Productivity of the sown pastures created in the conditions of the Central Yakutia, first of all, depends on security of grasses with nitrogen. The rational combination of biological and mineral nitrogen helps to solve the problems of plant protein in the permafrost soils of Yakutia. The need to use a biological source of nitrogen is currently due to the lack and high cost of nitrogen fertilizers supplied. An important environmentally friendly source of nitrogen is biological nitrogen accumulated by perennial legumes due to symbiosis with nodule bacteria. Legumes have the unique ability to provide themselves with the necessary amount of biological nitrogen and enrich the soil with it. The aim of the research is to study the effect of alfalfa sowing on the productivity of legume-grass stand during haying. Research on the effect of seeding alfalfa on productivity conducted in the scientific station of Institute. Overseeding alfalfa were the summer sowing. Experience laid on the herbage of the seventh year of life (1997). Experience had 8 options: 4 options grasses - lakokraski Sitnikova grade Mancari, awnless brome variety Khaptagayskiy, legume-grass pasture includes grasses and alfalfa sickle grade Yakut yellow in 4-fold repetition. The efficiency of mineral nitrogen (N120) against the background of P60K60 was studied, inoculation of alfalfa seeds was carried out using the bacterial preparation Yakut local strain KB № 1. The article presents the results of studies on the effect of alfalfa seeding on the productivity of old-age cereal and legume-grass. An optimal species composition of cereal, legume-cereal grass, yield formation, and determines the productivity of seeded grass stands when haying use. According to the results of studies, the seeded grass of the thirteenth year of life with the introduction of N120 formed the maximum yield in the cereal grass to 2,4 t/ha of dry matter and exceeded the control by 118%, the exchange energy of 19,8,GJ/ha of raw protein 449 kg/ha, feed units 1,2 thousand from 1 ha. Higher productivity was obtained by switching on alfalfa legume-cereal grass under scarification - 1.4 thousand feed. Significant increase in the sowing of inoculated alfalfa seeds obtained a maximum yield of 3.4 t/ha of dry matter. Under the influence of inoculation of seeds, the productivity of grass increases by 353 feed unit per 1 ha, exchange energy per 5.6 GJ, crude protein per 3.0 C. dry matter. The highest increase in nitrogen collection was obtained in the variant with alfalfa sowing at inoculation up to 604 kg/ha, which can replace the use of mineral nitrogen at a dose of 224 kg per hectare. Thus, to increase the productivity of sown legume-grass stands, it is necessary to use the bacterial preparation Yakut local strain KB № 1.