Salinity and sodicity induced changes in dispersible clay and saturated hydraulic conductivity in sulfatic soils

Irrigation is becoming a more commonly used practice on glacially derived s oils of the Northern Great Plains. Threshold salinity and sodicity water qu ality criteria for soil-water compatibility in these sulfatic soils are not well defined. This study was conducted to relate soil salinity and sodicit y to clay dispersion and saturated hydraulic conductivity (K-sat) in four r epresentative soils. Soil salinity (EC treatment levels of 0.1 and 0.4 S m( -1)) and sodicity (SAR treatment levels of 3, 9, and 15) levels were establ ished to produce a range of conditions similar to those that might be found under irrigation. The response of each soil to changes in salinity and sod icity was unique. In general, as sodicity increased clay dispersion also in crease, but the magnitude of the increase varied among the soils. In two of the soils, clay dispersion across a range of sodicity levels was lower und er the 0.4 S m(-1) treatment than under the 0.1 S m(-1) treatment and in th e other two soils, clay dispersion across a range of sodicity levels was si milar between the two salinity treatments. Changes in K-sat were greatest i n the finer textured soil (decreasing an order of magnitude across the rang e of sodicity levels), but was unchanged in the coarse textured soils. Resu lts suggest that these sulfatic soils are more susceptible to sodicity indu ced deterioration than chloridic soils. These results and earlier field obs ervations suggest that sustainable irrigation may be limited to sites with a water source having a SAR <5 and an EC not exceeding 0.3 S m(-1) for thes e sulfatic glacially derived soils.