INFLUENCE OF SLOPE AND EXPOSITION ON WATER-BALANCE OF LOESS SOILS

Laboratory and field measurements as well as deterministic simulation models were used to determine the water components of loess derived so ils 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 nort hern exposition. Crop rotation was sugar beet, winter wheat, sugar bee t. Results show that the soil water budget is strongly related to slop e position, relief and plant available water in the rootzone. It was f ound that drainage at the bottom of a slope is often higher than on to p of the slope. On slopes with northern exposition groundwater recharg e increases with inclination whereas actual evapotranspiration decreas es. For slopes with southern exposition the opposite reaction can be e xpected. The thickness of loess deposits and the root depth determine the plant available water; a sensitivity study demonstrates how ground water recharge decreases with the amount of plant available water. Thi s reaction is independent of the exposition of the slope. Field and si mulation studies show that runoff occurs under sugar beet whenever soi l is bare or sparsely covered, rainfall intensity is high and topsoil is sealed. Moreover, in loess derived soils interflow may occur on sit es with stagnic horizons. Sensitivity analyses show that this process probably takes place whenever saturated hydraulic conductivity of this horizon is less than 10 cm/d.