REDUCING NITRATE-LOSSES UNDER MAIZE BY AD JUSTED FERTILIZER STRATEGIES ON SOILS WITH HIGH N-LEACHING RISK

The dry matter yield and N-uptake of maize as well as NO3 leaching in the percolating water were examined for different amounts and distribu tions of N-fertilizer on soils with an available water capacity < 40 m m and 180 mm to 240 mm, respectivly. On soils with a low available wat er capacity, yield was reduced to a third due to N-leaching losses in the early stages, and to water stress. Leaching losses on shallow soil s exceeded those on deep soils 3 to 4 times. Nitrate concentration in the percolating water was higher than the threshold value of the drink ing water standard (50 mg NO3/l). This limit could more easily be met on deep soils. Nitrate leaching losses occurred soley during the early stages, when high nitrate contents in soils were determined, owing to low N-uptake of the plants. Hence, N-losses were reduced and the N-ef ficiency of maize was improved by application of fertilizer later in t he growing season (plant height 15 cm), without yield loss. N-fertiliz er amounts from 80 kg N/ha up to 120 kg N/ha were sufficient to reach the maximum yield. In this case negative N-balances were observed. Thi s will reduce the N-content of soils and lower the N-release.