Studies on nitrate leaching and changes in the nitrogen balance during a long-term mineral fertilization experiment

On selected plots of a long-term NPK mineral fertilization experiment set u p in 1973 at the institute's Experimental Station in Nagyhorcsok, the nitra te-N content of the 0-600 cm soil layer, the depth distribution of the NO3- N and the nitrogen balance of the plots was studied in 1995, in the 22(nd) year of the experiment, similarly to the analyses carried out in the 12(th) and 17(th) years. After harvesting the indicator plant, rye, soil samples were taken every 20 cm from the control and from plots treated with 100, 200 and 300 kg N/ha/y ear. After the application of higher nitrogen rates, nitrate-N accumulation was detected in the sample soil layer. At an application rate of 200 kg N/ha/ye ar the average nitrate-N content in the upper 0-600 cm soil layer in these plots was 12 mg/kg at the first sampling, 18 mg/kg after 17 years and 20 mg /kg after 22 years. These figures were 21,35 and 43.2 mg/kg in the 300 kg N /ha/year treatments. Differences were recorded not only in the average nitrate-N values measured in the soil profiles of the fertilized treatments, but also in the course of the nitrate accumulation curves plotted for the sampling times. The long-term experiment made it possible to study the nutrient uptake and mineral nutrition of a number of crops, The analysis of the nitrogen cycle confirmed the observation that nitrogen fertilization adjusted to the requi rements of the cultivated crops and suited to the environmental conditions and growing site potential does not pollute the environment to an intolerab le extent. Over-fertilization can be avoided by determining the mineral-N r eserves of the soil and the N requirements of the cultivated crop.