Unsaturated soil water movement in hysteretic and water repellent field soils

Correct simulation of soil water fluxes in the unsaturated zone is needed for studies on leaching of contaminants. Both hysteresis and preferential flow affect soil water movement in the unsaturated zone. Hysteresis of the soil water characteristic and preferential flow in the case of water repellent soils were incorporated in a general agrohydrological numerical model. The model was applied to data sets from two locations with hysteretic and water repellent soils. It is shown that hysteresis retards soil water movement, while preferential flow enhances soil water movement. During infiltration events, hysteresis retains more water in the root zone than the amount computed for reference simulations that neglect hysteresis. However, generally in field conditions incorporation of hysteresis decreases the amount of simulated water storage. Furthermore, it is shown that in fields with shallow water tables and without pending, soil water fluxes are marginally affected by hysteresis and preferential flow. However, preferential flow directly affects the residence time of solutes in the unsaturated zone.