Assessment of soil hydraulic functions for modeling the soil water dynamics of a soybean field

The soil water dynamics of a soybean field in Groiss-Enzersdorf, Lower Aust ria was simulated during one vegetation period with the computer "SOIL"-mod el, using different laboratory and field methods for the determination of t he soil hydraulic input data. Hydraulic conductivity functions, as estimate d from soil water retention curves, were highly correlated with those measu red with an Evaporation Controlled Instantaneous Profile-method in the labo ratory, where the GUELPH-permeameter-method for establishing the saturated soil hydraulic conductivity (K-sat) was used. The data obtained, i.e. bulk density, tension infiltration, saturated conductivity, and simulation resul ts showed clearly that it is almost impossible to establish one unique soil hydraulic conductivity function of a tilled top soil during a vegetation p eriod. Water infiltration after a heavy thunderstorm following a 4 week dry period could only successfully be simulated using an empirical bybass flow algorithm of the computer model.