Prediction of hydraulic conductivity and sorptivity in soils at steady-state infiltration

The purpose of this study was (1) to find a matching factor (u) between infiltration rate and hydraulic conductivity during steady-state infiltration, and (2) to propose equations based on infiltration and soil moisture-retention functions for prediction of the hydraulic conductivity K(θ) within the rapidly (non-capillary) drainable pores (RDP) and capillary-matrix pores of soils. The K(θ) of capillary pores was divided into K(θ)_SDP, K(θ)_WHP and K(θ)_FCP within slowly drainable pores (SDP), water-holding pores (WHP) and fine capillary pores (FCP), respectively. Five soil profiles of calcareous sandy loam, alluvial saline and non-saline clay, located at the Nile Delta, were used to apply the proposed equations. The highest and the lowest values of K(θ)_RDP were observed in calcareous and saline clay soil profiles, respectively. Values of K(θ)_RDP remained higher than those for capillary pores in the studied soils. The predicted values of K(θ) in capillary and non-capillary pores classes were in the expected range for unsaturated hydraulic conductivity. Water sorptivity (S) was determined at initial unsaturated soil water conditions and calculated at steady-state infiltration (S _w) using a derived equation. There was a decrease in S with an increase in soil water content; i.e. at steady-state infiltration, S decreased by 35–40% in calcareous soils and by 45–60% in alluvial clay soils. The parameter values of u and S _w tended to be uniform in calcareous soils, but nonuniform in saline and non-saline clay soils.