Over the past decades, intensive farming has operated under conditions of progressive degradation of the soil cover, maintaining production levels only at the expense of inadequate expenditure of non-renewable energy resources. The soils have acquired irreversible excessive compaction in the sub-arable part of the profile, and the dehumification has acquired a threatening status. The humus content in the soils of Ukraine decreased by almost 25%, and the average annual losses amount to 0.6-0.7 t/ha. Therefore, the search for ways to guarantee the reproduction of soil organic matter, reliable control and restoration of the optimal humus status is extremely relevant. The purpose of the study is to activate natural nitrogen-fixing systems using a mix of green manure and by-products of agricultural crops of short-term leguminous crop rotation. Field experiments were conducted on light grey soils during 2018-2020 in the experimental field of Polissia National University in a leguminous short-term rotation system. This study uses general scientific methods to establish the area of research, plan and lay experiments, conduct observations and analysis; visual – during the implementation of phenological observations; field – to study the relationship with abiotic factors; physiological – to determine the symbiotic effectiveness of preparations of biological origin. The technology of growing agricultural crops in leguminous crop rotation, which ensures the supply of raw materials of organic origin and the accumulation of air nitrogen by root nodule bacteria, has been theoretically substantiated and improved. It is established that one hectare of crop rotation area receives 6.8 tonnes of dry organic raw materials, which corresponds to 78.3 kg/ha of biological nitrogen. It is found out that inoculation of soybean seeds with a preparation of biological origin – Optimise 400, and treatment of soybean crops at BBCH microstages 60-63 with a complex microfertiliser on a chelated basis Nanovit Super+Magnesium Sulphate contributes to the active development of nodule bacteria, the number and weight of which is 81-89 pcs per plant and 510-572 kg/ha. Thus, the active symbiotic potential was 34.2-38.9 thousand kg/day. It is proved that during the growing season soybeans generate 357-400 kg/ha of biological nitrogen in the air, which provides a seed yield of 2.96-2.64 t/ha and leaves 117-160 kg/ha of nitrogen in the soil. The practical value of this study lies in the possibility of enriching the soil with organic matter and the biological form of nitrogen.

Keywords: soil fertility, crop rotation, seed inoculation, foliar dressing, soybean yield.