Fluctuations of nitrogen levels in soil profile under conditions of a long-term fertilization experiment

Abstract

The present study is focused on the correlation between varied long-term fertilization and changes in soil nitrogen concentrations. It was found that all fertilization systems significantly increased the levels of total, mineral and organic nitrogen in the soil profile. Organic fertilizers (manure and slurry) contributed to a more considerable increase in the concentrations of total nitrogen and nitrogen undergoing hydrolysis in 6M HCl, compared to mineral fertilizers. Ammonia nitrogen dominated over nitrate nitrogen among mineral nitrogen forms. Organic fertilization contributed to nitrate nitrogen accumulation, while mineral fertilization to ammonia nitrogen storage. The highest accumulations of nitrate nitrogen and ammonia nitrogen were observed after the application of slurry and manure, respectively. Hydrolyzable nitrogen content and its proportion in total nitrogen generally decreased with soil depth. An increase in the levels of organic nitrogen forms, i.e. nitrogen contained in amino sugars and amino acids as well as ammonia nitrogen from decomposition of amides, amino sugars and amino acids, was conditioned primarily on the application of organic fertilizers, particularly manure. Amino acid-N dominated among hydrolyzable nitrogen compounds (77%), while amino sugar-N accounted for 5.6% only.