DISPLACEMENT OF N-15-LABELED NITRATE IN THE WINTER SEASON AND THE SUBSEQUENT UTILIZATION BY WINTER-WHEAT IN-FIELD EXPERIMENTS ON DIFFERENT SITES

The autumn-applied N-15-nitrate-tracers showed in 8 field experiments the nitrate-displacement untill spring, which is usually hidden by mineralization. On the heavier soils displacement was small. Therefore the nitrate from the autumn remained available to the winter wheat, or spent the winter partially inside the plants and - possibly - entered the organic N-fraction of the soils. On the sandy soil the nitrate-leaching was more pronounced; the plants incorporated not much of 15N and it's utilization during the growing season was small. Immobilization of the nitrate applied in autumn in the top soil was also small. Denitrification during the winter may have happened. Surplus of nitrogen after harvest may pollute the groundwater and should be avoided by adequate crop management.