by Calvin Trostle, Extension Agronomy, Lubbock, (806) 723-8432, ctrostle@ag.tamu.edu

The further west across Texas the more likely crops may encounter salty conditions, whether in irrigation water or in soil. In many cases water or soil conditions as determined by an appropriate test can ascertain the potential success of both traditional, alternative, or specialty crops. The numbers often suggest, when salinity in its different forms, is sufficient to conclude a producer should not plant a certain crop.

My preferred reference document for crop salt tolerances is “Irrigation Water Quality Standards and Salinity Management Strategies,” http://soiltesting.tamu.edu/publications/B-1667.pdf, compiled by Dr. Guy Fipps, Texas A&M AgriLife Extension biological and agricultural engineering, g-fipps@tamu.edu.

Some terms on water and soil salinity reports may be confusing. What is “mmhos/cm” or “dS/m”? Growers are more familiar with parts per million (commonly noted as milligrams per liter, or mg/L). Useful conversion factors are noted early in the above document (Table 2).

Tables 7 & 8 are useful as they highlight commonly established standard salinity tolerances among 59 field, vegetable, forage, and fruit crops. For example, an irrigation water with electrical conductivity, or ECwater, of 1,600 μmmhos (micromhos) = 1.6 mmhos/cm = 1.6 dS/m or ~1,120 ppm total dissolved solids (TDS). According to Table 4. “Permissible limits for classes of irrigation water,” this would be deemed a “Permissible” class of irrigation water. If you are irrigating grain sorghum, Table 8 (for irrigation water salinity tolerance) suggests this should be fine and you would experience no yield drag due to salinity from the irrigation water. Sorghum’s 100% yield potential suffers if EC is above the threshold of 2.7 mmhos/cm. But if you were growing corn in the same situation, Table 8 suggests that corn is sensitive to this level of irrigation water salinity (the threshold for potential limited growth in corn is 1.1 mmhos/cm).

Does this mean that sorghum would automatically be OK in the above irrigation environment? No. Soil salinity must also be considered as salts can accumulate in the soil root zone especially when there is a salt source in the irrigation water and rainfall is low thus little flushing or leaching of the salts. If ECsoil soil salinity > 4.0 mmhos/cm (Table 7, soil salinity tolerances for crops) then restricted growth may be expected. In this case cotton would be suitable for both the irrigation salt level (100% yield potential if ECwater as well as the soil salinity level.

How the information in can additionally be helpful is when a farmer asks about planting another crop in their rotation. Black-eyed peas (cowpea family) is a frequent consideration since it is a legume. But based on the information above (irrigation ECwater and ECsoil) AgriLife Extension would recommend the farmer not plant black-eyed pea due to likely intolerance of the existing salinity conditions, leading to poor growth and even crop failure.

Within crop tolerances, there are known individual varieties that may be salt tolerant more so than the general varieties or hybrids that are grown, but the documentation of that higher salt tolerance may be absent. Some crops that are known to have documented salt-tolerant varieties include alfalfa and barley.

In Texas crops bermudagrass is the standard for salt tolerant perennial grasses, barley for annual grasses.

For further information on salt tolerances among peanuts, cotton, grain sorghum, and corn, consult “Irrigation Water Quality: Critical salt levels for peanuts, cotton, corn, and grain sorghum,” http://cotton.tamu.edu/Irrigation/L-5417%20Irrigation%20Water%20Quality.pdf
The Texas A&M AgriLife Extension soil test lab offers salinity testing for irrigation waters and soils, see http://soiltesting.tamu.edu/webpages/forms.html

Figure 1. Water evaporation from clods in a row of peanuts leaves a white crystalline accumulation of salts on the soil indicating likely substantial soil salinity. Emerging peanuts are establishing, but later observations on this soil indicated peanut growth and development was less than 1/3 of normal.

Calvin Trostle
Professor and Extension Specialist
Lubbock, TX
803.746.6101
ctrostle@ag.tamu.edu