The objective of the research is to determine fertilizer dose, which regular applying provide preservation of the fertility of ordinary chernozem in Azov area of the Rostov region, as well as to determine the level of the yield in crop rotation at applying of the established fertilizer doses allowing to preserve humus content in soil. Experiments, recording, soil sampling were carried out according to the procedures of field experience. The factors under study were humus content in soil, different doses of organic and mineral fertilizers applied either separately or together in nine-field grain-row crop rotation. Humus content in soil was determined by the method of Tyurin in the reduction of N. V. Simakov. It was marked the increasing of the impact of applied fertilizers on yield formation. The greatest yield increase was marked in the variants where mineral and organic fertilizers were applied together. In most variants of the experiment the significant decrease from 0.07 to 0.34 % of organic matter content in arable topsoil and subsoil horizons was revealed. It was established, that for Azov zone of the Rostov region at a joint systematic applying of manure by the dose of 11.1 t/ha and mineral fertilizer by the doses of NPK 73, 23, 23 kg of active substance per hectare the humus percentage content in arable topsoil and subsoil horizons remains virtually unchanged, thereby facilitates to soil fertility preservation and stable yield through the whole crop rotation. At the recommended fertilizer dose and climatic conditions without sharp deviations from average-annual ones, norms of the yield of nine-field grain-row crop rotation will be more than 3.91 tons of grain units per hectare.
Keywords: humus, fertility preservation, fertilizer dose, crop rotation, yield, rotation, yield increase.
