Symbiotic Nitrogen Fixation of Northern Ecotype Soybean Varieties Cultivated in the Conditions of the Central Black Earth Region

Abstract

Thanks to the creation of cold-resistant soybean varieties of the northern ecotype, with a neutral reaction to day length, it became possible to advance its production in the northwest direction. The ability of soybeans to form an effective symbiosis with nodule bacteria determines its environmental-forming role in adaptive agriculture. In 2017–2019 seven varieties and two lines of soybeans have been studied in the field. The varieties Swapa, Lancetnaya, and Krasivaya Mecha have been studied for seven years. The following analyzes were carried out: registration of the above-ground mass and grain yield, the number and weight of nodules, nitrogen removal with the above-ground mass; calculation of the amount of fixed nitrogen in the air using the Hopkins–Peters coefficient; nitrogen content was determined by the Kjeldahl method. The symbiotic system of soybeans develops before the beans are filled, keeping nitrogen-fixing activity at a high level. In arid, unfavorable conditions for the symbiotic system, the number of nodules decreases compared with wet years by 39%, the weight of nodules—by 21%, and the weight of 1 nodule, on the contrary, increases by 68%. The close relationship between the productivity of soybeans and symbiotic indicators is confirmed by the values of the correlation coefficient at the medium and high levels r = 0.4–08. Under conditions of excess moisture, the intensive growth of nodules leads to competition with the generative organs for the distribution of assimilates, as evidenced by the negative correlation between the grain yield and the number and weight of nodules at the level r = −0.623 to −0.751. A positive correlation r = 0.655–0.735 was established between the nitrogen content in leaves and nodules in the budding phase. Over the years of research, the removal of nitrogen with the aboveground mass in soybean varieties varied in the budding phase from 41 to 200 mg/plant, in the filling of beans from 277 to 498 mg/plant; the amount of fixed nitrogen during the budding period was 27–130 mg/plant, in the filling of beans 180–324 mg/plant, depending on the variety and conditions of the year.