Seasonal dynamics of mineral nitrogen in the 10th and 30th years of a long-term field experiment in Hungary

Long-term field experiments are the most suitable tools for determining the optimal nutrient-supplying technologies that contribute to sustainable agriculture. Under certain environmental conditions (low precipitation, deep groundwater table, negative water balance), part of the applied nitrogen (N) can be found in the soil profile for a longer period and provide N nutrition for crops. A long-term field experiment has been running at Nagyhorcsok in Hungary since 1973. The nitrogen Cophosphorus Copotassium (NPK) application rates follow the overall nutrient-supplying categories (weak, medium, adequate, excessive) by the main nutrients and their combinations. The seasonal dynamics of exchangeable NH4 and NO3 were followed in 1983 and 2003. From certain treatments, two parallel average samples (20-20 subsamples were mixed to get average composite samples by plots) were collected 19 times from March through November from three soil layers. There was no difference in NH4-N between years, and its seasonal fluctuation was slight in both years, whereas there was an increase in NO3-N in accordance with the applied N rates. No significant difference occurred in the NO3-N of the N-0 < P0K0 and the N1P1K1 treatments during both years. A significantly higher NO3-N content was observed in the higher rate nutrient treatments. Both soil N forms were higher in 1983 than in 2003. Based on the experimental results, the fate and behavior of the surplus N in the soil can be characterized and the residual amount can be taken into account during the calculation of the N-fertilization demand of arable crops in relation to the N-fertilizer advisory system.