SOIL AND CROP BASED NITRATE LOSSES IN A D RINKING-WATER RESOURCE AREAWITH A HIGH N-LOSS RISK

From 1990 to 1992 field trials were conducted with maize, winter wheat and meadow, which were treated with stepped N-doses, and with several other crops (winter rape, catch crops, winter crops, fallow) grown un der normal farm practice on soils with available water capacity of 40 mm and 180 mm to 240 mm. Precipitation was below average during the tr ial period. NO3-N-leaching and NO3 concentration in the leachate was e xamined by taking soil samples and calculating a simplified soil-water -balance. Losses of NO3-N due to leaching were up to 3 to 4 times grea ter in deep soils than in shallow soils, because of lower N-uptake by crops and increased amount of leachate on shallow soils. Nitrate conce ntrations in the leachate in deep soils were within the range of the t hreshold value of the drinking water standard, when nitrogen fertilize r did not exceed the yield optimum. The threshold value was, however, seriously exceeded in some cases in shallow soils. The lowest nitrate loads occured under meadow and winter catch crops.