. Soil Sci. 69, 597–610. Rittenhouse, P.A., 1979. Potash and politics. Econ. Geol. 74, 353–357. Rosa-Magri, M.M., Avansini, S.H., Lopes-Assad, M.L., Tauk-Tornisielo, S.M., CeccatoAntonini, S.R., 2012. Release of potassium from rock powder by the Yeast Torulaspora globose. Braz. Arch. Biol. Technol. 55, 577–582. Sangeeth, K.P., Bhai, R.S., Srinivasan, V., 2012. Paenibacillus glucanolyticus, a promising potassium solubilizing bacterium isolated from black pepper (Piper nigrum L.) rhizosphere. J. Spices Aromat. Crops 21, 118–124. SanzScovino, J.I., Rowell, D.L., 1988. The use of feldspars as potassium fertilizers in the savannah of Columbia. Fertil. Res. 17, 71–83. Shanwal, A.V., Dahiya, S.S., 2006. Potassium dynamics and mineralogy. In: Lal, R. (Ed.), second ed. Encyclopedia of Soil Science, vol. 2. Taylor and Francis, Madison Avenue, New York, pp. 1359–1364. Sharpley, A.N., 1989. Relationship between soil potassium forms and mineralogy. Soil Sci. Soc. Am. J. 64, 87–98. Sheldrick, W.F., Syers, J.K., Lingard, J., 2002. A conceptual model for conducting nutrient audits at national, regional and global scales. Nutr. Cycl. Agroecosyst. 62, 61–67. Sheng, X.F., 2005. Growth promotion and increased potassium uptake of cotton and rape by a potassium releasing strain of Bacillus edaphicus. Soil Biol. Biochem. 37, 1918–1922. Sheng, X.F., He, L.Y., 2006. Solubilization of potassium-bearing minerals by a wildtype strain of Bacillus edaphicus and its mutants and increased potassium uptake by wheat. Can. J. Microbiol. 52, 66–72.

144

B.B. Basak et al.

Sheng, X.F., He, L.Y., Huang, W.Y., 2002. The conditions of releasing potassium by a silicate-dissolving bacterial strain NBT. Agric. Sci. China 1, 662–666. Sheng, X.F., Xia, J.J., Chen, J., 2003. Mutagenesis of the Bacillus edphicaus strain NBT and its effect on growth of chili and cotton. Agric. Sci. China 2, 40–41. Sheng, X.F., Zhao, F., He, H., Qiu, G., Chen, L., 2008. Isolation, characterization of silicate mineralsolubilizing Bacillus globisporus Q12 from the surface of weathered feldspar. Can. J. Microbiol. 54, 1064–1068. Shi, Z., Brunstad, Z.B., Harsh, J., Keller, C.K., 2014. Plant-driven mineral weathering: role of rhizospheric bioflims. In: Goldschmidt Abstracts, p. 2288. Silva, B., Paradelo, R., Vazquez, N., Garcıa-Rodeja, E., Barral, M.T., 2013. Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime. Environ. Earth Sci. 68, 429–437. Singh, G., Biswas, D.R., Marwaha, T.S., 2010. Mobilization of potassium from waste mica by plant growth promoting rhizobacteria and its assimilation by maize (Zea mays) and wheat (Triticum aestivum L.): a hydroponics study under phytotron growth chamber. J. Plant Nutr. 33, 1236–1251. Song, M., Pedruzzi, I., Peng, Y., Li, P., Liu, J., Yu, J., 2014. K-extraction from muscovite by the isolated fungi. Geomicrobiol. J. 32, 771–779. Sparks, D.L., 1987. Potassium dynamics in soils. Adv. Soil Sci. 6, 1–62. Sparks, D.L., Huang, P.M., 1985. Physical chemistry of soil potassium. In: Munson, R.D., et al. (Eds.), Potassium in Agriculture. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, WI, pp. 201–276. Sperberg, J.I., 1958. The incidence of apatite-solubilizing organisms in the rhizosphere and soil. Aust. J Agric. Res. Econ. 9, 778. Stamford, N.P., Andrade, I.P., da Silva Jr., S., Lira Jr., M.A., Silva Santos, C.E., de Freitas, A.D., Straaten, P.V., 2011. Nutrient uptake by Grape in a Brazilian soil affected by rock biofertilizer. J. Soil Sci. Plant Nutr. 11, 79–88. Steingrobe, B., Claassen, N., 2000. Potassium dynamics in the rhizosphere and K efficiency of crops. J. Soil Sci. Plant Nutr. 163, 101–106. Subba Rao, A., Brar, M.S., 2002. Potassium. In: Fundamentals of Soil Science, first ed. Indian Society of Soil Science (ISSS), New Delhi, pp. 369–380. Subhashini, D.V., 2015. Growth promotion and increased potassium uptake of tobacco by potassium-mobilizing bacterium Frateuria aurantia grown at different potassium levels in vertisols. Commun. Soil Sci. Plant Anal. 46, 210–220. Sugumaran, P., Janarthanam, B., 2007. Solubilization of potassium containing minerals by bacteria their effect on plant growth. World J. Agric. Sci. 3, 350–355. Supanjani, Hyo, S.H., Jae, S.J., Kyung, D.L., 2006. Rock phosphate-potassium and rocksolubilising bacteria as alternative, sustainable fertilizers. Agron. Sustain. Dev. 26, 233–240. Tripler, C.E., Kaushal, S.S., Likens, G.E., Todd Walter, M., 2006. Patterns in potassium dynamics in forest ecosystems. Ecol. Lett. 9, 451–466. Ullman, W.J., Kirchman, D.L., Welch, S.A., 1996. Laboratory evidence for microbially mediated silicate mineral dissolution in nature. Chem. Geol. 132, 11–17. Uroz, S., Calvaruso, C., Turpault, M.P., Pierrat, J.C., Mustin, C., Frey-Klett, P., 2007. Effect of the mycorrhizosphere on the genotypic and metabolic diversity of the bacterial communities involved in mineral weathering in a forest soil. Appl. Environ. Microbiol. 73, 3019–3027. Vandevivere, P., Welch, S.A., Ullman, W.J., Kirchman, D.L., 1994. Enhanced dissolution of silicate minerals by bacteria at near-neutral pH. Microb. Ecol. 27, 241–251. Vassy, J.K., 2003. Plant growth promoting bacteria as biofertilizers. Plant Soil 255, 571–586. Veresoglou, S.D., Mamolos, A.P., Thornton, B., Voulgari, O.K., Sen, R., Veresoglou, S., 2011. Medium-term fertilization of grassland plant communities masks plant specieslinked effects on soil microbial community structure. Plant Soil 344, 187–196.

Bio-Intervention of Naturally Occurring Silicate Minerals

145

Vora, M.S., Shelat, H.N., 1998. Torulospora globosa: a unique solubilizing tricalcium phosphate. Indian J. Agric. Sci. 68, 630–631. Wallander, H., Wickman, T., 1999. Biotite and microcline as potassium sources in ectomycorrhizal and non-ectomycorrhizal Pinus sylvestris seedlings. Mycorrhiza 9, 25–32. Walters, C., 1975. The Albrecht papers. Foundation Concepts, vol. 1 Acres USA, Louisiana, p. 515. Wang, J.G., Zhang, F.S., Cao, Y.P., Zhang, X.L., 2000. Effect of plant types on release of mineral potassium from gneiss. Nutr. Cycl. Agroecosyst. 56, 37–44. Weerasuriya, T.J., Pushpakumara, S., Cooray, P.I., 1993. Acidulated pegmatitic mica—a promising new multi-nutrient mineral fertilizer. Fertil. Res. 34, 67–77. Welch, S.A., Vandevivere, P., 1994. Effect of microbial and other naturally occurring polymers on mineral dissolution. Geophys. J. Roy. Astron. Soc. 12, 227–238. Welch, S.A., Taunton, A.E., Banfield, J.F., 2002. Effect of microorganisms and microbial metabolites on apatite dissolution. Geophys. J. Roy. Astron. Soc. 19, 343–367. Wu, S.C., Cao, Z.H., Li, Z.G., Cheung, K.C., Wong, M.H., 2005. Effects of biofertilizer containing N-fixer, P and K solubilizers and AM fungi on maize growth: a greenhouse trail. Geoderma 125, 155–166. Yadav, R.L., Prasad, Kamta, Gangwar, K.S., 1998. Prospects of Indian Agriculture with special reference to nutrient management under irrigated systems. In: Swarup, A., Damodar Reddy, D., Prasad, R.N. (Eds.), Long-Term Fertility Management Through Integrated Plant Nutrient Supply. Indian Institute of Soil Science, Bhopal, India, pp. 1–335. Yang, X., Li, Y., Lu, A., Wang, H., Zhu, Y., Ding, H., Wang, X., 2016. Effect of Bacillus mucilaginosus D4B1 on the structure and soil-conservation-related properties of montmorillonite. Appl. Clay Sci. 119, 141–145. Yao, Y., Yoneyama, T., Hayashi, H., 2003. Potassium uptake by Chinese cabbage (Brassica pekinensis Rupy.) from fused potassium silicate, a slow releasing fertilizer. Plant Soil 249, 279–286. Yousefi, A.A., Khavazi, K., Moezi, A.A., Rejali, F., Nadian, N.A., 2011. Phosphate solubilizing bacteria and arbuscular mycorrhizal fungi impacts on inorganic phosphorus fractions and wheat growth. World Appl. Sci. J. 15, 1310–1318. Youssef, G.H., Seddik, W.M., Osman, M.A., 2010. Efficiency of natural minerals in presence of different nitrogen forms and potassium dissolving bacteria on peanut and sesame yields. J. Am. Sci. 6, 647–660. Zarjani, J.K., Aliasgharzad, N., Oustan, S., Emadi, M., Ahmadi, A., 2013. Isolation and characterization of potassium solubilizing bacteria in some Iranian soils. Arch. Agron. Soil Sci. 59, 1713–1723. Zhao, F., Sheng, X., Huang, Z., He, L., 2008. Isolation of mineral potassium-solubilizing bacterial strains from agricultural soils in Shandong Province. Biodivers. Sci. 16, 593–600. Zhu, X., Lian, B., Yang, X., Liu, C., Zhu, L., 2013. Biotransformation of earthworm activity on potassium-bearing mineral powder. J. Earth Sci. 24, 65–74.

CHAPTER FOUR

Livestock Production and Its Impact on Nutrient Pollution and Greenhouse Gas Emissions K. Sakadevan1, M.-L. Nguyen2 Soil and Water Management & Crop Nutrition Section, International Atomic Energy Agency, Vienna, Austria 1 Corresponding author: e-mail address: [email protected]

Contents 1. 2. 3. 4.

Introduction Livestock for Economic Development and Consumer Demand Livestock Production and Land Use Change Environmental Impacts 4.1 Manure Management 4.2 Water Use in Livestock Production 4.3 Livestock and Soil Physical and Chemical Characteristics 4.4 Grazing and Soil Quality 4.5 Carbon and Nutrient Cycling 5. Nitrogen and Phosphorus Losses Under Livestock Production 5.1 Nitrogen 5.2 Phosphorus 6. Livestock Production and GHG Emission 6.1 Nitrous Oxide 6.2 Methane Emission 7. Isotopic and Nuclear Techniques for Assessing Soil–Crop–Livestock Interaction 8. Conclusion References

148 151 152 155 155 157 158 161 161 164 164 165 166 167 171 172 173 176

Abstract The livestock sector provides more than one-third of human protein needs and is a major provider of livelihood in almost all developing countries. While providing such immense benefits to the population, poor livestock management can potentially provide harmful environmental impacts at local, regional, and national levels which have not been adequately addressed in many countries with emerging economies. Twentysix percent of global land area is used for livestock production and forest lands are

2

Current address: Group ONE Consultancy Ltd., 11 Balfour Crescent, Riverlea, Hamilton 3216, New Zealand.

Advances in Agronomy, Volume 141 ISSN 0065-2113 http://dx.doi.org/10.1016/bs.agron.2016.10.002

#

2017 Elsevier Inc. All rights reserved.

147

148

K. Sakadevan and M.-L. Nguyen

continuously being lost to such activities. Land degradation through soil erosion and nutrient depletion is very common across pastures and rangelands. The intensification of livestock production led to large surpluses of on-farm nitrogen and phosphorus inputs that can potentially contribute to nonpoint source pollution of water resources in many parts of the world. The sector is one of the largest sources of greenhouse gases (GHGs) contributing around 14.5% of all human-induced GHG emissions, a major driver of use and pollution of freshwater (accounting 10% anthropogenic water use) and a contributor to the loss of biodiversity. About 60% of global biomass harvested annually to support all human activity is consumed by livestock industry, undermining the sustainability of allocating such large resource to the industry. Despite the negative impacts of livestock production, opportunities exist to balance the competing demands of livestock production and the environment. These include (1) improved technologies and practices that increase livestock productivity with optimal use of land and water, (2) reorienting grazing systems to provide environmental services for water, biodiversity, carbon sequestration, and resource conservation, (3) reducing GHG emission from livestock production, and (4) an effective management strategy for efficient and sustainable use of manure in livestock production. Further research, appropriate policy development, and institutional support are important to ensure the competitiveness of the industry. Integration of crops with livestock production provides opportunities for increasing resource use efficiencies and reducing environmental pollution, making the system resilient to impacts of climate change, reducing GHG emissions from the system, enhancing soil quality and fertility, and improving water quantity and quality. Appropriate techniques for assessing and monitoring impacts of livestock production are necessary for developing strategies and making the system profitable, sustainable, and resilient. Isotopic and nuclear techniques play an important role in such assessment and monitoring.

1. INTRODUCTION The global livestock production is increasing rapidly as the demand for livestock products for human consumption increased. In the past few decades, this growth was achieved through sufficient land availability and concentrated animal operating systems (FAO, 2006a,b). This increase in production is expected to continue into the future as real income grows in developing economies. Currently the sector accounts for 1.4% of world’s gross domestic product (GDP). It is a major contributor to human nutrition (protein) and health and provides a buffer against grain shortage assuring food security to human population (Smith et al., 2012). Livestock production is a major provider of livelihoods for larger part of the world’s poor, particularly in dry areas, and plays a crucial role in rural economies of most developing countries (Godfray et al., 2010;

149

Livestock Production and Its Impact

McDermott et al., 2010). It provides food for 1 billion of the world’s poor and contributed an average of more than 40% of global agricultural output (Steinfeld et al., 2006). With more than US $460 billion GDP in major agricultural economies (Table 1), more than 1500 million ha land area is currently used for livestock production through pasture management. In the next 10–15 years the livestock sector is expected to provide 50% of agricultural output in value terms. While global demand for food is expected to grow by 50% over the next 20 years to feed the growing human population, the demand for livestock products is expected to double during the same period (Thornton, 2010). Since the 1980s the demand for livestock products is stronger than for most other food items. Global meat production is projected to increase from 229 million tons in 1999/2001 to 465 million tons in 2050, and that of milk to increase from 580 to 1043 million tons (FAO, 2006a,b). Throughout the developing world, the integration of livestock with crops in the same farm (mixed crop-livestock systems) represents the backbone of family farming and provided 50% of the world’s meat, over 90% of its milk, and 50% of its cereals (Thornton and Herrero, 2010). For many poor farmers in developing countries, livestock manure is also a source of renewable energy and is an essential source of organic fertilizer for their crops. Meeting the increased demand for livestock products may put substantial pressure on land and water resource use and biodiversity conservation. Table 1 Value of Livestock Production in Selected Countries (FAO, 2005) % of Agricultural GDP

Country

Agricultural Land (Million ha)

Pasture Land (Million ha)

Argentina

129

100

5

37

Australia

455

408

61

34

Brazil

264

197

33

48

China

550

440

61

34

European Union 141

56

120

40

India

170

12

20

20

New Zealand

18

14

7

87

South Africa

100

84

3

46

United States

412

233

150

39

Livestock GDP (Billion US $)

150

K. Sakadevan and M.-L. Nguyen

Together with climate change and climate variability, these demands for resource uses add up to a formidable set of development challenges for both developed and developing countries. All together about 70% of agricultural land is currently used for livestock production either directly (grazing) or indirectly (concentrated livestock operations). Conversion of forests to cattle ranches is the biggest cause of deforestation in the Brazilian Amazon (Fearnside, 2008). Seventy percent of deforestation in the Brazilian Amazon is used for medium- to large-sized cattle ranches (Fearnside, 2005), and around 80% of the total deforested land is used for cattle grazing putting considerable stress on forest ecosystems (Greenpeace, 2009). Studies have shown that in countries such as the United States livestock production was estimated to account for 55% of soil and sediment erosion, and more than 30% of the total nitrogen (N) and phosphorus (P) loading to national drinking water resources (WRI, 2009). Livestock operation is considered as a primary accelerator of global nutrient cycling (Bouwman et al., 2009). International assessments showed that between 2000 and 2050, global livestock production will increase by 115% leading to 23% increase in global N and 54% increase in P surpluses (Bouwman et al., 2013). Most of the surplus N is then lost to the environment as volatilization, denitrification, leaching to groundwater, and runoff to surface waters, while the surplus P is lost by runoff to waterways and causes eutrophication leading to water quality issues. In addition to land and water quality degradation, livestock production emits greenhouse gases (GHGs) approximately 7.1 million tons of CO2 equivalent per annum (consisting of 44% methane (CH4), 29% nitrous dioxide (N2O), and 27% carbon dioxide (CO2); http://www.fao. org/news/story/en/item/197623/icode/), which represents 14.5% of all human-induced emission (Gerber et al., 2013). As resources required for sustaining the growth of livestock production are strained, future increase in livestock products must be accommodated within the existing resources including land, water, and nutrient (FAO, 2011). Improving resource use efficiency and reducing environmental foot prints (including impacts on climate) of livestock production are paramount for the sustainability of the sector. This chapter reviews the environmental impacts of livestock production, in particular the soil quality, GHG emission, and nutrient losses as influenced by grazing and manure management and opportunities to make livestock production sustainable for agricultural intensification, resource use efficiency, and environmental protection including climate change.

Livestock Production and Its Impact

151

2. LIVESTOCK FOR ECONOMIC DEVELOPMENT AND CONSUMER DEMAND Global livestock production is changing rapidly in response to: (1) population growth which is projected to exceed 9 billion by 2050, (2) rapid urbanization, and (3) growing incomes of people and their nutritional food requirement. It is expected that by 2030 about 5 billion people live in urban areas with unprecedented urban growth in Africa and Asia (UNFPA, 2008), leading to an increased demand for livestock products (Delgado, 2003). With significant contributions to global agricultural production, food supply, nutrition, rural employment, and soil fertility, livestock plays an important role providing income, poverty reduction, and livelihoods, among the rural population in developing countries (Moyo and Swanepoel, 2010; Perry and Sones, 2007; Randolph et al., 2007). Between 1950 and 2000 per capita income of rural communities grew annually at a rate of 2.1% globally. The FAO and World Bank reports showed that the expenditure on livestock products grows with income (Steinfeld et al., 2006). About 600 million poor people in Africa, Asia, and Latin America and Caribbean (LAC) depend on livestock for food and milk products, more than 1 billion people rely on livestock-based livelihoods, and more than 1.3 billion people are employed in livestock industry making it socially and politically significant in developing countries (Kristjanson et al., 2007). Between 1990 and 2002 global per capita meat and milk consumption increased by 55% and 20%, respectively, in developing countries and is projected to increase by 30% and 45%, respectively, by 2030 (FAO, 2006a,b, 2012). Rosegrant and Thornton (2008) reported that between 2000 and 2050 per capita consumption of meat is projected to increase in all regions of the world and by up to 100% in Sub-Saharan Africa making livestock industry a significant contributor to the global food and nutrition security. While the per capita meat and milk consumption in the developed countries is much higher than that in the developing countries (78 vs 28 kg/year and 202 vs 46 kg/year for meat and milk, respectively) during 1990 and 2002 (FAO, 2006a,b, 2012), the projected meat and milk consumption in developing countries will exceed (by 64% and 18% for meat and milk, respectively) the developed countries by 2015 (Fig. 1). Such an increased demand for livestock products comes with enormous challenges for the sustainability of the industry including the protection of land and water resources, managing the manure, and reducing GHG emissions from the

152

K. Sakadevan and M.-L. Nguyen

Total consumption (million tons)

350 300 250 200 Developing countries 150

Developed countries

100 50 0 1990

2002 Meat

2015

1990

2002 Milk

2015

Fig. 1 Change in livestock product consumption between 1990 and 2015 in developing and developed countries (Thornton and Herrero, 2010).

production system. With the existence of heterogeneity and complexities in the system, converting the extensive livestock system to intensive and sustainable production system is important to reduce negative impacts of livestock production on the environment (Havlı´k et al., 2014) including GHG emissions. In marginal semiarid and arid rangelands, the impacts of climate change (increased temperature and unpredicted rainfall) lead to frequent droughts and reduce the livestock productivity. This is notably true for southern Africa and Central Asia and causes soil water deficits, leading to overall productivity decline. In many other parts of semiarid region with no grazing (cut, carry, and feed systems), ground water is mainly extracted for fodder production and is driven by productivity gains and economic benefits (FAO, 2011). However, the sustainability of using such large volumes of groundwater for livestock production has been questioned.

3. LIVESTOCK PRODUCTION AND LAND USE CHANGE Livestock production is the largest land user on earth (directly or indirectly) and uses about 30% of the earth’s entire land surface, and subsistence farming is part of this land use in many developing countries across the globe, and in many part of the world, it is one of the main contributors to deforestation (Pan et al., 2007). Feed requirement links livestock production with land use which depends upon the type of feed used by livestock in a

Livestock Production and Its Impact

153

particular region (Herrero et al., 2013). In some countries, up to 85% of agricultural land is used for livestock production and contributes to a significant proportion of agricultural GDP (Table 1). In the last 200 years, grazing land expanded sixfold including areas in North America, South America, and Australia, where little or no livestock grazing occurred previously (Asner et al., 2004). Currently grazing land occupies about 26% of the global land area, and about 33% of all crop land is used for animal feed production (Steinfeld et al., 2006). Such a large allocation of land area for livestock production needs to be balanced with environmental services, biodiversity conservation, and socioeconomic developments. The poor feed quality in developing countries such as those in SubSaharan Africa means that livestock is mainly fed with nutrient deficient grasses and crop residues. However, in the developed countries (e.g., the United States and Europe), livestock production is intensive and nutrientrich feedstock is used. As a result the amount of feeds consumed by livestock in resource poor countries can be 10 times more than that consumed by livestock in developed countries to produce the same amount of protein. This means more land area is required for producing same amount of livestock in developing countries compared to developed countries. Because of this, more land needs to be cleared from forest contributing to deforestation. Additionally, more water resources are required to meet such a demand. Normally 1 ha of land can be used to grow crops (rice, potato, etc.) which can be used to feed up between 19 and 22 people annually. However, if the same area is used for meat production, only two people can be fed annually. Given that per capita land availability is below 0.30 ha globally, it is very difficult to sustain livestock production systems, particularly in the developing world where a majority of marginal farmers live. Tropical deforestation progresses at a high rate with serious consequences for the environment. Livestock’s role in deforestation is of particular importance in Latin America where the largest net losses of forests and carbon from landscape occurred (Barona et al., 2010; Fearnside, 2005, 2008). In tropical Latin America and sub-Saharan Africa, there is a rapid expansion of pastures for ranching, with 0.3–0.4% of forest lost to pasture annually (FAO, 2009), and such an expansion of pasture and arable land for feed production occurred largely at the expense of forest area (Table 2). Between 1961 and 2001, global arable and pasture lands increased (0.1–0.3% and 0.2–0.3% per annum for arable and pasture lands, respectively) at the expense of forest lands (0–0.1% per annum). In Central America, forest area has been reduced by almost 40% over the past four decades,

154

K. Sakadevan and M.-L. Nguyen

Table 2 Annual Land Use Change (%) in Latin America and the Sub-Saharan Africa From 1961 to 2001 (FAO, 2005, 2006a,b) Latin America Sub-Saharan Africa Year

Arable Land Pasture Forest Arable Land Pasture Forest

1961–1991

1.1

0.6

0.1

0.6

0.0

0.1

1991–2001

0.9

0.3

0.3

0.9

0.1

0.5

Share of total land (%) 7.4

30.5

47.0

6.7

34.7

27.0

( ) Sign indicates reduction in land use.

with pasture and cattle population increased rapidly over the same period. During the period between 2004 and 2005 an estimated 1.2 million ha of rainforest was cut down in Latin America for soybean expansion, a majority of which is used for animal feed production (Wassenaar et al., 2007). According to Brazilian National Institute of Space Science, about 18.9 million ha were deforested during 2000–2004 and up to 66% were for pasture (Barona et al., 2010). Over the period between 2000 and 2010 an average of 2.4 million ha of pasture land expanded on an annual basis at the expense of forest land in Latin America. The Intergovernmental Panel on Climate Change estimated that approximately 1.7 billion tons of CO2 per year is released to the atmosphere as a result of deforestation (IPCC, 2001), and more than 65% of this deforestation is used for animal production through either grazing or growing feed for animals. During 2010 and 2011, an estimated 6200 km2 of Amazonian forest has been cleared for agriculture, ranching, and soybean for livestock feed (INPE, 2010; Nepstad et al., 2006). The period 2002–2004 saw historically high rates of deforestation in Amazon primarily driven by beef and soybean production (Nepstad et al., 2006). Similarly, in Indonesia about 1 million ha of tropical forest has been removed through deforestation mainly for agriculture (Hansen et al., 2009). Throughout the tropical areas, about 10 million ha of forest has been cleared in 2010 (Houghton et al., 2012) for agriculture and grazing. The social, economic, and environmental costs of deforestation are enormous and are responsible for increased carbon dioxide emission to the atmosphere from land. In addition, the loss of biodiversity, soil erosion, and water quality degradation lead to less environmental well-being of the landscape and the population. It is clear that sustainable livestock production with reduced land clearance in tropical region is important for enhancing resource use efficiency, reducing land degradation, and improving sustainability of livestock production.

Livestock Production and Its Impact

155

4. ENVIRONMENTAL IMPACTS While providing significant social benefits in the form of improved nutrition and poverty alleviation, livestock production has often been subjected to substantial public scrutiny as a result of its impact on the environmental quality. In the process of providing social benefits, livestock production uses large quantities of water and fertilizer and also emits significant amounts of GHGs (Herrero et al., 2009). The negative impacts of livestock production increasingly become serious at local, regional, national, and global levels from land degradation and water pollution to the loss of biodiversity and climate change (Herrero and Thornton, 2013). The sector contributes approximately 14.5% (7.1 billion tons CO2 equivalent) of the global GHG emissions and accounts for 9% of anthropogenic CO2 emissions (1.92 billion tons CO2 equivalent), most of it is due to the decomposition and mineralization of soil organic matter (SOM) resulting from land clearance and the expansion of pastures and arable land for feed crops (Gerber et al., 2013). It generates even bigger shares of emissions of methane (CH4) and nitrous oxide (N2O) with the greater potential to warm the atmosphere. As much as 35% of anthropogenic CH4, mostly from enteric fermentation by ruminant, and 65% of N2O, mostly from manure and nitrogen fertilizer management, emitted to the atmosphere (http://www.fao. org/agriculture/lead/themes0/climate/en/). Major environmental impacts of livestock production arise from the following: (1) manure management, (2) deforestation, (3) unsustainable use of freshwater, (4) nutrient pollution, and (5) GHG emissions. These are briefly discussed in the subsequent sections.

4.1 Manure Management Livestock manure is a valuable source of nutrient for improving soil fertility and quality through enhancing SOM. The global manure production through the concentrated animal feeding operations has increased tremendously in recent years. Based upon animal density and international data, estimates showed that approximately 128 million tons of N and 24 million tons of P equivalent of manure produced annually (Potter et al., 2010). In the United States alone, approximately 24.4 million tons of manure per year came from beef cattle, 19 million tons of manure per year from dairy farming, 12.7 million tons per year of litter and manure from poultry, and 14.5 million tons per year from swine are produced. It has been estimated that

156

K. Sakadevan and M.-L. Nguyen

about 7.5 million tons of N and 2.3 million tons of P are generated in the United States annually by the livestock industry compared to 9 million tons N and 1.6 million tons P applied to agricultural land in the form of commercial fertilizers (http://rcrec-ona.ifas.ufl.edu/in-focus/IF7-21-06.shtml). In confined livestock production systems, the feed is almost entirely brought from the field (sometimes even transported from far). However, in the production process, animal products (for example, meat and milk) are removed, while the manure is left behind resulting in the disconnection between manure and the production area (the field). This leads to transportation costs and the associated GHG emissions if they are applied back to the field. In some situation, the manure is disposed without any environmental consideration to reduce costs. The enormous increase in manure production from livestock enterprises has generated environmental concerns due to limited land area for efficient manure application and spreading. While it is possible that the N and P in manure react slowly compared to mineral fertilizer N and P, they may be over applied to some areas leading to nutrient enrichment. This will increase nutrient losses and nitrous oxide (N2O) and methane (CH4) emission from agricultural lands. Manure management contributes to approximately 7–8% of agricultural GHG emission mainly as N2O and CH4 (IPCC, 2014). Water quality is increasingly become an important issue when manure application exceeds vegetation/crop requirements (Ribaudo et al., 2007). This mismanagement of manure often leads to direct discharge of liquid manure to surface waters through runoff and causes eutrophication which is characterized by high concentrations of N and P creating ecological imbalance in the water system. Such runoff could happen immediately after application depending on weather conditions (Smith et al., 2007a,b). Judicious and sustainable application of animal manure to land will contribute plant nutrients to crops and reduce the need for mineral fertilizers. However, in many countries, sustainable and environmentally sound manure management (production, storage, and application) practices have been very slow due to the fact that manure has been considered as a waste rather than a resource. There is every opportunity to reduce pollution risks (N and P input to surface and ground waters) and soil quality improvements through best practice livestock and manure management. Understanding the dynamics of nutrient applied through manure under a changing environmental conditions helps to develop management practices which will reduce environmental pollution risks of manure in livestock production systems.

157

Livestock Production and Its Impact

4.2 Water Use in Livestock Production Worldwide livestock production is a leading consumer of water and is divided into two categories of consumption, namely, (1) upstream that includes water used for forage and feed production and on-farm drinking water under grazing, and (2) the downstream includes water used for livestock processing such as making meat and milk products (Doreau et al., 2012; Ran, 2010). The sector accounts for approximately 10% of the global anthropogenic water use. This water demand for livestock production is influenced by several factors that include type of animal, its activity, the feed, and the quality of water available for the livestock (Lardy et al., 2008). Grain-fed beef production takes about 50 times the water required to produce the grain. Raising broiler chickens takes 3500 L of water to make a kilogram of meat. In comparison, soybean production uses 1500 L for kilogram of food produced and rice about 1700 L of water per kilogram of rice (http://www.news.cornell.edu/). Estimated daily water consumption for a range of livestock production is provided in Table 3. Water shortages already are severe in the arid and semiarid regions, including Western and Southern United States, and the situation is quickly becoming worse because of a rapidly growing population that requires more water for all of its needs, especially agriculture. Unsustainable use of freshwater for feed production, animal care, and slaughterhouses contributes to water scarcity and is depleting water resources in many agricultural landscapes (Burkholder et al., 2007; Walker et al., 2005). Table 3 Typical Daily Livestock Water Consumption (Brown, 2006; NSWDPI, 2007) Water Consumption (L/Day/Head) Type of Animal Sheep

Weaner

2–4

Ewes with lamb

4–10

Cattle

Lactating cow

40–100

Young stock

25–50

Swine

Weaner

7–23

Feeder

23–113

158

K. Sakadevan and M.-L. Nguyen

Most critical for livestock production in arid/semiarid areas is the availability of water. Livestock feed production accounts for about 45% of global agricultural water use (Zimmer and Renault, 2003). However, water use efficiency is low in grasslands and noncultivated fodder lands used for grazing. In a majority of livestock production systems in these areas, water management has been practiced without consideration to the interaction between livestock and water. While regional variation exists, the average water use efficiency in the production of barley, maize, wheat, and soybean for feed is only 10%, with Sub-Saharan Africa at 1% and Western Europe ranging from 25% to 29% (FAO, 2006a,b). Water used to produce fodder (indirect) is generally at least 50 times greater than water directly used by livestock. In general the water footprint of livestock products is larger than that of crop with equivalent nutritional value (Mekonnen and Hoekstra, 2012). For example, the average for beef is 20 times larger than for cereals and starchy roots. The sustainability of such practices is questionable as soon as groundwater is used to irrigate fodder crops (Steinfeld et al., 2006). In Australia, about 23% of dairy farms are irrigated and about 52% dairy farmers use supplemental irrigation with natural rainfall which will put enormous pressure on agricultural water in a country which has limited water availability (Dairy Australia, 2006; Nash and Barlow, 2009). Practices and technologies that improve the sustainability of water use in livestock production are important. These include (1) livestock feed sourcing, (2) grazing and watering strategies, and (3) integrating livestock with cropping systems that uses crop by-products (crop residues) by livestock as a major water saving practice. Reducing irrigation for feed production during certain period of the growing season also improves water sustainability and productivity in livestock production. With more than 40% contribution to gross agricultural productivity, any improvement in water use efficiency in livestock production will improve overall agricultural water productivity and environmental water footprints.

4.3 Livestock and Soil Physical and Chemical Characteristics The binding of soil particles with organic matter into aggregate is the major physical characteristic of soils that influence its function and suitability as a medium for plant growth and regulate the movement of air, water and nutrient in the soil, water retention, and physical environment for active microorganisms and plant roots (Cuttle, 2009). Global climate change alters rainfall regimes with the possibility of increased occurrence of droughts

Livestock Production and Its Impact

159

and higher frequencies of extreme rainfall events during the crop growing season. The spatial and temporal variability of rainfall increased the frequency of wetting and drying cycles which is likely to affect soil water content (Harper et al., 2005). The presence of grazing animal further accelerates the wetting and drying cycles (Cuttle, 2009). The resultant drying and wetting of soil is expected to modify soil structure through the physical processes of shrink–swell (Carter and Stewart, 1996) and affect water infiltration and GHG emissions under grazing systems. Soils with large clay contents (>60%) shrink as they dry and swell when they become wet again, forming large cracks and fissures. Crack formation results in rapid and direct movement of water and solutes (nutrients, metals, and dissolved organic matter) from surface soil to the unsaturated zone through bypass or preferential flow leading to possible losses of nutrients and water pollution from soil root zone which is generally available to plants (Nguyen et al., 1998; Rounsevell et al., 1999). Dry soil conditions for longer periods of the year would also result in intensification of wet upland grazing areas due to livestock concentration (Rounsevell et al., 1996). When the soil becomes wet, it is subjected to structural alteration under the influence of grazing animals, and this alteration increases with increasing soil water content (Mulholland and Fullen, 1991). This change in soil water content associated with soil wetting and drying cycles and livestock grazing affects a number of soil processes including hydrology and vegetation growth. Soil structural alterations associated with grazing animals including compaction, pugging, and poaching (Bilotta et al., 2007). Compaction reduces soil pore space and permanently removes air and water from the soil leading to mechanical disruption of soil aggregate, reducing aggregate stability, increasing the bulk density and penetration resistance of the soil, and creating anaerobic conditions in the soil (Abdalla et al., 2009; Donkor et al., 2002; Mwendera and Mohamed Saleem, 1997). As the drainage is impeded due to poaching, the soil becomes prone to surface runoff and erosion leading to sedimentation and water quality problems downstream (Mulholland and Fullen, 1991). Soil infiltration can be reduced by up to 80% under the influence of grazing. For example, Trimble and Mendel (1995) reviewed the impact of livestock on soil infiltration and showed that it can be decreased from approximately 50 mm/h on lightly grazed to 25 mm/h on heavily grazed lands. Similarly, Heathwaite et al. (1990) showed that infiltration capacity was reduced by 80% and surface runoff increased by 12 times on heavily grazed compared to ungrazed pastures. In Alberta, Canada, the bulk

160

K. Sakadevan and M.-L. Nguyen

density and penetration power of soil were significantly greater by 15% and 17% in short duration grazing with 4.16 animal unit months per hectare compared to continuous grazing with 2.08 animal unit months per hectare, suggesting that the duration of grazing influences the characteristics of the soil (Donkor et al., 2002). Studies carried out in tallgrass prairie pastures showed that for ungrazed pasture the largest infiltration was 29.5 cm/day for a clay loam soil and 27.5 for a silt loam soil, while the grazing treatments had lower infiltration irrespective of soil types (Daniel et al., 2002). In northern China, soil characterization under grazed and ungrazed systems has shown that the bulk density significantly increased under grazing (Zhou et al., 2010). Changes in soil physical characteristics can influence the processes affecting soil processes and nutrient transformations by altering soil moisture, soil redox potential, and plant uptake processes (Bilotta et al., 2007; Di et al., 2001). For example, in both temperate and tropical regions the presence of grazing animals significantly increased soil erosion under pastures (Hamza and Anderson, 2005). The National Land and Water Resources Audit in Australia has found that soil erosion from native pastures (with grazing) in the northern region of Australia accounts for 76% of continent’s total soil erosion, and across these grazing lands the rate of soil loss is several times greater than the soil formation (NLWRA, 2001). As many as 100 million ha of rangeland is considered highly erodible in the United States (USDANRCS, 1992). Improved technologies and grazing management practices can help reduce impacts of soil physical and chemical characteristics on soil erosion. For example, in the United States, soil erosion losses from crop lands have been reduced from 1.2 million tons per year in 1992 to 960 million tons per year in 2007 (NRCS, 2010). Within the context of agricultural productivity the most obvious chemical characteristics influenced by grazing are nutrients (nitrogen and phosphorus) that have a direct and positive effect on plant growth and SOM, a determinant for soil quality. SOM, the precursor to soil sustainability, is an important part of the labile (reactive) pool which also determines the ability of soil to retain water and nutrients. Studies have shown that soil organic C and N, and microbial biomass C and N increased or at least remain stable under grazed pastures compared to soils in croplands (Grace et al., 1998). Grazed pastures provide a quick way to build carbon by growing perennial plants continuously throughout the year and minimize disturbances to soil compared to cropping (Kirkegaard et al., 2007). Land management practices such as conservation agriculture (minimum or no tillage, crop rotation,

Livestock Production and Its Impact

161

cover crops, mulching, integration of livestock with cropping, and the introduction of legumes) that influence SOM are important for enhancing soil physical and chemical characteristics and minimizing livestock impacts on land degradation.

4.4 Grazing and Soil Quality Soil physical, chemical, and biological properties collectively determine the quality of the soil and are affected by grazing. In New Zealand, after an extensive soil quality measurement program, the total C, total N, mineralizable N, pH, Olsen P, bulk density, and macroporosity were considered for regional soil quality assessment (Sparling et al., 2004). The assessment showed that while pasture soils are less vulnerable to adverse impacts on soil quality than crop lands, they are not completely resilient to withstand the negative impacts of the feed and grazing pressure (Cuttle, 2009; Sparling et al., 2004). Poor and uncontrolled grazing increases the loss of vegetative cover due to trampling and grazing plants too close to the soil (Nguyen et al., 1998). This weakens the root systems and compacts the soil leading to reduced soil quality. The degradations to soil quality can increase the soil erosion and nutrient losses from pastures and can, in turn, pollute surface waters. For example, in Africa overgrazing of marginal lands resulted in soil erosion and degradation (Lal, 1990). Overgrazing in livestock management is the main cause of soil degradation in Africa (50%), in the South Pacific, and in Australia (80%) (http://www.goodplanet.info/eng/Pollution/Soils/Soildegradation/(theme)/1662). In temperate regions, intensively managed grazing systems can result in decreased pasture yield, biodiversity losses, reduced soil weight-bearing capacity, soil quality, soil erosion, and overland flow (CAST, 2002). Improving grazing management (reducing stock numbers or changing grazing period from long to short duration) retains complete vegetative cover, increased organic matter of the soil leading to improved soil structure that will allow greater water infiltration. This will allow more water used for plant growth rather than running off the land (Bilotta et al., 2007; Kemp and Michalk, 2005).

4.5 Carbon and Nutrient Cycling Large areas occupied by grazing lands, their climate, and soil diversity, and the potential to improve their use and productivity make grazing lands important for sequestering C, mitigating emissions, and other aspects of global climate change (Lal and Follett, 2009). However, soil C stocks have

162

K. Sakadevan and M.-L. Nguyen

shown both increases and decreases in response to different levels of grazing and are complex and depend upon various factors including pasture growth, pasture utilization by grazing animals, environmental factors, and the inherent soil properties (Schuman et al., 2002; Zhou et al., 2010). Grazing can increase the net primary productivity and dung and urine deposition on pasture lands. As a small proportion (15–25%) of the ingested nutrients are essentially retained in animal products and the remaining excreted to soil as dung and urine, animal wastes are an important soil fertility pathway in grazed pastures (West and Mallarino, 1996). Grazing enhances nutrient cycling; stimulates root respiration, root exudates, and carbon allocation below ground (Wardle and Bardgett, 2004); and increased soil C stock (Schuman et al., 2002). Productive and sustainable grazing lands with highquality vegetation and soils provide high rates of C sequestration and low levels of carbon dioxide (CO2) emissions. The total soil C sequestration potential for US grazing lands is approximately 70 million tons of C/year. This figure represents a C store of about 1.6 times the size of the CO2–C emission from all other US agriculture and about 4.4 times the CO2–C emission for all grazing lands (Lal and Follett, 2009). Similarly a review of 115 studies in 17 countries mainly with nontropical grasslands showed that a general improvement in soil carbon content (more than 70% of studies) and the improvement are influenced by management practices that include fertilizer application, grazing management, irrigation, and other conservation practices (Conant et al., 2001). Grazing animal behavior directly influences the distribution of nutrients to various landscape positions. Animals may graze in one area but move to another area to rest or to drink water. Animal excreta (dung and urine) may thus be plentiful in the resting area and around a watering place than in the grazing area, resulting in a net transfer of nutrients and thus improving the fertility of soil in the resting area (Saggar et al., 1990). Grazing promotes nutrient cycling through rapid breakdown of organic matter into smaller particles in the system, so organic matter is available more readily for bacteria and fungi. Microorganisms use the organic matter as an energy source and can release nutrients back into the soil for plant uptake (Bloem et al., 2006). Thus nutrient management under grazing is highly complex, as a result of the uneven distributions of nutrients in pastures (Nguyen et al., 1989), the difference in nutrient element requirements for pasture growth, and the difference in mobility between nutrients and the tendency of nutrient (especially N) to escape from the system (Fig. 2).

163

Livestock Production and Its Impact

Product

Milk, wool, meat

Outputs Fertilizer Legume N Rainfall

Inputs

Animal uptake

Farm

Feed

Animal return

Losses Leaching, runoff and erosion, ammonia volatilization, and denitrification

Fig. 2 Nutrient cycling in a grazed pasture system.

In the absence of fertilizer or outside manure inputs, continuous grazing will cause a gradual decrease of plant nutrients in the soil (Lory and Roberts, 2000). In concentrated dairy and other livestock operating systems, nutrient return from animals fed with high concentration of grain and protein supplements can be substantial. Winter feeds also form a substantial input into the pasture nutrient budget when animals are fed with hay while being kept on pasture. A dairy cow, for example, can return approximately 67 kg N, 14 kg P, and 10 kg K/year through dung and urine (Lory and Roberts, 2000). A uniform distribution of nutrients throughout a paddock is required for the productive use of nutrients for plant and animal growth. However, studies have shown that urine spots occupied 16.7% of the pasture, while manure spots occupied 18.8%, following 1108 grazing days per hectare (Dalrymple, 1994). Such an uneven distribution of dung and urine creates a large spatial variation in soil nutrients leading to large losses of nutrient through leaching, surface runoff, and in the case of N with volatilization and denitrification. Short period rotation of animals may help to reduce the spatial variability in the distribution of urine and dung and may reduce losses of nutrients from the production system. Grazing management practices which ensure uniform distribution of excreta can help improve both soil quality and fertility and reduce losses from the system.

164

K. Sakadevan and M.-L. Nguyen

5. NITROGEN AND PHOSPHORUS LOSSES UNDER LIVESTOCK PRODUCTION Livestock production systems are one of the major causes of humaninduced global N and P cycles (Bouwman et al., 2013). At the beginning of 1900, N and P input and output in livestock production were generally balanced and ever since the inputs were increasing compared to outputs (Bouwman et al., 2009).

5.1 Nitrogen In livestock production system, about 55–95% of N intake is normally returned to the land as dung and urine. Generally at a global scale about 40–50% of the amount of N voided through dung and urine is collected from production areas such as paddocks, barns, and stables, and only 50% of this amount is recycled to crop land (Oenema and Tamminga, 2005). This translates to between 80 and 130 million tons of N annually which is either as large as or larger than the amount of fertilizer N used. Under intensive grazing management systems in which animals at a high stocking density are rotated through several paddocks at short time intervals (12–24 h), about 2% of the fecal N and 25% urinary N leached beneath the root zone (Stout et al., 2000a,b). The high rates of N fertilizer application and/or biological N fixation in these grazing systems and the uneven recycling of N through urine and dung in pastures could increase N leaching and contributing to increased groundwater nitrate levels. High nitrate leaching was observed when a severe drought followed good growing conditions, causing legume nodules to die and release nitrogen into the soil (Stout et al., 2000a). Nitrogen losses from sheep-grazed pastures in New Zealand showed that overland flow and interflow losses ranged from