Error and uncertainty with the determination of the soil water retention function and saturated hydraulic conductivity for soil water modelling

Simulation of soil water movement in Richards’ equation based soil-water models requires knowledge of the soil water retention function and saturated hydraulic conductivity. Traditionally these parameters have been determined by desorption which is costly and time consuming. In this study we compared VGM parameter values determined by desorption with two rapid approaches, laboratory evaporative flux and inverse solution of in situ cumulative infiltration from tension infiltrometers. Methodology had a profound effect on all VGM parameters except n. Methodology influenced saturated hydraulic conductivity values which varied by up to four orders of magnitude. Both rapid assessment procedures were improved by knowledge of the residual water content èr or moisture content at -1500 kPa. In water repellent or vertic soils differences in VGM values resulted in a lack of confidence in all procedures.