Influence of slope and exposition on water balance of loess soils

Abstract

AbstractLaboratory and field measurements as well as deterministic simulation models were used to determine the water components of loess derived soils with different expositions and slopes in the hilly region South of Hannover, Germany.Studies were investigated from 1987‐1990 on three positions of a loess slope with 8 % inclination, 200 m length and northern exposition. Crop rotation was sugar beet, winter wheat, sugar beet.Results show that the soil water budget is strongly related to slope position, relief and plant available water in the rootzone. It was found that drainage at the bottom of a slope is often higher than on top of the slope. On slopes with northern exposition groundwater recharge increases with inclination whereas actual evapotranspiration decreases. For slopes with southern exposition the opposite reaction can be expected. The thickness of loess deposits and the root depth determine the plant available water; a sensitivity study demonstrates how groundwater recharge decreases with the amount of plant available water. This reaction is independent of the exposition of the slope. Field and simulation studies show that runoff occurs under sugar beet whenever soil is bare or sparsely covered, rainfall intensity is high and topsoil is sealed. Moreover, in loess derived soils interflow may occur on sites with stagnic horizons. Sensitivity analyses show that this process probably takes place whenever saturated hydraulic conductivity of this horizon is less than 10cm/d.