Long term simulation of soil/crop interactions to estimate management zones and consequences for site specific nitrogen management considering water protection

Simulations of water and nitrogen dynamics and crop growth of winter wheat were carried out for two fields in different landscapes of Germany. One field in the north west showed a clear spatial structure of soil texture. Spatial yield data for three years were used to validate the model. Stable high and low yield areas were derived from simulations over 32 years. The more homogeneous textured field in the south-east of Germany showed spatial yield patterns mainly due to the relief. Simulations of 21 years showed small areas of low yield while in most of the field, the response was indifferent from year to year. Model results indicated small problematic areas on both fields with nitrate concentrations of the seepage above 50 mg NO₃ l^-1 under conventional fertilization. Fertilizer scenarios were used to estimate the amount of maximum annual nitrogen fertilization to meet drinking water quality standards.