Soil Salinity Testing

1. Soil Salinity indicates the total amount of soluble salts in solution in a given soil sample. A total salinity test indicates the saltiness level of the soil, but does not identify which salts or ions comprise that salinity, which may be important. In the western United States the most common ions of concern are calcium (Ca), magnesium (Mg), and sodium (Na). Total salinity is measured by an Electrical Conductivity (EC) test. When comparing test results to soil classifications or restriction of use tables, always make sure that the units of measure are the same (see Appendix 1 for units of measure and conversion values).

It should be noted that Electrical Conductivity may be measured by the saturated paste extract or soil:water dilution methods. Although the two tests are expressed by the same units of measure, the values are not comparable. Soils are classified into five categories based on the concentration of ions present in a representative sample as measured by EC or Total Dissolved Solids (TDS), see Table 1.

2. Soil Salinity Classifications and Interpretations. Table 1 lists soils salinity classes and use restrictions based on two different methods of testing, the saturated paste and dilution methods, respectively. Salinity and use restriction classes are somewhat arbitrary as changes actually occur gradually. Once you know your soil-salt level, it will be necessary to determine which trees and shrubs grow well under those conditions. Most woody plants adapted to climatic conditions in the northern Great Plains and Intermountain West survive and grow well on Non-Saline to Very Slightly Saline soils. The number of woody species that will reach their full growth potential on soils with ECs >8 dS/m (“Moderately” or “Strongly Saline”) is very limited. A number of species will survive but grow at a reduced rate and vigor on soils with ECs between 6 and 10 dS/m. For approximations of tree and shrub soil salinity tolerances, see HortNote No. 6, Selecting Plant Species for Salt-Affected Soils.

These values are only approximations of salinity tolerance; actual tolerance may be less depending on field conditions. Also, see Conservation Tree/Shrub Suitability Groups (CTSG) in Section II, Windbreak Interpretations in the Montana FOTG or eFOTG (see References) for a list of tree and shrub species adapted to salt-affected soils.

Needle Necrosis in Ponderosa Pine Caused by High Soil Salinity

3. Soil Salinity Management Options. If your soil test indicates that salts are likely to be a problem, some corrective action will be necessary. What steps to take depends on the soil salinity level, expense that you are willing to incur, type of planting (conservation planting versus ornamental landscape), other environmental factors (soil, climate), cultural treatments (management) the landowner is willing to practice, and more. If supplemental water is available, reducing soil salinity typically involves using less salty irrigation water to leach salts from the soil profile. If the irrigation water is also high in salts, it will be necessary to filter the water or dilute it with lower salinity water before applying it to the soil. The periodic use of lower salinity water (ECw <2 dS/m; TDS <1,280 ppm) to flush or leach salts from the soil profile is another option. For leaching to be successful, the irrigation water must readily infiltrate and percolate through the soil profile. Caution must be taken to avoid creating additional salinity problems downstream resulting from the improper deposition of drainage water. The type of water delivery system influences leaching of salts from the soil profile, with properly placed drip, soaker, bubbler and flood irrigation preferred to sprinkler irrigation. Increasing irrigation frequency on well-drained soils helps prevent salt accumulation in the upper soil profile, but this practice can be complicated by the need to periodically deep flush salts through the soil, and may contribute to shallow rooting of some plants. The installation of soil drains and/or deep ripping of the soil to fracture impervious soil layers (pans) may be necessary for effective leaching. The use of salt tolerant trees and shrubs, particularly on dryland plantings, is another management option as previously described. It is recommended that landowners consult their local county extension agent or USDA Natural Resources Conservation Service office for specific recommendations.

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Last Modified: 08/21/2008