Summary The long-lasting effect of high doses of organic or inorganic fertilizers on the bare fallow soil is. shown as follows. Of the organic substances supplied in the fertilizers 12–15 per cents accumulate in the soil, of the supplied nitrogen in the organic form 30–35 per cents remain in soil and of the nitrogen supplied in the mineral form approximately 8 per cents. The C: N ratio is lowest in the plots treated with inorganic fertilizers (5–6), and the C: Norg ratio is close to 10 in all the plots. Organic fertilization increases the intensity of microbial proceses in the soil, inorganic fertilization limits it strongly. The stability of organic substances is largest in non-fertilized plots, and it is lowest in the plots with inorganic fertilization. Organic fertilization improves all the parameters of soil fertility (humus, nutrients, structure, water regime), inorganic fertilization deteriorates them, and, basides, it causes a strong decrease of the pH value.