Influence of Crop Rotation, Intermediate Crops, and Organic Fertilizers on the Soil Enzymatic Activity and Humus Content in Organic Farming Systems

The influence of crop rotation systems with different portions of nitrogen-fixing crops, intermediate crops, and organic fertilizers on the enzymatic activity and humus content of soils in organic farming was studied. The highest activity of the urease and invertase enzymes was determined in the soil under the crop rotation with 43% nitrogen-fixing crops and with perennial grasses applied twice per rotation. The application of manure and the growing of intermediate crops for green fertilizers did not provide any significant increase in the content of humus. The activity of urease slightly correlated with the humus content (r = 0.30 at the significance level of 0.05 and r = 0.39 at the significance level of 0.01).