VERTICAL WATER AND NITRATE MOVEMENT INTO DEEPER SOIL LAYERS ON FIELDSLOCATED IN THE SOUTH OF GERMANY

In Southern Bavaria, selected fields from deep loess and sandy sedimen ts were sampled to a depth of maximum 10 m every 4 months, in order to determine the basic processes of water and nitrate movement in the co urse of the year. The downward movement of water and nitrate followed the principle of piston flow only in the intermediate vadose zone of l oess soils with a leaching distance amounting 0.8 m per year. On the o ther hand an accelerated as well as a delayed transport was observed i n the zone of evapo-transpiration of loess soils and in the whole prof ile of sandy soils, not being in accordance with the simple simulation model FLOTRA based on the classic theories of transport (Darcy flow, convection-dispersion-equation). Preferential flow led to the leaching of nitrate from the top soil to the lower boundary of the evapotransp iration zone of loess soils in 2 m depth in winter and spring. In sand y soils nitrate was leached to the groundwater table in 4-6 m depth af ter extensive rainfall.