The aim of the research was to determine the possibility of increasing the mineral nitrogen content in the soil under conditions of waste (straw, melasse wort) application. The studies were based on a field experiment carried out on podzolic soil, the textural group – light loamy sand. The scheme of the experiment consisted of three blocks with 6 randomized treatments each: 0 (0), NPK (NPK), farmyard manure (FYM), straw + mineral nitrogen (S + N), straw+melasse wort (S + W), melasse wort (W). Waste substances were used at the beginning of the experiment. Doses of the waste were calculated on the basis of total nitrogen (Nt) amount supplied with FYM at 25 t ha-1 (about 125 kg Nt ha-1). Chickling vetch (cultivar Darek) in 1999, potatoes (cultivar Sante) in 2000 and winter wheat (cultivar Mewa) in 2001 were used as the test plants. The soil samples were collected before the beginning of vegetation (I term), as well as after plant harvesting (II term), from 0–20 cm, 20–30 cm, 30–60 cm, 60–90 cm depths, from each fertilization treatment. The content of ammonium nitrogen and nitrate nitrogen was determined in the samples. The results showed that organic waste application caused an increase of inorganic nitrogen content in most experimental treatments, in comparison to the control (without fertilization). The factor that favored nitrate and ammonium nitrogen accumulation the most was fertilization with straw and melasse wort. The content of the analysed mineral forms was the greatest in the surface layer of the soil and decreased with the depth of the soil profile. However, more than one accumulation zone was sometimes observed. The study indicated that, in most experimental treatments, the ammonium form of nitrogen dominated over the nitrate one.