Response to land degradation 9781578081523, 1578081521, 9781578081530, 157808153X, 9781138468658

Table of contents :
Content: Foreword, Preface and Acknowledgments, Contributors, Chapter 1 Introduction, Chapter 2 Setting the scene, Chapter 3 Driving forces and pressures, Chapter 4 State of the world's land resources, Chapter 5 Impacts on society and the environment, Chapter 6 Tools for monitoring and assessment, Chapter 7 Conservation and rehabilitation, Chapter 8 Institutional innovations, Chapter 9 Law and policy, Chapter 10 International initiatives, Chapter 11 Future responses, Index, The Editors

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RESPONSE TO LAND DEGRADATION

A joint publication of

The Soil and Water Conservation Society of Thailand (SWCST), Bangkok The Land Development Department (LDD), Bangkok The World Association of Soil and Water Conservation (WASWC), Ankeny, Iowa The International Board for Soil Research and Management (IBSRAM), Bangkok The International Soil Reference and Information Centre (ISRIC), Wageningen The Department of Land and Water Conservation (DLWC), Sydney The University of Maryland at College Park (UMCP), Maryland Cover design: Pankaj Gairola, New Delhi, India Picture credits: p. 40, H. Tumawis; p. 74, Rungsun Im-Erb; p. 76, S.A. Shahid;

p. 221, L.-O. Westerberg; p. 296, P.C. Huszar; p. 306, B. Shrestha; p. 307, R. Allen; p. 318, Samran Sombatpanit; p. 321, Ruam Duey Chuey Kan Publisher, Bangkok; p. 326, Webshots.com; p. 332, W. Critchley; p. 334, Webshots.com Final editing: IBSRAM, Bangkok, Thailand (IBSRAM's programmes merged with those of the

International Water Management Institute after March 31, 200 I).

This publication is being issued also as: IBSRAM Proceedings No. 20 SWCST Special Publication LDD Technical Publication WASWC Official Publication

RESPONSE TO LAND DEGRADATION

Editors E. Michael Bridges Ian D. Hannam L. Roel Oldeman Frits W.T. Penning de Vries Sara J. Scherr Samran Sombatpanit

with assistance from Robin N. Leslie Tanadol Compo Apuntree Prueksapong

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

A SCIENCE PUBLISHERS BOOK

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 First issued in hardback 2019 © 2001 by Soil and Water Conservation Society of Thailand CRC Press is an imprint of Taylor & Francis Group, an Informa business

No claim to original U.S. Government works ISBN-13: 978-1-57808-152-3 (pbk) ISBN -13: 978-1-138-46865-8 (hbk) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.coml) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923,978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Response to Land degradation / editors E. Michael Bridges ._ [et al.] with assistance From Robin N. Leslie, Tanadol Compo, Apuntree Pruekspong. p.cm. Includes bibliographical references (p.). ISBN 1-57808-153-X - ISBN 1-57808-152-1 (pbk. : alk. Paper) 1. Soil degradation. 2. Soil conservation. 3. Land degradation. 4. Land use. I.Bridges, E. M. (Edwin Michael) S623 .R43 2001 333.76'153--dc21 2001049005

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Foreword T h e hum an record o f caring for th e environm ent, particularly land, has been poor. U se o r m isuse o f the land by hum ans is at the centre o f a co m p lex w eb o f env iro n m en tal, social and econom ic pressures. D ecisions about use o f land are driven by p o w erful com peting econom ic and social forces th at frequently have little regard fo r th e long-term care o f th e environm ent, or land in particular. C onsequently, th ro u g h o u t history, land degradation has been a feature accom panying hum an society everyw here. Seen purely in financial term s by m ost m odern societies, land is a part o f the hum an en v iro n m ent that legitim ately can be exploited, and the soil upon it form s only a sm all item upon a financial balance sheet. In m any societies, land is ow ned by p ersons o r co m panies and represents w ealth, w hereas the soil on th e land surface is regarded o n ly as th e ecological basis for vegetation and/or the production o f crops. In v irtu ally all situations, land and soil m ay be exploited; they m ay be abused by ag ri-b u sin ess to obtain increased profits, or by im poverished, hungry, subsistence farm ers struggling to feed th eir fam ilies. A t both these extrem es, th e pressures o f tod ay o u tw eig h any concern th at the natural resources o f the land m ay be required to su stain future generations. It tends to be left to soil scientists, environm entalists, ag ricultural extension w orkers, social scien tists and enlightened idealists to draw atten tio n to the w orldw ide problem s o f land degradation. It has becom e apparent th at th ere is a need to adopt a new philosophy con cern in g soil, one that regards soil in an ecological sense, and that considers both hum ans and th e natural w orld as parts o f th e sam e ecosystem .

Dr. K la u s T ö p fe r E xecutive D irector U nited N atio n s E nvironm ent Program m e

Preface and Acknowledgments

In his rem arks concluding the 16th W orld Soil C ongress o f the International Union o f Soil Sciences held in M ontpellier, France, in A ugust 1998 the incom ing president, M r Som pong T heeraw ong, stated that: Scientists have contributed to fe e d in g a n d clothing 5.6 billion p e o p le today; our challenge is to b u ild on this so that we can do the sam e f o r 8 billion p eo p le in the y e a r 2020. The reality is that w e have to do this not only w ith alm ost the sam e am ount o f land, b ut also w ith land, w hich in m any p a rts o f the w o rld is being deg ra d ed a n d is rapidly losing its productivity. Loss o f productivity is one o f the m ajor problem s affecting food production and security w orldw ide. T he challenge w as therefore taken up by the O rganizing C om m ittee o f the 2nd International C onference on Land D egradation (IC LD ) in the structure o f the conference and the proposal for this book. T he ICLD2 w as organized by the Soil and W ater C onservation Society o f T hailand (SW C ST ), the Land D evelopm ent D epartm ent (L D D ) and the International W orking G roup on Land D egradation and D esertification (IW G L D D ) o f the International U nion o f Soil Sciences held in January 1999 in Khon K aen, Thailand. This m eeting, attended by 260 scientists, w as preceded by the 1st ICLD C onference held at A dana, T urkey in June 1996, and will itself be follow ed by the 3rd ICLD C onference to be held in Rio de Janeiro, B razil in Septem ber 2001. The 1999 ICLD C onference concluded that: The g rea test pro b lem s o f so il degradation f o r fo o d secu rity in developing countries in 2020 w ill be fo u n d in the d en sely p o p u la te d m arginal lands w hich require m obilization o f long-term investm ent a n d appropriate technology developm ent. P rior to the K hon K aen conference, an international scientific editorial panel w as set up to take a selection o f the papers from the conference and com bine them , w ith additional invited papers and exam ples, to produce a state-of-the-art publication at the beginning o f the new m illennium , covering all aspects o f land degradation, and how people w ere attem pting to counter it. T his panel began w ork im m ediately after conclusion o f the K hon K aen conference and adopted the D PSIR fram ew ork (driving forces, pressures, state, im pacts, and responses) developed by the European Environm ent A gency for the structure o f this volum e. This approach also led naturally to the title Response to L a n d Degradation. D uring the tw o years since the Khon Kaen conference, the scientific editors have gathered to g eth er and edited all the papers and shorter contributions appropriate for the book. T hirty-nine original papers with SO boxes containing additional illustrative m aterial fall into 11 chapters th at describe land degradation and the hum an response at all scales from local practical initiatives to w orld-scale studies o f the problem . It is hoped that this collection o f papers will provide useful m aterial for researchers, students, national and regional planners, national and international policy-m akers and the decision-m akers w ho im plem ent land m anagem ent policies. A special attem pt has been m ade to present the hum an and social aspects o f land degradation as w ell as the physical and purely agricultural aspects, for w ithout the full cooperation o f local people, new technologies and rem edies for land degradation are rarely successful.

V III

M any individuals and organizations have been involved in the production o f this book, from organizing the initial conference at w hich m any o f the papers w ere first presented, to its eventual publication. The initiative o f SW CST, LDD and IW GLDD in organizing the 2nd ICLD was tim ely and com m endable; the papers presented w ere all o f a high standard and this is reflected in the contributions o f individual scientists chosen to appear in this volum e. Financial support for the conference w as received from the Asian D evelopm ent Bank, the Canadian International D evelopm ent Agency, the Food and A griculture O rganization o f the United N ations, the Japan International C ooperation Agency, the International Board for Soil R esearch and M anagem ent, the International Union o f Soil Sciences, the N atural R esources C onservation Service o f the USDA, the Soil and Fertilizer Society o f Thailand and the W orld Association o f Soil and W ater C onservation. T heir generous support is greatly appreciated. Individuals w ho have been supportive throughout this project include M r Som pong Theeraw ong, President o f the SW CST and the IUSS, Charoen C haroencham ratcheep the Secretary-G eneral and Pojanee M oncharoen the treasurer o f SW C ST respectively. LDD Director-G eneral Sim a M orakul and LDD Technical D eputy D irector-G eneral C haiyasit A necksam phant gave full institutional support. Hari Eswaran, IW GLDD C hief, coordinated all the technical program m es, David Sanders, W A SW C President, helped to identify funding sources and IBSRAM D irector-G eneral, Eric C rasw ell, provided personnel and editing facilities that enabled a polished presentation o f the m aterial in this book. W infried E.H. Blum, IUSS Secretary-G eneral, constantly gave sound advice on the topics discussed. T he N SW M inister and the D irector-G eneral o f the D epartm ent o f Land and W ater C onservation N SW are thanked for providing the expertise o f a senior staff m em ber throughout the editorial process. The editorial panel also would like to record their appreciation o f organizations and their personnel w ho have provided invaluable assistance throughout: G odert van Lynden and Alfred H artem ink from the staff o f the International Soil Reference and Inform ation C entre (ISRIC) at W ageningen in The N etherlands undertook editorial work, and Jacqueline Resink provided the ASSOD map; A puntree Prueksapong, B unjirtluk Jintaridth, N ongkran M aneew an, Chaiyanam D issataporn, Pratum porn Funnpheng, M arasri H untprasert, B enjarat A nanpongsuk and C hulalak Suttirord o f the LDD S taff in Bangkok assisted with the editorial process; the Ruam Duey C huey Kan Publisher, Bangkok, provided an illustration; staff o f the IBSRAM office in Bangkok Robin Leslie assisted by Tanadol Com po, carried out much o f the final stages o f editing and contributed to m aking cam era-ready pages. The help and active cooperation o f all these people is much appreciated. Special thanks are due to all authors o f papers and boxes, both original material from the conference and the additional invited contributions, w ithout which this com prehensive state-of-the-art book would not have been produced. Lastly, the editors wish to thank their organizations for allow ing them use o f facilities and the w orking tim e spent during the editing o f this book.

The Editors

Contents Foreword Preface and Acknowledgments Contributors

v vii XV

Chapter 1 Introduction Box 1.1 Using the soil DPSIR framework—driving forces, pressures, state, impacts, and responses— for evaluating land degradation W.E.H. Blum Box 1.2 Ecological soil standards I D. Hannam

Chapter 2 Setting the scene Land and civilization: An historical perspective A.S.R. Juo andL.R Wilding Land degradation: An overview H. Eswaran, R. Lai and R E Reich Food production and environmental degradation EM . Bridges and L.R. Oldeman Box 2.1 What happens on earth in one minute? M. Movillon, B. Richards and H. Tumawis

Chapter 3 Driving forces and pressures

l

4 8

11 13 20 36 40

45 Demographic transition, resource management, and institutional change D. Southgate 47 Land pressure and soil nutrient depletion in sub-Saharan Africa P. Drechsel and F.W.T. Penning De Vries 55 Box 3.1 Population and land quality on tropical hillsides S.R. Templeton and S.J. Scherr 65 Adoption o f soil conservation practices in developing countries: Policy and institutional factors S. Pandey 66 Box 3.2 Giant tiger shrimp cultivation and the salinization of arable land in Thailand Rungsun Im-Erb, Promote Yamclee, Suthat Prosayakul, Prosit Tanprapas and Pirach Pongwichian 74 Box 3.3 Causes and impacts of land degradation in the arid environment o f Kuwait S.A. Shahid and S. A S. Omar 76 Box 3.4 Climate change and land degradation in Iceland U. Helldén and R. Ólafsdóttir 78

X

Chapter 4 State of the world’s land resources Land quality and food security in Asia F. H. Beinroth, H. Eswaran andP.E Reich Box 4.1 Land degradation in Malaysia J. Shamshuddin Box 4.2 Soil degradation and land use: A case study from India G. Byju and T Varghese Box 4.3 Land degradation and land use policy in Vietnam N. Van Bo, T Phien and N. Tu Šiem Land resource stresses and desertification in Africa P.F. Reich, S. T. Numbern, R.A. Almaraz andH. Eswaran Box 4.4 An assessment of land degradation in Thailand Sunan Kunaporn, Pichai Wichaidit, Taweesak Vearasilp, Kanitasri Hoontrakul and H. Eswaran Box 4.5 Land resource stress and desertification vulnerability in Thailand Pojanee Moncharoen, Taweesak Vearasilp, Kanitasri Hoontrakul and H. Eswaran Land degradation in Bangladesh MdM. Rahman, G. Mostafa, S.Razia andJ. U. Shoaib Box 4.6 Landscape-scale changes in soil properties between 1967 and 1995 in Bangladesh MdM. Ali and T Wakatsuki Soil degradation in Sri Lanka A.N. Jayakody Land degradation in Hungary Á. Kertész Box 4.7 Soil acidification under Stylosanthes seed production systems in Thailand and Australia A. Noble, Sawaeng Ruaysoongnern, I. Willett and B. Palmer Box 4.8 Soil degradation through deforestation in Petchabun, Thailand Boonma Deesaeng, Cholada Temkunatham, Somchai Onasa and Sangchan Srisaichua Box 4.9 Rehabilitation of the organic carbon pool in red soils of China Li Zhongpei and Zhang Taolin

Chapter 5 Impacts on society and the environment The future food security and economic consequences of soil degradation in the developing world S.J. Scherr Land degradation, food security, and agro-biodiversity—examining an old problem in a new way A. Tengberg and M. Stocking Productivity growth and resource degradation in Pakistan’s Punjab M. Ali and D. Byerlee

81 83 98 99 100 101

115

116 117 124 130 140

149

150 151 153

155

171 186

XI Box 5.1 Economic implications of land degradation in a large irrigation project in India B.V.C. REDDY, HONNAIAH and L.ACHOTH Valuing the off-site effects o f land degradation T. ENTERS Box 5.2 Impacts o f land clearing on biodiversity and environmental quality in the Western Australian Wheatbelt A. GLANZNIG and M. KENNEDY The global environmental impacts o f agricultural land degradation in developing countries S. PAGIOLA Box 5.3 A critical approach to indications of degradation: A case study from northeastern Botswana A.C. DAHLBERG Box 5.4 Mass movements in East Africa: Transient or long-term land degradation? L.O. WESTERBERG and C. CHRISTIANSSON

Chapter 6 Tools for monitoring and assessment Linking methodologies for assessing land resources, their problems and possible solutions at small scales L.R. OLDEMAN and G. WJ. VAN LYNDEN Spatial natural resource monitoring in Mpumalanga Province of South Africa K J. WESSELS, H.M. VAN DEN BERG and D.J. PRETORIUS Tools for identification, assessment, and monitoring of land degradation APISIT EIUMNOH Box 6.1 Remote sensing and GIS-aided land degradation monitoring: The case of Chi sub-watershed, Thailand APISIT EIUMNOH and R.P. SHRESTHA Application o f remote sensing techniques for the study o f soil salinity in semi-arid Uzbekistan E.I. KARAVANOVA, D.P. SHRESTHA and D.S. ORLOV The economic appraisal o f soil and water conservation measures J.DEGRAAFF Box 6.2 Assessing soil erosion and water pollution hazards associated with logging in New South Wales, Australia N. A. ABRAHAM, P.J. FOGARTY and S.J. BEAMAN Box 6.3 Soil loss map o f Thailand LANDDEVELOPMENTDEPARTMENTSTAFF Box 6.4 Soil productivity rating for soil degradation assessment in the Philippines: A case study in Isabela Province P.P. EVANGELISTA, C.M. NICOLAS, R.B. CARATING, T. OHKURA and Y. KATO Box 6.5 Soil microbial community structure as an indicator o f soil pollution caused by gasoline spills I.S. KIM, V.N. IVANOV and E.V. STABNOKOVA Box 6.6 Participatory GIS as a tool for land use planning in northern Thailand O. PUGIN1ER

200 201

206 207

219 220 223

225 237 249

260

261 274

284 285

286

287 288

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Chapter 7 Conservation and rehabilitation Land degradation and renewal in the Gran Chaco of South America PC. Huszar andE.H. Bucher Strategies to address land degradation issues in the Hindu Kush-Himalayas R. Allen Thailand’s response to land degradation: The need to control soil erosion Samran Sompatpanit Uncertain steps? Terraces in the tropics W. Critchley, Samran Sombatpanit and S.M. Medina Box 7.1 Land degradation and soil conservation in China Li Rui, Yang Qinke, Zhang Xiaoping and Li Zhiguang Box 7.2 Occurrence, prevention, and amelioration of soil salinity PA. Mendoza, Yang Jingsong and Terdsak Subhasaram Box 7.3 Using Sloping Agricultural Land Technology (SALT) for soil management on Sri Lanka tea lands PB. Ekanayake Box 7.4 Sludge utilization in degraded and agricultural land Orathai Sukreeyapongse and Supamard Panichsakpatana Box 7.5 Sylvipasture system to rehabilitate degraded grassland D. Santoso, Sukristiyonubowo, I.G.P. Wigena and E. Santos a Box 7.6 No-tillage system in Paraná State, south Brazil A. Calegari Box 7.7 A participatory approach towards integrated soil management S. Kauffman Box 7.8 Sustainable rehabilitation of degraded volcanic ash soils in Mexico U. Fechter-Escamilla and G. Werner

291 293 304 314 325 339 340

341 342 343 344 345 347

Chapter 8 Institutional innovations Incentives for soil conservation T Enters Box 8.1 Land tenure and soil conservation—new evidence from Southeast Asia A. N eef and Chapika Sangkapitux Application of a land management model to address land degradation in New South Wales, Australia I. J. Packer Box 8.2 The catchment approach to soil and water conservation in Kenya J. K. Kiara Box 8.3 Conservation of biodiversity through Landcare M. Sutherland and B. Scars brick Box 8.4 Farmer-led community institutions to reverse land degradation in the 21st century D.P Garrity Box 8.5 Environmental regeneration for poverty eradication in India A. Agarwal

349 351 361

362 370 372 373 374

xiii Participatory technology development for sustainable land management Я.-Ζλ Bechstedt

Chapter 9 Law and policy A global view o f the law and policy to manage land degradation ID. Hannam Land degradation and native vegetation clearance in the 1990s: Addressing biodiversity loss in Australia A. Glanznig and M. Kennedy Law and policy to manage land degradation in the Philippines R.N. Concepcion and G.P. Nilo Conservation policy and socioeconomic development in Russia during the 20th century A.Gennadiyev Box 9.1 Strategies for rehabilitation of degraded land in Vietnam N. Van Bo, T Phien and N. Tu Šiem Box 9.2 ASIALAND: A policy for sloping land management Adisak Sajjapongse and Ту Phommasack Box 9.3 Laws and policy to manage land degradation in Malaysia J. Shamshuddin Box 9.4 Laws and policy for managing land degradation in Thailand Sopon Chomchan Box 9.5 Waste minimization strategies in the USA Liu-Hsiung Chuang

Chapter 10 International initiatives

375 383 385

395 404 414 422 423 424 425 426

427 Land degradation and international environmental law I. D. Hannam andB. W Boer 429 Box 10.1 The World Soil Charter D. Sanders 439 Box 10.2 Land degradation and biodiversity conservation: International challenges A.J. Rupp 440 Land degradation: Information needs and challenges to research F.W.T. Penning de Vries 441 Investments in land improvement by the Asian Development Bank D. Nangju 449 Rangeland development for the rural poor in developing countries: The experience of IFAD A.E. Sidahmed 455 Lessons from World Bank natural resource management projects M. Mani and A. Liebenthal 466 Box 10.3 The Soil Fertility Initiative for Sub-Saharan Africa J. Farah and M. Toure 475 Box 10.4 WOC AT: World Overview of Conservation Approaches and Technologies H Hurni 476

x iv

Box 10.5 The Asia Soil Conservation Network for the Humid Tropics (ASOCON) F.J. Dent

477

Chapter 11 Future responses

479

Index The Editors

488 509

Contributors Abraham , N.A. New South Wales Department of Land and Water Conservation, P.O. Box 3720, Parramatta, NSW 2124, Australia. E-mail: [email protected] Achoth, L. Department of Agricultural Economics, GKVK, University of Agricultural Sciences, Bangalore560065, India. Agarwal, A. Centre for Science and Environment, 41 Tughlakabad Institutional Area, New Delhi-110 062, India. E-mail: [email protected] AH, M. Socioeconomic Unit, Asian Vegetable Research and Development Center (AVRDC), P.O. Box 42, Tainan, Taiwan. Phone: +886-6-583-7801 ext. 460 (office), 808 (res.), Fax: +886-6-583-0009, E-mail: [email protected]!.org.tw Ali, Md. M. Bangladesh Institute ofNuclear Agriculture, Mymensingh, Bangladesh. E-mail: [email protected] Allen, R. People and Resource Dynamics Project, International Centre for Integrated Mountain Development (ICIMOD), P.O. Box 3226, Kathmandu, Nepal. Phone: +977-1-525313, Fax: +977-1 -524529, Email: [email protected]

Beaman, S.J. New South Wales Department o f Land and Water Conservation, P.O. Box 3720, Parramatta, NSW 2124, Australia. Bechstedt, H.-D. Moo BaanCasalena 1,41/14Nimitai Road, Minburi, Bangkok 10510, Thailand. Phone: 662-914-5853, E-mail: [email protected] Beinroth, F.H. Department o f Agronomy and Soils, University of Puerto Rico, Mayaguez, Puerto Rico 00681 -5000,USA. Phone: +1-787-833-2865, Fax:+1 -787-265-0220, E-mail: f [email protected] Blum, W.E.H. International Union of Soil Sciences, c/o Institute of Soil Research, University of Agricultural Sciences, Gregor Mendel-Str. 33,1180 Vienna, Austria. iuss@edv 1.boku.ac.at Boer, B.W. Faculty o f Law, University of Sydney, 117 Phillip Street, Sydney 2000, Australia. Phone: +61 2-9351 -0317, Fax: +61 -2-9351 -0264, E-mail: [email protected] Bridges, E.M. 3 The Green, Hampton, Fakenham, Norfolk NRZ17LG, United Kingdom. E-Mail: [email protected] Bucher, E.H. Director, Centro de Zoologia Aplicada, Universidad Nacionai de Cordoba, Cordoba, Argentina. Byerlee, D. Rural Development Department, The World Bank, 1818 H St. NW, Washington, D.C. 20433, USA. Phone: +1-202-458-7287, Fax: +1-202-614-0065, E-mail: [email protected] Byju, G. Department of Soil Science, Kerala Agricultural University, Vellayani-695522, Kerala, India. Email: [email protected] C aleg a ri, A. Agronomic Institute (IAPAR), P.O. Box 481, Londrina-Paraná, Brazil. E-mail: [email protected] C arating, R.B. Bureau o f Soils and Water Management, Department of Agriculture, Quezon City 1100, The Philippines. Chomchan, S. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand.

XVI C hristiansson, C. Environment and Development Studies Unit (EDSU), Department of Physical Geography, Stockholm University, S-10691, Stockholm, Sweden. C huang, Liu-H siung Resources Economics and Social Sciences Division, Natural Resources Conservation Service, USDA, P.O. Box 2890, W ashington, D.C., 20013 USA. E-mail: [email protected] Concepcion, R.N. Bureau of Soils and Water Management, Diliman, Quezon City, The Philippines. Phone: +63-2-923-0454/920-4382, Fax: +63-2-920-4318, E-mail: [email protected] Critchley, W. Centre for Development Cooperation Services, Vrije Universiteit Amsterdam, De Boelelaan 1115, 1081 HV Amsterdam, The Netherlands. Phone: +31-20-444-9078, Fax: +31-20-4449095, E-mail: [email protected] D ahlberg, A.C. Environment and Development Studies Unit (EDSU), Department o f Physical Geography, Stockholm University, S-10691 Stockholm, Sweden. E-mail: [email protected] Deesaeng, B. Forest Environment Research and Development Division, Forest Research Office, Royal Forest Department, Bangkok 10900, Thailand. E-mail: bmuav@hotmaі1.com De G raaff, J. Erosion and Soil and Water Conservation Group, Department of Environmental Sciences, Wageningen Agricultural University, Nieuwe Kanal 11, 6709 PA Wageningen, The Netherlands. Phone: +31-317-482-881, Fax: +31-317-484-759, E-mail: [email protected] Dent, F.J. FAO Regional Office for Asia and the Pacific, 39 Phra Atit Rd., Bangkok 10200, Thailand. E-mail: [email protected] Drechsel, P. 1WMI Ghana Office, c/o University of Science and Technology, Rumasi, Ghana. Phone & Fax: +233-51 -60206, E-mail: [email protected] Eiumnoh, A. School of Environment, Resources and Development, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand. Phone: +66-2-524-5588/524-5577, Fax: +66-2-524-5597, E-mail: [email protected] Ekanayake, P.B. Tea Research Institute of Sri Lanka, P.O. Box 130 Kandy, Sri Lanka. Enters, T. FAO Regional Office for Asia and the Pacific, 39 Phra Atit Rd., Bangkok 10200, Thailand. Phone: +66-2-281 -7844 ext. 328, Fax: +662-280-0445, E-mail: Thomas. [email protected] Eswaran, H. World Soil Resources, USDA-NRCS, P.O. Box 2890, Washington, D.C. 20013, USA. Phone: +1 -202-690-0333, Fax:+1 -202-720-4593, E-mail: [email protected] Evangelista, P.P. Bureau of Soils and Water Management, Department of Agriculture, Quezon City 1100, Philippines. E-mail: [email protected] Farah, J. The World Bank, 1818 H St.,NW, Washington, D.C. 20433, USA. E-mail: [email protected] Fechter-Escamilla, U. Institute for Soil Science and Soil Conservation, Justus-Liebig University, Schottstrasse 2-4, D-35390 Giessen, Germany. E-mail: [email protected] Fogarty, P.J. New South Wales Department of Land and Water Conservation, P.O. Box 3720, Parramatta, NSW 2124, Australia. G arrity, D.P. Southeast Asian Regional Research Programme, International Centre for Research in Agroforestry, P.O. Box 161 Bogor 16001, Indonesia. E-mail: [email protected] Gennadiyev, A. Faculty of Geography, Moscow State University, Moscow, 119899 Russia. Phone: +7-95939-1420, Fax: +7-95-932-8836, E-mail: [email protected]

xvii

Glanznig, A. Community Biodiversity Network and Humane Society International. P.O. Box 439 Avalon, NSW 2107, Australia. E-mail: [email protected] Hannam , I.D. NSW Department of Land and Water Conservation, 10 Valentine Avenue, Paramatta, NSW 2106, Australia. [email protected] Helldén, U. Department of Physical Geography, University of Lund, Sölvegatan 13, S-223 62 Lund, Sweden. E-mail: [email protected] H onnaiah Department of Agricultural Economics, GKVK, University of Agricultural Sciences, Bangalore-560065, India. Hoontrakul, K. Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. E-mail: [email protected] Hurni, H. Centre for Development and Environment, University of Berne, Hallerstrasse 12, 3012 Berne, Switzerland. E-mail: [email protected] Huszar, P.C.. Department of Agricultural and Resource Economics, Colorado State University, Ft. C ollins, CO 80525, USA. Phone: + 1-970-491-6948, Fax: + 1-970-491-2067, E-m ail: [email protected] Im -Erb, R. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand. E-mail: [email protected] Ivanov, V.N. Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology, Kwangju 500-712, Republic of Korea. Jayakody, A.N. Department of Soil Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka. Phone: +94-8-88239/88354, Fax: +94-8-88041, E-mail: [email protected] Juo, A.S.R. Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77845, USA. Phone: +1 -409-845-8841, Fax: +1 -409-862-1712, E-mail: [email protected] Karavanova, E.I. Soil Science Department, M.V. Lomonosov Moscow State University, 119899, Moscow, Russia. Fax: +7 (0) 95-939-0989, E-mail: [email protected] Kato, Y. National Institute of Agricultural and Environmental Sciences, Tsukuba, Ibaraki, Japan. Kauffman, S. International Soil Reference and Information Centre (ISRIC), P.O. Box 353, 6700 AJ Wageningen, The Netherlands. E-mail: [email protected] Kennedy, M. Community Biodiversity Network and Humane Society International. P.O. Box 439 Avalon, NSW 2107, Australia. E-mail: [email protected] Kertész, Á. Geographical Research Institute, Hungarian Academy of Sciences, P.O. Box 64, Budapest, H1388 Hungary. Phone/Fax: +36-1-311-7814, E-mail: [email protected] Kiara, J.K. Soil and Water Conservation Branch, Ministry of Agriculture, P.O. Box 30028, Nairobi, Kenya. E-mail: c/o [email protected] Kim, I.S. Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology, Kwangju 500-712, Republic of Korea. K unaporn, S. Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. E-mail: ssd [email protected] Lai, R. The Ohio State University, 2021 Coffey Road, Columbus, OH 43210, USA. Phone: +1-614292-9069, Fax: +1-614-292-7432, E-mail: [email protected]

xviii Li, Rui Institute of Soil and Water Conservation, CAS/M WR, 26 Xinong Rd., Yangling, Shaanxi Province 712100, People’s Republic of China. E-mail: [email protected] Li, Zhiguang Institute of Soil and Water Conservation, CAS/MWR, 26 Xinong Rd., Yangling, Shaanxi Province 712100, People’s Republic of China. Liebenthal, A. Operations Evaluation Department, Sector and Thematic Evaluations Group, The World Bank, Washington, D.C. 20433, USA. Phone: +1-202-458-7139, Fax: +1-202-522-3123. E-mail: [email protected] Mani, M. Operations Evaluation Department, Sector and Thematic Evaluations Group, The World Bank, Washington, D.C. 20433, USA. Phone:+1-202-458-7139, Fax: +1-202-522-3123, E-mail: [email protected] (new) Medina, S.M. Farming Systems and Soil Resources Institute, University of the Philippines, Los Bafíos, Laguna 4031, The Philippines. Phone: +63-49-536-1967, E-mail: [email protected] and [email protected]

Mendoza, P.A. Farming Systems and Soil Resources Institute, UPCA, Los Baftos 4031, The Philippines. Email: [email protected] M oncharoen, P. Soil Analysis Division, Land Development Department, Bangkok 10900, Thailand. Mostafa, G. Soil Resource Development Institute, Ministry of Agriculture, Krishi Khamar Sarak, Dhaka1215, Bangladesh. Phone: +880-2-911-0844/911-3363, Fax: +880-2-810600 Movillon, M. Riceworld Museum, The International Rice Research Institute, MCPO Box 3127, Makati City 1271, The Philippines. E-mail: [email protected] Nangju, D. Asian Development Bank, P.O. Box 789,0980 Manila, Philippines. Phone: +63-2-632-5542/6312666, Fax: +63-2-636-2186, E-mail: dnang,[email protected] Neef, A. University of Hohenheim, D-70593 Stuttgart, Germany. E-mail: a [email protected] Nicolas, C.M. Bureau of Soils and Water Management, Department of Agriculture, Quezon City 1100, Philippines. Nilo, G.P. Bureau of Soils and Water Management, Diliman, Quezon City, The Philippines. Phone: +63-2923-0454/920-4382, Fax: +63-2-920-4318. N oble, A. CSIRO Land and Water, PMP, P.O. A itkenvale, Townsville, A ustralia. E-mail: [email protected] O hkura, T. National Institute of Agricultural and Environmental Sciences, Tsukuba, Ibaraki, Japan. Ólafsdóttir, R. Department of Physical Geography, University of Lund, Sölvegatan 13, S-223 62 Lund, Sweden. Oldeman, L.R. International Soil Reference and Information Centre (ISRIC) PO. Box 353, 6700, AJ Wageningen, The Netherlands. Phone: +31-317-471735, Fax:: +31-317-471700, E-mail: [email protected] Omar, S.A.S. Aridland Agriculture Department, Kuwait Institute for Scientific Research, P.O. Box 24885, Safwat 13109, Kuwait. Onasa, S. Forest Environment Research and Development Division, Forest Research Office, Royal Forest Department, Bangkok 10900, Thailand. Orlov, D.S. Soil Science Department, M.V. Lomonosov Moscow State University, 119899, Moscow, Russia. Fax:+7 (0)95-939-0989.

xıx Packer, I. J. Department o f Land and Water Conservation, P.O. Box 510, Cowra, NSW 2794, Australia. Phone: +61-2-6341-1600, Fax: +61-2-6342-2565, E-mail: [email protected] Pagiola, S. The Environment Department, World Bank, 1818 H St., NW, Washington, D.C. 20433, USA. Phone: +1-202-458-2997, Fax: +1-202-522-1735, E-mail: [email protected] Palmer, B. CSIRO Land and Water, PMP, P.O. Aitkenvale, Townsville, Australia. Pandey, S. Social Sciences Division, The International Rice Research Institute, MCPO Box 3127, Makati City 1271, Philippines. Phone: +63-2-845-0563 ext. 774 (off.), 243 (res.), Fax: +63-2-8911292, E-mail: [email protected] Panichsakpatana, S. Department o f Soils, Kasetsart University, Bangkok 10900, Thailand. Penning de Vries, F.W.T. IWMI Southeast Asian Regional Office, P.O. Box 9-109, Chatuchak, Bangkok 10900, Thailand. Phone: +66-2-941-2500, Fax: +66-2-561-1230, E-mail: [email protected] Phien, T. National Institute for Soils and Fertilizers, Tuliem, Chem, Hanoi, Vietnam. Phommasack, T. Soil Survey and Land Classification Centre, P.O. Box 811, Dong Dok, Vientiane, Lao P.D.R. Pongwichian, P. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand. Pretorius, D.J. National Department of Agriculture, Directorate Agricultural Resource Conservation, Private BagX120, Pretoria 0001, South Africa. Phone: +27-12-319-7545, Fax: +27-12-329-5938, E-mail: [email protected]

Prosayakul, S. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand. Puginier, O. Department of Agricultural Extension and Communication, Humboldt University, Luisenstrasse 53,10099, Berlin, Germany. E-mail: [email protected] Rahm an, Md. M. Soil Resource Development Institute, Ministry of Agriculture, Krishi Khamar Sarak, Dhaka-1215, Bangladesh. Phone: +880-2-911-0844/911-3363, Fax: +880-2-810600, E-mail: [email protected] Razia, S. Soil Resource Development Institute, Ministry of Agriculture, Krishi Khamar Sarak, Dhaka-1215, Bangladesh. Phone: +880-2-911-0844/911-3363, Fax: +880-2-810600 Reddy, B.V.C Department of Agricultural Economics, GKVK, University of Agricultural Sciences, Bangalore560065, India. E-mail: [email protected] Reich, P.F. USDA Natural Resources Conservation Service, P.O. Box 2890, Washington, D.C 20013, USA. Phone: +1-202-690-0037, Fax: +1-202-720-4593, E-mail: Pau 1.Reich@usda. gov Richards, B. Riceworld Museum, The International Rice Research Institute, MCPO Box 3127, Makati City 1271, The Philippines. Ruaysoongnern, S. Department o f Land Resources and Environment, Khon Kaen University, Khon Kaen 40000, Thailand. E-mail: [email protected] Rupp, A.J. World Heritage Branch, Environment Australia. G.P.O. Box 787, Canberra, ACT 2601, Australia. E-mail: [email protected] Sajjapongse, A. P.O. Box 9-109, Chatuchak, Bangkok 10900, Thailand. E-mail: [email protected] Sanders, D. World Association of Soil and Water Conservation, Flat 1, Queen Quay, Welsh Back, Bristol BS1 4SL, UK. E-mail: [email protected]

XX Sangkapitux, C. Department of Agriculture and Resource Economics, Kasetsart University, Bangkok 10900, Thailand. E-mail: [email protected] Santosa, E. Center for Soil and Agroclimate Research, J. İr. H. Juanda 98, Bogor 16123, Indonesia. Santoso, D. Center for Soil and Agroclimate Research, J. Ir. H. Juanda 98, Bogor 16123, Indonesia. Scarsbrick, B. Landcare Australia Limited, 6 Help St., Chatswood, NSW 2067, Australia. E-mail: [email protected] Scherr, S. J. Agricultural and Resource Economics Department, 2200 Symons Hall, University of Maryland, College Park, MD 20742, USA. Phone: +1-301-405-8360, +1-703-758-2548, Fax: +1-301-314-9091, E-mail: [email protected] Shahid, S.A. Aridland Agriculture Department, Kuwait Institute for Scientific Research, P.O. Box 24885, Safwat 13109, Kuwait. E-mail: [email protected] Shamshuddin, J. Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. E-mail: [email protected] Shoaib, J.U. Soil Resource Development Institute, Ministry of Agriculture, Krishi Khamar Sarak, Dhaka1215, Bangladesh. Phone: +880-2-911-0844/911-3363, Fax: +880-2-810600. Shrestha, D.P. Soil Science Division, ITC, P.O. Box 6, Enschede, The Netherlands. Phone: +31-53-48742664, Fax: +31-53-487-4379, E-mail: [email protected] Shrestha, R.P. School of Environment, Resources and Development, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand. Phone: +66-2-524-5588/524-5577, Fax: +66-2-524-5597, E-mail: [email protected] Sidahmed, A.E. Technical Advisory Division, International Fund for Agricultural Development (IFAD), Via del Serafico 107,00143 Rome, Italy. Phone: +39-6-5459-2455/5459-2513, Fax: +39-6-5459-2018, E-mail: [email protected] Sompatpanit, S. World Association of Soil and Water Conservation, 67/141 Amonphant 9, Soi Senanikom 1, Bangkok 10230, Thailand. Tel. 66-2-570-3641, Fax: 66-2-562-0732, E-mail: sombal pan ii@hotmai I.com Southgate, D. Department of Agricultural Economics, Ohio State University, 2120 Fyffe Road, Columbus, Ohio 43210, USA. Phone: + 1-614-292-2432, Fax: +1-614-292-4749, E-mail: southgate [email protected] Srisaichua, S. Agricultural Chemistry Division, Department of Agriculture, Bangkok 10900, Thailand. Stabnokova, E.V. Department of Environmental Science and Engineering, Kwangju Institute o f Science and Technology, Kwangju 500-712, Republic of Korea. Stocking, M. School of Development Studies, University of East Anglia, Norwich NR4 7TJ, United Kingdom. Phone: +44-1603-592-339/456-161, Fax: +44-1603-451 -999, E-mail: [email protected] Subhasaram , T. Department of Chemistry, Mahasarakham University, Mahasarakham, Thailand. E-mail: [email protected]

Sukreeyapongse, O. Land Development Department, Bangkok 10900, Thailand. Sukristiyonubowo Center for Soil and Agroclimate Research, J. Ir. H. Juanda 98, Bogor 16123, Indonesia. Sutherland, M, Landcare Australia Limited, 6 Help St., Chatswood, NSW 2067, Australia. E-mail: [email protected] Tanprapas, P. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand.

XXI Temkmiatham, C. Forest Environment Research and Development Division, Forest Research Office, Royal Forest Department, Bangkok 10900, Thailand. Templeton, S.R. Department of Agricultural and Applied Economics, 259 Barre Hall, Clemson University, Clemson, S. Carolina 29634-0355, USA. E-mail: [email protected] Tengberg, A. GEF Unit, United Nations Environment Programme, P.O. Box 30552, Nairobi, Kenya. Phone: +254-2-624-147, Fax: +254-2-624-041, E-mail: [email protected] Toure, M. The World Bank, 1818 H St, NW, Washington, D.C. 20433, USA. E-mail: [email protected]: TÙ Siem, N. National Institute for Soils and Fertilizers, Tuliem, Chem, Hanoi, Vietnam. Tùmawis, H. Riceworld Museum, The International Rice Research Institute, MCPO Box 3127, Makati City 1271, The Philippines. E-mail: [email protected] Van Bo, N. National Institute for Soils and Fertilizers, Tuliem, Chem, Hanoi, Vietnam. E-mail: [email protected] Van Den Berg, H.M. Agricultural Research Council, Institute for Soil, Climate and Water, Division of GeoInformatics, Private Bag X79, Pretoria 0001, South Africa. Phone: +27-12-326-4205 ext. 260, Fax: +27-12-3231157. Van Lynden, G.W.J. International Soil Reference and information Centre (ISRIC), P.O. Box 353,6700 AJ Wageningen, The Netherlands. Phone: +31-317-471735, Fax: +31-317-471700, E-mail: [email protected] Varghese, T. Department o f Soil Science, Kerala Agricultural University, Vellayani-695522, Kerala, India. Vearasilp, T. Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. E-mail: ssd [email protected] W akatsuki, T. Faculty of Life and Environmental Science, Shimane University, Matsue, Japan. Werner, G. Institute for Soil Science and Soil Conservation, Justus-Liebig University, Schottstrasse 2^1, D-35390 Giessen, Germany. Wessels, K.J. Agricultural Research Council, Institute for Soil, Climate and Water, Division of GeoInformatics, Private Bag X79, Pretoria 0001, South Africa. Phone: +27-12-326-4205 ext. 260, Fax: +27-12-3231157, E-mail: k [email protected] Westerberg, L.O. Environment and Development Studies Unit (EDSU), Department of Physical Geography, Stockholm University, S-10691, Stockholm, Sweden. E-mail: [email protected] W ichaidit, P. Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. E-mail: ssd [email protected] Wigena, I.G.P. Center for Soil and Agroclimate Research, J. Ir. H. Juanda 98, Bogor 16123, Indonesia. Wilding, L.P. Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77845, USA. Phone: +1-409-845-8841, Fax: +1-409-862-1712, E-mail: [email protected] Willett, I. ACIAR, G.P.O. Box 1571, Canberra, ACT 2601, Australia. Xi, Zhongpei Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing 210008, People’s Republic of China. E-mail: [email protected] Yamclee, P. Land Development Department, Phaholyothin Rd., Bangkok 10900, Thailand. Yang, Jingsong Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China. E-mail: [email protected]

xxii Yang, Qinke Institute of Soil and Water Conservation, CAS/M WR, 26 Xinong Rd., Yangling, Shaanxi Province 712100, People’s Republic of China. Zhang, Taolin Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing 210008, People’s Republic o f China. Zhang, Xiaoping Institute of Soil and Water Conservation, CAS/MWR, 26 Xinong Rd., Yangling, Shaanxi Province 712100, People’s Republic of China.

1 Introduction A steadily increasing world population and continuing degradation o f extensive areas o f land threaten the fundamental processes o f the natural and agricultural ecosystems on earth and the quality o f human life. Although there may be contrary arguments, the capacity o f the earth is finite, as is its capacity to provide fo o d and fibre fo r consumption throughout ecosystems along the fo o d chain to human beings. Destruction o f habitat ensures loss o f biodiversity and a loss o f resilience in natural ecosystems; poor standards o f husbandry can lead to degradation o f land under agriculture and may be compounded by industrial pollutants. In this introduction and subsequent chapters, the problems o f land degradation are discussed within a framework o f driving forces, pressures, state, impacts, and responses (DPSIR). This framework provides a comprehensive view fo r the analysis o f the problems and offers a methodology within which responses to land degradation can be developed. Definitions are given in an attempt to provide a standardized vocabulary and common understanding o f the terms used. This is essential in developing an international setting fo r what this book describes as an ‘enabling environment ’ to bring land degradation under control. In order that this can take place, it is necessary tofirst adopt sound ecological standards as a basis fo r the future use o f land and soils. The current, exploitative, cultural attitude towards land and soils is unsuccessful in providing a sustainable form ofproduction and so alternative strategies need to be developed urgently. These must be effective at all levels from the practical point o f view o f the individual land user, as well as from the standpoint o f national, regional, and international policies. t has been forecast that the population of the world will increase from the present 6.0 billion to around 7.6 billion by 2020 (estimated from the data in Table 1 and Figure 1). In order to provide sufficient food, both for these additional people and to raise the standard of provision for those who currently have an inadequate diet, a large increase in food production must take place. This increase in food production must come from approximately the same land area that is now being farmed, as the remainder is too dry, too wet, too cold or too steep and mountainous to make a significant contribution. This inevitably means greater

I

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In tro d u ctio n

pressure will be put on prime lands, and especially those with the most fertile soils, to provide the extra food required. Whether productivity can be increased or even maintained on prime lands is not clear. As demand increases further, there will be increasing pressure also for cropping on more sensitive and less productive areas, such as semi-arid pastoral land. Fortunately, in the past 50 years, despite the enormous increases in agricultural production that have taken place, there are still large areas where land quality has remained fairly stable. There is growing recognition, however, among people working in rural development that land degradation, particularly salinization, soil erosion, soil nutrient depletion, and physical deterioration of soil structure, is widespread and increasing. Dramatic impacts of land degradation have been documented in some areas, with loss of productive lands, and even the displacement of people from their homelands. Where significant degradation has occurred, it often represents a serious threat to food security, particularly in poorer developing countries. Land degradation also threatens other environmental resources, both through direct effects, such as reduced habitat quality for biodiversity, and hydrological functions, and indirectly by forcing farmers to clear additional land to compensate for yield declines or land abandonment. Table 1. World population growth. Year

W orld population (millions)

1804 1927 1960 1974 1987 2000 2050

1,000 2,000 3,000 4,000 5,000 6,000 8,900

Figure 1. Possibilities in the demographic future.

Source: UN (1998). Source: Adapted from Cincotta and Engel man (2000).

The long-term impacts of land degradation depend upon future trends in land management, and the resilience of soils for recovery. It has been shown that in some cases market forces, and the selfinterest of landowners to maintain the fertility and productivity of their lands, will eventually bring land degradation under control. In other cases, however, forests have been destroyed, soils have been eroded down to bedrock or become highly saline. The cost of restorative action for advanced degradation is prohibitively expensive and beyond the capabilities of individual farmers with little or no income. Some of the regions of the world where land degradation is currently most severe are the breadbaskets and rice bowls of their countries or areas of large, poor rural populations with few alternative livelihood options. However, opinions have been divided about the global significance of land degradation for food security and the level of priority it should receive in public investment. Many soil scientists, ecologists, environmentalists, and agriculturalists and others who work ‘out in the field’ see continuing depletion and removal of natural vegetation, loss of biodiversity, and the erosion, pollution, and compaction of soils. To them, these are clear signs that environmental degradation is a major threat to biological diversity, future agricultural productivity, and the quality of life on earth, which justify an energetic response. Others, however, in particular economists, planners, and social scientists, want to understand how the economic, social, and environmental losses associated with land degradation compare with those caused by other

The Editors

3

factors. They argue that investments in land conservation and rehabilitation must compete for scarce resources with efforts to resolve other pressing problems, such as pest damage, post-harvest losses, marketing problems, bad pricing policies, and declining agricultural research budgets. Before committing scarce investment resources, they also want to see evidence that interventions really work. Until fairly recently, these questions about the extent and impacts of land degradation, and the desirability of investments in land rehabilitation, have been debated largely without the benefit of reliable data. Fortunately, the past decade has seen the generation of important new data sets on land quality, the impacts of land degradation, and the efficacy and efficiency o f technologies, institutions, and policies to promote good land husbandry. An objective o f this book is to make known more widely the scientific advances made by diverse disciplines, and the practical lessons learned by various development actors, on how to respond appropriately and effectively to land degradation. This introduction briefly describes the framework and structure of the book, defines key terms that will be used throughout, and suggests a new approach for promoting good land husbandry and rehabilitation.

Framework Degradation is the result of a number of interrelated factors that can result in a downward spiral, ending in land that is chemically or physically too degraded for productive use or environmental service, and often also results in degraded visual amenity. The existing driving forces produce pressures that result in the current state of land resources, with a negative im pact on society and the environment. This, in turn, may stimulate a response. Human activity may directly or indirectly influence the degradation or rehabilitation process at every stage. This sequence has been referred to as the DPSIR (driving forces, pressures, state, impacts, responses) framework within which the human response to degradation takes place (Box 1.1). The DPSIR framework has been adopted for the organization o f this book. The book is structured into 11 chapters. The Introduction forms the opening chapter. Chapter 2, Setting the scene, provides an overview of the issues of land degradation from historical and contemporary perspectives. Chapters 3-5 analyze degradation processes themselves in the sequence of driving forces and pressures, state of the w orld’s soil resources, and impacts upon society and the environment. The driving forces fuelling land degradation may result from increased human population, urban expansion, war, tourism, agricultural production demands, transport, infrastructure, industrial or extractive activity and natural events such as climate change or simple water stress. These forces introduce pressures into the environment through noxious emissions to air, water, and land; nutrient mining; deforestation; forest and rangeland fires; or overgrazing. The state of land resources is described at global, regional, and national scales, using data that have become available only recently. Land degradation is interpreted in terms of the immediate past land use history and pressures that have brought about its current state, and includes biological or physical deterioration, eutrophication or nutrient depletion, salinization, acidification or chemical contamination. These changes in the state of land resources may have significant impacts on food supply, agricultural incomes, and environmental services of the land, such as habitat for biodiversity and hydrological functions. Impacts are estimated at a global scale, and documented in greater detail in national and sub-regional case studies. Chapters 6-10 describe the responses humans have made to the problems of land degradation. Chapter 6 describes tools for m onitoring and assessment that have been recently developed. These methods have revolutionized the study of land degradation in the past two decades. Chapter 7 tells how conservation of agricultural land and rehabilitation of degraded land are being implemented, emphasizing

Introduction

4

Box 1.1 Using the soil DPSIR framework—driving forces, pressures, state, im pacts, and responses— for evaluating land degradation

W.E.H. Blum1 The DPSIR framework is an approach to soil and land degradation, developed by the European Environment Agency, for describing, monitoring, and controlling environmental problems (EEA, 1999). The approach is based on the use of indicators, which may be direct or indirect, ecological, technical, socioeconomic or cultural. The first key question is: What is the driving force behind the problem? The problem itself is then sub-divided in three stages: the pressure, deriving from the driving force, the state that the pressure creates, and the impact that results from the state. The second key question is how to respond so as to change the driving forces, in order to alleviate or to reverse the problem. The diagram below shows the framework of driving force, pressure, state, impact, and response. It can be used by scientists, technicians, farmers, and others at the grass roots level to identify a problem. At the same time the approach may be used by politicians and decision-makers to respond to a situation, thus bringing together all persons concerned.

- Human population growth - Livestock population growth - Land development - Land use policies - Tourism development - Growth of demand in agricultural products - Price and income changes - Infrastructure development (land use conversion) - Industry/energy/mining development - Natural climatic events - Climate change - Water stress

T he D P SIR fram ew ork applied to so il

Driving forces

Responses

Impacts

Pressures

- Improved monitoring and assessment of land quality and conservation/ rehabilitation strategies - Technical innovations for land conservation/rehabilitation - Institution innovations to support farmers in land conservation/rehabilitation - National laws and policy to regulate and encourage land conservation/rehabilitation - International conventions and investments to encourage land conservation/rehabilitation

State - Emission to air, water and land - Soil sealing through construction and infrastructure - Deforestation - Forest and rangeland fires - Nutrient mining - Exposure of bare soil - Overcultivation - Overgrazing - Overexploitation of vegetation - Changes in water extraction and flow

Soil degradation

- Local and diffuse contamination - Soil acidification - Salinization - Nutrient loading (soil eutrophication) - Nutrient depletion - Physical deterioration - Biological deterioration Soil loss

- Soil sealing - Soil erosion - Large-scale land movement

- Habitat destruction and loss of biodiversity - Reduced or more uneven watei flows - Water stress - Deterioration of water quality - Decline in agricultural production - Decline in agricultural income and wealth - Downstream economic damage from sedimentation - Change in human population size and spatial distribution - Climate change Continued on next page

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For example, a driving force can be the lowering of prices for agricultural commodities on local markets, thus decreasing the income of farmers. The pressure o f reduced income and inability to replace nutrients by fertilizers results in nutrient mining. This leads to soil degradation by nutrient depletion. Arable land on sloping terrain may be prone to soil erosion if no anti-erosion measures are taken because o f lack o f funds. The resulting change in soil function and decrease in soil fertility have the direct impact o f reducing biomass and subsequently food production. Indirect impacts may be changes in population size and distribution in rural areas, as a result of low income. The response should, wherever possible, be directed at the driving force, i.e. towards improving market conditions and maintaining reasonable market prices for agricultural commodities, rather than remedying the state of the soil or alleviating the pressure itself by supplying fertilizers to farmers. In this example, the ideal response might be economic or social, rather than technical. Indicators for evaluating land degradation using the DPSIR framework should have the following characteristics: -

policy relevance: data should be more demand- (issue) than supply-driven and include important political features; analytical soundness: indicators must be scientifically based and clearly show a cause-response relationship; easy interpretation: indicators should be easily understandable for stakeholders, especially farmers, as well as for decision-makers and politicians; measurability: indicators should be feasible and cost-effective concerning data collection, processing, and dissemination.

These should characterize indicators used at all stages within the DPSIR framework. Applied correctly, the DPSIR framework can be an effective tool for analyzing and developing strategies to combat land degradation. EEA (European Environment Agency). 1999. Environment in the European Union at the Tbrn of the Century, Environmental Assessment Report No. 2. Copenhagen: EEA. 1 International Union of Soil Sciences, c/o Institute of Soil Research, University of Agricultural Sciences, Gregor MendelStr. 33, 1180 Vienna, Austria, [email protected]

new technological approaches. Institutional innovations are also emerging, to support the farmers who are the principal land managers. Key innovations described in Chapter 8 include a range o f participatory approaches to land conservation and rehabilitation, and direct and indirect incentives to farmers. To encourage these innovations at a national scale requires suitable reform of national law and policy (Chapter 9) related to land tenure, land use and management, public investment and resource pricing. International initiatives (Chapter 10) provide an essential umbrella of agreements, protocols, and conventions, and critical investment resources, to encourage and support national actions to promote sustainable land management. The final chapter, Future responses, summarizes the salient points from the papers presented for policy-makers, and stresses the need for maintaining or forming institutions and organizations—at local, national, and international levels—that have the intellectual capability and organizational responsibility to address land degradation problems and promote appropriate legislation and policy.

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Introduction

Concepts and terms Land and soil are important components of ecosystems and of the wider environment in which all plants and animals live. A natural environment is theoretically one that is relatively unchanged or disturbed by human culture. However, the reality is more complex. The concept of the environment involves also the availability of resources that maintain biodiversity in any one area, including the climate, soil, and vegetation conditions that provide suitable habitats for different species. Humans are an integral part of the environment, as they are dependent upon it for all their food, fuel, and fibre requirements. As a result of the increase in human population and the rapidly evolving technological society, no part of the world can be said to be completely unaffected by human activities. The boundary between natural and cultural changes of the environment has become blurred. Thus, the definition of ‘land’ must be comprehensive, encompassing more than just topography, soils, and landscape. One of the tasks of this introduction is to make clear what is understood by the terminology used to describe problems of land and soil degradation, as different branches of science approach the subject from different viewpoints. The following are some definitions of the key terms used in this book.

Land and resource concepts Land: A delineable area of the earth’s terrestrial surface, encompassing all attributes of the biosphere immediately above or below this surface, including those near the surface, the climate, the soil and terrain forms, the surface hydrology (including shallow lakes, rivers, marshes, and swamps), the surface sedimentary layers and associated groundwater reserve, the animal populations, the human settlement pattern and physical results of past and present human activity (terracing, water storage or drainage structures, roads, and buildings, etc.) (FAO, 1995). Soil: The unconsolidated mineral or organic material at the surface of the earth, capable of supporting plant life (Bridges, 1997). or

An integral part of the earth’s ecosystems, situated at the interface between the earth’s surface and bedrock. It is sub-divided into successive horizontal layers with specific physical, chemical, and biological characteristics. From the standpoint of history of soil use, and from an ecological and environmental point of view, the concept of soil also embraces porous sedimentary rocks and other permeable materials, together with the water that these contain and the reserves of underground water (Council of Europe, 1990). Soil landscape: An area of land that has recognizable and specifiable topography and soils, which is capable of being presented on maps and of being described by concise statements. A soil landscape has a characteristic landform with one or more taxonomic units occurring in a defined way. It is often associated with the physiographic features of the landscape and is similar to a soil association (Houghton and Charman, 1986). Soil resource: The total extent of soil within a given area available as a natural medium for plant growth. It is limited and exhaustible, and thus, its management must aim to avoid degradation to ensure its potential productive capability is maintained or improved (Houghton and Charman, 1986). Soil quality: The capacity of a specific type of soil to function, within natural or fabricated ecosystems or, land use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation (Karlen et al., 1995).

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Degradation concepts Soil degradation: A process that lowers the current and/or the potential capability of soil to produce goods or services (FAO/UNEP/UNESCO, 1979). or Aspects of physical, chemical, and/or biological deterioration including loss of organic matter, decline in soil fertility, decline in structural condition, erosion, adverse changes in salinity, acidity or alkalinity, and the effects of toxic chemicals, pollutants or excessive flooding (Houghton and Charman, 1986). or A loss or a reduction of soil functions or soil uses (Blum, 1997). Land degradation: It encompasses soil degradation and the deterioration of natural landscapes and vegetation. Human-induced degradation includes the adverse effects of overgrazing, excessive tillage, overclearing, erosion and sediment deposition, extractive industries, urbanization, disposal of industrial wastes, road construction, decline of plant communities, the effects of animals and noxious plants, and pollution of the air with its effect on land (Houghton and Charman, 1986). Desertification: Land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities (UN, 1994).

Towards a new approach to land use policy and action We have learned, from research and experience that the problems and challenges of land degradation cannot be dealt with in isolation from the total environment. The subject must be approached at all levels, from the education o f the individual farmer, to local, regional, and national governments, to international environmental strategies and instruments. The maintenance of the world’s land and soil resources and their conservation, or even enhancement of their fertility and other qualities, is essential, not only for the present, but for the maintenance of biodiversity and the survival of future generations. This is the principle of sustainability, defined at the FAO/Netherlands Den Bosch (SARD— Sustainable Agriculture and Rural Development) Conference (FAO, 1991) as: The management and conservation o f the natural resource base, and the orientation o f technological and institutional change in such a manner as to ensure the attainment and satisfaction o f human needs fo r present and future generations. Such sustainable development (in agriculture, forestry and fishery sectors) which conserves land, water, plant and animal genetic resources, is environmentally non-degrading, technologically appropriate, economically viable, and socially acceptable. International conferences such as the SARD meeting and the United Nations Conference on the Environment and Development (UNCED) in Rio de Janeiro in 1992 have raised international awareness and have put in place frameworks within which the world community, and particularly national governments, can attempt to check the onward march of land degradation. So that sustainable land management is encouraged, national governments must develop their own strategic material, policies, and laws to achieve this desirable end. Such developments should include new ways of approaching and dealing with land degradation problems and provide a philosophical basis and an intellectual climate in which attitudes are changed. It is vitally important that ideas and decision support systems that are based on the principles of

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Introduction

Box 1.2 Ecological soil standards

ID. Наппат'

Soil is an important ecosystem, one that is basic to life on earth, so strategies for its use should be bound by sound policy, legal, and institutional instruments that include the prevention of the loss of its functions. These environmental policies, agreements, and instruments for sustainable land management must be underpinned by a sound, ecologically-based philosophy. •

•

•

•

First, there is a need for recognition of the problem. Current cultural attitudes to the land and soils are often contemptuous and exploitative. Fresh concepts must be developed to recognize that soils are valuable assets that can be damaged and that require careful ‘husbandry’ in a similar manner to the crops grown and animals reared on the land. Second, there is a need to develop new ideologies from within the professional organizations that care for the soil. In the past these have been technocentric and exploitative, often lacking strong social or ecological dimensions. Third, because professional disciplines tend to internalize the logic of their work, they seldom step outside their customary framework to question their basic assumptions. This creates inertia against examining the outcomes of our practices. By following the principles of ecologically sustainable development (i.e. inter-generational equity, applying the precautionary action, and the principles of biological diversity), land management decisions would be made in the best interests of the soil and its users. Fourth, there is a need to re-think what we are doing, rather than re-fashioning dated concepts.

To address these needs, a change in attitude is required by the politicians, administrators, and bureaucrats who are responsible for environmental institutions, their policies, and laws. Then the necessary changes can be made to those laws and policies, and to the institutions that administer them. A new legislative and policy paradigm for land and soil, based on an ecological consciousness, is essential to establish harmony between humans and land, humans and soil, and between humans and ecosystems generally. Underpinning this paradigm shift should be a variety o f ‘ecological soil standards’. These standards would include processes for maintaining or improving the ecological integrity of soil, which, in turn, is based on the preservation of ecosystems. Hannam, I.D. 1998. An ecological perspective of soil conservation policy and law in Australia. In: Towards Sustainable Land Use: Furthering Co-operation Between People and Institutions, eds. H.-P. Blume, H. Eger, E. Fleischhauer, A. Hebel, C. Reij and K.G. Steiner, 945-952. Advances in Geoecology 31. Reiskirchen, Germany: Catena Verlag. 1 NSW Department of Land and Water Conservation, 10 Valentine Avenue, Paramatta, NSW 2106, Australia. ihannanw/'dlwc.iisw.gov.au

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ecological sustainability are communicated to and shared, not only with planners and policy-makers, but particularly those who actually own and work the land (Box 1.2). The ultimate solutions to land degradation will arise from creative cooperation in research between agricultural, environmental, and social scientists, and in development action between farmers, conservationists, and policy-makers. Fortunately, interest, concern, and insights about land degradation have arisen from all sides. This is evident in the papers contained in this volume, which were contributed by over 100 professionals including economists, planners, social scientists, agriculturalists, soil scientists, and environmentalists. The wide range of views presented here reflects the many facets that must be considered when studying and responding to the problem of land degradation. Significant questions certainly remain, and further research is clearly needed to refine our knowledge and support site-specific efforts to improve land husbandry. The editors believe strongly, however, that this diverse evidence supports the conclusion that land degradation is a serious global concern, and also that we now have many promising tools and strategies for effective and targeted response, from the farm to global scale. The time has come to act upon this knowledge.

References BLUM, W.E.H. 1997. Basic concepts: Degradation, resilience, and rehabilitation. In: Methodsfor Assessment o f Soil Degradation, eds. R. Lai, W.E.H. Blum, C. Valentin and B.A. Stewart, 1-16. Advances in Soil Science Series. New York: CRC Press. BRIDGES, E.M. 1997. World Soils. 3d ed. Cambridge: Cambridge University Press. CINCOTTA, R.P. and ENGELMAN, R. 2000. Nature s Place: Human Population and the Future o f Biological Diversity, p. 8. Washington, D.C.: Population Action International. COUNCIL OF EUROPE. 1990. European Conservation Strategy. Recommendations for the 6,h European Ministerial Conference on the Environment. Strasbourg: Council of Europe. FAO. 1991. Conference on Agriculture and the Environment. ‘S-Hertogenbosch, The Netherlands. Rome: FAO. FAO. 1995. Planning for Sustained Use o f Land Resources: Towards a New Approach, Rome: FAO. FAO/UNEP/UNESCO. 1979. A provisional methodology for soil degradation assessment. 84 pp. Rome: FAO. HOUGHTON, P.D. and CHARMAN, P.E.V. 1986. Glossary o f Terms Used in Soil Conservation, Sydney, Australia: Soil Conservation Service of New South Wales. KARLEN, D.L., MAUSBACH, J.W., DORAN, J.W., CLINE, R.G., HARRIS, R.F. and SCHUMAN, G.E. 1995. Soil quality: A concept, definition, and framework for evaluation. Soil Science Society o f America Journal, 61, 4—10. UN. 1994. Convention on Desertification. Information Programme on Sustainable Development. New York: UN. UN. 1998. World Population Prospects 1950-2050 (the 1996 Revision). New York: UN Population Division.

2 Setting the scene The three papers that follow set the scene for this book. The contribution by Juo and Wilding provides a long-term retrospective view o f the problem, stressing that despite successive attempts throughout history, humans have yet to solve the challenges provided by land degradation. Two hundred years ago, Thomas Robert Malthus drew attention to the potential problem of human food supply and since then we have looked over the 'Malthusian precipice’, but the threatened disaster has not happened (Greenland et a l, 1998*). Until the 20th century, there were always new lands to open up for agriculture, allowing despoiled and degraded areas to be abandoned. This option is no longer open, and the question remains, will human ingenuity and technology continue to be able to provide our daily bread throughout the21sl century? Bridges and Oldem an discuss the manner in which agriculture has changed the landscape in response to human demand for food. The paper echoes the optimistic view that the world’s natural resources have sufficient biological potential to provide food, for the anticipated world population. However, this hope is tempered by the realization that it can only be achieved at a cost of certain degradation o f the environment. This cost must be treated like any other production expense, and minimized by adopting ecologically sound agricultural and land use policies throughout the world. The box by Movillon and colleagues illustrates the historical and up-to-the-minute increase in the earth’s population. This phenomenon is being reflected by a decrease in the global extent of productive land due to its conversion to other uses. The contribution by Esw aran and colleagues surveys the problem of land degradation and desertification. The authors present evidence of alarmingly high soil erosion and land degradation rates, and vulnerability to desertification from various continents. Also they describe serious productivity declines on some lands as a result o f these processes. They stress the need to distinguish between myths and scientific facts. Hard facts, not hearsay, are required for assessing and developing strategies to combat land degradation. These contributions suggest that there can be little argument about the necessity to reduce the scale of land degradation currently taking place. When degradation occurred in historical times, there was always new land to cultivate. Now there is no more vacant land to bring into cultivation for food production, and high standards of sustainable husbandry are urgently needed. E.M. Bridges and I.D. Hannam 1 Greenland, D.J., Gregory, P J. and Nye, P.H., eds. 1998. Land Resources: On the Edge o f the Malthusian Precipice. Wallingford: CABI and The Royal Society.

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Setting the Scene

S ettin g th e scene

Land and civilization: An historical perspective A.S.R. JUO and L.P. WILDING'

The rise and fa ll o f ancient civilized societies can be related to land use or misuse. Fertile soils on the floodplains o f major rivers in different parts o f the world gave rise to early agrarian societies. The civilizations o f Babylon, Egypt, India, and China all grew up alongside major rivers. In Europe, the Greeks and Romans were nourished by crops grown in the shallow, fertile soils derived from limestone in the mild climate o f the lands around the Mediterranean. The Aztec, Maya, and Inca societies arose on the rich volcanic soils o f the tropical highlands o f Latin America. Many later societies also evolved in the fertile valleys o f large rivers. They include people who lived alongside the Mekong and Chao Phraya in Southeast Asia; the Danube, the Rhine, the Elbe, the Volga, and the Thames in Europe; and the Mississippi and Missouri in North America. Land degradation was the major cause o f the decline and fa i t o f many ancient societies. Deforestation and soil erosion upstream, resulted in floods and siltation that overwhelmed many early agrarian societies. Our modern industrial society is exerting even greater stress upon the world ’s land resources. Cities continue to expand overfertile farmlands, the impounded waters o f dams built fo r hydroelectric generation and water supplies have flooded valleys with fertile alluvial soils. In many countries, derelict, mined lands and disposal o f urban-industrial wastes in landfills have created serious environmental concern. One o f the great strengths o f modem agriculture is that it can produce large amounts offood and fibre with minimal inputs o f human labour; it is however heavily dependent upon fossilfuel inputs. On the negative side, intensification ofagriculture in many parts o f the world has resulted in salinization o f irrigated lands in the drier regions and the loss o f forest vegetation in the humid tropics. Humans today are capable o f either enhancing or impoverishing the natural resource base o f the world much faster than in ancient times. The fundamental question that still remains after 7,000years o f human endeavour is: What is the best way to manage land resources to safeguard the well being o f future human generations, and to sustain allforms o f life-supporting ecosystems on earth? n ancient philosopher once wrote: History is a constant reminder. Great empires rose on land o f plenty and great empires declined because o f mankind ’s brutality to the land and to one another. Sadly, that observation, made more than a thousand years ago, still holds true today. Humans and land have been on a collision course ever since arable farming and herding began. Throughout history, agrarian societies thrived on fertile land, but their civilizations declined as a result of land degradation, warfare, and other self-destructive activities. Babylon grew up on the banks of the Tigris and Euphrates rivers, Egypt is known as the ‘gift of the Nile’ and India is referred to as the ‘daughter of the Ganges’. China is said to owe her joy and sorrow to two great rivers, the Huang He and the Yangtze (Duran and Duran, 1968). In Europe, the Greeks and Romans were nourished by crops grown in the shallow, fertile soils derived from limestone in the mild climate of the lands around the Mediterranean. The Aztec, Maya, and

A

1 Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77845, USA. Phone: + 1-409-8458841, Fax: +1-409-862-1712, E-mail: [email protected] and [email protected]

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Land and civilization: An historical perspective

Inca societies arose on the rich volcanic soils of the tropical highlands of Latin America. Many later societies also evolved in the fertile valleys along large rivers. They include people who lived alongside the Mekong and Chao Phraya in Southeast Asia; the Danube, the Rhine, the Elbe, the Volga and the Thames in Europe; and the Mississippi and Missouri in North America. Humans today possess such powerful tools and knowledge that we can either enhance or impoverish the natural resource base of the earth much faster than our ancestors of ancient times. In this paper, we attempt to present an historical overview about the rise and fall of ancient societies as related to land use or misuse. The paper concludes with a few thoughts regarding the potential impact of modem human activities on land and on the natural world as a whole.

Land and ancient agrarian societies Babylon: About 7,000 years ago, the fertile soils on the alluvial plains between the Tigris and Euphrates rivers and along the Nile gave rise to two of the oldest recorded civilized societies. Sophisticated irrigation and crop production systems were developed and farmlands were kept productive for more than 1,000 years. The alluvial plain of Mesopotamia, now Iraq, is traditionally known as the Garden of Eden. Eleven successive empires have risen and fallen but today Babylon has long become a desolated region dotted with ruins and buried canals. What went wrong? Two sets of explanations have been put forward, but both seem to lead to the same conclusion. A recent study by Weiss et a l (1993) attributes the collapse of the agricultural civilization in northern Mesopotamia primarily to climate change. At 2200 BC, archaeological and soil data indicate that there was a marked increase in aridity and wind erosion. An earlier report by Lowdermilk ( 1953) concluded that the fall of ancient Babylon and the later agrarian cultural centres in the Middle East during Biblical times was not merely caused by the decline in soil fertility. Rather, deforestation and overgrazing in the mountains disrupted the hydrological balance of the rivers. Successive floods swept down on to the plains, burying farmlands and filling irrigation canals with sediment. This was the beginning of the perennial conflict between two groups of land users: the shepherds in the mountains and the farmers on the plains. For nearly 13 centuries, the shallow but fertile soils of the uplands were eroded and the cities and farmlands downstream buried under some 4 m of sediment. Soil scientists and archaeologists have noted the different layers of alluvium as being representative of former land use characteristics. Lowdermilk’s report on soil erosion in ancient times helped gain public support for the soil conservation movement in the USA after the devastating man-made ‘Dust Bowl’ on the Great Plains. It led to the establishment of National Soil Erosion Services in the USA in the 1930s and the subsequent implementation of nationwide research work on soil erosion and conservation during the 1950s. Egypt: The emergence of the ‘desert civilization’ in the Nile Valley is a different story. The alluvial soils, enriched by the annual floodwaters of the Nile, have sustained a productive agriculture for more than 6,000 years. The mountains of Ethiopia and East Africa remained relatively undisturbed by human activities in early times and were not subject to soil erosion, so this was not a major cause for the fall of the Egyptian empires. Nor were there serious conflicts between the agrarian Egyptians and the inhabitants of upstream watershed areas. Instead, the fall of ancient Egypt was caused by territorial expansion first by the Greeks and later by the Romans who emerged as more powerful nations in the Mediterranean region (Duran and Duran, 1968). Not until recent times has population pressure caused expansion of irrigated agriculture on to marginal lands. Additionally, large dams were built upstream to control seasonal flooding, to irrigate dry land, and to generate electric power for the expanding urban population of the lower Nile Valley. Modification of the natural hydrological regime of the Nile has resulted in severe problems of salinization, especially in the Delta. But in spite of limited areas of fertile land, Egypt remains predominantly an agrarian society.

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China: Early Chinese dynasties owed much of their joys and sorrows to the Huang He (or Yellow River). Its fertile alluvial valleys and plains in semi-arid northern China were the setting for the rise of an agrarian society about 5,000 years ago. Periodic floods enriched the soils of the valleys and plains, but resulted in the loss of much human life. Historians have noted that the rise and fall of early Chinese dynasties often coincided with catastrophic floods of the Huang He. However, there were other forces contributing to the rise and fall of the northern Chinese empires. Conflict extended over a period o f 2,000 years between the agrarian Chinese and their nomadic neighbours, and as a result, forests in the mountains were destroyed. Frequent floods and famines weakened the northern empires and forced the Chinese to migrate southwards into the valley and delta of the Yangtze River during the Soong Dynasty (960-1279 AD). Relocation of the Chinese cultural centre led to the development of the intensive rice-fish-silk farming system o f the humid lower Yangtze Delta that has sustained agricultural productivity for more than 1,000 years. This is reflected in Chinese folklore that describes the quality of life in the southern Chinese cities of Suzhou and Hangzhou as sublime. Nevertheless, the prosperous agrarian economy in China began to disintegrate during the 19th century. The collapse o f the last Chinese Imperial Dynasty, Ching 1644-1911 AD, can be attributed not only to rapid population growth, but also to China’s inability to deal with the economic and political expansion o f the industrializing nations of Western Europe, especially during the 19th century. However, the intensive rice-fish-silk production system and the sophisticated water management technology remain productive and sustainable to the present day. Furthermore, the teaching of China’s philosophers, and the work o f poets and painters, influence the quality o f life in many societies in Asia and other parts of the world (de Riencourt, 1965). Mesoamerica: The rise of earlier agrarian civilization is not only restricted to rich alluvial soils along large rivers. The agrarian empires of the Aztec, Inca, and Maya arose largely on the rich volcanic soils of the tropical highlands. Archaeologists are still puzzled why 200,000 people left the metropolis of Teotihuacan during the 8thcentury (Viola and Margolis, 1991). Urban expansion, nutrient depletion of cropland, especially phosphorus, and more importantly, the inability to transport large quantities o f food grain from distant fields may all have contributed to the disintegration of this large urban centre long before the arrival of the Spanish (Borlaug, personal communication). Historical evidence also indicates that early Mesoamerican inhabitants were grain farmers and that agricultural activities were restricted to fertile lands surrounding the urban centres with large areas remaining under natural vegetation (Viola and Margolis, 1991). However, the most significant change in land use occurred after the introduction and expansion o f livestock farming by Spanish and Portuguese immigrants during the past 500 years. Removal o f tropical forests for cattle ranching has been the major cause o f soil erosion on the sloping lands o f Central and South America. Greeks and Romans: The ancient Greek and Roman civilizations had a profound influence on the later European and modem Western culture. The reasons for the growth and decline of the Greeks and Romans as economic and political powers around the Mediterranean are well-documented (Duran and Duran, 1968; Delouche, 1993). The use of the fertile but shallow soils on the rolling landscapes of the region resulted in erosion. Subsequently, the Greeks turned eastwards to Persia and northern India for more productive land, and the Romans looked for fertile lands in Europe and North Africa to feed their growing domestic populations. In 146 DC, the Romans conquered Carthage and the productive flat farmlands along the Mediterranean coast o f North Africa became the ‘wheat granary of Rome’ for several hundred years. The ruins o f the large Roman city of Thamugadi, built about 100 AD with a 2,500-seat theatre and 17 Roman baths are witness to the importance of the region to Rome. Overgrazing in the mountains led to soil erosion and sedimentation that progressively buried the city on the plain. It remained buried until excavated by French archaeologists in the early 1900s. The nearby village of Timgad today has only a few hundred

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Land and civilization: An historical perspective

inhabitants (Lowdermilk, 1953; Delouche, 1993). Once again, man-made soil erosion caused the decline of an agrarian civilization. Later agrarian cultures: In more recent times, the rise of societies in Southeast Asia and Europe can be attributed to the development of agricultural systems based on the fertile soils of the Mekong, Chao Phraya, Danube, Rhine, Rhone, and Thames river valleys. Rice-based agriculture has sustained the Buddhist civilizations of Indochina, and in Europe integration of crop and livestock farming helped to avoid the historic conflict between farming and nomadic societies. On sloping land, forests were replaced by permanent pasture and soil erosion was minimized. Fallowing, green manure, and crop rotation were used to maintain soil fertility and crop yields. The agricultural prosperity achieved in pre-industrial Europe led to rapid population growth and farming intensified and expanded on to marginal land. Evidence o f past erosion is common in Europe, and an example is the ancient seaport of Aiques Mortes in southern France. Now more than 10 km from the sea, this walled city was once a major port during the 12thcentury Crusader Wars (Pieri, personal communication). The decline of European agrarian civilization was rescued by developments in science that improved farming technology and provided the nutrients required by growing crops. European nations, led by Spain and Portugal, followed by England, Holland, and France also expanded their territorial influences overseas. Industrialization, mass emigration to America, imports of cheap grain, and colonization allowed a great flowering of literature, philosophy, art, and music as well as further progress in science and technology. This culminated in the age o f ‘overproduction and overconsumption’. All these developments during the golden age of western civilization have occurred in the last 300 years, and can be related to land resources and agriculture.

Land and industrial civilizations The impact of the industrial revolution on land and the natural world in general has been both positive and negative. On the positive side, we now have the capability to produce sufficient food and fibre with minimum input of labour, as the use of modem tools and technology has greatly enhanced agricultural productivity. High-yielding crop varieties and breeds of livestock have been developed that respond to high levels of input and management. Mechanization of cultivation, sowing, pest control, and harvesting has allowed extensive growth of high-yielding crops in monoculture. Large dams have been constructed to store and divert water for irrigation and power generation. On arid and semi-arid lands, water from fossil aquifers is being used for irrigation of farmland as well as domestic and industrial purposes. In humid regions, strongly leached acid soils are limed and fertilized for continuous crop and livestock production. On the negative side, our food and fibre production systems have become heavily dependent on fossil fuel and other manufactured inputs such as mineral fertilizers and chemical pesticides. Urban expansion has resulted in the loss of large tracts of once prime farmland. Forested land is being converted to agriculture and to meet the need for timber, paper, and fuel. Aquifers are showing signs of significant depletion through excessive pumping and salinization has again become a major problem on irrigated lands in drier regions. The use of large-scale mechanization and lack of appropriate tillage were largely responsible for the ‘Dust Bowl’ in the Great Plains of the USA in the 1930s. In northeast USA, upstream soil erosion caused by tobacco cultivation and accompanying downstream sedimentation have turned the once navigable upper Chesapeake Bay into swampland (Trimble, 1985). In the Palouse area of northwest USA, annual soil loss from mechanized wheat cultivation between 1939 and 1979 averaged 10 million tons in Whitman County alone. Despite the development of soil conservation measures during the past 60 years, they have not been widely adopted by farmers in the area until recently (Shepherd, 1985).

A .S.R . Juo and L.P. W ild in g

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In recent years, researchers, planners, and farmers have begun to question the sustainability of industrial agriculture and the wisdom o f land use policy and practices adopted by many nations. They urge the development of long-term strategies to deal with many critical land use issues, such as urban expansion, decline o f soil fertility, pollution of surface and groundwater, deforestation in the tropics, and the loss of plant and animal resources (Barrow, 1991). However, remedial interventions for these land degradation problems require costly capital investment and are often in conflict with the pursuit of short­ term economic gains o f industrialized societies. The industrial civilization o f the 20th century may be defined as the rapid conversion of natural resources into goods and services and the two ultimate products are wealth and waste (Figure 1). Wealth is mostly expressed in the form o f stocks and bonds and wastes are mostly polluting or toxic materials. Sustainability o f the industrial model o f development would depend upon how human society as a whole can enhance and conserve the non-renewable resources, ensure fair distribution of wealth, recycle non­ toxic materials, and regulate the production of toxic wastes.

Figure 1. The industrial civilization.

The concept o f sustainable development in the industrialized nations in recent years has created confusion and uncertainty in many developing nations. For decades these countries have attempted to mimic the economic progress achieved by the industrialized nations. Now that thinkers and planners in the industrialized nations caution that their model of development is not sustainable, many developing nations are forced to re-think their future. Sustainable development in the industrial nations calls for a re-examination of the pursuit of unlimited economic growth at the expense of a finite natural resource base. Questions related to land resources that are frequently asked in conferences and workshops on sustainable development are: • • •

How can we sustain the high material standard of living in the industrial nations indefinitely without exhausting the earth’s non-renewable resources? How can the developing nations be helped to achieve a similar standard of living without adversely affecting the economic well-being of the industrialized nations? How can we conserve and protect the earth’s remaining natural forests, especially in the Amazon and Congo Basins to prevent further disruptions of the global hydrological cycles and related climate change?

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Land and civilization: An historical perspective

There is no clear answer to these scientifically challenging questions. However, it has become increasingly obvious that the path of economic development, based on unlimited resources, is not a sustainable one.

Land use and conservation: Challenges ahead The earth’s land masses have been and will continue to be divided into many nations. Unfortunately, the quantity and quality of land resources amongst the nations vary widely. There are the land-rich nations, such as the USA, Canada, Australia, and New Zealand where there is an abundance of arable land, and a low density of rural population. Their high standard of living is supported by a high energy-input agriculture, manufacturing, and international trade. At the opposite extreme are land-poor nations, such as Haiti, Rwanda, Nepal, and Bangladesh, where rural population has long exceeded the land’s carrying capacity at present levels of input and management and poverty is widespread. For the land-rich nations, major issues for sustainable land management in the future would be to prevent and reduce soil, water, and air pollution from agriculture and industry, and to convert and preserve more land for forest, grassland, and wildlife habitats. In the land-poor nations, land degradation is set to continue unless economic and technical assistance is provided by the international community. The situation of land use in the majority of nations lies between these two extremes. For more than 20 years, Meadows et a l (1992) have worked to develop a computer model that would predict the ‘limits of growth’ of human society. A simplified version of their World 3 Model appeared in a 1993 issue of American Scientist (Hayes, 1993). Land and land use are used as basic building blocks in the model (Figure 2). The model supports the hypothesis that the growth in human population and the consumption of resources in the rapidly industrializing world must be curtailed. The message is clear: “If we don’t stop burning the candle at both ends, we shall soon be left in the dark”.

Figure 2. World 3 Model (Meadows et al, 1992 as cited by Hayes, 1993).

A.S.R. Juo and L.P. Wilding

19

In the final analysis, soil, water, vegetation, and mineral resources are basic components of land. The health of the world’s land resources is vital to the very survival of humans, as well as all plant and animal species. For better or worse humans have altered the face of the earth significantly during the past 300 years so that the land and other natural resources have been exploited in almost every comer of the planet (Geographic, 1988). Technological success has enriched our lives but has impoverished the earth’s natural resources. Ecologists have cautioned that the nature and scale of human activities, if allowed to proceed at the current pace, may indeed lead to catastrophic changes beyond control. One cannot but ask the question, has the human race been acting responsibly towards the use and conservation of the earth’s natural resources? In the future, land resources must be managed better to safeguard the well-being of future generations of human society and to sustain all forms of life-supporting ecosystems on earth.

References BARROW, C. J. 1991. Land Degradation. Cambridge: Cambridge University Press. DELOUCHE, F., ed. 1993. An Illustrated History o f Europe. New York: Henry Holt & Co. DE RIENCOURT, A. 1965. The Soul o f China: An Interpretation o f Chinese History. New York: Harper Colophon Books. DURAN, W. and DURAN, A. 1968. The Lessons o f History. New York: Simon and Schuster. GEOGRAPHIC. 1988. Earth 88: Changing Geography Perspectives. Washington, D.C.: National Geographic Society. HAYES, B. 1993. Balanced on a pencil point. American Scientist, 81,510-516. LOWDERMILK, W.C. 1953. Conquest o f Land Through Seven Thousand Years. Agriculture Bulletin No. 99. Soil Conservation Service, Washington, D.C.: United States Department of Agriculture. (Revised 1975.) MEADOWS, D.H., MEADOWS, D.L. and RANDERS, J. 1992. Beyond the Limits: Confronting Global Collapse, Envisioning a Sustainable Future. Post Mills, Vermont: Cheldes Green Publishing. SHEPHERD, J.F. 1985. Soil conservation in the northwest wheat producing areas. In: The History o f Soil and Water Conservation, eds. D. Helms and S. Flader, 79-88. Washington, D.C.: Agricultural History Society. TRIMBLE, S. W. 1985. Perspectives of the history of soil erosion control in the eastern United States. In: The History o f Soil and Water Conservation, eds. D. Helms and S. Flader, 60-78. Washington, D.C.: Agricultural History Society. VIOLA, H.J. and MARGOLIS, C., eds. 1991. Seeds of Change. Washington, D.C.: Smithsonian Institution Press. WEISS, H., COURTY, M.A., WETTERSTROM, W., GUICHART, F., SENIOR, L., MEADOW, R. and CURNOW, A. 1993. The genesis and collapse of third millennium North Mesopotamian civilization. Science, 261,995-1004.

Land degradation: An overview H. ES WARAN1, R. LAL2and P. F. REICH3

Land degradation will remain an important global issue fo r the 21st century because o f its adverse impact on agronomic productivity, the environment, and its effect on food security and the quality o f life. Productivity impacts o f land degradation are due to a decline in land quality on site where degradation occurs (e.g. erosion) and o ff site where sediments are deposited. However, the on­ site impacts o f land degradation on productivity are easily masked due to use o f additional inputs and adoption o f improved technology and have led some to question the negative effects o f desertification. The relative magnitude o f economic losses due to productivity decline versus environmental deterioration also has created a debate. Some economists argue that the on-site impact o f soil erosion and other degradative processes are not severe enough to warrant implementing any action plan at a national or an international level. Land managers (farmers), they argue, should take care o f the restorative inputs needed to enhance productivity. Agronomists and soil scientists, on the other hand, argue that land is a non-renewable resource at a human time-scale and some adverse effects o f degradative processes on land quality are irreversible, e.g. reduction in effective rooting depth. The masking effect o f improved technology provides a false sense o f security. The productivity o f some lands has declined by 50% due to soil erosion and desertification. Yield reduction in Africa due to past soil erosion may range from 2 to 40%, with a mean loss o f 8.2% fo r the continent. In South Asia, annual loss in productivity is estimated at 36 million tons o f cereal equivalent valued at US$5,400 million by water erosion, and US$1,800 million due to wind erosion. It is estimated that the total annual cost o f erosion from agriculture in the USA is about US$44 billion per year, i.e. about US$247per ha o f cropland and pasture. On a global scale the annual loss o f 75 billion tons o f soil costs the world about US$400 billion per year, or approximately US$70 per person per year. Only about 3% o f the global land surface can be considered as prime or Class I land and this is not found in the tropics. Another 8% o f land is in Classes H and III. This 1I%> o f land mustfeed the six billion people today and the 7.6 billion expected in 2020. Desertification is experienced on 33% o f the global land surface and affects more than one billion people, half o f whom live in Africa. and degradation, a decline in land quality caused by human activities, has been a major global issue during the 20th century and will remain high on the international agenda in the 21st century. The importance of land degradation among global issues is enhanced because of its impact on world food security and quality of the environment. High population density is not necessarily related to land

L

1 World Soil Resources, USDA-NRCS, P.O. Box 2890, Washington, D.C. 20013, USA. Phone: +1-202-690-0333, Fax: +1202-720-4593, E-mail: [email protected] 2 The Ohio State University, 2021 Coffey Road, Columbus, OH 43210, USA. Phone: +1-614-292-9069, Fax: +1 -614-2927432, E-mail: [email protected] 3 USDA-NRCS, P.O. Box 2890, Washington, D.C. 20013, USA. Phone: +1-202-690-0037, Fax. +1-202-720-4593, E-mail: [email protected]

Н. Eswaran, R. Lai and P.F. Reich

21

degradation; it is what a population does to the land that determines the extent of degradation. People can be a major asset in reversing a trend towards degradation. However, they need to be healthy and politically and economically motivated to care for the land, as subsistence agriculture, poverty, and illiteracy can be important causes of land and environmental degradation. Land degradation can be considered in terms of the loss of actual or potential productivity or utility as a result of natural or anthropic factors; it is the decline in land quality or reduction in its productivity. In the context of productivity, land degradation results from a mismatch between land quality and land use (Beinroth et al, 1994). Mechanisms that initiate land degradation include physical, chemical, and biological processes (Lai, 1994). Important among physical processes are a decline in soil structure leading to crusting, compaction, erosion, desertification, anaerobism, environmental pollution, and unsustainable use of natural resources. Significant chemical processes include acidification, leaching, salinization, decrease in cation retention capacity, and fertility depletion. Biological processes include reduction in total and biomass carbon, and decline in land biodiversity. The latter comprises important concerns related to eutrophication o f surface water, contamination of groundwater, and emissions of trace gases (C 0 2, CH4, N20 , NOx) from terrestrial/aquatic ecosystems to the atmosphere. Soil structure is the important property that affects all three degradative processes. Thus, land degradation is a biophysical process driven by socioeconomic and political causes. Factors o f land degradation are the biophysical processes and attributes that determine the kind of degradative processes, e.g. erosion, salinization, etc. These include land quality (Eswaran et a l, 2000) as affected by its intrinsic properties of climate, terrain and landscape position, climax vegetation, and biodiversity, especially soil biodiversity. Causes of land degradation are the agents that determine the rate of degradation. These are biophysical (land use and land management, including deforestation and tillage methods), socioeconomic (e.g. land tenure, marketing, institutional support, income and human health), and political (e.g. incentives, political stability) forces that influence the effectiveness of processes and factors o f land degradation. Depending on their inherent characteristics and the climate, lands vary from highly resistant, or stable, to those that are vulnerable and extremely sensitive to degradation. Fragility, extreme sensitivity to degradation processes, may refer to the whole land, a degradation process (e.g. erosion) or a property (e.g. soil structure). Stable or resistant lands do not necessarily resist change. They are in a stable steady state condition with the new environment. Under stress, fragile lands degrade to a new steady state and the altered state is unfavourable to plant growth and less capable o f performing environmental regulatory functions.

Effects of land degradation on productivity Information on the economic impact of land degradation by different processes on a global scale is not available. Some information for local and regional scales is available and has been reviewed by Lai (1998). In Canada, for example, on-farm effects of land degradation were estimated to range from US$700 to US$915 million in 1984(Girt, 1986). The economic impact ofland degradation is extremely severe in densely populated South Asia, and sub-Saharan Africa. On plot and field scales, erosion can cause yield reductions of 30 to 90% in some root-restrictive shallow lands o f West Africa (Mbagwu et a l, 1984; Lal, 1987). Yield reductions of 20 to 40% have been measured for row crops in Ohio (Fahnestock et al., 1995) and elsewhere in Midwest USA (Schumacher et al, 1994). In the Andean region of Colombia, workers from the University of Hohenheim, Germany (Ruppenthal, 1995), have observed severe losses due to accelerated erosion on some lands. Few attempts

22

Land degradation: An overview

have been made to assess the global economic impact of erosion. The productivity of some lands in Africa (Dregne, 1990) has declined by 50% as a result of soil erosion and desertification. Yield reduction in Africa (Lal, 1995) due to past soil erosion may range from 2 to 40%, with a mean loss of 8.2% for the continent. If accelerated erosion continues unabated, yield reductions by 2020 may be 16.5%. Annual reduction in total production for 1989 due to accelerated erosion was 8.2 million tons for cereals, 9.2 million tons for roots and tubers, and 0.6 million tons for pulses. There are also serious (20%) productivity losses caused by erosion in Asia, especially in India, China, Iran, Israel, Jordan, Lebanon, Nepal, and Pakistan (Dregne, 1992). In South Asia, annual loss in productivity is estimated at 36 million tons of cereal equivalent valued at US$5,400 million by water erosion, and US$1,800 million due to wind erosion (UNEP, 1994). It is estimated that the total annual cost of erosion from agriculture in the USA is about US$44 billion per year, about US$247 per ha of cropland and pasture. On a global scale the annual loss of 75 billion tons of soil costs (at US$3 per ton of soil for nutrients and US$2 per ton of soil, for water) the world about US$400 billion per year, or approximately US$70 per person per year (Lal, 1998). Soil compaction is a worldwide problem, especially with the adoption of mechanized agriculture. It has caused yield reductions of 25 to 50% in some regions of Europe (Ericksson et al., 1974) and North America, and between 40 and 90% in West African countries (Charreau, 1972; Kayombo and Lal, 1994). In Ohio, reductions in crop yields are 25% in maize, 20% in soybeans, and 30% in oats over a seven-year period (Lai, 1996). On-farm losses through land compaction in the USA have been estimated at US$1.2 billion per year (Gill, 1971). Nutrient depletion as a form of land degradation has a severe economic impact at the global scale, especially in sub-Saharan Africa. Stoorvogel et a l (1993) have estimated nutrient balances for 38 countries in sub-Saharan Africa. Annual depletion rates of soil fertility were estimated at 22 kg N, 3 kg P, and 15 kg K h a 1. In Zimbabwe, soil erosion results in an annual loss of N and P alone totalling US$1.5 billion. In South Asia, the annual economic loss is estimated at US$600 million for nutrient loss by erosion, and US$1,200 million due to soil fertility depletion (Stocking, 1986; UNEP, 1994). An estimated 950 million ha of salt-affected lands occur in arid and semi-arid regions, nearly 33% of the potentially arable land area of the world. Productivity of irrigated lands is severely threatened by build up of salt in the root zone. In South Asia, annual economic loss is estimated at US$500 million from waterlogging, and US$ 1,500 million due to salinization (UNEP, 1994). Potential and actual economic impact globally is not known. It is not known either for soil acidity and the resultant toxicity of high concentrations of Al and Mn in the root zone, a serious problem in sub-humid and humid regions (Eswaran et a l , 1997a). It is in the context of these global economic and environmental impacts of land degradation, and numerous functions of value to humans, that land degradation, desertification, and resilience concepts are relevant (Eswaran, 1993). They are also important in developing technologies for reversing land degradation trends and mitigating the greenhouse effect through land and ecosystem restoration. As land resources are essentially non-renewable, it is necessary to adopt a positive approach to sustainable management of these finite resources.

Views on land degradation Land degradation has received widespread debate at the global level as evidenced by the literature: UNEP, 1992; Johnson and Lewis, 1995; Oldeman et a l, 1992; Middleton and Thomas, 1997;Dregne, 1992;Maingnet, 1994; Lai and Stewart, 1994; Lai et al, 1997. At least two distinct schools have emerged regarding the prediction, severity, and impact of land degradation. One school believes that it is a serious global threat posing a major challenge to humans in terms of its adverse impact on biomass productivity and environment

Н. Eswaran, R. Lai and P.F. Reich

23

quality (Pimentel e ta i, 1995; Dregne and Chou, 1994). Ecologists, soil scientists, and agronomists primarily support this argument. The second school, comprising primarily economists, believes that if land degradation is a severe issue, why market forces have not taken care of it. Supporters argue that land managers (e.g. farmers) have vested interest in their land and will not let it degrade to the point that it is detrimental to their profits (Crosson, 1997). There are a number o f factors that perpetuate the debate on land degradation: 1.

Definition: There are numerous terms and definitions that are a source of confusion, misunderstanding, and misinterpretation. A wide range of terms is used in the literature, often with distinct disciplinaryoriented meaning, and leading to misinterpretation among disciplines. Some common terms used are soil degradation, land degradation, and desertification. While there is a clear distinction between ‘soil’ and ‘land’ (the term land refers to an ecosystem comprising land, landscape, terrain, vegetation, water, climate), there is no clear distinction between the terms ‘land degradation’ and ‘desertification’. Desertification refers to land degradation in arid, semi-arid, and sub-humid areas due to anthropic activities (UNEP, 1993; Darkoh, 1995). Many researchers argue that this definition of desertification is too. narrow because severe land degradation resulting from anthropic activities can also occur in the temperate humid regions and the humid tropics. The term ‘degradation’ or ‘desertification’ refers to irreversible decline in the ‘biological potential’ of the land. The ‘biological potential’ in turn depends on numerous interacting factors and is difficult to define. The confusion is further exacerbated by the definition of ‘dryland’ where different definitions are used. It is important to standardize the terminology, and develop a precise, objective, and unambiguous definition accepted by all disciplines.

2.

Extent and rate o f land degradation: Because of different definitions and terminology, a large variation in the available statistics on the extent and rate of land degradation also exists. Two principal sources of data include the global estimates of desertification by Dregne and Chou ( 1994), and of land degradation by the International Soil Reference and Information Centre (Oldeman et al., 1992; Oldeman, 1994). Table 1 shows that degraded lands in dry areas of the world amount to 3.6 billion ha or 70% of the total 5.2 billion ha of the total land areas considered in these regions. In comparison, in Table 2, Oldeman (1994), shows that the global extent of land degradation (by all processes and all ecoregions) is about 1.9 billion ha. The principal difference between the two estimates is the status of vegetation. Although the estimates by Dregne and Chou cover only dry areas, they also include the status of vegetation on the rangeland. Therefore, the estimates in Tables 3 and 4 are not directly comparable. There is also a difference in terminology used to express the severity of land degradation. Dregne and Chou used the terms slight, moderate, severe, and very severe to designate the severity of degradation. Oldeman used the terms light, moderate, strong, and extreme, and these terms may not be comparable to those o f Dregne and Chou. Oldeman et a l (1992), on the basis of expert judgment, attempted to differentiate natural from human-induced degradation. Eswaran and Reich ( 1998) attempted to evaluate vulnerability to land degradation and desertification. Differences in terminology and approaches, and also the areas included in the assessment, mean that the estimates of the three workers are difficult to compare (Tables 1,2, and 3).

Land degradation: An overview

24

Table 1. Estimates of all degraded lands (in million km2) in dry areas (Dregne and Chou, 1994). Continent

Total area

Africa Asia Australia and the Pacific Europe North America South America Total

Degraded area f

% degraded

14.326 18.814 7.012 1.456 5.782 4.207

10.458 13.417 3.759 0.943 4.286 3.058

73 71 54 65 74 73

51.597

35.922

70

t Comprises land and vegetation.

Table 2. Estimates of the global extent (in million km2) of land degradation (Oldeman, 1994). Type Water erosion Wind erosion Chemical degradation Physical degradation Total

Light

Moderate

Strong + extreme

Total

3.43 2.69 0.93 0.44

5.27 2.54 1.03 0.27

2.24 0.26 0.43 0.12

10.94 5.49 2.39 0.83

7.49

9.11

3.05

19.65

Table 3. Vulnerability to desertification and wind and water erosion (Eswaran and Reich, 1998). Only arid, semi-arid, and sub-humid areas (in million km2) are considered according to the definition of UNEP. Estimates of water erosion include humid areas. Severity Low Moderate High Very high Total

3.

Desertification

W ater erosion

Wind erosion

14.653 13.668 7.135 7.863

17.331 15.373 10.970 12.196

9.250 6.308 7.795 9.320

43.319

55.870

32.373

Land-vegetation relationships: The problem is farther confounded by the definition of the term ‘vegetation degradation’. It may imply reduction in biomass, decrease in species diversity, or decline in quality in terms of the nutritional value for livestock and wildlife. There is a need for establishing distinct criteria for evaluating vegetation degradation. Table 4 shows an example of vegetation degradation in Australia, but in combination with soil erosion. The quantity and quality of vegetation are not considered.

Н. Eswaran, R. Lai and P.F. Reich

25

Table 4. Vegetation degradation in pastoral areas of Australia (Woods, 1983; Mabbutt, 1992).

Type Total Undegraded Degraded i. Vegetation degradation with little erosion ii. Vegetation degradation and some erosion iii. Vegetation degradation and substantial erosion iv. Vegetation degradation and severe erosion v. Dryland salinity

4.

Area (‘000 km2) 3.4 1.5 1.9 1.0 0.5 0.3 0.1 0.001

Land degradation processes: Different processes of land degradation also confound the available statistics on soil and/or land degradation. Principal processes of land degradation include erosion by water and wind, chemical degradation (comprising acidification, salinization, leaching etc.) and physical degradation (comprising crusting, compaction, hard-setting etc.). Some lands or landscape units are affected by more than one process, of water and wind erosion, salinization, and crusting or compaction. Unless a clear distinction is made, there is a considerable chance of overlap and double accounting. Table 5 shows an example of overlapping degradative processes with increasing risks of double accounting.

Table 5. Land degradation on cropland in Australia (Woods, 1983; Mabbutt, 1992). Type Total Undegraded Degraded i. Water erosion ii. Wind erosion iii. Combined water and wind erosion iv. Salinity and water erosion v. Others

5.

Area (‘000 km2) 443 142 301 206 52 42 0.9 0.5

Methods o f assessment o f land degradation: Global assessment of land degradation is not an easy task, and a wide range of methods is used (Lai et a l, 1997). Therefore, data generated by different methods are not comparable. Further, most statistics refer to the risks of degradation or desertification (based on climatic factors and land use) rather than the actual (present) state of the land. Table 3 shows vulnerability to desertification and erosion, and these estimates are much higher than those by Dregne and Chou (Table 1) and Oldeman (Table 2), and are suggestive o f the risks of land degradation. The actual degradation may not occur because of judicious land use and advances in land management technologies. Comparison of these data on different estimates shows wide variations because o f different methods and criteria used, and highlights the importance of developing uniform criteria and standardizing methods of assessment of land degradation.

26 6.

Land degradation: An overview Land degradation and productivity: A major shortcoming of the available statistics on land degradation is the lack of cause-effect relationship between severity of degradation and productivity. Criteria for designating different classes of land degradation (e.g. low, moderate, high) are generally based on land properties rather than their impact on productivity. In fact, assessing the productivity effects of land degradation is a challenging task (Lai, 1998). Difficulties in obtaining global estimates of the impact of land degradation on productivity in turn created problems and raised skepticism. Table 6 from the International Board for Soil Research and Management (IBSRAM) indicates the problems involved in relating land degradation by erosion to crop yield. The data from China show that despite significant differences in cumulative soil loss and water runoff, there were no differences in com yield. Similar inferences can be drawn with regard to the impact of cumulative soil erosion on yield office in Thailand. Whereas soil loss ranged from 330 to 1,4781h a 1, the corresponding yield of rice ranged from 4.0 to 5.31h a 1. The lowest yield was obtained from treatments causing the least soil loss. Crop yield is an integrative effect of numerous variables. In addition, erosional (and other degradative processes) effects on crop yield or biomass potential depend on changes in land quality with respect to specific parameters. Table 7 shows that the yield of sisal was correlated with pH, CEC, and Al saturation but not with soil organic C and N contents. Assessing the productivity effects of land degradation requires a thorough understanding of the processes involved at the soil-plantatmosphere continuum. These processes are influenced strongly by land use and management.

Table 6. Cumulative soil loss and runoff in relation to crop yield in three ASIALAND Sloping Lands Network countries (Sajjapongse, 1998). Country

China Philippines

Thailand

Treatment

Period

Crop

Controlf 1992-95 Alley cropping Control 1990-94 Alley cropping (low input) Alley cropping (high input) Control 1989-95 Hillside ditch Alley cropping Agroforestry

Com Com Com Com Com Rice Rice Rice Rice

Soil loss (Mg h a 1) 122 59 341 26 15 1,478 134 330 850

Runoff (mm)

Cumulative yield (Mg ha*1)

762 602 801 43 31 1,392 446 538 872

15.3 15.9 5.6 14.3 18.7 4.5 4.8 4.0 5.3

f Control = Farmer’s practice

Table 7. Relationship between yield of sisal and soil fertility (0-20 cm depth) decline in Tanga region of Tanzania (Hartemink, 1995). Land properties Yield levels

pH (1:2.5 in H20 ) Soil organic carbon (%) Total soil nitrogen (%) Cation exchange capacity (cmol kg*1) Al saturation (% ECEC)

2.3

6.50 1.60 0.11 9.30 0

Sisal yield (Mg h a 1) 1.8 1.5 Property value 5.40 1.90 0.16 7.00 20.00

5.00 1.50 0.12 5.00 50.00

Н. Eswaran, R. Lai and P.F. Reich

27

Issues and challenges There are sufficient studies and reviews (e.g. Barrow, 1991; Blaikie and Brookfield, 1987; Johnson and Lewis, 1995) that clearly demonstrate the fact that land degradation affects all facets of life. Many issues that confront those working in the domain of land resources include technologies to reduce degradation and also the techniques to assess and monitor land degradation. A number of questions remain unanswered and these include: •

Is land degradation inevitable?

•

Are there adequate early warning indicators o f land degradation?

•

•

The absence of land tenure and the resulting lack of stewardship is a major issue in some countries that detracts from adequate care for the land; how can this be resolved? Declining soil quality resulting largely from human-induced degradation triggers social unrest; what is the societal responsibility of soil scientists? How can soil scientists better participate in developing public policy?

•

Local actions have global impact; what are the areas for international collaboration?

•

Who pays, who wins in the economics of land degradation?

•

Degradation results in loss of intergenerational equity and the value o f bequests. How do we quantify and create awareness? Is there a link between land degradation and the health of humans and animals?

•

• • • •

Declining soil quality leads to diminishing economic growth in countries where wealth is largely agrarian. How can the rates of resource consumption be quantified? Land degradation often destroys or reduces the natural beauty of landscapes. How might the aesthetic value of land be quantified? How to create greater awareness of the perils of land degradation in society and political leadership?

There are three steps involved in the process of addressing the problem: assessment, monitoring, and application o f mitigating technologies. All three steps are in the purview o f agriculturists and specifically, soil scientists. The latter clearly have the responsibility for soil science, and over the past decade substantial progress has been made in communicating the dangers o f land degradation. However, much remains to be done. Soil science has made significant contributions to the task of soil resource assessment but its practitioners have shown little or no interest in the additional task of monitoring the resource base (Mermut and Eswaran, 1997). This still remains a new area of investigation requiring guidelines, standards, and procedures. The challenge is to adopt an internationally acceptable procedure for this task. Soil scientists have an obligation not only to show the spatial distribution of stressed systems but also to provide reasonable estimates of their rates of degradation. They should develop early warning indicators of degradation to enable them to collaborate with others, such as social scientists, to develop and implement mitigating technologies. Soil scientists also have a role in assisting national decision-makers to develop appropriate land use policies. There are many, usually confounding, reasons why land users permit their land to degrade. Many of the reasons are related to societal perceptions of land and the values they place on land. Degradation is also a slow imperceptible process and so many people are not aware that their land is degrading. Creating awareness and building up a sense of stewardship are important steps in the challenge of

Figure 1. Desertification vulnerability.

oo

K)

Land degradation: An overview

29

Н. Eswaran, R. Lai and P.F. Reich

reducing degradation. Consequently, appropriate technology is only a partial answer. The main solution lies in the behaviour of the farmer who is subject to economic and social pressures of the community/ country in which he/she lives. Food security, environmental balance, and land degradation are strongly inter-linked and each must be addressed in the context of the other to have measurable impact. This is the challenge of the 2 1st century for which we must be prepared.

Desertification Desertification is a form o f land degradation occurring particularly, but not exclusively, in semi-arid areas. Figure 1 indicates the areas of the world vulnerable to desertification. The semi-arid to weakly arid areas of Africa are particularly vulnerable, as they have fragile soils, localized high population densities, and generally a low-input form of agriculture. About 33% of the global land surface (42million km2) is subject to desertification. Table 8 shows the vulnerability of land to desertification in some Asian countries. Twenty-five percent of the region is affected and if not addressed the quality of life o f large sections of the population will be affected. Many of these countries cannot afford losses in agricultural productivity. There are no good estimates of the number o f persons affected by desertification nor o f the number who directly or indirectly contribute to the process. A recent study by Reich et al. (this volume) provides some estimates for Africa. Table 8. Estimates o f vulnerability to desertification in some Asian countries. C ountries

Afghanistan Bangladesh Bhutan Brunei China India Indonesia Japan Cambodia Laos Malaysia Mongolia Myanmar Nepal North Korea Pakistan Papua New Guinea Philippines Singapore South Korea Sri Lanka Taiwan Thailand Vietnam Total

Total land area (km2)

647,500 133,910 47,000 6,627 9,326,410 2,973,190 1,826,440 374,744 176,520 230,800 328,550 1,565,000 657,740 136,800 120,410 778,720 452,860 298,170 638 98,190 64,740 32,260 511,770 325,360 21,115,069

Vulnerability to desertification Moderate H igh

Low

Very high Area

%

Area

%

Area

%

Area

%

2,954 85,163 1,407

0.46 63.60 2.99

39,088

6.04

43,838

6.77

436,480

67.41

262,410 1,277,328 29,596

2.81 42.96 1.62

239,107 744,148 46,290

2.56 25.03 2.53

65,638 206,317 5,289

0.70 6.94 0.29

72,214 165,912 232 693

0.77 5.58 0.01 0.18

45,731 48,963

25.91 21.21

118,155 35,386

66.94 15.33

26,345 130,903 20,131

1.68 19.90 14.72

40,511 140,387 8,698

2.59 21.34 6.36

19 20,630

3.14

2,104 13,477 228

0.13 2.05 0.17

31,474 4,892 20,952

4.04 1.08 7.03

39,605 8,175 16,621

5.09 1.81 5.57

17,032 27 1,708

2.19 0.01 0.57

181,503

23.31 0.00 0.00

6,337 2,902 90,241 47,516

9.79 9.00 17.63 14.60

24,393 201 320,581 59,238

37.68 0.62 62.64 18.21

3,421 277 7,265 375

5.28 0.86 1.42 0.12

2,135,245

10.11

1,880,584

8.91

371,836

1.76

0.00 0.00 0.00 0.00 872,843

4.13

зо

Land degradation: An overview

As shown in Table 9, a high population density in an area that is highly vulnerable to desertification poses a very high risk for further land degradation. Conversely, a low population density in an area where the vulnerability is also low poses, in principle, a low risk. The Mediterranean countries of North Africa are very highly prone to desertification. In Morocco, for example, erosion is so extensive that the petrocalcic horizon of some Palexeralfs is exposed at the surface. In the Sahel, there are pockets of very high-risk areas. The West African countries, with their dense populations, have a major problem to contain the processes of land degradation. Table 10 provides the area in each o f the classes of Table 9. About 2.5 million km2of land are under low risk, 3.6 are under moderate risk, 4.6 are under high risk, and 2.9 million km2are under very high risk. The region that has high propensity is located along the desert margins and occupies about 5% of the landmass. It is estimated that about 22 million people (2.9% of total population) live in this area. The low, moderate, and high vulnerability classes occupy 14,16, and 11% respectively and together impact about 485 million people. Cumulatively, desertification affects about 500 million Africans and though they have relatively good soil resources (Eswaran et al, 1997b,c) their productivity will be seriously undermined by land degradation and desertification. Table 9. Matrix for risk assessment of human-induced desertification. 1 = low risk; 2,3 = moderate risk; 4,5,6 = high risk; 7, 8, 9 = very high risk. (After Reich et al, 1999.) Vulnerability class 41

1 2 4

3 5 7

6 8 9

Table 10. Land area (1,000 km2) of Africa in risk classes. (After Reich et al, 1999.) Vulnerability class 40

2,476 2,608 2,643

1,005 1,180 1,074

750 976 825

A new agenda Although soils are an ecologically important component of the environment, the availability of research and development funds does not match their significance in terms of the cost to society if soils become degraded. The perception that enough is already known about soils, so that generalizations can be made for all soils, is incorrect. There is also a failure to recognize that agriculture is one of the major ‘stressors’ of the environment (Virmani et al, 1994), particularly from a soil degradation point of view (Beinroth et al, 1994). If these attitudes prevail, major catastrophes in the future become more probable. The purpose of such discussions is to emphasize that soil is virtually a non-renewable resource. It is a basic philosophy that society has an obligation to protect soil, conserve it, or even enhance its

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quality for future generations. The role of society in sustaining agriculture can be demonstrated, and conversely, the role of soil in sustaining society. The paradigms that brought some countries of the world to agricultural affluence must be evaluated, as well as the policies and practices that have contributed to land degradation and decline in productivity in other countries. We need to look at current concerns, and the urgent need to develop new paradigms for managing soil resources, as proposed by Sanchez ( 1994) for example, that will carry us through the next few decades. Some of the valid arguments of the past now have little validity in the face of contemporary environmental degradation. New concepts must be defined, the research gaps identified, and the needs that will enable our institutions to meet the challenges and requirements of the next 20 years must be indicated. Land degradation results from mismanagement of land and thus deals with two interlocking, complex systems: the natural ecosystem and the human social system. Interactions between the two systems determine the success or failure of resource management programmes. To avert the catastrophe resulting from land degradation, which threatens many parts of the world, the following concepts from Eswaran and Dumanski (1994) are relevant: • • •

• •

•

Environment and agriculture are intrinsically linked and research and development must address both of them. Land degradation is as much a socioeconomic problem as it is a biophysical problem. Land degradation and economic growth or lack of it (poverty) are intractably linked; (people living in the lower part of the poverty spiral are in a weak position to provide the stewardship necessary to sustain the resource base. As a consequence, they move further down the poverty spiral— a vicious cycle is set in motion). Implementation o f mitigation research to manage land degradation can only succeed if land users have control and commitment to maintain the quality of the resources. The focus o f agricultural research should shift from increasing productivity to enhancing sustainability, recognizing that land degradation caused by agriculture can be minimized and made compatible with the environment. Land use must match land quality; appropriate national policies should be implemented to ensure this occurs to reduce land degradation; (a framework for evaluation of sustainable land management [Dumanski et a l, 1992] is a powerful tool to assess such discrepancies and assure sustainability).

The thrust o f a new agenda for resource assessment and monitoring with respect to land degradation (including desertification), has several components. It must be stressed that any research and development activity should be in the larger context of the ecosystem as addressed by Sanchez ( 1994) and Greenland et al. (1994). Components o f a national strategy to address land degradation (and desertification) comprise: • •

Studies on long-term water needs (quality and quantity). A network of monitoring sites to detect changes in natural resource conditions.

•

Working with farmers by understanding and incorporating indigenous knowledge.

•

Including land degradation aspects in research on cropping and farming systems, and soil and water management. Convincing decision-makers that climate change, desertification, quality of life, and sustainability are all interlinked and addressing one helps the other. Initiating research on a new paradigm that is holistic and focuses on these issues.

• •

Land degradation: An overview

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A ‘scale-sensitive information system’ or database on land degradation must be made available for the vertical network of decision-makers to enable them to make effective policies concerning the use and management of resources. Decision-makers at all levels of society should be able to participate in the design and implementation of any tool that affects the social, economic, and ecological well-being. This ensures successful implementation of the programme.

Conclusions Agenda 21 (UNCED, 1992, Chapter 12) emphasizes land degradation through desertification, and the international community, particularly through UN organizations, has launched several activities to address it. Other aspects of land degradation only receive a casual mention in Agenda 21, and are briefly considered in Chapter 10 under the general heading, “Integrated Approach to the Planning and Management of Land Resources”. In this sense the problem of land degradation has been diluted and as such has not received the global attention that it deserves. Though the stated objective in Agenda 21 is, “to strengthen regional and global systematic observation networks linked to the development of national systems for the observation of land degradation and desertification caused both by climate fluctuations and by human impact, and to identify priority areas for action”, we believe that we have yet to mobilize the soil science community to develop a proactive programme in this area. Land degradation remains a serious global threat but the science concerning it contains both myths and facts. The debate is perpetuated by confusion, misunderstanding, and misinterpretation of the available information. Important challenges are: • • • • • • •

To mobilize the scientific community to mount an integrated programme for methods, standards, data collection, and research networks for assessment and monitoring of soil and land degradation. To develop land use models that incorporate both natural and human-induced factors that contribute to land degradation and that could be used for land use planning and management. To develop information systems that link environmental monitoring, accounting, and impact assessment to land degradation. To help develop policies that encourage sustainable land use and management and assist in the greater use o f land resource information for sustainable agriculture. To develop economic instruments for the assessment of land degradation and encourage the sustainable use of land resources. To rationalize the wide range of terminology and definitions with different meanings among different disciplines associated with land degradation. To standardize methods of assessment of the extent of land degradation.

•

To develop non-uniform criteria for assessing the severity of land degradation.

•

To overcome the difficulty in evaluating the on-farm economic impact of land degradation on productivity.

There is an urgent need to address these issues through a multi-disciplinary approach, but the most urgent need is to develop an objective, quantifiable, and precise concept based on scientific principles.

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References BARROW, C.J. 1991. Land Degradation: Development and Breakdown o f Terrestrial Environments. Cambridge: Cambridge University Press. BEINROTH, F.H., ESWARAN, H., REICH, P.F. and VAN DEN BERG, E. 1994. Land related stresses in agroecosystems. In: Stressed Ecosystems and Sustainable Agriculture, eds. S.M. Virmani, J.C. Katyal, H. Eswaran, and I.P. Abrol. New Delhi: Oxford and IBH. BLAIKIE, P. and BROOKFIELD, H. 1987. Land Degradation and Society. London: Methuen. CHARREAU, C. 1972. Problemes poses par I’utilization agricole des sols tropicaux par des cultures annuelles. Agronomie Tropicale, 27,905-929. CROSSON, P.R. 1997. The on-farm economic costs of erosion. In: Methods for Assessment o f Land Degradation, eds. R. Lai, W.E.H. Blum, C. Valentin and B.A. Stewart. Boca Raton: CRC. DARKOH, M.K. 1995. The deterioration of the environment in Africa’s drylands and river basins. Desertification Control Bulletin, 24,35-41. DREGNE, H.E. 1990. Erosion and soil productivity in Africa. Journal o f Soil and Water Conservation, 45,431-436. DREGNE, H.E., ed. 1992. Degradation and Restoration o f Arid Lands. Lubbock: Texas Technical University. DREGNE, H.E. and CHOU, N.T. 1994. Global desertification dimensions and costs. In: Degradation and Restoration o f Arid Lands, ed. H.E. Dregne. Lubbock: Texas Technical University. DUMANSKI, J., ESWARAN, H. and LATHAM, M. 1992. A proposal for an international framework for evaluating sustainable land management. In: Evaluationfor Sustainable Land Management in the Developing World, eds. J. Dumanski, E. Pushparajah, M. Latham, and R. Myers. IBSRAM Proceedings No. 12, Voi. 2,25-45. Bangkok: IBSRAM. ERIKSSON, J., HAKANSSON, I. and DANFORS, B. 1974. The Effect o f Soil Compaction on Soil Structure and Crop Yields. Bulletin 354. Uppsala: Swedish Institute of Agricultural Engineering. ESWARAN, H. 1993. Soil resilience and sustainable land management in the context of Agenda 21. In: Soil Resilience and Sustainable Land Use, eds. D.J Greenland and I. Szabolcs, 21-32. Wallingford: CADI. ESWARAN, H. and DUMANSKI, J. 1994. Land degradation and sustainable agriculture: A global perspective. In: Proceedings o f the 8,hInternational Soil Conservation Organization (ISCO) Conference, eds. L.S. Bhushan, I.P. Abrol, and M.S. Rama Mohan Rao. Voi. 1, 208-226. Dehra Dunn: Indian Association of Soil and Water Conservationists. ESWARAN, H., REICH, P.F. and BEINROTH, F.H. 1997a. Global distribution of soils with acidity. In: Plant-Soil Interactions at Low pH: Sustainable Agriculture and Forestry Production. eds. A.Z. Moniz, A.M.C. Furiani, R.E. Schaffen, N.K. Fageria, C. A. Rosolem and H. Cantarella, 159-164. (Proceedings of the 4Λ International Symposium on Plant-Soil Interactions at Low pH, Belo Horizonte, Minas Gerais, Brazil.) ESWARAN, H., ALMARAZ, R., VAN DEN BERG, E. and REICH, P.F. 1997b. An assessment of the soil resources of Africa in relation to productivity. Geoderma, 77,1-18. ESWARAN, H, ALMARAZ, R., REICH, P.F. and ZDRULI, P.F. 1997c. Soil quality and soil productivity in Africa. Journal o f Sustainable Agriculture, 10,75-94. ESWARAN, H. and REICH, P.F. 1998. Deseriification: a global assessment and risks to sustainability. Proceedings of the 16AInternational Congress of Soil Science, Montpellier, France. ESWARAN, H., ARNOLD, R. W., BEINROTH, F.H. and REICH, P.F. 2000. A global assessment of land quality. In preparation. FAHNESTOCK, P., LAL, R. and HALL, G.F. 1995. Land use and erosional effects on two Ohio Alfisols. Crop yields. Journal o f Sustainable Agriculture, 7,85-100. GILL, W.R. 1971. Economic Assessment o f Soil Compaction. St. Joseph: ASAE Monograph. GIRT, J. 1986. The on-farm economics of sustainability and public intervention. Canadian Farm Economics, 20, 3—8. GREENLAND, D.J., BOWEN, G., ESWARAN, H., RHOADES, R. and VALENTIN, C. 1994. Soil, Water, and Nutrient Management Research: A New Agenda. IBSRAM Position Paper. Bangkok: IBSRAM.

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HARTEMINK, A.E. 1995. Land fertility decline under sisal cultivation in Tanzania ISRIC Technical Paper 28. Wageningen: ISRIC. JOHNSON, D.L. and LEWIS, L.A. 1995. Land Degradation: Creation and Destruction. Oxford: Blackwell. KAYOMBO, B. and LAL, R. 1994. Response o f tropical crops to soil compaction. In: Soil Compaction in Crop Production, eds. B.D. Sloane and C. Van Ouwerkkerk, 287-315. Amsterdam: Elsevier. LAL. R. 1987. Response o f maize and cassava to removal o f surface soil from an Alfisol in Nigeria. International Journal o f Tropical Agriculture, 5, 77-92. LAL, R. 1994. Tillage effects on soil degradation, soil resilience, soil quality, and sustainability. Soil Tillage Research, 27, 1-8. LAL, R. 1995. Erosion-crop productivity relationships for soils o f Africa. Soil Science Society o f America Journal, 5 9,661-667 LAL, R. 1996. Axle load and tillage effects on soil degradation and rehabilitation in Western Nigeria. I. Soil physical and hydrological properties. Land Degradation Review, 7, 19-45. LAL, R. 1998. Soil erosion impact on agronomic productivity and environment quality. Critical Reviews in Plant Sciences, 17,319-464. LAL, R. and STEWART, B.A., eds. 1994. Land Degradation. Advances in Soil Science. Voi. 11, New York: Springer. LAL, R., BLUM, W.E.H., VALENTIN, C. and STEWART, B.A., eds. 1997. Methods fo r Assessment o f Land Degradation. Boca Raton: CRC. MABBUTT, J.A. 1992. Degradation o f the Australian drylands: a historical approach. In: Degradation and Restoration o f Arid Lands, ed. H.E. Dregne, 27-98. Lubbock: Texas Technical University. MAINGNET, M., ed. 1994. Desertification: Natural Background and Human Mismanagement. Berlin: Springer. MBAGWU, J.S., LAL, R. and SCOTT, T.W. 1984. Effects o f desurfacing o f Alfisols and Ultisols in southern Nigeria. I. Crop performance. Soil Science Society o f America Journal, 48, 828-833. MERMUT, A.R. and ESWARAN, H. 1997. Opportunities for soil science in a milieu o f reduced funds. Canadian Journal o f Soil Science, 77, 1-7. MIDDLETON, N. and THOMAS. D.S.G. 1997. World Atlas o f Desertification. 2d ed. 182 pp. Published for UNEP. London: Edward Arnold. OLDEM AN, L.R. 1994. The global extent o f land degradation. In: Land Resilience and Sustainable Land Use, eds. D.J. Greenland and I. Szabolcs, 99-118. Wallingford: CABI. OLDEMAN, L.R., HAKKELING, R.T.A. and SOMBROEK, W.G. 1992. World Map o f the Status o f Humaninduced Soil Degradation: An Explanatory Note. Wageningen: ISRIC. PIMENTEL, D., HARVEY, C., RESOSUDARM O, R, SINCLAIR, K.. KURZ, D„ MCNAIR, M., C R IS I, S„ SHPRITZ, L., FITTON, L., SAFFOURI, R. and BLAIR, R. 1995. Environmental and economic costs o f soil erosion. Science, 267, 1117-1123. REICH, P.F., NUMBEM, S.T., ALMARAZ, R.A. and ESWARAN, I I. 1999. Land resource stresses and desertification in Africa. (This volume.) RUPPENTHAL, M. 1995. Soil Conservation in Andean Cropping Systems: Soil Erosion and Crop Productivity in Traditional and Forage-Legume Based Cassava Cropping Systems in the South Colombian Andes. Weikershemi: Verlag Josef Margraf. SAJJAPONGSE, A. 1998. ASIALAND Management o f Sloping Lands Network: An Overview o f Phase 3. Network Document No. 23, Bangkok: IBSRAM. SANCHEZ, P.A. 1994. Tropical soil fertility research: Towards the second paradigm. Proceedings o f the 15th International Congress o f Soil Science, Acapulco, Mexico, 1,65-88. SCHUMACHER, Т Е ., LINDSTROM , M.J., MOKMA, D.L. and NELSON, W.W. 1994. Corn yields: erosion relationships o f representative loess and till soils in the North Central United Stales. Journal o f Soil and Water Conservation , 49. 77-81. STOCKING, M. 1986. The cost o f soil erosion in Zimbabwe in terms o f the loss o f three major nutrients. C onsultant’s Working Paper No. 3., Soil Conservation Programme. Rome: FAO Land and Water Division.

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STOORVOGEL, J.J., SMALING, E.M.A. and JANSEN, B.J. 1993. Calculating soil nutrient balances in Africa at different scales. I. Supra-national scale. Fertilizer Research, 35,227-235. UNCED. 1992. United Nations Conference on Environment and .Development. Rio de Janeiro: UN. UNEP. 1992. World Atlas o f Desertification. London: Edward Arnold. UNEP. 1993. Good news in the fight against desertification. Desertification Control Bulletin, 22,3. UNEP. 1994. Land Degradation in South Asia: Its Severity, Causes and Effects upon the People. INDP/UNEP/FAO. World Soil Resources Report 78. Rome: FAO. VIRMANI, S.M., KATYAL, J.C., ESWARAN, H. and ABROL, I., eds. 1994. Stressed Agroecosystems and Sustainable Agriculture. New Delhi: Oxford and IBH. WOODS, L.E. 1983. Land Degradation in Australia. Department of Home Affairs and Environment. Canberra: Australian Government Printers.

Food production and environmental degradation E.M. BRIDGES1andL.R. OLDEMAN2

Despite its considerable environmental impact,fo o d production has not been regarded seriously as a cause o f environmental degradation. This paper examines the impact o f food production on the environment and discusses some o f the known methods fo r limiting detrimental effects o f cropping. Use o f the land fo r fo o d production has meant that in many cases the natural features o f relief vegetation, drainage, and soils have been changed or even completely removed, with an accompanying reduction in biodiversity. In some cases, land degradation has occurred to such a degree that it has already greatly reduced biological productivity, and in the worst examples it has been brought almost to zero. Land degradation is largely the result o f human inability to perceive the problem and o f indifference to it. In terms o f biological capacity, sufficient fo o d can be produced fo r the world population, using currently available technology and without excessive damage to the environment. Future strategies fo r fo o d production must be realistically based, sustainable, and environmentally friendly. Only national governments can provide the conditions in which these strategies can succeed. However, the social and economic conditions o f people must be such that they are able to use the available technology. Without full cooperation ofgovernments, non-governmental agencies, the private sector, and the fo o d producers, the goal offood security will remain elusive and land degradation a threat to the fo o d supplies o f future generations. he history o f agriculture has been the story o f the long-term struggle to provide sufficient food from an environment that has not always been conducive to the growth o f human food crops or the grazing o f domesticated herds. The first comprehensive accounts about how to produce crops successfully in the western world were written by the Greeks and Romans. In medieval times, the knowledge of antiquity was repeated in numerous texts and few advances were made until the agricultural revolution took place in Europe at the end o f the 18th century. Even at this stage o f development the problem of maintaining soil fertility continued. Soils rapidly became depleted o f their store o f plant nutrients and farmers were forced to rest land, or to resort to the addition o f animal and other wastes that still did not adequately restore soil fertility. This system o f agriculture was not sustainable. As a result, Jacks (1954) claimed that the medieval system o f land use in Europe was “designed to keep the forest at bay and to slow down the inevitable exhaustion o f the soil”. Successive advances in the 19th and 20th centuries provided a number of answers to the problems that troubled the medieval farmers. Mechanization gradually removed much o f the hard physical work, applied chemistry provided specific plant nutrients, and biology provided improved strains o f crop plants. The soils however, remain as the medium in which the vast majority of food crops are grown throughout the world. The question arises as to how soils are standing up to the impact o f food production.

T

13 The Green, Hampton, Fakenham, Norfolk NR21 7LG, United Kingdom. E-Mail: [email protected] 2International Soil Reference and Information Centre (ISR1C) P.O. Box 353,6700, AJ Wageningen, The Netherlands. Phone: +31-317-471735, Fax:: +31-317-471700, E-mail: [email protected]

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World land resources There are two established facts relevant to the impact of food production upon the environment. The first is that there is a finite amount of land suitable for food production. Secondly, the world population, reaching six billion in 2000, is likely to reach 8.9 billion by 2050 (UN, 1998). Since 1972 the per capita area of land declined from 0.36 to 0.26 ha in 1992 and regionally, in Southeast Asia, the ratio of cultivated land per person is expected to decline to 0.09 ha by 2020. The minimum amount of land required to provide a person with the minimum vegetarian diet on a sustainable basis is approximately 0.07 ha. (Fresco et al., 1998). The amount of land suited by its relief, soils, and climate to arable cropping is limited to about 11% of the total world land surface. A much larger area, 26% of the world’s land surface, is used primarily for pastoral agriculture. This land is in areas where relief, soil, and climate are less suitable for arable agriculture, but these lands are particularly vulnerable to exploitation by overgrazing and fire, and suffer insect plagues. Expansion of arable agriculture on to these lands requires greater input costs, more risk of crop failure, and increased environmental degradation. Except for limited areas in Africa and South America, there is little opportunity for arable expansion, so most additional food required to feed the burgeoning population has to come from intensification of agriculture on the land already under cultivation. Irrigated lands make an extremely valuable contribution to the world’s food production; 36% o f all crops and 50% of the total grain crop come from irrigated lands.

Use o f natural resources for food production Food production results in changes to the landscape through modification of the landforms, removal of the natural plant and animal species, and manipulation of the water and soils. Some of these actions are beneficial, others are detrimental (Bridges and de Bakker, 1997). Landscape modification: Physical modifications to the land surface have been made throughout history, and locally these have a very significant effect as removal of the natural vegetation, soil, subsoil, and even disruption of underlying geological strata may occur to provide a new level surface. Spectacular examples of terracing may be seen in Indonesia, China, South America, Yemen, and many other parts of the world where the whole landscape has been modified for the production of crops. Important aspects of terracing are that the flow o f water is carefully managed to avoid erosion and almost level surfaces are provided on otherwise strongly sloping land. Landscape alteration also occurs when drainage is modified and the surface o f the land subsides Modification and removal o f vegetation: Throughout history there has been a steady shrinkage of the forested areas as trees have been cut for construction, fuel or to clear land for cultivation. Localized and limited harvesting by indigenous people has little impact, but exploitation on a commercial basis inevitably will result in loss of biodiversity and degradation. It is important that remaining areas of natural forest are conserved for the high value species of plants and animals (often still unrecognized) that inhabit them. Clearance of the tropical rainforest for low-grade pasture for cattle has been criticized sharply as the biological productivity is reduced greatly compared with the natural state. Vegetation absorbs the impact of the rain, some o f which evaporates from leaf surfaces, so if it is removed more rain reaches the soil surface. Without vegetation cover, the soil is unprotected and the impact of raindrops detaches soil particles and erosion is initiated. Infiltration of water is more effective under forest with negligible overland flow and little surface-washing taking place. Also, deeply penetrating roots of trees help stabilize slopes, so landslides are more common following forest removal. Shifting cultivation in tropical rainforests is a

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Food production and environmental degradation

traditional method of land use that is gradually decreasing through population pressure. As population increases the interval between cropping has decreased, so that the fertility is not regained. The net result is loss of woodland and forest and degraded soils. Removal of the natural forest also results in changes in the micro-climate; humidity is reduced, and the range of temperatures increases. On natural grasslands overgrazing encourages the growth of shrubby plants, and reduction of the well-developed rooting system of the grasses no longer provides stability against erosion by wind and water. Deforestation (56,000 km2), overgrazing (49,000 km2), and overcultivation (44,700 km2) are blamed for 85% of desertification in China where the area of degraded land is stated to be increasing at an annual rate of 1,560 km2 (Gong, 1994). Desertification is a widespread result following removal of vegetation in semiarid and arid areas. In the absence of vegetation, coarse-textured soils are particularly vulnerable to erosion by wind, but silt-textured and organic soils may also become mobile when dry windy conditions follow cultivation. In many countries, windbreaks and shelterbelts have been planted to limit the effect of wind erosion. Almost complete removal of the original forest has occurred in most temperate regions of the world where climatic conditions are suitable for commercial crop growth. Reduction o f biodiversity: Natural ecosystems contain a great diversity of species but every plant or animal species lost must be regarded as biological degradation, and loss of key species can be catastrophic. Recent increased extinction rates have several causes including loss of habitat through overexploitation of natural resources, introduction of non-native species, pollution, and conversion of habitat to other uses including food production. Protection of endangered species themselves is inadequate, as without their habitat they cannot survive. This particularly applies to marshlands and other wetlands drained for agriculture and coastal swamps converted to prawn and fish farms. There are many examples of coastal marshes drained for agriculture that have developed acid sulphate soil conditions, with loss of habitat and minimal agricultural potential. Biodiversity exists in several forms; it is associated with natural vegetation and the associated fauna, but the term ‘agricultural biodiversity’ is defined here as the range of genetic variation existing within species of domesticated plants and animals. Agricultural biodiversity takes into account the complex interaction between genetic variation, variation caused by human intervention, and the influence of climate and soils. The success of plant and animalbreeding programmes has tended to restrict the number of local variants of crops and animals in favour of a limited range of improved varieties. Concern is being expressed that the base of the genetic reserve is becoming narrower, and that the genetic diversity of domesticated animals and crops, from which sources of pest resistance and other desirable traits can be drawn, is being lost. An example of a natural gene pool is the Silent Valley of the Western Ghats in India that has contributed 20 major genes for disease and pest resistance in rice. The soil microbial biomass deserves special attention in any discussion on biodiversity. Breakdown of organic debris in the soil is one of the critical soil functions in which many interacting microbial species are involved. Microorganisms are responsible for the recycling of plant nutrients from plant debris as well as the detoxification of pollutants and the suppression of pathogenic organisms. Mycorrhiza are concerned with the effective transport of nutrients from the soil into the plants. Overuse of fungicidal chemicals can disrupt the natural balance of these important soil components, and if overloaded with pollutants, their efficacy is reduced. Unbalanced nutrient management: Soils used for arable crops or grazing lose chemical elements through leaching and root uptake with every crop. This loss without replacement has been referred to in African countries as ‘soil mining’ (Stoorvogel and Smaling, 1990; van der Pol, 1992). The growing of animal feed cash crops in African countries to be sold to farms in Europe is effectively a transfer of plant nutrients from

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African to European soils. Although it is customary to return animal wastes to arable land, these alone are insufficient to replace the lost nutrients. Claims for successful ‘organic farming’ often disguise the fact that additional organic wastes are imported onto the farm to supplement the shortfall of nutrients. The soils o f some regions require essential soil micro-nutrients to be supplied before successful cropping can take place. Salinization: The presence of soluble salts in soils is an increasing problem in cultivated soils of arid and semi-arid regions of the world. Overuse of irrigation water has raised the level of the groundwater and use of irrigation water o f inferior quality and the absence or neglect of adequate drainage facilities have led to salinization. Salts may be leached successfully from saline soils if drainage is improved, but the impermeability of sodic soils makes this difficult, so many are uneconomic to reclaim.

The extent of degradation Following tfie publication of the GLASOD map it became possible for the first time to provide an estimate of the global extent o f human-induced soil degradation (Oldeman et a l, 1991 ; Oldeman, 1994). The total land area is slightly over 13,000 million ha o f which 15%, 1,965 million ha, have been degraded to some degree. If the area under agriculture alone (8,735 million ha) is used for computation, the figure for damaged lands rises to 22%. With the world population set to rise to over eight billion, human impact is bound to increase both for living space and for food. As it is accepted that most food must be produced from land already in agricultural production, the pressures upon the world’s soil resources will grow. Whilst there is a relationship between human population density and soil degradation, it is too simplistic to assume that a high population density automatically means soil degradation will occur. The Keita experiment in Nigeria has shown that a high population density can be instrumental in raising productivity and reducing environmental damage (FAO, 1995). Tiffen et al. (1994) cite a similar case in the Machakos District of Kenya. A study of human-induced soil degradation in South and Southeast Asia (ASSOD), using a more detailed version of the GLASOD methodology, revealed damage to 46% of the total land area of the world. Significantly, 18% showed negligible impact upon food production but 45% had a slight impact. A moderate impact on food production was observed on 24% of the affected land, while 13% showed a strong and, in some instances, extreme impact on food production (Van Lynden and Oldeman, 1997). The threat of land degradation is manifested in several ways and if conservation measures developed in the 1930s were applied, they would greatly reduce the problem. But often farmers do not have the financial and economic incentives to do anything about it. Natural leaching in humid climates combined with overcropping and overgrazing results in infertility on 135.3 million ha, and in arid and semi-arid climates 76.3 million ha are affected by the spread of salinity. Allhough not necessarily the direct result of food production, pollution on 21.8 million ha and acidification o f 5.7 million ha are underestimates of the area of soil problems that cause a limitation of agricultural or forest productivity. Fallout of heavy metals, dioxins, and radioactive nuclides has lowered the biological activity of many soils. Problems of human-induced chemical soil degradation are estimated to affect worldwide 239.1 million ha or 12.2% of the total land area affected by soil degradation. During the second half of the 20thcentury, there was an increase in the use of heavy machinery on farms for cultivation, seeding, and harvesting. The power and gross weight of this machinery has also increased, enabling untimely operations to take place in unfavourable weather conditions. Cultivation naturally leads to a lowering of organic matter content and a weakening of soil structure. The heavy

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F o o d p ro d u c tio n a n d en viro n m en ta l d e g ra d a tio n

B ox 2.1 W hat happens on earth in one m inute?

M. Movillon, B. Richards and H. Tumawis' This is a description of a population clock installed at the Riceworld Museum of the International Rice Research Institute (IRRI) in the Philippines. It is the first display that visitors see when entering the museum. The rapid population growth, as shown by the clock, is crucial to IRRI’s mandate; it is warning how urgently the world needs to increase its supply of rice. This clock is thus an effective educational tool to inform all parties concerned. The clock displays three items, the first two being the most important: (i) the world’s population (now more than 6 billion), which increases with time; (ii) the hectarage of productive land, which decreases with time; (iii) how many people were already living on earth when a visiting person was bom. The clock is computerized using the Java™ programme; the concept originated in Europe.

The increase in population is at present estimated at 80 million persons y ', that is the balance between the numbers of births and deaths. This estimate translates to 150 persons min*1or 2.5 persons s ', which the clock shows continuously, day and night. As the population increase rate will remain rather stable for approximately two decades and will start to decrease subsequently, the clock’s electronic and digital functions will be adjusted accordingly to follow the existing trend. Not surprisingly, the trend in the availability of productive land is opposite to that of population growth. In fact, the world’s productive land is a constantly changing resource. Climatic variations, natural disasters, and human intervention are ceaselessly at work changing the boundaries of productive land that include arable land, pastureland, and forestland. Despite the fact that arable land is continually being lost to urbanization, the total area under cultivation is rising because of deforestation, resulting in the clearing of marginal land, including sloping land, with subsequent loss of fertile topsoil and plant nutrients. The figure illustrating the trend of availability of productive land in the clock shows only how fast the land under cultivation is decreasing through land use conversion and other causes, without counting the new land obtained from the destruction of forests. This decreasing land rate is approximately 510 ha m in 1(=8.5 ha s 1or 4,467,600 ha y 1), and is in reverse proportion to population growth. However, the fact remains that the land lost to other uses normally has higher productivity than the land encroached from forests. The area of land that produces our food, provides us with firewood and construction timber, purifies the atmosphere, maintains precipitation levels, and slows erosion rates is decreasing continuously. 1 R icew orld M useum , The International R ice R esearch Institute, M C PO B ox 3 1 2 7 , Makati C ity 1 271, The Ph ilipp ines. m .m ov illo n @ cg ia r.o rg and h.tum aw is@ egiar.org

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machinery Шеп causes compaction that restricts drainage and impairs root penetration through the soil mass. Human-induced physical soil degradation is mainly a problem in Europe where 33 million ha are affected, but worldwide it amounts to 83.3 million ha or 4.2% of all degraded land.

Options for sustainable land management Reduction o f the impact of crop production on the environment is possible by concentrating upon practices that build upon ecological characteristics such as biological diversity, soil resilience, and efficient energy use and avoiding practices that are destructive to the environment. In future, sustainable food production must meet the goals o f increased production and productivity, reduced impact from pollution, and reduced resource degradation combined with social and economic viability (FAO, 1996). Environmentally sound options for increased productivity of cropping systems are centred on two main approaches that address plant nutrition and pest control in combination with agroforestry and animal husbandry. Integrated plant nutrition schemes: The concept o f integrated plant nutrition schemes is that the nutrients available to the farmer are used in an optimal manner. Nutrients are present in soils, manure, and crop residues as well as being available in the form of mineral fertilizers. Organic matter has the benefit of maintaining better soil structure, support for the micro-fauna living in the soil, and increasing the water­ holding capacity. Many farmers fail to achieve satisfactory yields because they cannot provide crops with nutrients at the right time. Fertilizer applications given at the wrong time can be counterproductive and ecologically unfriendly as they lead to pollution of watercourses and aquifers. It is necessary to take an integrated approach to plant nutrition, to ensure maximum efficiency of use by the crop and to reduce waste. Agroforestry: Agroforestry systems employ a combination of woody perennial species and agricultural crops. Widely known systems include plantation crops, with shade trees over tea or cacao plantations and alley cropping in tropical regions. The admixture of trees and crops is directly beneficial as nitrogen-fixing trees also provide fuel or supplementary fodder and can help diversify farm income. Most home gardens adopt some form o f mixed cropping with fruit trees and vegetable crops. The growth of trees is important in many countries for the fuel that they provide as fuel is necessary for food preparation and preservation. Integrated pest management: Crop losses through insect pests and fungal diseases impose a great limitation on the productivity of farms in many parts of the world. Although synthetic pesticides have enabled higher yields to be obtained, many agricultural pests have acquired a resistance. Effective, economic use of pesticides may be achieved by careful management, rigorous monitoring combined with an understanding o f pests’ life cycles, the use of pest-resistant crop varieties, and the use of chemical control as a last resort. Animal husbandry: As standards of living rise, there is an increasing demand for meat and dairy products. At present livestock consume about 16% of cereals, 20% of starchy foods, and 3% of oilseed grown. As demand for meat and dairy products grows, the requirement for cereals to feed livestock will also grow resulting in further pressure on the land. Use of multi-species grazing ensures better use o f pastures and restriction of stock to feedlots are options that are energy efficient. Mixed plant-animal farming systems are recommended by FAO because they provide flexibility, productivity, and sustainability. Overexploitation of the environment can be avoided, but problems remain in the disposal of slurry. Direct methane emissions from cattle to the atmosphere can be limited by appropriate feeding, and methane from slurry can be captured and used as biofuel.

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Conclusions The evidence of population growth and the impact of human-induced degradation demonstrated during the 1990s implies that pressures upon the soil resource will continue and will increase in intensity. Although food production has environmental consequences, leading to soil and land degradation, it is possible with existing technology to restrict its impact. Land degradation is largely the result of human inability to perceive the problem of, and of indifference or inaction to do anything about it. During the past decade, studies have begun to take place to determine the extent to which yields are being affected by soil and land degradation. Topsoil erosion losses may be simulated by removal of layers of soil from plots and comparing the decrease in yields with the unmodified soil. A nutrient balance can also be determined that takes into account crop uptake, the amount removed by a crop, and natural leaching. Each 100 tons of soil lost per hectare represents a total loss o f2,000-2,500 kg of humus, 200-300 kg of nitrogen, 100-200 kg of phosphate, and between 500 and 1,000 kg of potash. If yields are to be maintained these nutrients must be replaced. Work by Lai (1995) suggests a yield reduction of 2-5% for each millimetre of soil lost. Overall yield reduction caused by past soil erosion in Africa is estimated to be 9% and if current rates are continued, it will amount to 16.5% by 2020. The UN Conference on the Human Environment in Stockholm in 1972, the Brundtland Commission of 1987, the Den Bosch Declaration (FAO, 1991), and Agenda 21 of the United Nations Conference on the Environment and Development (UNCED) (UN, 1992) all stressed the need for the rapid evolution of policies and practical solutions for sustainable development in agriculture and the rural economy. Similar comments were made at the World Food Summit organized by FAO in Rome, ( 1996). UNCED (1992) called for “major adjustments in agricultural, environmental, and macro-economic policy at both national and international levels, in developed as well as in developing countries, to create conditions for sustainable agriculture and rural development (SARD). The priority must be on maintaining and improving the capacity of the higher potential agricultural lands to support an expanding population. However, conserving and rehabilitating the natural resources on lands of lower potential in order to maintain sustainable man/land ratios is also necessary”. It is also desirable and necessary to match the land potential with the use to which it is put; this will require well-documented soil information to fully understand and quantify the impact of food production on the environment. These goals cannot be attained without the fu ll cooperation of the world community. National governments, in partnership with inter-governmental agencies, non-governmental organizations, and the private sector must adopt strategies that are realistically based and environmentally sustainable. The principles of the Den Bosch Declaration and the objectives embodied in Agenda 21 will only be realized if technology and policy are accompanied by human participation, equity, and dialogue, enabling financial mechanisms, empowerment, and incentives to obtain results. These are the pathways towards environmentally sound agriculture and food security. Without them, the available technology and policy tools will not have lasting effects and degradation will grow inexorably. One of the principal duties of professional soil scientists is to draw attention to the global problem of land degradation and to exert our influence to ensure the soil resource remains in good condition for the use of future generations.

Acknowledgments The authors are grateful for the permission of FAO and ISRIC to use material gathered during the preparation of a report on the impact of food production on the environment for the 1996 FAO World Food Summit. A concise version, prepared by Dr. J. Tschirley, was presented to delegates at the World Food Summit in

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Rome as Technical Background Document No. 11. The authors acknowledge with thanks the guidance of Professor L.O. Fresco and the help of Ir M.H.C.W. Starren during this earlier work from which the present paper has been developed.

References BRIDGES, E.M. and DE BARKER, H. 1997. Soil as an artifact: human impact on the soil resource. Land, 1, 197— 215. FAO. 1991. The Den Bosch Declaration and Agenda for Action on Sustainable Agriculture and Rural Development (SARD). FAO/Netherlands Conference on Agriculture and the Environment. Rome/Den Haag: FAO and Ministry of Agriculture, Nature Management and Fisheries. FAO. 1995. The Keita Integrated Rural Development Project. Rome: FAO. FAO. 1996. Food Production and Environmental Impact. Technical Background Document 11, World Food Summit. Rome: FAO. FRESCO, L.O., BRIDGES, E.M. and STARREN, M.H.C.W. 1998. Food Production and Environmental Impact. Technical Report. Wageningen: ISRIC. GONG, Z. 1994. Problem soils and their evolution in China. In: The Collection and Analysis o f Land Degradation Data. Publication 1994/3. Bangkok: FAO-RAPA. JACKS, G.V. 1954. Soil. London: Nelson. LAL, R. 1995. Erosion-crop productivity relationships for the soils of Africa. Soil Science Society o f America Journal, 59,661-667. OLDEMAN, L.R. 1994. An international methodology for an assessment of soil degradation land georeferenced soils and terrain database. In: The Collection and Analysis o f Land Degradation Data. Publication 1994/3, 35-60. Bangkok: FAO-RAPA. OLDEMAN, L.R., HAKKELING, R.T.A. and SOMBROEK, W.G. 1991. World Map o f the Status o f Humaninduced Soil Degradation. 2ded. Wageningen: ISRIC/UNEP. STOORVOGEL, J.J. and SMALING, E.M. A. 1990. Assessment of Soil Nutrient Depletion in Sub-Saharan Africa: 1983-2000. Report No. 28, Wageningen: Winand Staring Centre. TIFFEN, M., MORTIMORE, M. and GICHUKI, F. 1994. More People, Less Erosion. 311pp. Nairobi: ACT Press. UN. 1992. Conference on Environment and Development (UNCED). Agenda 21 : Programme of Action for Sustainable Development. New York: UN. UN. 1998. World Population Prospects 1950-2050 (the 1998 Revision). New York: UN Population Division. VAN DER POL, F. 1992. Soil Mining: an Unseen Contribution to Farm Income in Southern Mali. Amsterdam: Royal Tropical Institute. VAN LYNDEN, G. W. J. and OLDEMAN, L.R. 1997. The Assessment o f the Status o f Human-induced Soil Degradation in South and Southeast Asia. Nairobi/Rome/Wageningen: UNEP/FAO/ISRIC.

з Driving forces and pressures The causes of agricultural land degradation are both natural and human-induced. Land users have little control over climatic processes like intense rainfall, hurricanes, mass movements down mountain slopes, drought, windstorms, and floods, although farming has flourished most in regions with fewer of these pressures. Throughout the world, overcultivation, excess use o f chemical pesticides, overgrazing, excessive removal o f nutrients through crop harvest, clearing o f natural vegetation, and pollution are often responsible for land degradation. However these are merely the proximal causes of degradation. It is possible to reduce some of the impacts o f climate-induced degradation, and to control human-induced degradation, through suitable land use mosaics, management practices, and conservation investments. Effective strategies to improve land quality must be based on a sound understanding of the undo-lying causes o f degradation that lead to unsustainable use. The papers and boxes in this chapter explore these underlying causes. Southgate discusses the effects of population growth on land and resource management. He notes that nearly all developing countries have seen reduced population growth rates in recent decades and that the global population is expected to stabilize by the middle of this century. Population growth appears to have had mixed effects on natural resource management, as under many conditions local people adapt to population pressure through improved resource management. He emphasizes the impor­ tance o f local institutional development in ensuring such adaptive innovation. Drechsel and P a in in g de Vries present evidence that population growth and agricultural intensification have indeed been critical factors in recent land degradation in sub-Saharan Africa. Fallow periods have dropped significantly, yet effective strategies for nutrient replacement under more intensive cultivation have not been developed. They calculate that current economic development relies significantly on nutrient mining. Other economic and social factors affect the incentives for farmers to degrade or improve the land Templeton and S cherr provide evidence from research on tropical hillsides of a highly variable relationship between population pressure and land degradation. They argue that fanner responses to degradation reflect changes in the relative values of land and labour, which are affected by many other factors, such as market integration, access to information and technology, and characteristics o f the

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natural resource. Pandey expands upon this theme with a comprehensive overview of evidence on the policy and institutional factors that affect farmers’ incentives and capability to practise conservation farming. He argues and illustrates how tenure security, market access, price, and macro-economic policies affect incentives for good land husbandry. He concludes that a serious effort to address land degradation must involve the reform of policies that currently encourage degradation. O f course, in some cases farmers and agricultural policy-makers have little control over the factors that lead to land degradation. The case study presented by Im -Erb and colleagues shows how local economic development, in this case commercial shrimp farming in Thailand, can rapidly lead to agricultural land degradation. Policy intervention restricting shrimp farming was required to stop damage from salinization to rice fields and farm trees. Shahid and O m ar illustrate non-agricultural causes of land degradation on an even larger scale. Their case study o f Kuwait attributes the most severe land pollution, compaction, and loss o f vegetative cover to military activities, gravel mining, and oil production. It is increasingly recognized that many degraded landscapes result more from harsh climatic conditions than human mismanagement. The Kuwaiti case documents the role of natural forces in water and wind erosion and salinization. Helldén and Ólafsdóttir draw on historical evidence to show that widespread land degradation in parts o f Iceland was due more to climatic factors than to agricultural practices. A similar re-thinking of the determinants of land degradation in the Sahel has taken place, as other papers in this volume (e.g. Sidahmed) will document. Land degradation may accelerate with global warming, as a result o f expected increases in the severity o f weather events.

S.J. Scherr and I.D. Hannam

Demographie transition, resource management, and institutional change D. SOUTHGATE1

Rapid population growth is symptomatic o f the transition that Africa, Asia, and Latin America are makingfrom a demographic equilibrium characterized by high birth and death rates to an equilibrium in which fertility and mortality are both low. Driven by higher living standards, improved educational attainmentt and other changes, this transition still has the longest to run in rural areas. This is why large numbers ofpeople have been migrating to cities and agricultural frontiers. Population growth in the countryside also adds to the pressure on so ilw a ter, and other environmental inputs to agricultural production. It is frequently the case that natural resource depletion occurs as human numbers begin to increase. But as natural capital grows ever more scarce, adaptation o f agricultural and environmental management system s takes pla ce, with ways being found to conserve the environment while simultaneously enhancing crop and livestock output. Environmentally sound adaptation is greatly impeded by the weakness o f local institutions, resulting either from mounting demographic pressure or from the undermining o f those institutions by outside authorities. or practically all o f its existence as a species, humankind’s survival, while not exactly tenuous, was never completely assured. Nearly everyone dedicated most o f his or her time to the gathering, hunting or raising o f food. Crop failure was never a remote possibility. Neither were sharp declines in wildlife populations, which were a source o f protein. Accordingly, hunger and disease were a constant threat to life. People proved to be marvelously adept at coping with conditions that were, by modem standards, harsh. Wherever possible, sources o f food were diversified. For example, those living in or close to mountains grew familiar with nearby environmental niches and the sustenance that each niche could provide. Local biodiversity is lower in temperate grasslands and the globe’s high latitudes, which obliged the people inhabiting those places to become expert at acquiring whatever could be eaten. There has been another dimension to coping and survival, one having to do with mechanisms for cooperation. Indeed, it is no exaggeration to say that these mechanisms played a major role in the success o f our remote ancestors. Regardless o f what induced human precursors to descend from the trees and to walk upright, cooperation among individuals was needed to capture prey that usually was more fleet of foot. In addition, groups o f individuals that found ways to share personal risks, taking care of the sick and injured, for example, possessed a clear advantage over socially atomized populations. The advantages o f cooperation multiplied as agriculture spread. Hayami ( 1990) calls attention to the rules for water allocation that villages in Southeast and East Asia have developed and employed to contain the local spillovers that could interfere with irrigated rice production. Due to their value in resolving Department of Agricultural Economics, Ohio State University, 2120 Fyffe Road, Columbus, Ohio 43210, USA. Phone: +1-614-292-2432, Fax: +1-614-292-4749, E-mail: [email protected]

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awrf

institutional change

conflicts and sharing risks, rules governing access to and management of natural resources, institutions, as many economists call them, have arisen in just about every place where crops and livestock have been produced. The emergence of agriculture, which occurred in various parts of the world several thousand years ago, was accompanied by an increase in human numbers. Together, these inter-related events stimulated the further development of institutions, including the governing of natural resource management (NRM). In modem times, however, population growth has accelerated markedly. Local institutions, serviceable and ubiquitous though they have been, have been severely challenged. More than occasionally, they have proved unable to bear the strain. This paper reviews the inter-relationships between population growth, NRM, and local institutions, and the current challenges to the capacity of local institutions to facilitate adjustment of NRM under population growth.

Patterns of population growth Population growth and changes in the spatial distribution of populations are obviously key driving forces for change in NRM and natural resource conditions. In considering the past and likely future roles of population in explaining land degradation, however, it is critical to understand the ‘demographic transition’ and the migration that often accompanies an increase in human numbers.

Demographic transition For most of human history, population growth followed the pattem described two hundred years ago by Malthus (1798). Food availability would increase, because of an improvement in agricultural technology, an expansion of trade, territorial acquisition or some other reason. People would respond by procreating, their numbers increasing exponentially. This could not go on indefinitely, given that food supplies only grew in a linear fashion. Eventually, demographic equilibrium (i.e. no natural increase or decrease) would be reached, with birth and death rates falling into line with each other. During the 19thcentury, a different engine of demographic change was clearly at work. In Europe and other affluent places, a shift was taking place from one state of demographic equilibrium to another. The pre-transition equilibrium, observed in traditional, mral societies, had been characterized by a high incidence of mortality and fertility, i.e. annual birth and death rates averaging 50 to 60 per thousand of the population. Much lower rates, in the order of 10 to 15 per thousand, were to be observed later after the transition had mn its full course, in societies that had grown wealthy, educated, and mainly urban. The process of achieving the latter equilibrium, which has been completed or is currently under way in virtually every part of the world, always starts with a decline in the incidence of mortality. Conceivably, birth and death rates could fall simultaneously. However, this has never been the case. Instead, the total fertility rate (TFR), which is defined as the expected number of births per woman of child-bearing age, exhibits little change for at least a few years after the onset of demographic transition. Even after the TFR has started to trail off, as it always does in response to increased education (especially among women), higher living standards, urbanization, improved access to birth control, and other factors, the number of births per thousand population can remain stubbornly high for many years. This is because the average age of a population undergoing demographic transition is low, which means that large numbers of females are reaching sexual maturity at any particular time. Even though, on average, they have fewer children than their mothers and grandmothers did, birth rates will not diminish very much and natural increase will continue. Another characteristic of a young population, which contributes to natural increase, is that

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death rates are veiy low , lower, in fact, than the rates observed once the transition is over and people are older and therefore m ote susceptible to life-threatening disease. These general features o f the shift from one demographic state o f equilibrium to the other are depicted schem atically in Figure 1. By today’s standards, the demographic transition that various countries undertook more than one hundred years ago and have now com pleted w as relatively gradual. Prior scientific understanding o f factors contributing to the loss o f life w as rudimentary, o f course. Furthermore, new information about linkages between medical and sanitation improvements, on the one hand, and exposure to disease, on the other, took quite a long time to dissem inate. Accordingly, many decades were required for death rates to fall from pre-transition to modem levels. M ortality d eclin e has b een m uch m ore sudden in the developing world, where the traditional equivalence between births and deaths was maintained into the 20* century. Since containing fatal disease freq u en tly has in v o lv ed ap p lyin g m ed ical and sanitation practices already known in other places, as opposed to developing these practices from scratch, very rapid progress often has been made. Inoculating the vast majority o f a country ’s children, for exam ple, som etim es has been accom plished in a few w eeks or months. Virtually overnight, then, age-old threats to life have been eliminated. Between quick reductions in death rates and lagged declines in the number o f births, natural increase has been dramatic in the developing world during the past several decades. At one tim e or another, population growth in various African, Asian, Figure 1. The demographic transition. and Latin American countries has exceeded 3% per annum. Doubts about demographic equilibrium ever being reached in the developing world have been expressed in the past. They are no longer circulated very w idely, at least in professional circles. Recent evidence establishes incontrovertibly that there are few places where TFRs remain at pre-transition levels. Even in sub-Saharan Africa, where most people are poor, uneducated, and live in rural areas, w om en have begun to have few er children. In much o f Asia and Latin America, urbanization, incom e growth, the spread o f formal education, and dim inished infant mortality are causing households to make use o f anti­ contraceptive technology, w hich is much more available than it used to be. Accordingly, population growth now has to do mainly with the predominance o f people in their teens, tw enties, and thirties, who bear children and are not very susceptible to mortal illness. Given these demographic changes in the developing world, which accounted for the lion’s share o f global population growth during the 20* century, as w ell as outright population decline in many affluent nations, human numbers have stopped increasing exponentially. Indeed, most experts doubt that the human population, w hich just surpassed six billion, w ill ever double again. The most likely scenario is that growth w ill cease, at a total population o f 10.0 to 11.5 billion, approximately one hundred years from now (Bos eta i., 1994; United Nations Population D ivision, 1996).

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Migration in response to demographic transition in the countryside Obviously, the incidence of overall population growth is far from uniform. Demographic transition began at different times in various places. Many local factors influence the shift from the pre-transition equilibrium to the post-transition one. Fertility still exceeds mortality by a wide margin among some groups, and will continue to do so for a long time to come. Many, if not most, of the latter groups inhabit the African, Asian or Latin American countryside. The contrast between Colombia and Tanzania is instructive in this regard. The former nation is largely urbanized, 74% of the population living in incorporated cities and towns. By contrast, nearly three-quarters of all Tanzanians reside in rural areas. Given this discrepancy, which coincides with a large gap between the two countries’ per capita GDPs (2,140 versus 170, in 1996 US dollars) and elevated illiteracy in Tanzania, there is a great difference between the two countries’ TFRs: 3.0 births per Colombian woman and 5.7 births per woman in Tanzania (Population Reference Bureau, 1999). One obvious response of rural people to mounting population density is to move. This is what tens of millions o f Africans, Asians, and Latin Americans have elected to do. Cities have been, and continue to be, the destination o f most migrants leaving the countryside. It is for this reason that dozens of countries have been transformed quite suddenly from predominantly rural to mainly urban. Ecuador is a case in point. As recently as the 1974 census, three-fifths of the national population resided in rural areas. But by 1990, the urban share had risen to 55% (Southgate and Whitaker, 1990,14). Although smaller numbers o f people are involved, there is another migratory response to natural increase in rural areas, which is to move to forested hinterlands. Tens o f thousands of Ecuadorians have chosen this option in recent decades, which helps to explain why rural population densities have not risen appreciably in many parts of the country. Meanwhile, demographic pressure has mounted significantly in the Amazonian lowlands of eastern Ecuador, which are traversed by active frontiers of colonization (Southgate and Whitaker, 1990,13-14).

The resource impacts of rural population growth Not every rural African, Asian or Latin American responds to demographic transition by leaving for a city or an agricultural frontier. Thus, population density has been rising in many areas. There is a wide spectrum of views concerning the environmental consequences o f this change. Some argue that the increased intensity o f farming observed where rural population densities are rising poses a severe threat to various natural resources (Ehrlich et al., 1993). Others take an opposing view, contending that mounting demographic pressure often induces the adoption o f agricultural practices that raise output while simultaneously improving resource management (Hyden et al., 1993). Having reviewed more than 70 studies conducted in the Himalayas, Andes, East Africa, and other hilly or mountainous parts of the world, Templeton and Scherr ( 1999) conclude that the relationship between demographic change and land resources is neither uniformly negative nor always positive. Instead, the linkage is best captured by a U-shaped function (Figure 2) relating land productivity, which is measured on the vertical axis, to relative land-labour costs, which are measured on the horizontal axis. Before the onset of demographic transition, rural population density is low. From an economic perspective, labour is much more scarce than land, which by definition is relatively abundant. As human numbers increase, land’s relative value starts to rise. But because labour continues to be much more scarce, people find it expedient to respond to commodity demand growth by depleting the renewable resources that surround them. For example, fallowing cycles might be abbreviated or erodible lands might be cleared for crop production. Also, incentives to invest in conservation measures are weak. All this is reflected in the initial, downward-sloping part o f the U-shaped curve.

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As demographic pressure builds and environmental degradation takes a toll, land becomes progressively more scarce. Past some point (i.e. the nadir of the U-curve), additional population growth causes more effort to be dedicated to the management of natural resources, which are now the limiting factor of production. So it is that some of the most productive land in the developing world is found precisely where population density is very high. The terraces that have been put in place in Southeast Asia, to conserve soil and to derive more benefit from water supplies, are an example of this phenomenon. While conceding that there are exceptions to the U-shaped relationship between land productivity and relative land scarcity depicted in Figure 2, Templeton and Scherr (1999) point out that there is considerable evidence that rural population growth first results in land degradation, but later contributes to improved land productivity. The downward-sloping portion of the U-curve is illustrated by the finding of Cruz et ah (1992) that, between the early 1960s and middle 1980s, 3.0% annual growth in the upland population o f the Philippines coincided with increases in cropped area averaging 2.5% per annum. Most o f the land that was cleared is steeply sloped, and hence highly erodible. Another example of increased rural population density coinciding with the depletion of land resources has to do with planting frequency. In particular, Turner et al. (1977) have documented that fields are used more often for crop production in a statistical analysis of secondary data for 29 groups o f subsistence cultivators in various tropical settings. If fallowing cycles fall below the time needed for land to recover between one cropping period and the next, and if there is no change in technology, land quality will deteriorate. The specific population density at which additional human numbers lead to higher, not lower, land productivity cannot be identified precisely. U n d o u b ted ly , it v aries from place to place. Nevertheless, elevated densities (i.e. those above 100 people km*2) are, as Templeton and Scherr (1999) indicate, correlated with terracing, composting, and other improvements. This correlation is documented in a study of 57 farming communities in Asia, Africa, and Latin A m erica. In particular, Pingali and Binswanger (1987) have found that agriculturalists who use land at least twice a year, because the local population and its food needs are high, are more inclined to make land investm ents and to use inorganic fertilizer than those who farm their land only once a year. The U-shaped function also applies to Figure 2. Land management and the relative scarcity o f livestock production. Domesticated animal densities land and labour. increase as human population density rises from low to medium. Quite often herders drive their livestock onto open access land not previously used for grazing, thereby exacerbating erosion and soil compaction problems. But as human numbers continue to grow, reaching moderate to high densities, crop production becomes a more important land use. Under these circumstances, less extensive methods o f livestock production are required. Many o f these methods, such as using sloping land to grow fodder that is harvested periodically and fed to domesticated animals, have positive environmental repercussions. Changes o f this sort have occurred during the past several decades in the Machakos District o f Kenya (Tiffen et al., 1994).

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Finally, if the hypothesis of a U-shaped relationship between land productivity and land’s relative scarcity value is valid, population decline, resulting for example from accelerated emigration, can lead to impaired land quality under certain circumstances. Blaikie and Brookfield ( 1987) point out that this sequence of events is observed in a number o f hilly regions where land improvements have been made but where outside employment is drawing away labourers, either permanently or temporarily. As new work options present themselves, the opportunity cost of labour inputs to conservation rises. Furthermore, population decline diminishes the value of natural resources, and therefore the benefits of conservation.

The role of institutions A simplistic and pessimistic perspective on human interaction with the natural environment derives from the premise that nature has some intrinsic capacity to support human life. As long as our activities are consistent with the environment’s carrying capacity, however that capacity is defined and measured, then these activities are considered to be ‘sustainable.’ But if human activity grows to exceed carrying capacity, because there are more people or because per capita demands on the environment have risen and are therefore deemed unsustainable, then sooner or later a correction is bound to occur. This view o f the sustainability issue leads to an interesting line of inquiry, which is to determine exactly what sorts of human pressure the natural environment in different places can withstand. As a rule, the findings of this research are conditional. That is, one can determine the maximum agricultural output that a certain parcel o f land can yield indefinitely, given existing technology. However, switching to a different technology, as farmers do repeatedly, allows for a sustainable rise in yields. Recognizing this response, one appreciates just how difficult it is to identify the precise output flow that a given landscape is inherently capable of producing. Important though it is, technological change is not the only way that humans—who of course are innately adaptable beings—manipulate nature to their own ends. As stressed at the beginning of this paper, farming communities also institutionalize rules of access to and management of natural resources, so as to raise living standards in the face of environmental constraints. O f course, institutional development typically accompanies technological change and vice versa. For example, irrigated rice production in the terraced hills o f Southeast Asia is inconceivable in the absence of rules that local communities have worked out to allocate water. Population growth in the countryside, at least low to moderate growth, fosters the institutional change needed to avoid deterioration o f the local environment. For example, Hayami and Ruttan (1985) document that increasing human numbers in the Japanese countryside before the 19th century caused villagers to agree to rules governing wood extraction from communal forests as well as schemes for mobilizing collective labour to maintain those resources. However, demographic change can also be a cause of institutional deterioration, especially when that change is sudden. For example, a rapidly growing population might find it difficult to agree on rules to protect scarce natural resources, or even to continue abiding by rules that have been respected in the past. Damage to institutions is particularly likely where population growth has to do largely with immigration, along agricultural frontiers for example. This is because institutional conservation, which is favoured where people are interested in maintaining longstanding relations with one another, is not to be expected where large numbers of people with no prior local attachments are arriving on the scene. Traditional institutions being as resilient as they are in stable communities, their loss typically has not been caused exclusively by population growth, which, to repeat, augments environmental values and thereby strengthens incentives to put local resource management regimes in place. More often than

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not, damage to local institutions has been the result o f subversion, frequently intentional, by outside authorities. Spanish conquest o f the Incan and Aztec empires, in the early 1500s, resulted in the wholesale appropriation o f vast tracts o f land. This experience was to be repeated during the next 400 years in Asia, Africa, and Oceania. European empires ebbed after the turn of the 20th century. In recent decades, the source of subversion has shifted to national capitals in the developing world. The problem is illustrated by the nationalization o f ‘panchayat’ forests in Nepal in 1958. Perhaps influenced by early contributions to the economic literature on open access problems, in which no distinction was made between resources owned by no one at all and common properties (which by definition are owned by a well-identified group that typically observes its own resource use and management guidelines), authorities in Kathmandu decided that tree-covered land should belong to the government. Had the public sector actually invested in management and controlled access, environmental benefits might have accrued, although the injustice of taking village resources without compensation would have had to be redressed. However, no management occurred. Neither was access controlled. All the results o f nationalization, then, were negative. To be specific, forests in which villagers previously had some sort o f ownership stake—an imperfect one— one might argue, were converted into a truly open access resource (Bromley and Chapagain, 1984). Traditional institutions are not a panacea for all environmental problems in the developing world. Hayami (1990), for example, points out that village-level arrangements do not address conflicts encompassing an entire river basin, in which a plethora o f agents and interests are likely to be involved. Nevertheless, the complementarity between social capital and environmental wealth is better appreciated now than it used to be. Follies o f the sort that Nepal’s government engaged in 40 years ago still occur. However, there is a growing realization that environmental degradation can easily occur if local institutions are tampered with, dismantled or disregarded. Likewise, it is now recognized that environmental damage that seems to result from mounting demographic pressure often has institutional roots. A case in point in many settings is the excessive colonization o f tropical forests that national governments treat as open access resources, thereby abrogating the rights and destroying the institutions o f long-term forest dwellers.

Summary and conclusions Though less widely accepted than it used to be, the neo-Malthusian view o f population trends continues to circulate. At a global level, this view is clearly erroneous. No longer increasing exponentially, total human numbers have passed the inflection point o f the demographic transition. Due to urbanization, better educational attainment, and other factors, women throughout the world are having fewer children than their mothers and grandmothers did. Population growth, which continues but at a slackening pace, now has to do mainly with large cohorts o f young people—the result of high human fertility in past decades. Even with the demographic momentum resulting from low average age, there will probably never be another doubling o f the human population. This is not to deny that demographic pressure is still increasing at a rapid pace in many countries and areas. The environmental changes experienced in those places vary. Where natural resources are still relatively abundant, population increases usually lead to resource depletion. But where cumulative growth has made environmental wealth scarce, the response is often to improve resource management. To be sure, there are exceptions to this general pattem. As emphasized in this paper, much o f the variability in the response to increased resource scarcity has to do with community-level institutions. Interest in the contribution that local institutions can make to sound environmental management is fairly recent, and critical research needs must still be addressed. Among these is investigation o f the challenge

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Demographie transition, resource management, and institutional change

of strengthening or establishing community arrangements where they have been undermined in the past or never have existed. There is little real guidance about how to accomplish this, although one supposes that the fundamental medical ethic—-first, do no harm—applies fully. With respect to local institutions, harm usually takes the form o f an imbalance between national governments* claims on resources and what the public sector is truly able to control and to manage. Quite often, achieving the right balance requires restoring or strengthening local communities* prerogatives.

References BLAIKIE, P. and BROOKFIELD, H., eds. 1987. Land Degradation and Society. London: Methuen. BOS, E., VU, M., MASSIAH, E. and BULATAO, R. 1994. World Population Projections, 1994-95 Edition. Baltimore: Johns Hopkins University Press. BROMLEY, D. and CHAP AGAIN, D. 1994. The village against the center: resource depletion in South Asia. American Journal o f Agricultural Economics, 66,868-873. CRUZ, M., MEYER, C., REPETTO, R. and WOODWARD, R. 1992. Population Growth, Poverty, and Environmental Stress: Frontier Migration in the Philippines and Costa Rica. Washington, D.C.: World Resources Institute. EHRLICH, P., EHRLICH, A. and DAILY, G. 1993. Food security, population, and environment. Population and Development Review, 19,1-32. HAY AMI, Y. 1990. Community, market, and state. In: Agriculture and Governments in an Interdependent World: Proceedings o f the Twentieth International Conference o f Agricultural Economists, eds. A. Maunder and A. Valdės, 3-14. Aldershot, England: Dartmouth Publishing. HAYAMI, Y. and RUTTAN, V. 1985. Agricultural Development: An International Perspective, Revised and Expanded Edition. Baltimore: Johns Hopkins University Press. HYDEN, G., KATES, R. and TURNER II, B.L. 1993. Beyond intensification. In: Population Growth and Agricultural Change in Africa, eds. B.L. Turner, G. Hyden and R. Kates, 401-439. Gainesville: University of Florida Press. MALTHUS, T.R. 1798. An Essay on the Principle o f Population. Amherst, NY: Prometheus Books. (Re-printed in 1998.) PINGALI, P. and BINSWANGER, H. 1987. Population density and agricultural intensification: a study of the evolution of technologies in tropical agriculture. In: Population Growth and Economic Development: Issues and Evidence, eds. D.G. Johnson and R.D. Lee, 27-55. Madison: University of Wisconsin Press. POPULATION REFERENCE BUREAU. 1999.1998 World Population Data Sheet. Washington, D.C.: Population Reference Bureau. SOUTHGATE, D. and WHITAKER, M. 1994. Economic Progress and the Environment: One Developing Country ’s Policy Crisis. New York: Oxford University Press. TEMPLETON, S.R. and SCHERR, S.J. 1999. Effects of demographic and related microeconomic change on land quality in hills and mountains of developing countries. World Development, 27,903-918. TIFFEN, M., MORTIMORE, M. and GICHUKI, F. 1994. More People, Less Erosion: Environmental Recovery in Kenya. Chichester: John Wiley & Sons. TURNER II, B.L., HANHAM, R. and PORTARARO, A. 1977. Population pressure and agricultural intensity. Annals ofthe Association o f American Geographers, 67,384-396. UNITED NATIONS POPULATION DIVISION. 1996. World Population Prospects: The 1996 Revision. New York: UN Population Division.

Land pressure and soil nutrient depletion in sub-Saharan Africa P. DRECHSEL' and F.W.T. PENNING DE VRIES12

Soil nutrient depletion and other forms o f soil degradation threaten future soil productivity, especially in sub-Saharan Africa (SSA). Even under optimistic assumptions, data from SS A show that Ξ­ Ι 2 years offallow are needed to replenish the nitrogen pool after 2-3 years o f cropping. This implies that fo r sustainable soil management at the current level o f fertilizer and manure inputs, it would only be possible to cultivate annually about 20% o f the arable land. This situation rarely exists today in SSA where, through population pressure, the average percentage o f land cultivated is about 60%. The data illustrate that soil conservation and improved nutrient management are crucial but can only reduce the speed o f nutrient depletion. Availability and efficient use o f farm external inputs will be required to make a broad impact. Data from 37 countries in SSA show a significant relationship between nutrient depletion and land pressure indicators and thus illustrate the unsustainable population-agriculture-environment nexus on the continent. Nutrient depletion accounts fo r about 7% o f the agricultural share o f the average gross domestic product o f SSA, indicating nutrient mining is a significant factor in current economic development. utrient depletion, or nutrient mining, refers to a net loss of plant nutrients from the soil or production system because there is a negative balance between nutrient inputs and outputs. Nowhere is nutrient depletion more widely found, and of more serious concern to food security, than in subSaharan Africa (SSA) (Cleaver and Schreiber, 1994; Smaling, 1993). Africa’s population continues to grow at higher rates than on any other continent. Estimates indicate that by 2020, Africa will need to import more than 30 million tons o f cereal each year to fill the gap between demand and supply (Henao and Baanante, 1999). Soil fertility depletion is considered as the main biophysical limiting factor for raising per capita food production in the majority of small African farms (Sanchez et al., 1997). For nations whose economies depend mostly on agriculture, unchecked soil fertility decline poses a major threat to economic development. Even in the Sahelian area, it is often the availability o f nutrients that limits productivity and not the water supply (Penning de Vries and Djiteye, 1982). While there is much literature on soil degradation in general and soil erosion in particular, there is very little reference to nutrient depletion, especially its relation to population density and economic growth. The objectives of this paper are:

N

1 IWMI Ghana Office, c/o University of Science and Technology, Kumasi, Ghana. Phone & Fax: +233-51-60206, E-mail: [email protected] 2 IWMI Southeast Asian Regional Office, P.O. Box 9-109, Chatuchak, Bangkok 10900, Thailand. Phone: +66-2-9412500, Fax: +66-2-561-1230, E-mail: [email protected] Note: On 1 April 2001, all of IBSRAM’s programmes merged with those of the International Water Management Institute (IWMI) based in Sri Lanka.

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Land pressure and soil nutrient depletion in sub-Saharan Africa 1. To provide an overview assessment of soil nutrient depletion through analysis of the nutrient balance. 2. To demonstrate the relation between nutrient depletion and population density. 3. To indicate the macro-economic impact o f soil nutrient depletion.

The causes o f nutrient depletion and the different strategies and policies for soil fertility conservation are only briefly discussed, as they have been described comprehensively and summarized elsewhere, for example, by Donovan and Casey ( 1998) and Scoones and Toulmin ( 1999).

The nutrient balance as an indicator of soil degradation In tropical slash-and-bum systems, the common indicator of nutrient depletion is yield decline after only a few cropping seasons without external inputs. Decreasing possibilities of shifting cultivation and reduced fallow periods raise the risk of yield decline and demand methodologies to assess and monitor land quality and its change over time. The classical approach is through analysis and comparison of soil fertility parameters between different treatments in experimental field trials, preferably over several seasons or years. However, such experiments are costly to maintain and are influenced by rainfall variability. It is difficult to select analytical methods that will measure changes in the most significant soil nutrient stocks. Alternatively, the soil may be considered as a ‘black box’ and the nutrient inflows and outflows analyzed. This approach assumes that, in the long run, soil fertility is determined mostly by the degree to which nutrient exports (e.g. uptake by crops plus losses attributed to processes such as leaching, erosion, runoff, volatilization, and denitrification) are balanced by nutrient imports (supplied by fertilization or dry and wet deposition for example). Quantification of the different nutrient flows allows calculation of the net difference o f the inputs and outputs o f nutrients, i.e. the nutrient balance. This approach allows, besides quantification and valuation o f the different processes of nutrient depletion, modelling and identification of options to prevent nutrient mismanagement. Consequently, the nutrient balance model was short-listed as a potential land quality indicator (Pieri et a l , 1995). In a landmark publication, Stoorvogel and Smaling ( 1990) quantified nutrient depletion per land use class at the national and sub-continental scale for nearly all countries o f SSA. The nutrient balance was described for N, P, and K with different input and output factors. A range of studies followed, focusing on finer-tuned farm and village level estimates of nutrient flows and budgets (cf. Drechsel and Gyiele, 1999; Scoones and Toulmin, 1999). Stoorvogel and Smaling (1990) showed that nutrient losses are only partially compensated for by natural and man-made inputs, thus the annual NPK balances for SSA are negative, with minus 22-26 kg N, 6-7 kg P20 5, and 18-23 kg K20 ha’1у 1from 1983 to 2000. As the authors aggregate differently available nutrient pools, a wide variety of land use systems, crops, and agro-ecological zones in each country, the data are certainly only approximations of the problem. Scoones and Toulmin (1998) highlight some of the shortcomings and challenges of the nutrient budget approach.

Nutrient depletion vs. fallow input Nutrient losses do not imply any problem as long as adequate fallow periods are possible for soil nutrient replenishment. The data presented by Stoorvogel and Smaling (1990) consider fallow land and related inputs through dust, rain, weathering, etc. If we consider the nutrient flows on actual harvested cropland only (i.e. without fallow land and fallow inputs), nutrient depletion rates in upland3SSA double (42 kg N and 13 kg P20 5and 34 kg K20 ha*' y 1).

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57

Stoorvogel and Smaling (1990) assume a positive balance for fallows with a low annual gain of 2 kg N, 2 kg P20 5, and 1 kg K20 ha*1. This implies that a fallow period of 21 years is necessary to balance the negative budget of 42 kg N through just one year of cropping, while P replenishment would ‘only’ need about six years o f fallow. Even if we assume a much higher fallow input of about 10 kg N ha'1 y*1(cf. Van Duivenbooden, 1992), it would still take about eight to 12 years to balance the N deficit of a cropping period of 2-3 years. With respect to P and K there might be some variations between soil types and climates, but the literature on this subject is scanty in SSA. Using the factor R to represent the ratio between cropping and fallow periods334, we calculate an overall R threshold for natural (fallow) N replenishment o f about 0.2 at the current level o f fertilizer and manure input. In other words, for sustainable soil management at the current level o f inputs only 20% of the arable land can be cultivated annually. Today this situation is rare in SSA. In 1983, the average R value was about 0.55 and is projected to be about 0.60 in 20005. Thus most farming systems mine nutrients, as they cannot afford the required fallow periods. The remaining land reserves are often of low inherent fertility, poorly regenerated or difficult to access. Most soils with higher fertility, such as lowland soils with natural nutrient input through sedimentation, Nitisols or Andosols, are in most cases already under cultivation.

Relative importance o f the different depletion processes According to the data provided by Stoorvogel and Smaling (1990), crop removal (product and residues) and erosion appear to be the predominant causes o f nutrient depletion (Figure 1). Together, they account for about 70% o f all N losses, nearly 90% of all K losses, and 100% of the P losses.

Figure 1. Composition of N, P, K outputs on rainfed soils of SSA. The figure summarizes all output data provided by Stoorvogel and Smaling (1990) per country and the different FAO land/water classes for rainfed land (FAO, 1986). 3 'Upland* comprises all soil types with the exclusion of naturally flooded lowlands with extra nutrient supply through sedimentation.

4 R - years of cultivation/(years of cultivation + fallow years). 5 Land scarcity is not the only cause of high R values. Access to social and economic infrastructure, tenure systems or inheritance patterns may also restrict farmers* free access to land.

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Land pressure and soil nutrient depletion in sub-Saharan Africa

In comparison with erosion, nutrient leaching appears to be a minor contributor to N and K depletion. Only in 6% of all cases, mostly from areas of humid SSA with very low erosion rates, are N and K losses through leaching of similar or higher importance than erosion. Leaching losses certainly increase with the amount of fertilizer or (green) manure applied and can be more significant for nutrients other than N, P, or K. Substantial leaching losses of Mg and Ca, mobilized by nitrate, are described by Pieri ( 1985,1992) and Poss and Saragoni (1992). Even if upland SSA scenarios are calculated with zero erosion, runoff, and leaching, there is still a negative N and K balance because o f the amount of nutrients lost in the harvested crop and its residues. The data indicate that although soil conservation is crucial, it can only reduce the speed of nutrient depletion. This corresponds with empirical evidence; although soil conservation measures are usually very effective in reducing soil erosion, a yield impact is often barely observed if no other inputs are provided simultaneously (Grohs, 1994; Steiner and Drechsel, 1998; Herweg and Ludi, 1999). An exception will be an increased availability o f soil moisture in water constrained production systems.

Relation between nutrient depletion and land pressure Land quality refers specifically to the capacity of land for sustainable use and environmentally sound management. Pressure on land can lead to various forms of land quality degradation, although the relationships may lack consistency (cf. Scherr et al., 1995). FAO estimates of the actual supporting capacity of land range from 10 to 500 persons km*2(Henao and Baanante, 1999). Critical levels are determined by the availability of (or access to) resources, such as fertile land, water, fuelwood or capital and the growing needs of an expanding population. Farmers try to overcome these constraints by moving to other places where land may be available; by searching for better market conditions or off-farm income; or by seeking innovations and technical solutions (cf. Barbier, 1988). Case studies, for example from the West African savannah, show that in agricultural areas with similar soil, climate, and cultural methods, land may be more subject to degradation where the rural population is of the order of 30 persons km*2 than it is with 80 persons km*2. In fact, in some areas with abundant land, extensification (with higher return to labour but ‘squandering’ of land resources) can enhance soil degradation, while in other areas some rural societies have evolved site-adapted production systems which can satisfy their needs without obvious soil degradation (Pieri, 1992). A famous example from East Africa of farmers’ adaptation to changing conditions was documented by Tiffen et a l ( 1994). The authors describe reduced soil erosion under fivefold population increase through improved farming methods. However, they failed to note that conservation of soil and water may actually increase the potential for nutrient mining through crop uptake (Simpson et a l , 1996). Figure 2 shows the relationship between nutrient depletion rates and rural population densities at the national level6(R2=0.70, p 20 kg h a 1) is likely (Figure 4). The thresholds derived from Figures 3 and 4 are of restricted value at lower scales, given increasing biophysical and socioeconomic variability as discussed briefly above.

Figure 3. Relation between N balance (kg ha*1y 1) and the percentage of arable land under fallow in SSA. Very high N depletion rates (>40 kg ha*1y*1) are in areas with less than 50% of arable land under fallow (data are from FAO land/ water classes per country; n=l 15).

Assessing the costs of nutrient depletion The negative consequences of nutrient mining are recognized widely, but few attempts have been made to estimate the magnitude of the costs involved, especially beyond those related to erosion. A variety of methods have been discussed to internalize environmental issues in traditional economic assessments (e.g. Bojö, 1996). For nutrient mining, however, two relatively simple approaches, the replacement costs approach (RCA) and productivity change approach (PCA), are most often used (Drechsel and Gyiele, 1999). The PCA has the advantage that it need not differentiate nutrients or nutrient fractions. What 7 Low: < 10 kg; moderate: 10-20 kg; high 21-40 kg; very high: >40 kg N h a 1; as classified by Stoorvogel and Smaling (1990) irrespective of site-specific soil nutrient stocks. 8 ‘Potential* means actual cropland plus reserves (FAO, 1986).

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Figure 4. Nutrient depletion (here: kg N h a 1) is worst in countries with low land reserves. Data o f the same period (1980-1983) o f 37 SS A countries from F A O (1986) and Stoorvogel and Smaling (1990).

counts is the yield as a function o f all soil benefits. The RCA does not focus on crop yields but on the additional ‘inputs’ that are required to compensate for reduced soil fertility. This method allows one to assign a monetary value to the depleted nutrients based on the cost of purchasing an equivalent amount o f chemical fertilizers9. The RCA is simple to apply when the nutrient balance has been calculated already. Both approaches, RCA and PCA, have been discussed critically by Bojö (1996) in a review o f die economic losses (mostly) through soil erosion in eight countries o f SSA. An assessment of the on-site replacement costs o f annual NPK depletion in SSA was given by Drechsel and Gyiele (1999; cf Scherr, this volume). With respect to SSA, they found that in certain countries, such as Rwanda, Tanzania, Mozambique, and Niger, the value of nutrient depletion accounts for 12% or more of the agricultural share in the gross domestic product (AGDP). This suggests nutrient mining is a significant underlying factor in economic development (Table 1). Table 1 also shows that for the whole o f SSA, nutrient mining accounts for about 7% o f the subcontinental AGDP. Dividing the total costs of nutrient depletion in SSA (US$3,922 million) by the population engaged in agriculture shows that every farmer or farm worker contributes about US$32 to die annual nutrient deficit in SSA. For every hectare o f annual and permanent cropland in SSA, the average costs are about US$20.

9 Organic fertilizers or local fertilizers, such as rock phosphate, are very seldom considered in replacement cost calculations, as their actual availability for soil amelioration is usually constrained.

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Table 1. SSA nations grouped according to the costs o f nutrient depletion in % AGDP. Countries Benin, Botswana, Cameroon, Central African Republic, Dem. Rep. Congo, Rep. Congo, Gabon, Ghana, Guinea, Kenya, Mauritania, Mauritius, Sierra Leone, Swaziland, Zambia, Zimbabwe Angola, Burkina Faso, Burundi, Chad, Côte d ’Ivoire, Ethiopia, Lesotho, Madagascar, Malawi, Mali, Nigeria, Senegal, Togo, Uganda Mozambique, Niger, Rwanda, Tanzania SSA (average)

% of AGDP

11 7

Source: Drechsel and Gyiele (1999).

This cost assessment is based on a range of assumptions, given the aggregation of nutrient depletion data by Stoorvogel and Smaling (1990). Although these estimates are certainly crude, they represent the best information available from a single source, and have the advantage of using a uniform estimation method for all countries. As non-available nutrients lost through erosion do not have the same price as available (fertilizer) nutrients, the depletion data were adjusted for nutrient availability. Thus, countries with high nutrient depletion rates mostly through erosion, such as Malawi, are not automatically countries with high on-site nutrient depletion costs.

Conclusions The paper shows increasing land degradation through nutrient depletion with increasing population pressure and land use intensity, as described by Cleaver and Schreiber ( 1994). The estimated average use of mineral fertilizer required to meet soil nutrient needs at current levels of production is about 40-50 kg NPK ha*1y 1. The current average use of fertilizer in SSA (less than 10 kg NPK ha'1y 1), does not meet this demand and is largely used on cash and plantation crops. Soil conservation, recycling of crop residues, livestock management, and better use o f organic fertilizers will be required in smallholdings, but cannot close the gap, as several models show. Henao and Baanante ( 1999) calculated that good nutrient management and soil conservation can counteract nutrient depletion and reduce mineral fertilizer requirements by as much as 44% o f the amount recommended to maintain current average crop yields10. A model used by the International Centre for Research in Agroforestry (ICRAF) showed that agroforestry systems, using increased biological N fixation, deep N uptake, and manure, cannot offset the nitrogen deficit resulting from the larger nutrient removal from the farm in harvested products. The intensification of agroforestry systems on smallholder farms may even accelerate nutrient depletion if external nutrient inputs are not supplied (Shepherd et al., 1996). Like most authors, therefore, we advocate an integrated soil fertility management approach in currently cultivated lands, using both organic and inorganic inputs. It is thus 10 The model used by Henao and Baanante (1999) assumes that most crop residues will be left on the soil, thus implying the availability of alternative options for fuel, fodder, etc. for which crop residues are also used.

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essential that national governments, with assistance from the international community, establish an environment that allows the efficient use and availability o f external nutrient inputs accompanied by measures for soil fertility conservation adapted to farmers’ local opportunities and constraints.

Acknowledgments We thank the UK Department for International Development (DFID) for support of this study as part of the project “Confronting soil erosion and nutrient depletion in the humid/sub-humid tropics” of the Soil, Water, and Nutrient Management (SWNM) Program. Special thanks go to Hydro Agri International (France) and their partners in Africa who supported the fertilizer retail price survey with data.

References BARBIER, В. 1998. Induced innovation and land degradation: Results from a bioeconomic model of a village in West Africa. Agricultural Economics, 19,15-25. BOJ0,J. 1996. The costs of land degradation in Sub-Saharan Africa. Ecological Economics, 16,161-173. CLEAVER, K.M. and SCHREIBER, G. A. 1994. Reversing the Spiral The Population, Agriculture and Environment Nexus in Sub-Saharan Africa. Washington, D.C.: World Bank. DONOVAN, G. and CASEY, F. 1998. Soil Fertility Management in Sub-Saharan Africa. World Bank Technical Paper No. 408.60 pp. Washington, D.C.: World Bank. DRECHSEL, P. and GYIELE, L. 1999. The Economic Assessment o f Soil Nutrient Depletion: Analytical Issues for Framework Development. IBSRAM/SWNM Issues in Sustainable Land Management 7. Bangkok: IBSRAM. FAO. 1986. Atlas o f African Agriculture. African Agriculture: The Next 25 Years. ARC/86/3,72 pp. Rome: FAO. GREENLAND, D.J., BOWEN, G., ESWARAN, H., RHOADES, R. and VALENTIN, C. 1994. Soil, Water, and Nutrient Management Research—A New Agenda. IBSRAM Position Paper. 72 pp. Bangkok: IBSRAM. GROHS, F. 1994. Economics o f Soil Degradation, Erosion and Conservation: A Case Study o f Zimbabwe. Arbeiten zur Agrarwirtschaft in Entwicklungsländern. 171 pp. Kiel: Wissenschafts-verlag Vauk Kiel KG. HENAO, J. and BAANANTE, C. 1999. Estimating Rates o f Nutrient Depletion in Soils o f Agricultural Lands o f Africa. IFDC Technical Bulletin T48,76 pp. Muscle Shoals, Alabama, USA: IFDC. HERWEG, K. and LUDI, E. 1999. The performance of selected soil and water conservation measures—case studies from Ethiopia and Eritrea. Catena, 36(1/2), 99-114. PENNING DE VRIES, F.W.T. and DJITAYE, M.A. 1982. La productivité des paturages sahéliens: une étude des sols, des vegetations et de l ’exploitation de cette resource naturelle. Agricultural Research Report 918,525 pp. PIERI, C. 1985. Bilans minéraux des systèmes de cultures pluviales en zones arides et semi-arides. L Agronomie Tropicale, 40,1-20. PIERI, C. 1992. Fertility o f Soils. A Futurefo r Farming in the West African Savannah, 348 pp. Berlin: Springer. PIERI, C., DUMANSKI, J., HAMBLIN, A. and YOUNG, A. 1995. Land Quality Indicators. World Bank Discussion Papers 315,63 pp. Washington, D.C.: World Bank. POSS, R. and SARAGONI, Η. 1992. Leaching of nitrate, calcium and magnesium under maize cultivation on an oxisol in Togo. Fertilizer Research, 33,123-133. SANCHEZ, P.A., SHEPHERD, K.D., SOULE, M.J., PLACE, F.M., BURESH, R.J., IZAC, A.-M. N., MOKWUNYE, A.U., KWESIGA, F.R., NDIRITU, C.G. and WOOMER, P.L. 1997. Soil fertility replenishment in Africa: An investment in natural resource capital. In: Replenishing Soil Fertility in Africa, eds. R.J. Buresh, P. A. Sanchez and F. Calhoun, 1-46. SSSA Special Publication No. 51, Madison, Wisconsin: SSSA/ICRAF. SCHERR, S.J., JACKSON, L.A. and TEMPLETON, S. 1995. Living on the edge: Crafting land use policies for the tropical hillsides in 2020. Paper presented at the workshop on Land Degradation in the Developing World: Implications for Food, Agriculture, and the Environment to the Year 2020, April 4-6, Annapolis, MD., USA. SCOONES, I. and TOULMIN, C. 1998. Soil nutrient balances: What use for policy? Agriculture, Ecosystems & Environment, 71, (1-3), 255-267.

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SCOONES, I. and TOULMIN, C. 1999. Policies for Soil Fertility Management in Africa. A report prepared for the Department for International Development (DFID). 128 pp. Brighton and Edinburgh: IDS and IIED. SHEPHERD, K.D., OHLSSON, E., OKALEBO, J.R. and NDUFA, J.F. 1996. Potential impact of agroforestry on soil nutrient balances at the farm scale in the East African Highlands. Fertilizer Research, 44,87-99. SIMPSON J.R., OKALEBO, J.R. and LUBULWA, G. 1996. The Problem o f Maintaining Soil Fertility in Eastern Kenya: A Review o f Relevant Research. ACIAR Monograph No. 41,60 pp. Canberra: ACIAR. SMALING, E.M.A. 1993. Soil nutrient depletion in sub-Saharan Africa. In: The Role o f Plant Nutrientsfor Sustainable Food Crop Production in Sub-Saharan Africa, eds. H. van Reuler and W.H. Prins, 53-67, Leidschendam: VKP. STEINER, K.G. and DRECHSEL, P. 1998. Experiences with participatory on-farm research on erosion control in Southern Rwanda. In: On-farm Research on Sustainable Land Management in Sub-Saharan Africa: Approaches, Experiences, and Lessons, eds. P. Drechsel and L. Gyiele, 205-214, IBSRAM Proceedings No. 19. Bangkok: IBSRAM. STOORVOGEL J.J. and SMALING, E.M.A. 1990. Assessment o f Soil Nutrient Depletion in Sub-Saharan Africa: 1983-2000. Voi. 1, Report 28,137 pp. Wageningen: Winand Staring Centre. TIFFEN, M., MORTIMER, M. and GICHUKI, F. 1994. More People, Less Erosion. Environmental Recovery in Kenya. 311 pp. Chichester: John Wiley & Sons. VAN DUIVENBOODEN, N. 1992. Sustainability in Terms o f Nutrient Elements with Special Reference to West Africa. CABO-DLO Report 160, 261 pp.

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Box 3.1 Population and land quality on tropical hillsides

S.R. Templeton1and S.J. Scherr2 The human population in many hilly and mountainous regions of developing countries is growing rapidly. This growth is associated with agricultural expansion and intensification. The apparent ecological vulnerability of hillside and mountain environments has led to widespread concern that agricultural use will inevitably lead to land degradation. Resulting policy action often seeks to restrict population or agricultural growth. The relationship between population and diverse aspects of land quality in hills and mountains of developing countries was assessed based on more than 70 empirical studies, mainly from Central America, the Andes, East Africa, and Southeast Asia (Templeton and Scherr, 1999). Evidence included analyses of aerial photographs taken over time, statistical analyses of plot, household, regional or national data, and researchers’ deductions based on descriptive statistics, personal observation or local histories. This evidence suggests that population growth, especially from low initial densities (8.5. The extremely acid soils, which are mainly the acid sulphate soils (both potential and actual) occupy a small area around the Niger Delta and occur sporadically along the coastal plains of West Africa. The soils that have high aluminium problems occupy about 15% of the continent and are mainly in the moist parts o f the semi-arid zones and the sub-humid areas. Many of the Ultisols and some Alfisols have acid surface and sub-surface horizons which, coupled to the moisture stress conditions, make these soils extremely difficult to manage under low-input conditions. In West Africa, the annual additions of dust from the Sahara brought by the Harmattan w inds, raise the pH of the surface horizons and so the problem is less acute, but subsoil acidity remains. Soil depth is frequently understood as being depth to rock or an impermeable layer. The term ‘effective soil depth* is used here to include chemical barriers, which reduce the volume of the soil for root exploitation. Limited effective soil depth is a problem in more than 50% of the soils and this reduces the potential o f the soil for crop production. Wind and water erosion is extensive in many parts of Africa. Excluding the current deserts, which occupy about 46% o f the land mass, about 25% of the land is prone to water erosion and about 22% to wind erosion. High intensities o f these erosion forms occur mainly in the semi-arid and sub-humid areas. The soils in Central Africa are largely low activity Oxisols and Ultisols and are less susceptible to water erosion, unless severely mismanaged. These estimates include human-induced erosion, good estimates for which are available in Oldeman et al, ( 1991).

Assessment of sustainable development potentials Soil properties, including soil climate, provide some preliminary information to address land quality. Land quality is used here to indicate the ability of the soil to perform its function of sustaining agriculture under the current low-input system o f agriculture. There are areas, particularly in South Africa and some other countries, where agriculture is characterized by medium- or high-input systems and a separate assessment can be made for such situations. Low input implies that large-scale irrigation is absent, use of fertilizers, and pest and weed control is minimal, and soil management does not require high-energy mechanized equipment. The soil classification name provides adequate information to make this preliminary assessment on a continental scale. The properties incorporated in the soil name are empirically related to crop performance and a judgment is made on the potential of the soil for sustaining agriculture. A more refined assessment would require a significantly larger database.

Land resource stresses and land quality Using information from the soil and climate resources of Africa, an assessment was made initially of the land resource stresses in the country. Twenty-five stress classes were defined and prioritized according to the severity of the constraint in terms of the effort required to correct it for agricultural use and the data is presented in Table 2. The units on the soil map of Africa were sequentially tested (commencing from class 25) until the soil condition was matched by one of the classes. Soils that did not match any of the classes 2-25, were considered to have few constraints and the inherent land quality (ILQ) was designated as Class I. Depending on the severity of the constraint, subsequent stress classes are assigned to ILQs. The results of the spatial analysis using geographic information system are presented in Table 2.

106

Land resource stresses and desertification in Africa

Fifty-five percent of the land is unsuitable for any kind of sustainable agriculture apart from nomadic grazing. These lands are largely the deserts that include salt flats, dune, and rock lands, and the steep to very steep lands. The constraints for managed agricultural systems are so great that such lands must be maintained in their natural state. Though some soils in desert areas may have favourable attributes for irrigated agriculture, their quality in this general appraisal is ranked low for two reasons. First, the high initial and continuing investments needed to assure the required performance of the soils, and secondly, the rapid buildup of salinity and/or alkalinity that is a continuing problem in this environment. Though agriculture on these lands is considered unsustainable, about 30% of the population of Africa or about 250 million people are living on or are dependent on this land (Eswaran et a l , 1997a,b). A large portion of these people live on the desert margins of the Sahara and Kalahari regions and along the larger rivers that traverse the areas, such as the Nile and the Okavango Delta. Classes I to IV occupy about 10.6% of the land area (Table 2). About 3.1 million km2of land with these qualities support about 400 million people. The soils are relatively free of major constraints and rainfall is usually stable and adequate for one major crop. Moisture stress ranges are minimal and when present, rainfall is confined to the short dry season. Zones with adequate rain during the year and generally with a dry season of less than one or two months, have some form of plantation agriculture or are under forests. The soils with low quality (Classes V and VI) are those that have limitations which are not easily overcome with low-input agriculture. The limitations include high soil acidity, impermeable layers in the soil, frequent waterlogging, propensity to accumulate salts or some attributes, which require major investments to correct and to manage. Such soils occupy about 38% or 11.2 million km2 of land and currently support about 200 million persons (23%). The quality of these soils may be an inherent property of the land or it may be due to human-induced degradation over long periods of time (Oldeman et al, 1991). The present analysis does not make this distinction.

Vulnerability to desertification The results of the empirical assessment of vulnerability to desertification are presented in Table 3 and a map showing the distribution of these classes in Africa is presented in Figure 1. The region that has high propensity is located along the desert margins and occupies about 5% of the land mass. It is estimated that about 22 million people (2.9% of the total population) live in this area. The low, moderate, and high vulnerability classes occupy 14,16, and 11% respectively and together impact about 485 million people. Table 4 presents estimates of vulnerable areas for each country of Africa. Practically every country of Africa is prone to desertification, but the Sahelian countries at the southern fringe of the Sahara are particularly vulnerable. Only about 19% of Niger is non-desert and of this 17% belongs to high and very high vulnerability classes. The Mediterranean countries of North Africa have similar large areas subject to this land degradation process as do countries on the fringe of the Kalahari Desert.

P.F. R eich, S.T. Numbern, R .A . Alm araz and H. Eswaran

Figure 1. Desertification vulnerability of Africa.

107

Land resource stresses and desertification in Africa

108

Table 2. Major land resources stresses and land quality assessment of Africa. Land stresses Stress class 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Land area Water bodies Total area

Kinds of stress Few constraints High shrink/swell Low organic matter High soil temperatures Seasonal excess water Minor root restrictions Short duration low temperatures Low structural stability High anion exchange capacity Impeded drainage Seasonal moisture stress High aluminium Calcareous, gypseous Nutrient leaching Low nutrient holding capacity High P and N retention Acid sulphate Low moisture and nutrient status Low water holding capacity High organic matter Salinity/alkalinity Shallow soils Steep lands Extended low temperatures Extended moisture stress

Inherent land quality Area (1,000 km1)

Class

118.1 107.6 310.9 901.0 198.9 566.5 0.014 333.7 43.8 520.5 3,814.9 1,573.2 434.2 109.9 2,141.0 932.2 16.6 0 2,219.5 17.0 360.7 1,016.9 20.3 0 13,551.4 29,309.1 216.7

I 11 11 11 III 111 III IV IV IV V V V V VI VI VI VI VI VII VII VII VIII VIII IX

Area

Area

(1,000 km1)

(%)

118.1

0.4

1,319.6

4.5

765.4

2.6

898.0

3.1

5,932.3

20.2

5,309.3

18.1

1,394.7

4.8

20.3 13,551.4

0.1 46.2

29,525.8

Table 3. Estimates of land area belonging to vulnerability classes and corresponding number of impacted population. Vulnerability class

Area subject to desertification km1

Low Moderate High Very high

4,225,000 4,741,000 3,213,000 1,466,000

% 14.2 15.9 10.8 4.9

Population affected Millions 154.5 196.1 134.8 22.4

% of African pop. 19.9 25.3 17.4 2.9

109

P.F. Reich, S.T. Numbern, R.A. Almaraz and H. Eswaran Table 4. Assessment o f lands vulnerable to desertification in Africa. Country

Area

V ulnerability

O ther lands

Total

Low

M oderate

High

Very high

Dry

Humid

land area

Area

4,224

4,740

3,213

1,465

12,728

3,429

29,802

%

14.18

15.91

10.78

4.92

42.72

11.51

Area

24 1.04 407 32.70 6 5.44 35 6.07 31 11.62 18 71.63 147 31.49 382 61.42 40 3.25 62 18.40 653 28.56 52 16.44

52 2.18 485 33.96 69 63.13 74 12.66 103 37.32 0.3 1.17 59 12.75 145 23.31 92 7.42 25 7.39 140 6.13 201 63.27

168 7.07 272 21.86 34 31.43 38 6.65 124 45.34

116 4.91 25 2.03

2,018 84.76 30 2.43

986 0.04 25 2.02

1,000 km 2

% of total Africa

Algeria

% Angola

Area

% Benin

Area

% Botswana

Area

% Burkina Faso

Area

% Burundi

Area

% Cameroon

Area

% Cent. Afr. Rep.

Area

% Chad

Area

% Congo, Rep.

Area

% Congo, Dem. Rep. Côte d’Ivoire

Area

% Area

% Djibouti

29 6.30 62

Area

% Egypt

Area

% Eq. Guinea

Area

% Eritrea

Area

% Ethiopia

Area

% Gabon

Area

% Gambia

Area

% Ghana

Area

% Guinea

Area

%

1 0.13 1 2.73 4 3.70 265 23.73 110 42.81 0.1 1.07 17 7.47 11 15.15

1 0.15 0.5 1.72 12 10.58 73 6.56 16 6.33 1 11.18 112 48.78 180 73.22

6 0.66 2 9.45 23 19.65 131 11.74 2 0.81 8 32.92 34 15.15 1 0.43

1,246 110

138 23.67 12 4.64

3 14.65 17 1.74 1 3.60 14 11.82 87 7.80 1 0.53 0.5 4.83 2 1.04

273 6 27.29 228 4S.60 32 5.24

4 0.86

90 7.24 0.3 0.09

585

298 50.95 1 0.59

10.03 302 24.29 2 0.58 23 /.05 0.1 0.03

2,381

469 622 1,251

724 57.89 251 73.54 1,470 64.26 64 29.25

341 2,287 318 21

18 35.35 968 97.32

64 53.54 344 30.78

25

995 23 82.51 0.9 0.71 217 19.39 127 49.51

28 121 1,119 257 10

63 27.57 21 11.20

230 245

Continued on next page

по Guinea Bissau Kenya Lesotho Liberia Libya Madagascar Malawi Mali Mauritania Morocco Mozambique Namibia Niger Nigeria Rwanda Senegal Sierra Leone Somalia South Africa Sudan Swaziland Tanzania Togo Tunisia Uganda

Land resource stresses and desertification in Africa Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area % Area %

-----------ĩ ~ 15.39 27 4.S3 0 0.08 0.7 0.78 28 1.60 123 21.26 41 43.89 16 1.36

30 6.93 196 25.00 23 2.82 16 1.31 59 6.53 9 37.01 10 5.49 46 64.98

161 13.22 263 11.09 5 31.01 222 25.38 9 17.69 16 10.91 69 34.72

23 S3.72 38 6.75 1 4.15 2 2.78 5 0.33 145 24.99 42 45.09 116 9.55 3 0.39 80 17.97 260 33.28 137 16.64

512 56.24

40 21.25 11 15.98

100 8.26 430 18.13

3 17.96 524 59.79

33 60.79 8 5.60 27 13.67

Ö77 -----о 0.24 70 12.34 0.6 2.07 1 1.30 41 2.35 94 16.27 2 2.41 216 17.73 14 1.38 78 17.48 200 25.5S 74 9.08 109 8.66 260 28.59

89 46.46 1 1.44 0.1 0.01 82 6.75 305 12.86 1 10.23 82 9.44 11 21.30 21 13.63 1 0.53

0.65 94 16.69

2 1.81 42 2.43 20 3.57 0.5 0.52 51 4.22 53 5.23 43 9.84 34 4.46 85 10.40 108 8.58 29 3.23

37 19.46 0.8 1.10 29 4.78 94 7.77 175 7.37 1 S. 62 11 1.27

13 8.57 0.1 0.03

2 ?" 252 44.40

1,641 93.29 14 2.53

819 67.15 958 93.00 213 47.76 56 7.27 503 61.06 1,031 81.44 3 0.39

85 14.99 28 93.70 89 93.33

182 31.39 1 8.08

96

581 94 1,220 1,030

0.1 0.02 34 4.42

446 784 825 1,266

45 5.02 15 62.99

910 24 192

11 16.50

93 60.10

зо

1,759

14 7.35

597 95.21 554 45.43 1,200 50.51 2 14.30 2 0.25

569

71 627

226

1,219

18.57 0.8 0.04

2,376

3

17

17.89 34 3.87 0.1 0.22

1

878 54 155

1.19

0.2

101

0.14

50.90

199

Continued on next page

P.F. Reich, S.T. Numbern, R.A. Almaraz and H. Eswaran WTSüEüi------

111

----- ж

Area

% Zambia

Area

% Zimbabwe

Area

%

417 56.30 122 31.61

199 26.91 141 36.47

112 15.17 68 17.76

16 4.22

30 8.00

11 1.61 1 1.95

740 386

Given the distribution of soils with different qualities, the need to attain a semblance of food security by existing populations coupled to the potentials of desertification, an important concern, as posed by Conway and Barbier ( 1988), is the level of risk faced by the people with respect to sustainability. For this analysis, risk is considered in terms of the quality of the land and the level of inputs. This approach is similar to that of FAO (1982) in their study of the population-carrying capacity of countries. A low quality soil under a traditional low-input system poses a very high risk for the farmer. However, it does not imply that a soil with high quality but under a similar low-input system has a lower risk. Such a land may be initially productive but with mismanagement, productivity may be quickly lost and thus, risk of agricultural sustainability is still high. In this study, risk of sustainability is evaluated in a qualitative way, which can be significantly improved when better and more reliable databases become available. It is estimated that currently, there is about 22% (6.7 million km2) of land which has a low to very low risk for sustainable use. As inputs increase and management is more refined and responsible, an additional 4 million km2of land can be brought into this class. At the other extreme, there is about 54% (16.6 million km2) of land that has very high to excessive risk. The lands with very high risk (8.2% or 0.7 million km2) are mostly at the desert margins in the Sahel and along the eastern seaboard of Africa. There is also a large contiguous area in Zaire where the Kalahari sands have penetrated. About 200 million people live on these deserts and desert margins.

Risk of human-induced desertification Accelerated land degradation takes place with increasing population density and particularly under lowinput systems. In some situations, this generalization may not be true but this assumption was made to evaluate risk of human-induced desertification in Africa. Three classes of population density (< 1 0 ,11-40, and >41 persons km'2) were used and a map of these three classes was superimposed on the vulnerability to desertification map. A matrix (Table 5) was developed to relate vulnerability and population density to risk of human-induced desertification. Table 5. Matr ix for assessment of risk of human-induced desertification. Population density (persons km 2)

V ulnerability class

Low Moderate High/very high

41

1 2 4

3 5 7

6 8 9

Note: 1 = low risk; 2, 3 = moderate risk; 4, 5, 6 = high risk; 7, 8, 9 = very high risk.

Land resource stresses and desertification in Africa

112

As shown in Table 5, a high population density in an area that is highly vulnerable to desertification poses a very high risk for further land degradation. Conversely, a low population density in an area where the vulnerability is also low, poses in principle, a low risk. Figure 2 shows the distribution of the risk classes. The Mediterranean countries of North Africa are very highly prone to desertification. In Morocco, for example, erosion is so extensive that the petrocalcic horizon of some Palexeralfs is exposed at the surface. In the Sahel, there are pockets of very high risk areas. The West African countries, with their dense populations, have a major problem in containing the processes of land degradation. Table 6 provides the area in each of the classes of Table 5. About 2.5 million km2of land are low risk, 3.6 million km2are moderate risk, 4.6 million km2are high risk, and 2.9 million km2are very high risk. Table 6. Land area (1,000 km2) in risk classes. Vulnerability class Low Moderate High/very high

Population density (persons km 2) 41

2,476 2,608 2,643

1,005 1,180 1,074

750 976 825

Concluding remarks The challenge to African agriculture is not only to enhance production to meet the increased food demands of the expanding population, but also the judicious use of soils so that their productivity is sustained in the foreseeable future. The earlier study of Eswaran et al. (1997a,b) showed that 55% of the land area in Africa is unsuitable for agriculture, and 11% has high quality soils that can effectively be managed to sustain more than double its current population. These soils are spread among many countries making it difficult to develop a continent-level strategy to equitably help all countries. Africa has more than 8 million km2 of land with rainfed crop potential, however much of it has not been used for this purpose. This potential land reserve needs to be carefully evaluated so that rational policies can be developed for their exploitation. The present study shows: 1.

2.

3.

Under low-input systems, the potential productivity of the soils cannot be realized and further that stability of production will be difficult to achieve. A systematic decline in productivity is the result of degradation processes. Desertification is rampant in much of the continent and will permanently destroy the agricultural production potential. Correcting the degradation effects will be more expensive and the low resilience characteristics of many of the soils suggests that high levels of productivity cannot be expected even after mitigation technologies are used. Under current systems, most of the countries will be unsustainable and if desertification is not controlled, their ability to attain sustainability will be significantly reduced.

P.F. R eich, S.T. Num bern, R .A . Alm araz and H. Eswaran

Figure 2. Risk of human-induced desertification.

113

114

Land resource stresses and desertification in Africa

References AUBREVILLE, A. 1949. Climats, Forets, et Desertification de l'Afrique Tropicale. Paris: Società des Editions Géographiques, Maritimes et Coloniales. BADI ANE, O. and DELGADO, C.L., eds. 1995. A 2020 Visionfor Food, Agriculture, and the Environment in SubSaharan Africa. Food, Agriculture, and the Environment Discussion Paper 4. Washington, D.C.: IFPRI. BARNES, D.F. 1990. Population growth, wood fuels, and resource problems in sub-Saharan Africa. Industry and Energy Dept. Working Paper No. 26. Washington, D.C. : World Bank. BEINROTH, F.H., ESWARAN, H., REICH, P.F. and VAN DEN BERG, E. 1994. Land related stresses in agroecosystems. In: Stressed Ecosystems and Sustainable Agriculture, eds. S.M. Virmani, J.C. Katyal, H. Eswaran and I P. Abrol. New Delhi, India: Oxford and IBH. BRINKMAN, R. 1990. Resilience against climate change. In: Soils on a Warmer Earth, eds. H.W. Scharpenseel, M. Shoemaker and A. Ayoub, 51-60. Amsterdam: Elsevier. CLEAVER, K.M. and SCHREIBER, G.A. 1994. Reversing the Spiral: The Population, Agriculture, and Environment Nexus in Sub-Saharan Africa. Washington, D.C. : World Bank. CONWAY, G.R. and BARBIER, E.B. 1988. After a green revolution: Sustainable and equitable agricultural development. In: Futures, 651 -670. December, 1988. DEICHMANN, U. 1994. A medium resolution population density database for Africa. Unpublished document. Department of Geography, University of California, Santa Barbara, California, USA. DREGNE, H.E. 1977. Desertification of arid lands. Economic Geography, 53,329. ESWARAN, H. 1992. Role of soil information in meeting the challenges of sustainable land management ( 18th Dr. R. V. Tamhane memorial lecture/ Journal o f the Indian Society o f Soil Science, 40,6-24. ESWARAN, H., ALMARAZ, R., VAN DEN BERG, E. and REICH, P.F. 1997a. An assessment of soil resources of Africa in relation to soil productivity. Geoderma, 77, 1-18. ESWARAN, H., OFORI, C., MOKWUNYE, U., IDI-ISSA, I., OUATTARA, B., SANT’ANNA, R. and HOOGMOED, W. 1997b. Non-adoption of sustainable land management technologies in West Africa. In press. ESWARAN, H. and REICH, P.F. 1998. Desertification: A global assessment and risks to sustainability. In: Proceedings o f the 16,h International Congress o f Soil Science, Montpellier, France. CD ROM. FAO. 1976. A Framework fo r Land Evaluation. FAO Soils Bulletin No. 32. 72 pp. Rome: FAO. FAO. 1982. Potential Population Supporting Capacities o f Lands in the Developing World. Technical Report of Project INT/75/P13. 139 pp. Rome: FAO. LAL, R. 1994. Methods and Guidelinesfo r Assessing Sustainable Use o f Soil and Water Resources in the Tropics. SMSS Technical Monograph No. 21.78 pp. Washington, D.C.: NRCS. OLDEMAN, L.R., HAKKELING, R.T.A. and SOMBROEK, W.G. 1991. World Map o f the Status o f HumanInduced Soil Degradation: An Explanatory Note. 34 pp. Wageningen: ISRIC. UNCED. 1993. AGENDA 21: Program o f Action for Sustainable Development. 294 pp. New York: UN. UNEP. 1986. Arid Land Development and the Combat against Desertification: An Integrated Approach. Centre for International Projects, GKNT, 146 pp. Moscow: USSR Commission for UNEP. UNEP. 1993. World Atlas o f Desertification. 69 pp. London: Edward Arnold. VIRMANI, S.M., KATYAL, J.C., ESWARAN, H. and ABROL, L, eds. 1994. Stressed Agroecosystems and Sustainable Agriculture. New Delhi: Oxford & IBH.

115

L.R. Oldeman, G. W. J. van Lynden and A.E. Hartemink

Box 4.4 An assessment of land degradation in Thailand

Sunan Kunaporn', Pichai Wichaidit1, Taweesak Vearasilp1, Kanitasri Hoontrakul1 and H. Eswaran2 Major land degradation processes include physical (decline in soil structure, crusting, compaction, erosion), chemical (acidification, salinization, nutrient and fertility depletion) and biological (reduction of soil carbon and soil biodiversity) processes (Greenland et a l, 1994). Accelerated land degradation is a biophysical process driven by socioeconomic and political causes. High population density is not necessarily related to soil degradation but what people do to the land determines the extent of degradation. Two basic differences in approach have been used in this study to develop a national land degradation assessment. First, all forms of degradation were considered irrespective of whether they were natural or human-induced. Second, the vulnerability to degradation was used as the central focus due to paucity o f information. Thus, according to land degradation vulnerability classes, areas were computed from the GIS-generated map, and are shown in km2and % of country’s area in the table below. Factors causing

Intensity classest

land degradation

Slight km 2

Water erosion Physical Chemical Biological

1,911 20,238 10,395 10,169

Severe

Moderate km 1

% 0.37 3.92 2.01 1.97

27,173 44,121 6,591 3,087

% 5.26 8.54 1.27 0.60

km 2 309,591 61,009 20,899 1,751

% 59.89 11.80 4.04 0.34

+ Total land area of Thailand is approximately 511,770 km2.

Land degradation reduces the productivity of the land and affects the income and well-being of the poor. There are several short-term solutions but a longer term one should be sustainable land management through matching land use with land quality. The nation’s strategic plan comprises sustainable agriculture and crop diversity, which can be achieved by assessment and monitoring of the land resource. Greenland, D. J., Bowen, G., Eswaran, H., Rhoades, R. and Valentin, C. 1994. Soil, Water, and Nutrient Management Research—A New Agenda. 72 pp. IBSRAM Position Paper. Bangkok: IBSRAM. 1 Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. ssd [email protected] 2 World Soil Resources, USDA Natural Resources Conservation Service, P.O. Box 2890, Washington, D.C. 20013, USA. Hari .Eswaranfòusda.gov

116

State of the world's land resources

Box 4.5 Land resource stress and desertification vulnerability in Thailand Pojanee Moncharoen1, Taweesak Vearasilp2, Kanitasri

Hoontrakul2 and H. Eswaran3 The recent economic crises in Thailand have placed additional strains on the management of land for sustainable production. Resource-poor farmers are decreasing the off-farm inputs from levels that were already low, and, coupled to a lower price for their produce, the ability of the economically disadvantaged farmers to invest in conservation measures and adopt some tenets of sustainability has been significantly reduced. The prognosis for the near future is exacerbated land degradation, which entangles the farmers in the poverty spiral. To develop appropriate policies to address this issue, the Land Development Department is considering several options, for which a starting point is a re-assessment of land resource constraints. The Soil Map of Thailand at a scale of 1:1 million was used for the national evaluation and more detailed maps for other site-specific constraints. The national soil map was combined with climatic and land use data to evaluate important land-related constraints to agriculture. Experience and expert knowledge provided the basis for assigning the constraints to the polygons on the map. The constraints were ranked based on the ability of the farmer to manage the land. Each polygon was assigned the most limiting factor, appreciating that some soils have multiple constraints. Finally, based on the analysis, an assessment was made on vulnerability to desertification. The following table gives types of land resource stress and desertification vulnerability classes for Thailand. Area Land resource stress

Seasonal moisture deficit Salinity/alkalinity Low water holding capacity Soil acidity High organic matter Low nutrient availability High shrink/swell capacity Excessive soil water Few major constraints Total land area

km 2

% of country

44,599 10,133 14,744 396,934 544 21,000 3,132 10,815 9,869

8.71 1.98 2.88 77.56 0.11 4.10 0.61 2.11 1.93

511,770

100.00

D esertification vulnerability class

Low Moderate High Very high Total

Area km 2

% of country

90,241 320,581 7,265 0

17.63 62.64 1.42 0

418,087

81.69

1 Soil Analysis Division, Land Development Department, Bangkok 10900, Thailand. 2 Soil Survey and Classification Division, Land Development Department, Bangkok 10900, Thailand. 3 World Soil Resources, USDA Natural Resources Conservation Service, P.O. Box 2890, Washington, D.C. 20013, USA. Hari [email protected]

Land degradation in Bangladesh MD. M. RAHMAN, G. MOSTAFA, S. RAZIA and J.U. SHOAIB’

Expansion o f shifting cultivation onto hilly lands and salinization has increased areas o f degraded land in Bangladesh. High hill areas cover about 756, 700 ha, o f which 32,500 ha are under shifting cultivation. In these areas, topsoil loss is about 1.5 million t y 1. The total area in low hill areas is about 573,900 ha out o f which 20,900 ha are under arum, ginger, turmeric, pineapples, etc. and the soil loss is estimated to be about 1.0 million t y l. Lack o f drainage capacity, flash floods, burial offertile land by sandy debris, and landslides are off-site effects. Deforestation, acidification, dwindling organic matter contents, and nutrient depletion are evident in the eroded soils. Increase o f cropping intensity accelerates nutrient mining and unbalanced use o f fertilizers results in imbalance o f soil nutrients. In the uplands more areas are low in P, K, and S than in areas under wetland cultivation. Zinc deficiency has increased under intensive irrigated rice cultivation and Mg, B, and Mn are also reported to be low. Long-term data indicate a decrease in soil nutrient contents and pH values in the extensively cultivated soils o f Bangladesh. About 1.8 million ha o f land are tidally flooded and waterlogged, o f which 0.8 million ha o f land are flooded daily to a depth o f 60-80 cm during summer. Salt-affected areas increased significantly from 0.83 million ha from 1964—1976. The areas with low pH (4.5-5.5) and extremely low pH (2.0-4.0) are 34,900 and 62,000 ha respectively. About 2.3 million ha o f land have adverse physical conditions and about 1.7 million ha are vulnerable to river bank erosion. To address these issues appropriate ameliorative measures with suitable farming practices are required. angladesh is situated between 24°34' and 26°38’ N and 88°01' and 92°41’ E and covers an area of about 148,000 km2. It has a tropical monsoonclimate. The annual rainfall ranges from 1,299 to 5,916 mm, o f which 80 to 90% is received between May and October. The mean maximum and minimum temperatures range from 24.5 to 35.8°C and 10.2 to 26.4°C respectively. Bangladesh, with its 9.09 million ha of cultivable land, has to feed about 129 million people. To maximize crop production, most of the present cultivable lands are being overused and cropping intensity has increased. In the hilly regions, more land is being cleared and either brought under shifting cultivation or other development activities which accelerate land degradation. Erosion in highland areas is spectacular but not yet quantified. In the intensively cultivated area, monocropping with modem varieties of cereals is taking place. In most areas, fertilizers are not used judiciously and as a result, the rate of depletion of certain nutrients from intensively cultivated land has increased. Analyses of yield data o f cereal crops over a period o f 10 years indicate that the yields o f most cereal crops have either declined or stagnated. In recent years, seawater has intruded further into the country. As a result, the quality of the land is gradually changing, especially in the coastal regions, where flooding depth has increased and salinity levels have changed through the intrusion of saline water. Land degradation has both direct and indirect impacts on

B

' Soil Resource Development Institute, Ministry of Agriculture, Krishi Khamar Sarak, Dhaka-1215, Bangladesh. Phone: +880-2-911-0844/911-3363, Fax: +880-2-810600, E-mail: [email protected]

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118

crop production and government strategies are attempting to limit its effects. In this paper, an effort is made to depict the present status of land degradation in Bangladesh.

Degradation of land The current status of land degradation in Bangladesh is assessed on the basis of past and present findings from soil surveys, special investigations, and research. Most of the data were obtained between 1964 and 1996 through reconnaissance soil surveys, semi-detailed and detailed soil surveys carried out by the Soil Resource Development Institute (SRDI) and Forestal, Forestry and Engineering International Ltd. of Canada. In addition, some recent data were obtained from the Soil Conservation and Watershed Management Centre (SCWMC) in Bandarban, Thana Land and Soil Resources Utilization Guide Programme carried out by SRDI, and investigations made by Bangladesh Agriculture Research Institute (BARI), Bangladesh Rice Research Institute (BRRI), and Bangladesh Agricultural University (BAU) and others. The Report on Land Degradation Situation in Bangladesh (BARC, 1998) was also consulted in the preparation of this paper. In Bangladesh, both natural and human-induced land degradation occur simultaneously. Water erosion, nutrient depletion, waterlogging, salinization, acidification, burial of fertile land by sandy alluvium, and riverbank erosion are all active processes. Various types of soil degradation in order of importance are discussed below.

Soil erosion by water Soil erosion is a serious problem in the hilly areas where shifting cultivation and massive deforestation of steep slopes have taken place. An estimate of the extent of land susceptible to different degrees of erosion in the hilly areas was 1.7 million ha (SRDI Staff, 1964-1976; Forestal Forestry, 1966; Saheed, 1995) and is given in Table 1. Table 1. Land susceptible to soil erosion in the hilly area of Bangladesh (in km2). Affected areas

Chittagong Hill Tracts Chittagong and Cox’s Bazar Greater Sylhet District Others (Comilla, Netrokona, Brahmanbaria, Jamalpur etc.) Total

Moderately susceptible to erosion 350 414 161 -

925 (5%)

Highly susceptible to erosion 1,814 949 462 35 3,260 (20%)

Very highly susceptible to erosion 10,765 954 964 102 12,785 (75%)

Total area

12,929 2,317 1,587 137 16,970

In shifting cultivation areas, the main crop is rainfed rice, and locally, rice mixed with maize (Zea mays), beans, chilli (Capsicum), summer vegetables, cotton (Gossypium spp.), arum (Colocasia esculenta), etc. In low hill areas, the main crops are arum, pineapples, turmeric (Curcuma domestica), ginger (Zingiber officinale), summer vegetables, etc., and locally, horticultural crops. Cultivation practices do not obey the principles of soil and water conservation practice and severe erosion is common. It has been estimated that soil losses of 4 2 1h a 1у 1occur through shifting cultivation on 30-46% slopes, mostly in high hill areas

Md. M. Rahman, G. Mostafa, S. Razia and J.U. Shoaib

119

(Shoaib et a l, 1997). Earlier they were estimated to be 7 -1201ha*1у 1on 40-80% slope, occurring as a result of shifting cultivation. It has been reported that the decrease in pH value, organic matter content, and depletion of major nutrients, are greater in eroded soils than in non-eroded soils (Farid et a l, 1992). Summarized data are given in Table 2. Table 2. Properties of degraded soils in hilly areas of Bangladesh. Area

Soil pH Nf

Khagrachari Manikchari Rangamati Raykhali Bandarban

Organic C

Total N

Available P

%

%

mg kg '

E

4.8-5.5 4.0-4.8 4.3-4.5 3.5-3.8 4.5-5.0 4.0-4.3 4.2—5.1 4.0-4.5 4.5-5.5 4.3-5.0

N 0.54 0.47 0.51 0.49 0.58

E 0.38 0.30 0.32 0.30 0.48

N 0.019 0.014 0.031 0.028 0.019

Available nutrients (cmol kg*1) K

Ca

E

N

E

N

E

0.015 0.010 0.020 0.015 0.017

0.47 1.30 0.70 0.81 0.87

0.66 0.26 0.30 0.35 0.56

0.08 0.04 0.04 0.04 0.07

0.05 0.02 0.04 0.02 0.06

N

Mg E

5.14 2.16 0.90 0.87 2.20 2.97 2.55 5.75 4.61

N

E

3.77 0.84

2.41 0.83 1.77 1.83 3.16

-

2.10 3.96

+ N = normal, E = eroded

Soil loss in high and low hills under shifting cultivation and growing arum, ginger, pineapple, and turmeric is estimated through a case study in Bandarban (Shoaib et a l, 1998) and data are summarized in Table 3. Table 3. Area of eroded soils and soil loss in a hilly region of Bangladesh. Land with crops grown High hill: >300 m asl (shifting cultivation) mainly rice. Low hill: 186%), introduction of high-yielding varieties and monocropping practices (i.e. rice-rice cropping pattern) accelerate nutrient mining. In addition, inadequate and unbalanced use of chemical fertilizers may eventually lead to nutrient imbalance in the soils. In two major cereal crops, e.g. rice and wheat, NPKS are applied at the ratio of 1:0.05:0.11:0.07 compared with the average recommended doses of 1:0.24:0.65:0.2, which clearly indicates not only more use of N fertilizer than P, K, and S fertilizer but also underdosage of P, K, and S fertilizer (BARC, 1997; Task Force Report, 1997). To what extent nutrient mining and nutrient imbalance have occurred is difficult to assess because of a lack of adequate reference data. Reference data other than pH, Ca, Mg, K, total N, and C are not available. This makes it difficult to evaluate present data

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120

on micro-nutrients. Yield data of most cereal crops and fertilizer use (Figure 1) covering the last decade indicate that there is a stagnation or perhaps decline, or at best, only a slight increase in yield (BARC, 1997; Task Force Report, 1997). Yield stagnation is also noticed in crops like wheat, potatoes, pulses, oilseeds, jute, sugarcane, etc. (Table 4). Long-term experiments, conducted by BRRI on yields of modem varieties of rice without use of K or S fertilizer, indicate a gradual reduction in yield (BRRI, 1985-1997). Table 4. Average yield of different crops (t h a1) . Year

Potato

1985/1986 1986/1987 1987/1988 1988/1989 1989/1990 1990/1991 1991/1992 1992/1993 1993/1994 1994/1995

10.2 10.0 10.3 9.8 9.1 10.0 10.8 10.9 11.0 11.1

Wheat

Jute

1.9 1.9 1.7 1.8 1.5 1.7 1.8 1.8 1.8 1.9

1.5 1.6 1.7 1.5 1.6 1.6 1.7 1.8 1.7 1.7

Oilseeds 0.79 0.78 0.82 0.76 0.76 0.79 0.81 0.84 0.84 0.85

Pulses

Sugarcane

0.70 0.71 0.73 0.67 0.69 0.72 0.72 0.72 0.75 0.75

41.4 41.9 41.6 39.0 39.8 40.2 39.7 40.6 39.3 41.4

It is believed that rapid nutrient mining by modem varieties of cereal crops, and consequently nutrient imbalance situations, are the major causes of yield stagnation or even yield decline. This is a sign of land degradation. A review of past literature (Task Force Report, 1997) indicates that, in general, Bangladesh soils are low in organic matter. Large areas under intensive rice cultivation are deficient in S and Zn. Currently, the extent of K deficiency is expanding and the P status of many areas is low. Magnesium deficiency was reported in light-textured sandy loam soils of the Tista Floodplain and the Himalayan Piedmont Plain. Micro-nutrients like В and Mn are also deficient in some light-textured and calcareous soils, respectively. Figures for boron deficiency in different crops, as observed by BARI and BAU, are presented in Table 5. Table 5. Boron deficiency effect on yield of different crops in different areas of Bangladesh.

1.

Crop

Place

Year

Wheat

BAU Farm Kandua On-farm Research Centre, Rangpur Ditto Kaunia, Rangpur Mahiganj, Rangpur Thakurgaon Nashipur, Dinajpur Gazipur Rangpur Gazipur Gazipur

(1989/1990) (1991/1992) (1989/1990)

41 28 37

(1990/1991) (1988/1989) (1988/1989) (1990/1991) (1990/1991)

26 48 25 18 15 34 33 10 8

2.

Cauliflower

3. 4.

Cabbage Tomato

Yield reduction (%)1

Md. M. Rahman, G. Mostafa, S. Razia and J.U. Shoaib

5. 6.

Broccoli Potato

7.

Betel nut

8. 9.

Mustard Grams

121

13 6 7 10 17 41 59

Gazipur Gazipur Rangpur Gazipur Rangpur Rangpur Rangpur

Many results from soil testing have been compared with the results of crop response experiments on P, K, S, and Zn conducted in 30 recognized agro-ecological zones (Figure 2) of Bangladesh (BARC, 1998; SRDI Staff Report, 1988-1996; Task Force Report, 1997). Information about areas with different nutrient status is summarized in Table 6. Areas with low P, K, and S status are generally more widespread in the uplands (where crops grown are rainfed, i.e. dryland crops) than in the wetlands (where crops, particularly paddy, are grown under irrigation). Table 6. Areas with different P, K, S, and Zn status based on soil data and crop response (million ha). Status Low Medium High

Phosphorus Upland Wetland 5.45 3.18 3.07 5.35 0.58 0.58

Potassium Upland Wetland 3.40 5.35 2.11 4.00 1.71 1.65

Sulphur Upland Wetland 4.58 3.33 4.36 4.09 1.40 0.43

Zinc 2.99 -

-

3

Figure 1. Trends in rice yield in Bangladesh, 1984-1995. Aus (MV): Early summer rice (modem variety), Aus (LV): Early summer rice (local variety)* T. Aman (MV): Transplanted late summer rice (modem variety), T. Aman (LV): Transplanted late summer rice (local variety), B. Aman (LV): Broadcast floating summer rice (local variety), Boro (MV): Winter rice (modem variety).

122

Figure 2. Agro-ecological regions of Bangladesh.

Land degradation in Bangladesh

Md. M. Rahman, G. Mostafa, S. Razia and J.U. Shoaib

123

Recently, a study was conducted to compare the characteristics of topsoil samples from some areas extensively used for cereal crop production with the characteristics of samples of the same soils collected 20 to 30 years ago from nearly the same places. The results are given in Table 7 and indicate that the pH values o f almost all recently collected soil samples are 1.0-1.4 units lower than the pH of soil samples collected earlier from the Tista Floodplain and Piedmont Plain soils. The Ca, Mg, and K contents of these soils have clearly decreased. Table 7. Changes in pH, organic matter, total nitrogen, available phosphorus, exchangeable calcium, magnesium, and potassium of soils under different physiographic units from 1967 to 1998 in Bangladesh. Old Brahmaputra Floodplain

Piedmont Plain

Tista Floodplain

Barind Tract

Old soil samples n=5

New soil samples n=5

Old soil samples n= 5

New soil samples n* 5

Old soil samples n=6

New soil samples n= 6

Old soil samples n=8

New soil samples n=8

5 .1-5.9 (5.5)

4 .8-5.4 (5.1)

4.8-5.5 (5.2)

4.0-4.5 (4.2)

5.0-5.9 (5.5)

4.4-5.1 (4.1)

4 .5-5.7 (5.0)

4.2-5.4 (4.7)

Organic matter %

0.84-1.72 (1 1 3 )

0.97-2.02 (1.71)

0.6-2.02 (1 3 1 )

Total N %

0.05-0.11 (0.07)

0.10-0.13 0.04-0.11 (0.08) (0.11)

Available P mg kg'1

11.1-18.8 (16.1)

5.5-17.5 (9.7)

2.9-13.7 (8.1)

2.4-10.3 (6.4)

4.7-25.0 (14.5)

3.9-32.0 (18.0)

3.0-20.0 (8.2)

3.0-20.0 (7.0)

Exchangeable Ca cmol kg'1

2.0-3.5 (2.62)

1.8-4.9 (3.7)

0.96-1.95 (1 5 9 )

0.50-2.0 (1 2 5 )

1.8-4.9 (2.67)

1.0-4.5 (2.12)

1.5-3.7 (2.48)

1.0-5.0 (2.36)

Exchangeable Mg cmol kg'1

0.4-1.61 (0.93)

0.54-1.75 0.10-1.95 (1 2 8 ) (0.88)

0.25-0.95 0.30-1.84 0.15-1.48 0.17-2.10 0.13-1.65 (0.79) (0.94) (0.73) (0.63) (0.65)

Exchangeable K cmol kg'1

0.10-0.27 (0.17)

0.06-0.19 0.08-0.19 (0.10) (0.13)

0.05-0.11 (0.09)

Soil properties

pH

0.83-2.38 0.97-1.87 0.90-2.28 (1 3 4 ) (1.60) (1.58)

1.03-1.8 1.24-2.41 (1.97) (1.43)

0.04-0.12 0.05-0.09 0.05-0.12 0.05-0.08 0.06-0.12 (0.09) (0.07) (0.10) (0.07) (0.08)

0.08-0.22 0.07-0.17 0.06-0.12 0.04-0.22 (0.10) (0.10) (0.13) (0.13)

Note: Old soil samples collected from 1964 to 1976; new soil samples collected in 1998; figures in parentheses are average values.

Although the change in pH values in the Barind Tract soil is small (0.3 unit), the Ca, Mg and K values (range values) have decreased from earlier findings which is an indication of soil degradation (Ali et a l , 1997). Organic matter, total N, and P contents have either increased or decreased slightly, but the K status in almost all soil samples, including those from the Old Brahmaputra Floodplain, has decreased. A similar study but using the whole soil profiles for analysis was conducted by Ali and Wakatsuki (Box 4.1, this volume). Long-term yield trends, for both modem and local varieties of transplanted and broadcast Aman (late summer) rice, indicate a decline that is in conformity with the concept of soil mining. On the other hand, yield trends for Boro (winter) rice and Aus (early summer) rice reveal slight increases, or perhaps stagnation, which could be explained by year to year variation in winter temperature, duration of winter, sunshine hours, and management, but perhaps these have suppressed the effect o f soil mining. However under controlled experimental conditions (Figure 3) there is clear evidence of declining yield trend.

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Box 4.6 Landscape-scale changes in soil properties between 1967 and 1995 in Bangladesh

Md. M. AW and T. Wakatsuki2

Bangladesh has a wide range of mineral soils developed on river floodplains in sedimentary deposits originating from the Himalayas and Assam Hills. Soils on lowlands and medium lowlands are periodically flooded, mildly acidic to alkaline Fluvisols, but non-flooded grey-brown loams occur on upland ridges between the rivers. This study was launched to evaluate whether soil properties have changed between 1967 and 1995. A total o f460 (213 for 1967 and 247 for 1995) samples were collected from the same sites in the different years and analyzed for pH, clay content, exchange acidity, exchangeable sodium, potassium, calcium, magnesium, effective CEC, available phosphorus, total carbon, and total nitrogen. The results are presented in Table 1. Table 1. Changes in soil properties during 1967-1995 in Bangladesh. Soil

Depth, cm

properties

Highlands 1967

1995

%Δ

Medium lowlands 1967 1995 %Δ

Lowlands 1995

%Δ

Clay (%)

0-15 15-100

18.65 28.91

13.58 23.91

-27.2 -17.3

28.92 24.29

24.58 24.36

-15.2 +0.3

46.75 43.41

44.81 40.99

-4.2 -5.6

Soil pH (H20 ) Exch. acid. (kmol h a 1)

0-15 15-100

5.43 5.68

5.01 5.34

-7.7 -6.0

6.56 7.02

6.34 6.85

-3.4 -2.4

6.08 6.62

6.04 6.34

-0.7 -4.2

0-15 15-100

10.76 70.92

13.78 89.60

+28.1 +26.3

3.82 17.32

5.98 23.41

+56.5 +35.9

8.48 44.44

8.84 54.58

+4.3 +22.8

Exch. Na (kmol h a 1)

0-15 15-100

3.34 20.17

2.13 15.34

-36.2 -24.0

19.26 69.24

18.26 87.46

-5.2 +26.3

15.12 48.24

17.14 52.96

-13.4 -9.8

Exch. K (kmol ha*')

0-15 15-100

2.88 19.80

1.61 16.46

-44.1 -16.9

5.88 27.42

3.90 25.84

-33.7 -5.8

8.75 45.44

6.85 37.72

-21.7 -17.0

Exch. Ca (kmol ha*‘)

0-15 15-100

37.13 591.99

31.97 457.86

-13.9 -22.7

207.82 1,866.84

0-15 15-100

11.58 229.58

8.16 173.72

-29.5 -24.3

66.43 587.94

-15.4 244.09 239.09 -5.0 2,255.75 2,079.40 84.41 -10.7 83.97 -9.1 681.49 625.47

-2.1 -7.8

Exch. Mg (kmol h a 1)

254.57 1,964.33 74.39 646.50

eCEC (kmol ha*1)

0-15 15-100

65.75 932.46

57.65 752.99

-12.3 -19.3

348.92 2,724.73

302.38 2,591.49

-13.3 360.86 355.88 -4.9 3,075.36 2,850.14

Available P (kg ha *)

0-15 15-100

60.53 186.67

59.86 172.75

-1.1 -7.5

74.76 227.85

72.86 253.93

-2.5 + 11.5

95.26 273.40

67.91 231.74

-1.4 -7.3 -28.7 -15.2

Total C (t h a 1)

0-15 15-100

19.62 60.07

18.12 52.24

-7.7 -13.0

20.72 66.86

20.51 59.01

-1.0 -11.7

36.24 173.32

26.32 89.36

-27.4 -34.9

Total N (t ha ')

0-15 15-100

2.17 6.72

1.94 5.90

-10.6 -12.2

2.23 6.58

2.09 6.07

-6.3 -7.8

3.50 13.61

2.75 9.33

-21.4 31.5

1967

-0.5 -8.2

Δ = Changes calculated as the difference between 1967 and 1995 data: - = decrease, + = increase

Results and discussion Soil properties showed a clear relationship to their situation upon the landscape. Soil pH was lowest in the upland soils (pH 5.7) and above pH 6.0 in flooded soils. Exchangeable bases were highest in the lowlands as were total carbon and nitrogen. Soil pH had decreased and Continued on next page

M d. M . R ahm an, G. M ostafa, S. R azia and J.U. Shoaib

125

exchangeable acidity increased at all soil sampling locations. The eCEC had decreased as the content of component exchangeable cations decreased. Total caibon and nitrogen content fell in all groups of soils. Topographic position and intensive anthropological effects played important roles in the pattern of change in soil properties. Ali, Md. M., Saheed, S.M., Kubota, D., Masunaga, T. and Wakatsuki, T. 1997. Soil degradation during the period 1967-1995 in Bangladesh. I. Carbon and nitrogen. Soil Science and Plant Nutrition, 43,863-878. 1Bangladesh Institute of Nuclear Agriculture, Mymensingh, Bangladesh, [email protected] 2 Faculty of Life and Environmental Science, Shimane University, Matsue, Japan.

Figure 3. Long-term effect of'zero' potash and sulphur fertilizer on yield of rice crop.

W aterlogging pro b lem s Waterlogging may arise for considerable periods of time through flooding or insufficient drainage capacity, improperly designed infrastructure developments, seepage of irrigation water from neighbouring irrigated areas, topographical position (low-lying areas) or tidal flooding. In all situations, soils become either temporarily or permanently waterlogged. In the temporarily waterlogged areas, or project areas where the internal drainage situation was not properly taken into account, existence of a water table near the surface, or at shallow depth, reduces soil aeration and causes other problems. Physical and chemical properties of

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126

the soil are expected to deteriorate and microbial activities become restricted. In such a situation, the growth of many crops becomes restricted, which might be the reason for lower cropping intensity (BBAS, 1995). To what extent soil properties have deteriorated has not yet been quantified. Some S and Zn deficiencies are reported for the areas where soils are under wetland rice cultivation. About 0.8 million ha in Barisal, Patuakhali, Barguna, Jhalakati, and Chandpur Districts in the coastal region are flooded daily to a depth of 60-80 cm during the summer season which restricts cultivation of improved varieties of rice crops. In the coastal region, 1.8 million ha of land are tidally flooded and seasonally waterlogged; additionally, 1.0 million ha experience salinity. About 8,000 ha of the low-lying areas of Bil Dakatia and adjacent areas in Khulna and Jessore Districts are almost permanently waterlogged through siltation of drainage channels.

Salinization and alkalinization In Bangladesh more than 20% of the net cultivable land is in the coastal area. In this area, about 0.83 million ha out of 2.85 million ha are affected by different degrees of salinity in the dry season (Karim et a i, 1990; SRDI Staff Report, 1964-1976). Since 1990, soil and water salinity concentrations have been measured throughout the year at 126 salinity-monitoring sites distributed throughout the coastal regions of Bangladesh. Based on these data, field verification, and other salinity-related data, boundaries are delineated according to the degrees of salinity, and areas are calculated. Further field surveys to verify the saltaffected area and its boundaries are needed. The total salt-affected area increased from 0.83 to 3.05 million ha (SRDI StaflfReport, 1997). Table 8 shows that 0.71,1.2, and 0.78 million ha of land have salinity levels at 4-8 dS m*1, 8-15 d S n r1, and >15 dS n r1, respectively. At these salinity levels, crop production is restricted in the dry season. Table 8. Areas of salt-affected soils in the coastal regions of Bangladesh (up to 1995). District

Salt-affected areas with salinity ranges 900 m). In 1871 the land:man ratio was 2.7, whereas currently it is about 0.38. During the 20thcentury forest cover was reduced by about 50%. Alfisols, Oxisols, andUltisols are widespread.

S

Soil degradation Almost 50% of the arable soils in Asia are degraded by sealing, compaction, erosion, and disturbance through mining, irrigation and drainage, application of agrochemicals, contamination, and deforestation (SAIC, 1996). Such human-induced degradation reduces the present and/or future potential of soils to support human life (van Lynden, 1995). The extent of degraded soils in Sri Lanka is small compared to other Asian countries. Bangladesh, India, and Pakistan have 0.83 million ha (Hanan, 1993), 9.08 million ha (Rao, 1993), and 19.5 million ha (Abdulla, 1993) of salt-affected soils respectively. Soil degradation is significant in Sri Lanka as the land to man ratio has been lowered drastically in the past decades.

Department of Soil Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka. Phone: +94-888239/88354, Fax: +94-8-88041, E-mail: [email protected]

A .N . Jayakody

Figure 1. Major climatic zones of Sri Lanka.

Figure 2. Diagrammatic east-west section of Sri Lanka illustrating the major peneplains.

131

Soil degradation in Sri Lanka

132

Soil degradation in the Wet Zone soils is prominent and multifaceted as 75% of the population lives on 30% of the total land area. Soils of the Dry and Intermediate Zones, where 70% of the land area is found, are less degraded. The types of degradation are erosion by water, acidification, together with constraints caused by waterlogging, salinity/alkalinity, nutrient enrichment, and organic matter depletion.

Soil erosion Human activities in Sri Lanka, such as cropping on steep slopes, deforestation, building and road construction, gem mining, burning of grasslands, poor land management, and encroachment on forests have accelerated soil erosion. Erosion is a bigger problem in the Wet Zone than in the Dry Zone of the country. Soil erosion was first reported in 1875 by Hooker who requested the authorities to prohibit the use of lands above 1,500 m for cropping (Manthrithilaka, 1996). Erosion has increased in the past 150 years with the development of plantation agriculture. Ernst and Y oung ( 1992) identified soils in the mid- and upcountry regions as sensitive to erosion if mismanaged. High rainfall intensities, slope gradients up to 60%, and the nature of the soils contribute to natural erosion. Soils of the mid- and up-country areas are reported to have high erositivity (Wickramasinghe and Premalal, 1988). Tea was introduced in 1840, and the tea growing area has expanded to around 250,000 ha. As there is a need to conserve forests, the Government Forest Department launched the Forest Resources Development Project in 1983. The aim was to prepare a Forestry Master Plan for the country which is now in the implementation stage (Hewage, 1994). Hasselo and Sikurajapathy (1965) have estimated a loss of 250 t h a 1of soil during land preparation for replanting of tea. Soils are exposed to erosion until the canopy has closed and re-exposed at the pruning stage for about six months in each second year. Soils under tea have undergone these erosion cycles now for more than 100 years. According to Krishnarajah ( 1982) 300 mm of topsoil have been removed from upland areas over the past century. Green and Gunawardena (1993) reported a reduction of 60 mm in the water storage capacities of eroded soils. There are areas where the A horizon is either very thin or completely lost. Vegetable cultivation with poor land preparation is practised in mid- and up-country areas with at least three crops a year. Table 1 shows some soil loss data under different land use systems (Stocking, 1986). Table 1. Soil loss under different land uses (Stocking, 1986). Land use Seedling tea Well-managed tea Kandyan mixed garden Tobacco Capsicum Carrots Tobacco Cleared lands

Specification Without conservation With drains Almost natural Without conservation Without conservation Without conservation 45% slope without conservation 45% slope

Soil loss, t ha*1 у 1 40 2.5% have been observed in the Kandy, Kegalle, and Nuwara Eliya Districts of the Wet Zone, whereas in the Dry Zone values were frequently < 1%. Bronzing is frequently observed in the Wet Zone in fields fed by seepage water from hilly landscapes and in organic soils (Baba, 1958). Such soils also have low P and K availability and high soluble manganese and iron contents, but Bandara and Gunathilaka (1994) obtained yield increases by P and K applications.

Nutrient enrichment and impoverishment High applications of organic and inorganic fertilizers are reported in up-country vegetable cultivation with three or more crops per year. Applications of N, P, and K are higher than for tea and P and K have accumulated in the soil (Wijewardene and Amarasiri, 1990). Lathiff and Nayakakorala ( 1993) found 100-240 and 660-890 mg kg*1of available P and K respectively for soils in Nuwara Eliya. Plant nutrients in water bodies o f an intensively fertilized soil catena in Nuwara Eliya were also high (Jayakody, 1998). The Department of Agriculture and some NGOs are attempting to educate and request the farmers to apply fertilizers after soil testing. The author has tested the feasibility of field soil testing for approximate judgments o f nutrient availability in place o f laboratory analyses; this has proved to be useful. Lime requirements could also be checked through field testing. These testing procedures were successfully implemented by the Nuwara Eliya Environment Project of the Swedish Corporative Centre and Gibbon et al. (1998) found the procedures promising. Crop residue removal is a serious drain of nutrients. According to Lathiff and Amarasiri ( 1982) and Nagarajah et al. ( 1983), impoverishment of S and Zn could take place, especially in paddy soils, because of increased nutrient exploitation by improved varieties.

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Loss o f agricultural lands Arable soils are lost to commercial, industrial, residential, construction, and infrastructure development requirements. Between 1972 and 1982 the reduction of productive soils has been 30%, but this is higher in densely populated areas like Kandy, Colombo, Jaffna, and Mathara. Losses of fertile coconut plantations are in the range of 20-30%. Considerable tracts of fertile paddy fields have been infilled for various purposes. The storage dams of Kothmale, Victoria, Randenigala, and Rantambe were constructed during the 1980s and in the process, large areas were physically degraded by removal of topsoil and subsoil and also by sealing and mixing of soils. Gem mining in Rathnapura District is a major cause of soil degradation through removal of vegetation and soil, formation of craters, land subsidence, and collapse or sealing by mine spoil. There are about 15,000 gem pits under legal operation and another 15,000 operating illegally. The average extraction of spoil from a mine is around 56 m3 per year (Baldwin, 1991) and many of these heaps subsequently are washed away during rain. Alluvial sand mining is done without much control and collapse of riverbanks occurs and thus riparian soil erosion is common. Sand mining in Kelani River, in the vicinity of Colombo, has aggravated intrusion by seawater. Mining of graphite, phosphate, limestone, clay, etc. may also result in soil degradation.

Legal enactment on soil protection The Crown Land Encroachment Ordinance of 1840, and the Irrigation Ordinance of 1856 are the oldest legislations for soil protection in Sri Lanka. The Forest Ordinance of 1907 attempted to prohibit forest destruction that had direct relevance to soil protection. The Land Development Ordinance was ratified in 1935 as a measure to map state lands and to control soil erosion. The need to control erosion was clearly stated in the Soil Conservation Act of 1951 that paved the way for the establishment of the Soil Conservation Division of the Department of Agriculture in 1953. The act tried to take care of soil resource as follows: 1. 2. 3.

Ascertain the nature and the extent of soil erosion and damage to land by floods and droughts. Declaration of erodible areas by government gazette notifications. Establishment of regulations and guidelines to counteract erosion.

Adherence to proper land management was stated in the Agrarian Services Act of 1959, where the importance of soil fertility maintenance by fertilizers/manure was emphasized. The Water Resource Act ( 1964), the National Water Supply and Drainage Board Act ( 1974), the Land Grant Act (1979), the National Environmental Act of 1980, amended in 1988, and the Irrigation Ordinance (1990) also have highlighted the need for soil conservation and proper land management. Despite these acts, the socioeconomic problem of landlessness forces many people to encroach upon protected lands. The government itself has allocated lands for poor people at inappropriate locations. There are difficulties in convincing the land users/owners to implement soil protection measures, as they do not experience immediate gains by conserving soils. However, the government is promoting numerous programmes. Many organizations implement direct conservation measures, appropriate cropping and conservation systems, subsidy schemes, etc. Assistance in the form of planting materials, inorganic fertilizers, loans, and free instruction through trained extension personnel are in operation.

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Conclusions Agriculture started in Sri Lanka around 500 BC with small-scale irrigation systems. Accordingly, knowledge and experience about protection and improvement of soil fertility was available in the past. Cultivation systems such as the Kandyan Forest Gardens signal the importance of past knowledge. Sri Lanka has a long history o f traditional conservation legislation, but per capita land availability, economic pressures on farmers, and poverty have contributed to the acceleration of land degradation during the past two centuries. Intensified land use and overexploitation are major causes o f land degradation, but the exact extent is not known. Little attention is given to curb chemical degradation of soils. In many areas soil fertility has declined. The present socioeconomic, political, and administrative constraints do not enable the existing legislation to be implemented properly, because of the pressure on the land. It is pleasing to note that awareness regarding the protection of the soil resource is included in school syllabuses even at primary schools.

References ABDULLA, S., MUSTAQ, A., KAHN, A. and ALI, M. 1993. Problem soils of Pakistan—country report. A paper for SAARC Workshop on Problem Soils, 23-24 Nov., Kandy, Sri Lanka. BABA, I. 1958. Methods of diagnosing ‘Akiochi’ iron and hydrogen sulphide toxicity in the wet zone of Ceylon. Tropical Agriculturist Ceylon, 114,231-236. BALDWIN, M.F. 1991. Natural Resources o f Sri Lanka. Conditions and Trends. Colombo: NARES A. BANDARA, W.M.J. and GUNATHILAKA, G.A. 1994. Effect of applied K and P on bronzing in rice grown in iron toxic soils. Journal o f National Science Council, Sri Lanka, 22(2), 219-230. BOTSCHEK, J., JAYAKODY, A.N., NEU, A. and SKOWRONEK, A. 1994. Fertility assessment of a degraded tea land in Sri Lanka. Transactions o f 15th World Congress o f Soil Science, Acapulco, Mexico 7a, 310-320. BOTSCHEK, J., SKOWRONEK, A. and JAYAKODY, A.N. 1998. Soil degradation, soil assessment and soil rehabilitation in a former tea-growing area of Sri Lanka. Applied Geography and Development, 51,94-105. COORAY, P.G. 1984. The Geology o f Sri Lanka, 2d ed. Sri Lanka: National Museum Publications. DE ALWIS, K.A. and PANABOKKE, C.R. 1972. Handbook of the Soils of Sri Lanka. Journal o f Soil Science Society o f Sri Lanka, 2 , 1-97. Special issue. ERNST, A. and YOUNG, A. 1992. Study of the non-viable estates: Land suitability report and project option. Sri Lanka: Plantation Restructuring Unit, Ministry of Finance. GANGODAWILA, C.D. 1989. Land resources with problem soils in Sri Lanka. Report of the expert consultation of the Asian Network on Problem Soils. 247-260. Bangkok: FAO-RAPA. GIBBON, D., KODITHUWAKKU, A.A., LECAMWASAM, A. and GIRIHAGAMA, S.C. 1998. Evaluation report of the SCC Environment Project of Nuwara Eliya, Sri Lanka. Uppsala: Department of Rural Development Studies, Swedish University of Agricultural Sciences. GREEN, M.J.B. and GUNAWARDENA, E.R.N. 1993. Assessing the conservation value of Sri Lanka’s natural forests. IUCN/EMD Report No. 14. Gland, Switzerland: UNDP/FAO and Forest Department of Ministry of Lands, Irrigation and Mahaweli Development. HANAN, M.A. 1993. Problem soils of Bangladesh—country report. A paper for SAARC Workshop on Problem Soils, 23-24 Nov., Kandy, Sri Lanka. HASSELO, H.N. and SIKURAJAPATHY, M. 1965. Estimation of losses and erodibility of tea lands during replanting period. Journal o f National Agricultural Society, Ceylon, 2 , 13-21. HERATH, H.M.I. 1996. Studies on the acid sulphate soils from the Nilwala river basin. Project report. Department of Soil Science, University of Peradeniya, Sri Lanka. HEWAGE, T. 1994. Sri Lanka’s Forestry Sector and Revision of the Forestry Master Plan, Proceedings of the 5th Regional Workshop on Multipurpose Trees, 1-3 April, Kandy, Sri Lanka.

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HUMBEL, R. 1990. Decreasing extents of tea plantations, chances for agricultural diversification or ecological threat? Sri Lankan Journal o f Tea Science, 59(2), 65-81. JAYAKODY, A.N. and KULATHUNGA, L.H.D. 1997. Periodical changes in soil reaction due to incorporation of green manure to a degraded tea soil of the mid-country of Sri Lanka. In: Proceedings o f Annual Research Sessions 1997, 13-21. University of Peradeniya, Sri Lanka. JAYAKODY, A.N. 1998. Evaluation of major plant nutrients in water bodies at Pattipola in Sri Lanka where intensive vegetable cultivation is practiced. In: Proceedings and Abstracts o f Annual Research Sessions, 78. University of Peradeniya, Sri Lanka. JA YAMAN, T. and SUBRAMANIUM, S. 1975. The mineral status and physical composition of some cultivated and uncultivated tea soils of Sri Lanka, Sri Lankan Journal ofAgricultural Science, 11/12,65-81. JOACHIM, A.W.R. and PANDITHARATHNA, D.G. 1930. A soil erosion investigation. Tropical Agriculturist, Ceylon, 74,200-203. KALPAGE, F.S.C.P. 1967. Soils and Fertilisers. Colombo: Colombo Apothecaries. KRISHNARAJAH, P. 1982. Soil erosion and conservation in upper Mahaweli watershed. Paper presented at Annual Sessions of the Soil Science Society of Sri Lanka, 13 Nov. Peradeniya, Sri Lanka. LATHIFF, M.A. and AMARASIRI, S.L. 1982. Response to S fertilization in rice soils of Sri Lanka. Tropical Agriculturist, Sri Lanka, 138,93-98. LATHIFF, M.A. and NAYAKAKORALA, H.B. 1993. Problem soils of Sri Lanka. SAARC Workshop on Problem Soils, 23-24 Nov. Kandy, Sri Lanka. MANTHRITHILAKA, H. 1996. Prevention of erosion in tea lands, soil and water management of tea estates. Proceedings of a workshop, IFS-BNF-Project. Kandy, Sri Lanka. NAGARAJAH, S., NIZAR, B.M., JAUFFER, M.M.M. and DE SILVA, S.1983. Zinc as a limiting nutrient for rice growth in the mid-country of wet zone of Sri Lanka. Tropical Agriculturist, Sri Lanka, 139,67-74. NARESA 1991. Natural Resources of Sri Lanka—Conditions and Trends. Colombo, Sri Lanka: Natural Resources Science and Energy Authority. NAYAKAKORALA, H.B. 1998. Human induced soil degradation status in Sri Lanka. Journal o f Soil Science Society o f Sri Lanka, 10, 1-35. OLDEMAN, L.R., HAKKELING, R.T.A. and SOMBROEK, W.G. 1991. World Map o f the Status o f HumanInduced Soil Degradation: An Explanatory Note. Wageningen: ISRIC/UNEP. PANABOKKE, C.R. 1996. Soils and Agro-Ecological Environment o f Sri Lanka. Colombo, Sri Lanka: NARESA. PATHIRANA, R. and CHANDRASIRI, P.A.N. 1989. Evaluation of rice genotypes grown on the acid soils of the Nilwala river basin of southern Sri Lanka, In: Rice Production o f Acid Soils ofthe Tropics, eds. P. Deturk and F.N. Ponnamperuma, 265-270. Kandy, Sri Lanka: IFS. PERERA, M.B.A. 1989. Planned land use for the tea country. Sri Lankan Journal o f Tea Science, 58(2), 92-103. RAO, M.S.R.M. 1993. Problem soils of India—country report. SAARC Workshop on Problem Soils, 23-24 Nov. Kandy, Sri Lanka. SAIC. 1996. Land degradation. SAARC-SAIC News Letter, 6(4), 1. SENANAYAKA, K.S., CHOWDHRY, R. and SIVAKUMAR, M., eds. 1993. Causes and mechanisms of landslides in Sri Lanka. In: Proceedings o f the International Conference on Environmental Management, 223-226. New South Wales, Australia. STOCKING, M.A. 1986. Soil conservation in land use planning in Sri Lanka. Consultant’s Report No. 3, Colombo, Sri Lanka: UNDP/FAO Project, SRL 84/032. TOKUTOME, S. 1970. Report of the survey and classification of paddy soils of Ceylon, Peradeniya, Sri Lanka: CARI, Department of Agriculture. VAN LYNDEN, G. 1995. Guidelinesfo r the Assessment ofthe Status o f Human-Induced Soil Degradation in South and East Asia. Wageningen: ISRIC. WALLINGFORD HYDROLOGY INSTITUTE. 1995. Sedimentation studies in Upper Mahaweli Catchment in Sri Lanka, Wallingford, UK: Wallingford Hydrology Institute.

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WICKRAMASINGHE, K.N., NALLIAH, P. and WIJEDASA, M.A. 1985. Effect of urea and ammonium sulphate on the release of potassium, magnesium and calcium in acid tea soils. Sri Lanka Journal o f Tea Science, 54,11-17. WICKRAMASINGHE, L.A. and PREMALAL, R. 1988. Development of a rainfall erosivity map for Sri Lanka. In: Proceedings o f the 5thInternational Soil Conservation Organization (ISCO) Conference, ed. S. Rimwanich, 441450, Bangkok: Land Development Department. WIJEWARDHANA, J.D.H. and AMARASIRI, S.L. 1990. Comparison of phosphate sources on growth of vegetable on acid soils, Tropical Agriculturist, Sri Lanka, 146,57-65. YAPA, P.I. 1996. Characterisation of a salt affected catena, at Sevanagala, Sri Lanka. Study report for MSc degree, Post Graduate Institute of Agriculture, University of Peradeniya, Sri Lanka.

Land degradation in Hungary Á. KERTÉSZ1

Land degradation is related to both natural and human factors. Land degradation processes include so il erosion, acidification, a n d salinization/alkalization processes as w ell as p h ysica l degradation o f soils (compaction, structural damage, degradation processes caused by an extreme soil moisture regime) and biological degradation. The main driving fo rce is in most cases the water regime, or the availability o f water (e.g. permeability and water storage capacity influence soil erosion processes, and the groundwater level is o f crucial importance fo r salinization processes, etc.). Some land degradation processes in Hungary can be defined as desertification as a considerable part o f Hungary belongs to the dry sub-humid area. Desertification processes in the area can be characterized by the term aridification, which means increasing semi-aridity, manifested by the increase o f mean annual temperature and a corresponding decrease o f yearly precipitation. According to our results the average warming fo r the last 110 years is + 0 .0 1 0 4 °C yl, and precipitation decrease is 0.917 m m y 1. The physical processes o f aridification, including studies on groundw ater level change, soil moisture profile dynamics, soil development, and vegetation change were studied in detail in the D anube-Tisza Interfluve. We fo u n d a 2 -4 m drop in the annual mean groundwater level. With the gradual lowering o f the water table in alkali ponds, and with complete desiccation, the direct contact between groundwater and salt-affected soils is interrupted, the Solonchak soil dynamics cease, and heliophyte and hygrophyteplant associations disappear. According to the results o f this study, changes in vegetation proved to be an important tool indicating soil changes.

ccording to Johnson and Lewis (1995), land degradation is “the substantial decrease in either or both of an area’s biological productivity or usefulness due to human interference.” Although land degradation processes are induced both by natural and human factors, the role of human impact is definitely more important at the beginning of the 2 1st century. This applies especially to those countries of the world where agriculture still makes a considerable contribution to the national economy, as in Hungary and in several other Eastern Central European countries. Although the population working in agriculture is decreasing continuously, the proportion is relatively high (in Hungary, 7.9% in 1998, compared to 13.9% in 1992). In 1995,7% of the GDP was derived from agriculture. In Hungary agriculture has to be intensified as the percentage of agricultural area gradually diminishes. In 1985 it was 70.3% of the country’s total area, declining to 66.5% in 1996 (Table 1). As the productive area diminishes, these changes have an impact on land degradation. More intensive agriculture, accompanied by only small changes in the structure of land use accelerates degradation processes. Steep hillslopes are cultivated with less and less attention paid to erosion, and degraded soils cease to be cultivated because of the lack of funding for soil amelioration.

A

1 Geographical Research Institute, Hungarian Academy of Sciences, P.O. Box 64, Budapest, H-1388 Hungary. Phone/Fax: +36-1-311-7814, E-mail: [email protected]

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As soil is an important natural resource in Hungary, its protection and conservation is of primary importance (Várallyay, 1986). Land degradation is also a significant problem in other European countries, e.g. in the Mediterranean area (Brandt and Thornes, 1996). A review of the most significant land degradation processes will be given in the first part of this paper, followed by a presentation of research results concerning desertification processes. Table 1. Land use changes from 1985 to 1996 in Hungary (93,032 km2).

Arable Garden Orchard Vineyard Pasture Agricultural land (total) Forest Reed Fishpond Productive area (total) Uncultivated area Total

1985 (%)

1996 (%)

50.5 3.6

50.7

1.1

1.1 1.0

1.7 13.4 70.3 17.7 0.4 0.3 88.7 11.3

1.4 12.3 66.5 19.0 0.4 0.3 86.2 13.8

100.0

100.0

Land degradation processes

Soil erosion In Hungary more than one-third of agricultural land (2.3 million ha) is affected by water erosion (13.2% slightly, 13.6% moderately, and 8.5% severely eroded) and 1.5 million ha by wind erosion (Stefanovits and Várallyay, 1992) (see Table 2). Table 2. Soil erosion in Hungary (Stefanovits and Várallyay, 1992).

Area of the country Area of agricultural land Arable land Total eroded land Strongly Moderately Weakly

% of eroded land

Area in 1,000 ha

% of total area

% of agricultural land

9,303 6,484 4,713 2,291 554 885 852

100.0 69.7 50.7 24.7 6.0 9.5 9.2

-

-

100.0 73.0 35.3 8.5 13.6 13.2

-

100.0 24.1 38.5 37.4

Relief and drainage conditions make Hungary susceptible to water erosion processes. In the mountain and hill regions, surplus runoff, loss of soil, plant nutrients and fertilizers, and the accumulation of sediment, present problems over an area of 1,300,000 ha.

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In addition to rainfall, Hungary receives water from the encircling mountain ranges. In parallel with flood surges on rivers, groundwater levels rise in the lowlands, causing damage by excess water on 330,000 ha of agricultural land. As about 100 million tons of soil and 1.5 million tons of humus are removed every year in runoff (Stefanovits, 1977), erosion control is a central task for farming on hillslopes. Crop rotation planning and agronomic techniques (e.g. subsoiling and ribbed rolling) are employed to promote the infiltration of rainwater into the soil.

Wind erosion Soil erosion by wind affects 16% of Hungary’s surface. Damage is primarily caused on sandy soils where crop yields may be reduced by up to 50%. Improperly cultivated peat soils with decomposed, powdery surfaces also have low resistance to wind erosion. There is a strong seasonality in deflation with peaks in early spring and in summer. Improper farming practices may lead either to a powdering of the soil surface or compaction, and ultimately to deflation. In Hungary the major factor favouring wind erosion is the low cohesion of a dry soil surface. The obvious preventive measure is to ensure a proper vegetation cover, which reduces turbulent air motion at the surface.

Extreme soil reaction Both extremes, i.e. acidification and salinization/alkalization occur in Hungary. Acidification is related to non-calcareous parent material, to leaching, and to plant residue decomposition as well as to air pollution and to improper fertilizer application (especially N fertilizers). The latter is more significant than dry and wet acid deposition (Varallyay, 1989). However, the soils of Hungary are mostly affected by salinization and alkalization which are important land degradation processes. Salinization processes have been studied in detail for the last 100 years (see Szabolcs, 1989). Saline and alkaline soils cover large areas on the Great Hungarian Plain. Salinity and alkalinity on the surface, or in the deeper layers occur on 10.7% of the area of Hungary. The salt has accumulated mainly because of natural factors (surface and sub-surface water, local weathering, soil solution migration), but the effect of human activities is also very significant. Ineffective irrigation and drainage contribute to rising groundwater levels. The high salinity and the ion composition of the groundwater (Na+, H C 03\ C 0 32*, S 0 42) favour salinization and alkalization on the Great Hungarian Plain (Varallyay et al., 1993). The role of chemicals and fertilizers is also important.

Physical degradation Compaction, destruction of soil structure, and surface sealing are mainly caused by human activities such as overtillage, use of heavy machinery, etc. as in other countries where intensive agriculture is practised. A classification system was created for Hungarian soils according to their susceptibility to physical degradation (Varallyay and Leszták, 1990): 1. 2. 3. 4.

Non-susceptible soils: sandy soils without structure and with a low content of cementing compounds (such as carbonates or sesquioxides). Slightly susceptible soils: medium-textured soils with well-developed structure and high aggregate stability. Moderately susceptible soils: medium-textured soils with moderately developed structure and low aggregate stability. Soils susceptible to compaction and surface crusting but not to structural damage: sandy soils without structure but with a high content of cementing compounds, mainly carbonates.

Á. Kertész

5. 6. 7. 8.

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Soils susceptible to structural damage and compaction: Heavy-textured soils noted for swellingshrinkage and low structural stability. Soils susceptible to both structural damage and compaction due to salinity/alkalinity. Organic soils (peats). Shallow soils (solid rock or cemented layer near the surface).

Other degradation processes such as biological degradation, unfavourable changes in the nutrient regime, decrease of the buffering capacity are discussed elsewhere (Várallyay, 1994).

Desertification processes Desertification is the name given to a special group of land degradation processes. According to the United Nations Intergovernmental Convention to Combat Desertification, desertification means: land degradation in arid, sem i-arid and dry sub-hum id areas resulting from various factors including climatic variations and human activities (UNCOD, 1977). The word desertification has additional connotations and therefore in this case the use o f the term land degradation is preferred. Climate change, as a

consequence o f the Greenhouse Effect, is a major global process. Since desertification processes are strongly controlled by climate change their global importance will increase in the future in these regions of the world where there are arid, semi-arid, and sub-humid climates. The atmospheric conditions of arid, semi-arid, and sub-humid climates create large water deficits, i.e. potential evapotranspiration (ETP) is much greater than precipitation (P). These conditions are evaluated by a variety of indices, one of which is the FAO/UNESCO bioclimatic index: P/ETP (UNCOD, 1977). The threshold values of the bioclimatic zones are: •

The arid zone

• •

The semi-arid zone The sub-humid zone

: 0.03 < P/ETPO.20 : 0.20 < P/ETPO.50 : 0.50