Our work discusses the influence of the annual application of manure, slurry, and NPK fertilizer for a period of many years on the total, hydrolyzable, and mineral nitrogen content in the arable layer of lessive and brown soils. Annual fertilization resulted in an average increase in total nitrogen content of 27.3% in lessive soil and 48.4% in brown soil, and in the case of hydrolyzable nitrogen, increases of 25.6% and 51.3%, respectively, when compared to the control objects. In total nitrogen content the share of hydrolyzable nitrogen was found to be 59.7% in lessive soil and 63.3% in brown soil. The content of mineral nitrogen in fertilized objects showed an increase in the range of 5.5-20.6 mg·kg^-1 in lessive soil and 5.0-13.0 mg·kg^-1 in brown soil. For lessive soil, the percentage share of N-NH₄ and N NO₃ in mineral nitrogen was, on average, 55% and 45%, whereas in brown soil these figures were found to be 75% and 25%, respectively. A significant positive correlation was confirmed between the analyzed forms of nitrogen only in the case of brown soil.