Effect of Mineral Fertilization on NO3‐N Leaching on Clay Soil

Abstract To evaluate the environmentally friendly N fertilization practice is important to study the N balance of the soil as well as the NO3‐N accumulation and leaching in a given land site. This work aimed at providing data about the effect of N fertilization on the N balance of the soil and NO3‐N leaching on the basis of an 11‐year experiment. At four N application rates—0, 80, 160, 240 kg ha−1—of a long‐term NPK mineral fertilization experiment was set up in 1989, on chernozem meadow soil, at Szarvas, the NO3‐N content of the 0–300 cm soil layer, the depth distribution of the NO3‐N and the N balance of the selected plots were measured, in the 4th, 8th and 11th year of the experiment. On chernozem meadow soil with 3.0–3.2% humus the removal of N by the crops was 1126 kg ha−1 during the 11‐year experimental period. At an application rate of 80 kg N ha−1 the N balance was negative. At 160 kg ha−1 N fertilization the N balance went into equilibrium approximately in the 8th and 11th year. The 240 kg ha−1 N dose resulted in an increasingly positive N balance. The N pool in the soil increased at each N application rate compared to the unfertilized treatment. The leaching of NO3‐N began after the 4th year at on application rate of 160 kg N ha−1. After the 8th year the NO3‐N leaching was significant on each N treated plots and the zone at which the accumulation of NO3‐N was maximised was between 140 and 180 cm. Nitrogen leaching was observed without N fertilization if the growing season was dry and low N‐demanding crops were grown. The shifting of the water table after an extremely wet and dry period resulted in a huge NO3‐N losses. The harmful environmental side‐effects of N over‐fertilization can be avoided by determining the mineral N pool of the soil and the N requirements of the cultivated crop.