Soil hydraulic model parameters and methodology as affected by sodium salt solutions

Soil salinization from shallow ground waters is problematic in numerous regions of the world. These ground waters can degrade soil physical properties and require special land management to maintain soil salinity levels ideal for crop and rangeland production. The objectives of this study were to evaluate how saline and sodic solutions changed soil hydrologic properties and how hydrologic parameters change with solution composition. Four soils ranging in texture from sandy loam to silty clay, were saturated with solutions ranging in electrical conductivities (EC) of 0.5 to 8 dS m(-1) and sodium adsorption ratios (SAR) of 0 to 20. The hydraulic conductivity and water retention were measured using pressure plates, HYPROP evaporation method, and a dewpoint potentiometer. Data was fit with the van Genuchten and dual porosity models and the model parameters were evaluated. There was an increase in water retention and decrease in hydraulic conductivity when soils were near saturation as solution SAR increased and EC decreased at potentials near saturation. Water retention method combinations agreed well for low salinity treatments, but fitting parameters did not agree well for the higher salinity treatments. The coarser textured soil had a stronger disagreement in fitting parameters for the different water retention method combinations and greater salt build up near soil surface. Capillary rise of salt bearing waters of low EC and high SAR increases soil water retention and decreases hydraulic conductivity near saturation which will slow rates of downward water movement and salt leaching.