TEMPORAL VIABILITY OF SOIK HYDRAULIC-PROPERTIES WITH WETTING AND DRYING SUBSEQUENT TO TILLAGE

Modeling of water movement in soils requires mathematical representation of hydraulic conductivity and water retention functions. Hydraulic properties of soils are expected to vary over time during a cropping cycle, especially soon after tillage. Field experiments were conducted on two soils, a Typic Torrox and a Vertic Haplustoll, to evaluate the effect of soil deformation from repeated wetting and drying on soil properties such as hydraulic conductivity, sorptivity, and the water content-suction relationship. Hydraulic conductivity near saturation was the most sensitive measure of temporal changes of hydraulic properties, decreasing 100-fold with wetting and drying after tillage. Sorptivity measured with negative head, a simple and rapid method, was also sensitive to temporal changes and was judged the most appropriate for variability studies requiring a large number of samples. The impact of temporal changes in hydraulic functions on soil-water movement was demonstrated by a comparison of water content profiles predicted with a simulation model using input functions obtained before and after irrigation.