Nitrogen balance for 5 years (1997–2001) was studied in tree fertilization systems (only mineral, mineral and organic and only organic) in the long-term fertilization experiments caried out on the Experimental Fields in Skierniewice (since 1923), belonging to Warsaw Agricultural University. Dose of nitrogen in ammonium nitrate and farmyard manure (FYM), N uptake by plants and changes of total N content in a 0–65 cm soil layer for 5 years (one crop rotation) on fertilization systems were considered in the calculation of the N balance. Nitrogen uptake by plants was about 23–27 kg N ha-1 on the plots fertilized only with PK in mineral fertilization system. On the same fertilizer object (CaPK) but on the field with mineral-organic fertilization system and with legumes, the N uptake by crops was 4–5 times higher than only in mineral system. Percentage of nitrogen uptake by plants from the ammonium nitrate in only mineral fertilization system (CaNPK) ranged from 57–63% and 34% on mineral organic system. Utilization of N by crops from FYM was much lower in comparison to the mineral fertilizers and reached only 19%. The calculations of nitrogen balance indicate that the loss of N from ammonium nitrate was much lower (34–40%) in only mineral fertilization system than in mineral organic fertilization system (63%). The total N losses from plots treated with ammonium nitrate, FYM and legumes in the crops rotation were much lower (13% of the total N incom) than from the soil with only mineral system (24–25% of the total N incom). The highest N losses from the soil were in only organic fertilization system (48% of the total N incom).