The long-term dynamics of the humus content and reserves in the forest-steppe and steppe chernozems of the center of the Russian Plain was studied in a series: virgin land - perennial arable land. To the greatest extent, the transformation of the humus profile of chernozems as a result of plowing is manifested in its upper part. The depth of transformation spread reaches approximately 80-90 cm. In the series of subtypes: podzolic - leached - typical - ordinary chernozems, there are differences in the amount of humus lost. Long-term plowing of these soils leads to the humus content decrease. Therefore, real (t/ha) and apparent (%) humus losses in soils during their long- term plowing can differ significantly. The greatest losses of humus were recorded in leached chernozems – 15 t/ha. In podzolic and ordinary chernozems, the loss of humus reserves was approximately the same and amounted to 13 and 14 t/ha, respectively. Typical arable soils, as a rule, contain 15 t/ha fewer humus reserves than virgin soil. The humus level of chernozems varies significantly in the first years of use, then it stabilizes at a fairly high level according to the new regime of matter and energy circulation in agrocenoses. An objective assessment of changes in the main indicators of the humus state of chernozems during their long-term agricultural use should be carried out not by the percentage of humus but by its reserves, taking into account the corresponding values of the equilibrium addition density.

One of the ways to maintain soil fertility is to use organic fertilizers. One of them can be straw of cereal crops (winter wheat and barley). However, the process of its decomposition can be delayed for several years. It is possible to accelerate the transformation process by using the native strain of cellulosolytic micromycete (Humicola fuscoatra VNIISS 016). Its introduction together with straw before plowing stabilizes agrophytocenosis. The experiments were carried out in laboratory under simulated conditions close to field ones. Scheme of the experiment: 1. Straw; 2. Straw + N (40 mg/4 g, which corresponds to 40 kg/ha); 3. Straw + N + H. fuscoatra + PC (nutritional supplement – molasses) (Kolesnikova M.V., 2014). As a result of the studies, it was established that winter wheat straw without additional components lost 0.86 g in weight (from the initial 4 g), 1.03 g when adding nitrogen fertilizer to the straw, and 1.49 g when using H. fuscoatra. We found that the addition of nitrogen to the straw stimulate the process of its transformation. Straw with nitrogen decompose faster than straw without any additives (by 41.5%). However, the addition of the native strain of micromycete accelerate the process by 48.3%. Barley straw lost 0.82 g in weight, straw with nitrogen fertilizer lost 1.06 g, straw and H. fuscoatra – 1.13 g. Further, the decomposition rate increased in the following row: straw → straw + N, where the speed was 26.7% higher → straw + N + H. fuscoatra, the decomposition rate is – 85.3% higher.

A large role in the creation of soil fertility and water-resistant structure, in the processes of humus synthesis and mineralization, as well as in the provision of agricultural plants with elements of mineral nutrition, belongs to soil microorganisms. For leached chernozem, the influence of field crops on the main groups of microorganisms, which are involved in the formation of effective and potential soil fertility, and associated enzymes was established. The purpose of the work is to study the effect of agricultural plants on the structure of the microbial community of the soil and the activity of enzymes involved in the formation of effective and potential soil fertility. Soil samples were taken from the 0-25 cm layer. They differed in anthropogenic load: virgin soil and soil where crops were cultivated. To count the number of soil microorganisms in the crops and their rhizospheres, we used the method of culturing successive dilutions of the soil suspension on selective nutrient media. The catalase activity of the soil was determined by the gasometric method. It is based on measuring the decay rate of hydrogen peroxide when it is interconnected with the soil in terms of the amount of oxygen released. The method for determining phosphatase activity is based on the quantitative calculation of inorganic phosphorus, which is formed by the breakdown of organic phosphorus compounds under the action of phosphatases.