The paper gives the results of the research on determining the total and active symbiotic potential, as well as the formation of tubers bacteria mass of ultra-early soybean’s Ustia variety on light gray soils of Polissia, Ukraine. The nitrates and the ammonia are of great importance for the nitrogenous nutrition. The nitrates are received through the root system and by means of enzymes they take part in protein secretion. The atmosphere nitrogen is digested by tubers’ bacteria which take part in symbiosis with a root system. The soybeans inoculation by the preparation Optimise-200, by a pure culture of nitrogen fixating bacteria Bradyrhisobium japonieum contributes to the active side shoots growth and formation, their height is up to 68,2 cm, in other words their growth as to the control variant is 12,9 cm more that is equivalent to applying mineral fertilizers at the rate of N60P60K60 kg/ha. It has been established that seeds inoculation with the introduction of mineral fertilizers provides plants height growth by 13,7 cm, a mass of 1000 units of seeds is 160,7 g, that is by 4,5 g more as compared to inoculation. The maximal height of a plant-stand and of a lower fruit disposition above the soil surface is 86,0 and 19,2 cm correspondingly on the variant with the introduction of mineral fertilizers, inoculation and foliar fertilizing. A pre-sowing seed treatment with an inoculant Optimise-200, the introduction of mineral fertilizers at a rate of N60P60K60, the plants foliar treatment with nitrogen at a rate of 5 kg/ha and the introduction of a complex fertilizer on a chelate base Kristalon universal – 2,0 kg/ha in the period of beans formation contributes to an intensive development of tubers bacteria, the mass of which is 498 kg/ha, which in recalculation on biological nitrogen is 122 kg/ha, which is equivalent to 359 kg of ammonia nitrate and provides high soybean yields – 4,05 t/ha.

Keywords: soybeans, symbiotic productivity, biological nitrogen, tubers bacteria, yields