Hydraulic Property Modification of Saline-Sodic Soils By Addition of Calcium Chloride

     Saline-sodic soils have developed in some irrigated areas of eastern Montana, due in part to increasing total dissolved solids of irrigation water and sodium accumulation in these irrigated soils. This accumulation has resulted in reduced yields, prompting farmers to consider application of amendments without evaluating the potential impact on irrigation return flow quality and/or soil physical properties other than sodium displacement.

     Previous greenhouse experiments have been conducted with intact soil columns of loam, silt loam, and silty clay loam textures. Medicacto sativa L. was grown in soil columns irrigated with an accelerated salt-loading schedule using past, present and projected future irrigation water qualities from the Powder River. Following the final harvest, two studies were conducted. One study utilized undisturbed soil cores from two of the five replicated soil columns to characterize long?term irrigation and subsequent calcium chloride application effects on soil hydraulic properties and drainage water quality. Identical cores were treated with two rates of calcium chloride, 6.42 kg m^-2 and 7.73 kg m^-2. Calcium chloride solution was applied to the cores and passed through with a pressure head of 33.0 kPa to simulate free drainage. Leachate was collected and analyzed for sodium concentration. Following amendment application and leaching, replicated Tempe cell measurements in the pressure range 0-100 kPa were made to determine the effect of calcium chloride on soil hydraulic properties. Water outflow data were used to prepare moisture release curves and calculate pore size distribution.

     The second study utilized the remaining undisturbed soil columns to evaluate the effect of calcium chloride application on soil hydraulic properties. Calcium chloride was applied at a rate of 6.42 kg m^-2 to soil columns. Following calcium chloride application, a 5 cm irrigation was applied and allowed to drain below soil surface. Intact cores were taken from surface and placed in Tempe cells to determine effect of treatments on soil hydraulic properties.

     Irrigation of the soils with present and projected future water qualities resulted in decreased macroporosity and reduced soil hydraulic conductivity. Addition of calcium chloride increased the macroporosity but resulted in significantly elevated sodium concentration in drainage water. This elevated sodium concentration would likely have deleterious effects on groundwater quality.