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

Plant Materials Technical Note Number MT-60

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Plant Materials Technical Note Number MT-60 (PDF; 242 KB)

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

Introduction. Conservation professionals and landowners alike will probably be involved in planting trees and shrubs at some point in time. The suitability of soil for growing trees and shrubs depends largely on the quality of that soil. One “quality” criteria is the amount and types of dissolved salts found in soil. Salts in soil and water frequently limit woody plant survival and growth in the northern Great Plains and Intermountain West. For tree and shrub plantings, determining soil suitability involves comparing test results to some standard indicating whether the salt level is low, average, or high. Unfortunately, soil tests typically provide only numbers, with little or no explanation of their meaning. As a result, it is difficult to make decisions regarding the quality of a soil without consulting a specialist. This document is designed to help readers interpret soil test results to determine if salts are likely to pose serious problems for tree and shrub plantings.

It is important to recognize that soil, water, and plant interactions are complex and unpredictable, varying with the specific crop, soil characteristics, local climate, and management practices. In order to make meaningful soil quality interpretations when supplemental water is provided, it is necessary to consider both soil and water quality factors simultaneously. For more information on interpreting water quality test results, see Testing and Interpreting Salt-Affected Water for Tree and Shrub Plantings, Plant Materials Technical Note No. MT-61.  If the reader would like detailed information on salts in soil and water, see Determining the Suitability of Salt-Affected Water and Soil for Tree and Shrub Plantings, Plant Materials Technical Note No. MT-62.

What Soil Quality Tests Should a Person Request? There are several tests that can be conducted on a sample of potentially salt-affected soil to determine it’s suitability for growing trees and shrubs. The more information that is available to the landowner, the better the soil quality interpretation that can be made (see Analysis Reports 1 and 2 at the end of this document for examples of comprehensive soil salinity tests and explanations of the results). Again, in order for soil quality interpretations to be meaningful for a given plant species and management strategy on an irrigated site, it will also be necessary to know the water quality characteristics of the irrigation water. Four characteristics that help define the suitability of salt-affected soil for growing trees and shrubs include salinity, sodicity, pH, and texture.

Where Can a Person Have Their Soil Sample Tested? For a list of soil testing laboratories 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 Soil? Soil should be sampled well before planting to determine its suitability for trees and shrubs. Additionally, soil quality may vary over time, and should be tested at intervals, especially during the growing season. 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.

Again, these guidelines are provided in an attempt to help identify potential soil salts problems when planting trees and shrubs. For detailed information, or further assistance, contact your local NRCS, county extension, or conservation district office.

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Last Modified: 09/14/2009