ENVIRONMENTALLY AND SOCIALLY SUSTAINABLE DEVELOPMENT 1~~U) Rural Development Work in progresS 20842 for public discussion August 2000 Public Disclosure Authorized Salinity Management for Sustainable Irrigation IntegratingScience, Environment, and Economics Public Disclosure Authorized Public Disclosure Authorized f~~~~~~~~~~~~~~~~~~~~~~~~~~i:2 Public Disclosure Authorized Daniel Hillel wit/ an appendix by E. Feinerman ENVIRONMENTALLY AND SOCIALLY SUSTAINABLE DEVELOPMENT Rural Development Salinity Management for Sustainable Irrigation IntegratingScience, Enzvronment, and Economics DanielHillel withan appendixby E. Feinerman The WorldBank Washington,D.C. Copyright (©2000 The International Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W. Washington, D.C. 20433, U.S.A. All rights reserved Manufactured in the United States of America First printing August 2000 12340403020100 This report has been prepared by the staff of the World Bank. The judgments expressed do not necessarily reflect the views of the Board of Executive Directors or of the govermnents they represent. The World Bank does not guarantee the accuracy of the data included in this publication and accepts no responsibility for any consequence of their use. The boundaries, colors, denominations, and other in- formation shown on any map in this volume do not imply on the part of the World Bank Group any judg- ment on the legal status of any territory or the endorsement or acceptance of such boundaries. The material in this publication is copyrighted. The World Bank encourages dissemination of its work and will normally grant permission promptly. Permission to photocopy items for internal or personal use, for the internal or personal use of specific clients, or for educational classroom use, is granted by the World Bank, provided that the appropriate fee is paid directly to Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, U.S.A., telephone 978-750-8400, fax 978-750-4470. Please contact the Copyright Clearance Center before photocopying items. For permission to reprint individual articles or chapters, please fax your request with complete information to the Republication Department, Copyright Clearance Center, fax 978-750-4470. All other queries on rights and licenses should be addressed to the World Bank at the address above or faxed to 202-522-2422. Cover photograph: Salination in an irrigated field in Swift Current, Saskatchewan, Canada. Courtesy of Dr. Harold Steppuhn, Agriculture and Agri-Food Canada. Daniel Hillel is Professor Emeritus of Soil, Water, and Plant Sciences at the University of Massachusetts. He was contracted to do this study by the Sustainable Land Resource Management thematic group of the Rural Development Department at the World Bank. Library of Congress Cataloging-in-Publication Data has been applied for. , The text and the cover are printed on recycled paper, with a flood aqueous coating on the cover. Contents Acknowledgments vi Introduction. Posing the Question: Is Irrigation Sustainable? Chapter 1 The Nature of Salinity 5 Soil Salinity 5 Soil Sodicity 7 The Salt Balance 10 Chapter 2 Effects on Crops 15 Sensitivity to Salinity 16 Specific Element Effects 18 Chapter 3 Irrigation Water 23 Water Quality 23 Use of Brackish and Saline Water 24 Reuse of Wastewater 27 Chapter 4 Waterlogging and Drainage 30 High Water-table Conditions 30 Groundwater Drainage 32 Chapter 5 Salinity Control 36 Leaching Processes 36 Soil Amendments 45 Irrigation Practices 47 Chapter 6 Early Warning Systems 50 Need for Early Detection 50 Methods of Monitoring 50 Chapter 7 Scaling Up from the Field 56 Crop-Water Production Functions 56 Social and Institutional Issues 58 Policy Implications 59 iii iv Contents Conclusion. Irrigationis Sustainable-at a Cost 61 Appendix:Economic Aspects of Salinity Management 63 Representing Physical and BiologicalRelationships 63 Review of EconornicAnalyses 65 Bibliography 79 Index 89 List of Tables 1 Relative salt tolerances of various crops 20 2 Classificationof water quality according to total salt concentration 24 3 Prevalent depths and spacings of drainage pipes in different soil types 34 Al Estimated marginal rate of substitution among waters from various sources 69 A2 Nash-Harsanyi solution for three farm cooperative with joint use of brackish water 71 A3 Estimated income losses for various salinity levels of irrigation water 72 List of Boxes 1 Silt and salt in ancient Mesopotamia 2 2 How ancient Egypt escaped the scourge of salinity 4 3 Potential contribution of irrigation water to soil salinity 6 4 Sampling the soil solution 7 5 Measuring the salt concentration 7 6 Sodium adsorption ratio and exchangeable sodium percentage 10 7 Sample calculation of the salt balance 11 8 Saline seeps in Australia and North America 13 9 Models of root-zone salt concentration 36 10 Waterlogging and salination in the Indus River Basin 37 11 Sample calculation of the leaching requirement 38 12 Drainage problems in California 39 13 Summary of leaching methods 41 14 Factors determining flow rate to drains 43 15 Predicting water-table height in a drained field 44 16 Native gypsum and soil subsidence 46 17 The solubility of lime and gypsum in the soil 47 18 The shrinking and salination of the Aral Sea 48 19 Summary of early warning methods 51 20 Policy options to promote water conservation 56 21 Intergenerational issues 60 List of Figures 1 The process of waterlogging and salination 3 2 Distribution of a monovalent vs. a divalent cation (Ca++vs. Na+)adsorbed to a negatively charged clay particle. The divalent cation is held more closely and strongly to the particle 8 Contents v 3 Influence of ambient solution concentration (n, > n2) on thickness of the ionic layer surrounding clay particles. Higher concentration compresses the layer, promoting flocculation 8 4 Hydraulic conductivity of a sandy loam as related to total salt concentration of the soil solution and to the soil's exchangeable sodium percentage (ESP) 9 5 Formation of a saline seep 12 6 Salt accumulation patterns under furrow irrigation 14 7 Plant responses to salinity 15 8 Classification of crop tolerance to salinity 17 9 Effects of salinity and sodicity on plants 18 10 Diagram for assessing salinity and sodicity hazards of irrigation water 25 11 Irrigation return-flow system 28 12 Drainage water reuse and disposal for an irrigation region 28 13 Steady upward flow and evaporation from a sandy loam (n = 3) as a function of the suction at the soil surface, with water table at various depths 31 14 Groundwater drainage (a) under steady flow conditions, and (b) under unsteady conditions resulting in a falling water table 34 15 Depth of water per unit depth of soil required to leach saline soil by continuous or intermittent ponding 42 16 Water content distribution, during infiltration under flooding and under sprinkling at two intensities. Cumulative infiltration equals 80 mm 42 17 Observation wells to determine elevation of the water table 52 18 Set of plezometers to determine vertical pressure gradients under the water table. The condition illustrated suggests downward flow 52 Al Schematic representation of a water system at a regional level 64 Acknowledgments Ithankthe following members of the World sion of the manuscript and offered many con- Bank's Rural Development Department: structive suggestions for its improvement. Dr. Messrs. Johannes ter Vrugt, Eugene Terry,and Harold Steppuhn of Agriculture and Agri-Food JulianDumanski,forentrustingmewiththechal- Canada kindly provided the photographs of lenging assignment to compose this manual; Dr. salinized land. Mr. Jose Mendoza at GISS con- Shawki Barghouti, Senior Research Advisor, for tributed his expertise in creating the graphics. his leadership in irrigation development; and Ms. Finally, I express my special gratitude to Dr. Melissa Williams for her caring preparation of Cynthia Rosenzweig, of the NASA/Goddard In- the publication. Dr. John Letey of the University stitute for Space Studies and Columbia Univer- of California at Riverside reviewed an early ver- sity, for her help and encouragement. Dedicatedto the irrigatorsof arid landswho toil tofeed humanity vi INTRODUCTION Posingthe Question:Is IrrigationSustainable? I rrigation is the supply of water to agricul- serves as the root zone, for the immediate and tural crops by artificial means, designed to subsequent use of the crop. Inevitably, how- permit farming in arid regions and to off- ever, irrigation also entails the addition of wa- set drought in semi-arid regions. Even in areas ter-bome salts. Many arid-zone soils contain where total seasonal rainfall is adequate on natural reserves of salts, which are also mobi- average, it may be poorly distributed during lized by irrigation. Underlying groundwater in the year and variable from year to year. Wher- such zones may further contribute salts to the ever traditional rain-fed farming is a high-risk root zone by capillary rise. Finally,the roots of enterprise owing to scarce or uncertain pre- crop plants typically extract water from the soil cipitation, irrigation can help to ensure stable while leaving most of the salts behind, thus production. causing them to accumulate. Irrigation has long played a key role in feed- The problem is age-old. From its earliest in- ing expanding populations and is expected to ception in the FertileCrescent, some six or more play a still greater role in the future. It not only millenniaago, irrigated agriculture has induced raises the yields of specific crops,