NITROGEN BALANCES IN LONG-TERM FIELD EXPERIMENTS

The influence of fertilization with different N doses on nitrate-N con tent of the deeper soil layers were investigated in soils of long-term experiments at the experimental stations of the National Fertilizer E xperimental Network in Hungary. Distribution of nitrate-N with depth w as also studied in plots fertilized with different N doses. Although t hese experiments were set up according to an identical experimental pl an at every location, after 20 years of experimentation substantial di fferences could be detected in the nitrate-N contents, nitrate-N distr ibution profiles on plots of the same treatments, as well as in the yi eld and the nitrogen uptake of the cultivated plants at the various si tes. These differences are attributed to differences in soil propertie s and in environmental conditions existing at the individual experimen tal stations. The conclusions drawn from the data are very important w hen evaluating the role of nitrogen fertilization in the nitrate-conta mination of soils, surface, water and groundwater, and for a more prec ise determination of the N doses to be applied under specific soil and environmental conditions.