Testing and Interpreting Salt-Affected Water for Tree and Shrub Plantings

Plant Materials Technical Note Number MT-61

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Plant Materials Technical Note Number MT-61 (PDF; 185 KB)

September 2007
By Joseph Scianna, Research Horticulturist, USDA, NRCS, Plant Materials Center, Bridger, Montana
Tom Pick, Water Quality Specialist, USDA, NRCS, Bozeman, Montana
Robert Logar, State Staff Forester, USDA, NRCS, Bozeman, Montana

Introduction In many parts on the arid and semi-arid West, it is necessary to provide supplemental water to trees and shrubs to enhance their survival and growth. The quality of this water can dramatically influence plant survival and growth, and high levels of dissolved salts in irrigation water and soil are common, and frequently injurious to woody plants. Although it is relatively easy to classify irrigation water as “suitable” or “non-suiTable” for most plants on good quality or well-defined soil, suitability becomes more subjective when predicting the effect of marginal quality irrigation water on marginal or undefined soil. Furthermore, water quality is only one of several factors to be considered when using salt-affected water. Other considerations include the salinity (saltiness) of the soil, soil texture (relative amounts of sand, silt, and clay), the plant species in question, the local climate, and the types of cultural practices that will be implemented. In order to make meaningful water quality interpretations, it is necessary to consider both water and soil quality factors simultaneously. For soil salinity testing and interpretation, see Testing and Interpreting Salt-Affected Soil for Tree and Shrub Plantings, Plant Materials Technical Note No. MT-60. For approximations of tree and shrub salinity tolerance, see HortNote No. 6, Selecting Plant Species for Salt-Affected Soils.

This technical note provides basic guidelines for interpreting water quality tests and then making practical assessments of its suitability as irrigation water for tree and shrub plantings. The focus of this technical note is salt-affected water, since this condition frequently limits woody plant survival and growth in the northern Great Plains and Intermountain West. This document provides only simple guidelines and limited explanation. If the reader would like more detailed information, see Determining the Suitability of Salt-Affected Water and Soil for Tree and Shrub Plantings, Plant Materials Technical Note No. MT-62.

What Water Quality Tests Should a Person Request? There are several tests that can be conducted on a sample of potentially salt-affected water to determine it’s suitability for irrigating trees and shrubs. The more information that is available to the irrigator, the better the water quality interpretation that can be made. The following five tests are considered essential, and when evaluated together should provide a comprehensive overview of the suitability of a water source for irrigating tree and shrub plantings (see Analysis Reports 1 and 2 at the end of this document for examples of comprehensive water quality tests and interpretations for salt-affected water).

Where Can a Person Have Their Water Sample Tested? For a list of analytical services near you, reference your local phone book, conduct an Internet search, or access the document "Soil, Plant and Water Analytical Laboratories for Montana Agriculture" located at the Montana State University Extension, Publications, Agriculture & Natural Resources - Fertilizers Webpage.

When Should a Person Sample Their Water? Ground and surface water to be used for irrigation should be sampled before application to determine its suitability for trees and shrubs. Additionally, water quality should be tested over the course of the irrigation season. Since most tree and shrub irrigation occurs in late spring through mid-summer, initial testing in late spring to early summer of the year prior to planting is an ideal time to begin. Analytical laboratories usually list test costs, sampling, and preservation procedures on their web page.

• Water Salinity Testing
• Water Sodium Testing
• Testing for Specific Ions in Irrigation Water
• Water pH Testing and Management
• Water Carbonate Testing
• References
• Appendix

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Last Modified: 09/14/2009