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RESEARCH REPORT

82

Valuing Nutrients in Soil and Water Concepts and Techniques with Examples from IWMI Studies in the Developing World
Pay Drechsel, Mark Giordano and Lucy Gyiele

International Water Management I n s t i t u t e

IWMI is a Future Harvest Center supported by the CGIAR

Research Reports IWMI’s mission is to improve water and land resources management for food,livelihoods and nature. In serving this mission, IWMI concentrates on the integration of policies, technologies and management systems to achieve workable solutions to real problems—practical, relevant results in the field of irrigation and water and land resources. The publications in this series cover a wide range of subjects—from computer modeling to experience with water user associations—and vary incontent from directly applicable research to more basic studies, on which applied work ultimately depends. Some research reports are narrowly focused, analytical and detailed empirical studies; others are wide-ranging and synthetic overviews of generic problems. Although most of the reports are published by IWMI staff and their collaborators, we welcome contributions from others. Each report isreviewed internally by IWMI’s own staff and Fellows, and by external reviewers. The reports are published and distributed both in hard copy and electronically (www.iwmi.org) and where possible all data and analyses will be available as separate downloadable files. Reports may be copied freely and cited with due acknowledgment.

Research Report 82

Valuing Nutrients in Soil and Water: Conceptsand Techniques with Examples from IWMI Studies in the Developing World

Pay Drechsel, Mark Giordano and Lucy Gyiele

International Water Management Institute P O Box 2075, Colombo, Sri Lanka

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IWMI receives its principal funding from 58 governments, private foundations, and international and regional organizations known as the Consultative Group on International Agricultural Research(CGIAR). Support is also given by the Governments of Ghana, Pakistan, South Africa, Sri Lanka and Thailand.

The authors: Pay Drechsel is a Senior Scientist (Environmental and Soil Science) and IWMI's Subregional Director for West Africa: Mark Giordano is a Senior Scientist (Resource Economist). Both work for IWMI. Lucy Gyiele is an Agricultural Economist, who worked as a staff member of IWMI inWest Africa. The authors would like to thank Frits Penning de Vries for his support. His vision, cross-cutting through different IWMI themes towards a better integration of research aiming at increased water and soil productivity, was a major motivation. We would also like to thank Chris Scott for his contribution of the Mexican case study and are grateful to Thomas Enters, Meredith Giordano andour reviewers for their input and contributions to different versions of this study.

Drechsel, P; Giordano, M; Gyiele, L. 2004. Valuing nutrients in soil and water: Concepts and techniques with examples from IWMI studies in the developing world. Research Report 82. Colombo, Sri Lanka: International Water Management Institute. / soil fertility / soil properties / farming systems / wastewaters /irrigation / agriculture / water availability / water use / fertilizers / economic analysis / developing countries

ISSN 1026-0862 ISBN 92-9090-570-0 Copyright © 2004, by IWMI. All rights reserved. Please send inquiries and comments to: iwmi@cgiar.org

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Contents

Summary Introduction

v 1 2

Linkages between Soil Nutrients and Agricultural Water Use Measuring Soil Nutrients andNutrient Change 3 5

Economic Valuation of Nutrients and Nutrient Change

Valuing Nutrient Depletion in two different Farming Systems in Ghana Valuing Nutrients from Wastewater Irrigation in Mexico Nutrient Depletion and GDP in sub-Saharan Africa 19 22 17

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Considerations for the Economic Valuation of Soil Organic Matter Discussion and Conclusions Literature Cited 29 25

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