Water quality for agriculture


Water quality for agriculture

R.S. Ayers
Soil and Water Specialist (Emeritus)
University of California
Davis, California, USA

D.W. Westcot
Senior Land and Water Resources Specialist
California Regional Water Quality Control Board
Sacramento, California, USA


29 Rev. 1

Reprinted 1989, 1994

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-102263-1

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalla, 00100 Rome, Italy.

Food and Agriculture Organization of the United Nations Rome, 1985 © FAO


Water Quality for Agriculture was first published in 1976 as Irrigation and Drainage Paper 29. Although many of the basic concepts of salinity control and dealing with poor quality water remain the same, new data and experience have prompted us to revise the 1976 paper in order to keep the user up-to-date.

The document is now presented as a field guide for evaluating the suitability of a water for irrigation. Included are suggestions for obtaining maximum utilization of an existing or potential water supply. Guideline values given identify a potential problem water based on possible restrictions in use related to 1) salinity, 2) rate of water infiltration into the soil, 3) a specific ion toxicity, or 4) to some other miscellaneous effects. Discussions and examples are given along with possible management alternatives to deal with these potential problems.

This paper is intended to provide guidance to farm and project managers, consultants and engineers in evaluating and identifying potential problems related to water quality. It discusses possible restrictions on the use of the water and presents management options which may assist in farm or project management, planning and operation. The guidelines and discussions are based on reported experiences gained from many farm areas throughout the world, mostly in arid and semi-arid areas. A vast majority of the data has come from agriculture in the Western United States, therefore, caution and a critical attitude should be taken when applying the guidelines to specific local conditions. The guidelines can indicate potential problems and possible restrictions on use of the water but the true suitability of a given water depends on the specific conditions of use and on the management capability of the user. The guidelines should be useful in placing water quality effects in perspective with the other factors affecting crop production, the ultimate goal being to obtain maximum production per unit of available water.

Salinity is discussed from the standpoint of a reduction in soil-water availability to the crop. Recent research findings on plant response to salinity within the root zone have been incorporated into the guidelines to improve their predictive capability. Updated crop tolerance values have also become available and are included. A method is presented for calculating the leaching requirement for the crop considering the quality of water available. Values calculated by this procedure, if adopted, represent an appreciable water saving as compared to most older procedures.

A water infiltration problem related to water quality is usually associated with both the salinity and sodium content of the water. A procedure is presented to evaluate the potential of a water to cause an infiltration problem based on a combination of its salinity (ECw) and sodium adsorption ratio (SAR).

A specific ion toxicity is discussed as to the concentration of boron, sodium or chloride and their effect on yield of sensitive crops. Other less frequently encountered problems are discussed as miscellaneous problems. Tables showing recommended maximum concentrations of trace elements for irrigation water and for toxic substances in drinking water for livestock are also presented.


These guidelines are based on various preceding guidelines developed and used in irrigated agriculture in the Western United States. The format follows that used by the staff of the University of California, USA. Many of the basic data and the concepts of saline water use and management have been developed or proposed by the US Salinity Laboratory and the authors would like to express their grateful appreciation for this help, particularly to Drs. G.J. Hoffman, E.V. Maas, J.D. Rhoades, D.L. Suarez, and the Laboratory Director, J. van Schilfgaarde.

Drs. R.L. Branson and J.D. Oster (University of California), Dr. J. Van Hoorn (Wageningen), Mr. J.D. Doorenbos (Ministry of Agriculture, The Netherlands), and staff of the Land and Water Development Division (FAO) have been particularly helpful with suggestions and draft reviews. Thanks are also due to: Chrissi Smith-Redfern, Hazel Tonkin, Charlene Arora and Mary Westcot.

The paper is dedicated to the field person who must make decisions on the effective use of irrigation water. This paper attempts to take the solution and prevention of water quality problems to the field. The ultimate goal is that of maximum food production from the available supply of water.


In running text where symbols are used, e.g. ECdw, for mechanical reasons they have been typed level on the line. However, they appear correctly in the equations where greater flexibility is possible e.g. ECdw.

Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.





1.1 Introduction

1.2 Water Quality Problems

1.2.1 Salinity

1.2.2 Water infiltration rate

1.2.3 Toxicity

1.2.4 Miscellaneous

1.3 Approach to Evaluating Water Quality

1.4 Water Quality Guidelines


2.1 Introduction

2.2 Build-up of Soil Salinity

2.3 Salinity Effects on Crops

2.4 Management of Salinity Problems

2.4.1 Drainage

2.4.2 Salinity control by leaching

2.4.3 Crop tolerance to salinity

2.4.4 Cultural practices

2.4.5 Changing methods of irrigation

2.4.6 Land development for salinity control

2.4.7 Changing or blending water supplies


3.1 The Infiltration Problem

3.1.1 Infiltration problem evaluation

3.2 Management of Infiltration Problems

3.2.1 Soil and water amendments

3.2.2 Blending water supplies

3.2.3 Cultivation and deep tillage

3.2.4 Organic residues

3.2.5 Irrigation management


4.1 Specific Ions and Their Effects

4.1.1 Chloride

4.1.2 Sodium

4.1.3 Boron

4.2 Management of Toxicity Problems

4.2.1 Leaching

4.2.2 Crop selection

4.2.3 Cultural practices

4.2.4 Blending water supplies

4.3 Toxicity Effects due to Sprinkler Irrigation


5.1 Excess Nitrogen

5.2 Abnormal pH

5.3 Scale Deposits

5.4 Magnesium Problems

5.5 Trace Elements and Their Toxicity

5.5.1 Natural occurrence in water

5.5.2 Toxicities

5.5.3 Evaluation criteria

5.6 Nutrition and Water Quality

5.6.1 Nutrition and salinity

5.6.2 Water infiltration problems and nutrition

5.6.3 Nutrition and toxicity

5.6.4 Miscellaneous

5.7 Clogging Problems in Localized (Drip) Irrigation Systems

5.8 Corrosion and Encrustation

5.8.1 Metal corrosion

5.8.2 Concrete corrosion

5.9 Vector Problems Associated with Water Quality


6.1 Introduction

6.2 Use of Saline Water for Livestock

6.3 Toxic Substances in Livestock Water



8.1 Introduction

8.2 Protection of Irrigation Water Quality - Sacramento-San Joaquin Delta, USA

8.3 Re-use of Agricultural Drainage Water - Broadview Water District, USA

8.4 Use of an Exceptionally Low Salinity Water - Friant-Kern Canal, San Joaquin Valley, California, USA

8.5 High Bicarbonate Water Used for Overhead Sprinkler Irrigation - Denver, Colorado, USA

8.6 Use of Poor Quality Water - Bahrain

8.7 Drainage Problems - Imperial Valley, California, USA

8.8 Need for Drainage - Tigris-Euphrates River Basin, Iraq

8.9 High Salinity Water - Arizona, USA

8.10 Use of Agricultural Drainage Water for Production of Selected Crops - Imperial Valley and San Joaquin Valley, California, USA

8.11 Use of Marginal Quality Water - Medjerda Valley, Tunisia

8.12 Use of Poor Quality Water for Irrigation - United Arab Emirates

8.13 Irrigation Water Quality - Lake Chad, Africa

8.14 River Water Quality Variations - Ethiopia and Somalia

8.15 Groundwater Degradation - Wadi Dhuleil, Jordan

8.16 Surface Water Quality Degradation - Yemen Arab Republic

8.17 Sediment in the Irrigation Water Supply - Ethiopia

8.18 High Fluoride in Animal Drinking Water - New Mexico, USA

8.19 Poor Quality Groundwater for Livestock Drinking Water - New Mexico, USA

8.20 Fresno Irrigation Scheme Using Treated Wastewater - California, USA

8.21 Agricultural Use of Treated Wastewater - Braunschweig, FR Germany

8.22 Wastewater Irrigation - Bakersfield, California, USA

8.23 Wastewater Irrigation - Tuolumne Regional Water District, California, USA

8.24 Irrigation with Wastewater - Santa Rosa, California, USA

8.25 Use of Wastewater High in Boron - Calistoga, California, USA

Annex I Table - Water analysis of 250 selected irrigation supplies from various locations in the world

Annex II Glossary



1. Guidelines for interpretations of water quality for irrigation

2. Laboratory determinations needed to evaluate common irrigation water quality problems

3. Concentration factors (X) for predicting soil salinity (ECe) from irrigation water salinity (ECw) and the leaching fraction (LF)

4. Crop tolerance and yield potential of selected crops as influenced by irrigation water salinity (ECw) or soil salinity (ECe)

5. Relative salt tolerance of agricultural crops

6. Guidelines for interpreting laboratory data on water suitability for grapes

7. Relative salt tolerance of various crops at germination

8. Effect of planting rates on seedling establishment of crops sprinkle-irrigated with different quality water in Israel

9. Relative effect of fertilizer materials on the soil solution

10. Water quality from blended canal and well water

11. Calcium concentration (Cax) expected to remain in near-surface soil-water following irrigation with water of given HCO3/Ca ratio and ECw

12. Water and soil amendments and their relative effectiveness in supplying calcium

13. Average composition and equivalent acidity or basicity of fertilizer materials

14. Chloride tolerance of some fruit crop cultivars and rootstocks

15. Relative tolerance of selected crops to exchangeable sodium

16. Relative boron tolerance of agricultural crops

17. Citrus and stone fruit rootstocks listed in order of increasing boron accumulation and transport to leaves

18. Relative tolerance of selected crops to foliar injury from saline water applied by sprinklers

19. Leaf burn on alfalfa with three rates of water application by sprinkler irrigation in Imperial Valley, California

20. Sodium content in cotton leaves in percent oven dry weight

21. Recommended maximum concentrations of trace elements in irrigation water

22. Physical, chemical and biological contributors to clogging or localized (drip) irrigation systems as related to irrigation water quality

23. Standard water quality tests needed for design and operation of localized (drip) irrigation systems

24. Influence of water quality on the potential for clogging problems in localized (drip) irrigation systems

25. Procedure for calculation of pHc

26. Chlorine dosages for control of biological growths

27. Limit values for evaluating the aggressivity of water and soil to concrete

28. Water quality guide for livestock and poultry uses

29. Suggested limits for magnesium in drinking water for livestock

30. Guidelines for levels of toxic substances in livestock drinking water

31. Existing standards governing the use of renovated water in agriculture

32. Treatment processes suggested by the World Health Organization for wastewater re-use

33. Selected crop yield from the Safford Experiment Station as compared to average farm yields

34. Red Mountain Farms lint cotton yields (kg/ha)

35. Salinity of the Medjerda River at El Aroussia, Tunisia (monthly mean in dS/m)

36. Effect of irrigation method on tomato yield (kg/ha)

37. Effect of irrigation method on sodium and chloride concentration of the foliage of lemon trees (dry weight basis)

38. Trace element concentrations of three water supply wells in selected areas of New Mexico, USA

39. Fluoride in well water in mg/l

40. Salt and trace element content of a cattle water source

41. Water analyses for the Agua Negra Ranch (mg/l)

42. Trace element concentrations in Fresno municipal wastewater

43. Water quality in and around the Braunschweig treated wastewater use area

44. Trace element concentrations in wastewater from the Tuolumne Regional Water District

45. Trace element and nutrient content of wastewater from the City of Santa Rosa


1. Nomogram for determining the SAR value of irrigation water and for estimating the corresponding ESP value of a soil that is at equilibrium with the water

2. Salinity profile expected to develop after long-term use of water of ECw = 1.0 dS/m at various leaching fractions (LF)

3. Soil moisture retention curves for a clay loam soil at varying degrees of soil salinity (ECe)

4. Change in salinity of soil-water (ECsw) between irrigations of alfalfa due to ET use of stored water

5. Salinity profile with a high water table

6. Relation between capillary flow velocity and depth of water table

7. Effect of applied water salinity (ECw) upon root zone soil salinity (ECe) at various leaching fractions

8. Soil salinity (ECe) of a sandy-loam soil before and after 150 mm of rainfall

9. Soil salinity (ECe) profiles at the end of the irrigation season and after winter rainfall in citrus plantings

10. Divisions for relative salt tolerance ratings of agricultural crops

11. Method of determining maximum ECe

12. Flat top beds and irrigation practice

13. Salinity control with sloping beds

14. Sloping seedbeds

15. Sloping seedbeds used for salinity and temperature control

16. Bed shapes and salinity effects

17. Salt accumulation patterns for a) surface flooding, b) furrow irrigation, c) border irrigation, and d) localized irrigation

18. Influence of the irrigation system on the soil salinity pattern and yield of bell pepper at two levels of irrigation water quality

19. Depth of leaching water per unit depth of soil required to reclaim a saline soil by continuous ponding

20. Depth of leaching water per unit depth of soil required to reclaim a saline soil by ponding water intermittently

21. Relative rate of water infiltration as affected by salinity and sodium adsorption ratio

22. Depth of leaching water per unit depth of soil required to reclaim a soil inherently high in boron

23. Heavy metal content of the soil profile after 80 years of irrigation with wastewater

24. Concentration factor from applied water (ECw) to soil salinity (ECe) under subirrigation on organic peatland in the Sacramento-San Joaquin Delta, California, USA

25. Electrical conductivity of Lake Chad from 26 February to 10 April 1967


1. Calculation of concentration of deep percolation from the bottom of the root zone

2. Determination of average root zone salinity

3. Leaching requirement calculation

4. Determination of yield potential

5. Blending irrigation water for maize

6. Comparison of methods to calculate the sodium hazard of a water

7. Use of gypsum as an amendment

8. Blending irrigation water to reduce the SAR of a poor quality supply