Saline soils occur for the most part in arid or semiarid regions. Low rainfall, high evapotranspiration, and inadequate leaching cause salts to accumulate in the root zone of soil profiles. Salinity problems of economic significance arise when cultivated soils become saline as a result of irrigation (U.S. Salinity Staff, 1969). One concern of irrigators in the Powder River basin of Montana is that an increase in irrigation water salinity will result in soil degradation and diminished crop production (Gallagher, 1986).

     A greenhouse study was conducted to determine if crop yields and soil properties were affected under sustained irrigation with water quality of increasing salinity and sodicity. Twenty undisturbed soil columns were obtained from each of six soil sites and leached for 14 months with water quality treatments representing past, present, and future Powder River water quality. Columns were planted to alfalfa (Medicaao sativa L.) or western wheatgrass (Aqropyron smithii R.) and harvested on a monthly basis. Soil water samples were periodically collected from soil columns and tested for salinity by EC (electrical conductivity), SAR (sodium adsorption ratio), and pH. Soil columns were then dismantled and sampled at the end of 14 months of continuous irrigation.

     During the study period alfalfa yields did not significantly decline as a result of irrigation with water of past, present, or future water quality. However, long term irrigation and accelerated salt loading has resulted in significant amounts of salt and sodium accumulation in all soils of this study. All soils became saline or salinesodic when irrigated with water assumed to be representative of future irrigation water quality. This will likely present a problem to future irrigation management, especially if present irrigation water quality deteriorates further.