The effect of 6-years differential fertilization on soil properties (120-360 kg N/ha and two levels of organic-mineral fertilization) was studied in two parts using changing potassium rates. No influence of (A) 120 kg N on the concentration of analysed elements in the soil has been proved. The organic-mineral fertilization (D-240 N) caused a smaller decline in calcium and magnesium than mineral fertilization (B-240 N). The largest decrease in Ca and Mg and a significant increase in potassium was observed using the dose N-360 (C and E).