The studies were conducted to investigate the changes in selected properties of the soil under varying organic fertilization applied before forecrop (manure – 30 t ha-1 or stubble crop – white mustard – ploughed down with sugar beet leaves – 40 t ha-1) with increasing rates of nitrogen fertilizers (60, 100, 150 kg N ha-1). It was found that fertilizers did not significantly affect changes of the physical properties of medium soil. The content of humus in the soil was more affected by organic than nitrogen fertilization. Application of manure or stubble crop with sugar beet leaves increased the content of humus by 0.16 and 0.10%, respectively, compared to the soil without organic fertilization. Only the application of manure caused a significant increase in cellulose decomposition compared to the soil without organic fertilization. Ploughing down organic fertilizers decreased the index of cloddiness of the soil and increased the index of soil structure. These indices did not unequivocally depend on the rate of nitrogen fertilization.