DRY MATTER ACCUMULATION BY ALFALFA CROPS DEPENDING ON THE TYPE OF NITROGEN NUTRITION
The results of field studies of 2017-2019 on dry matter accumulation by alfalfa crops depending on the type of nitrogen nutrition and symbiotic activity of crops are discussed. The tests with Medicago varia Mart. were carried out under the environmental conditions of the pre-mountain zone of the Republic of North Ossetia - Alania on leached chernozem soil. Mineral and symbiotrophic types of nitrogen nutrition of alfalfa plants were compared. It was revealed that on the year of sowing, 3503-4252 kg ha of dry substance was accumulated for the growing season; the minimum amount was accumulated in crops of the control variant; the maximum amount - in the variant with the highest symbiotic activity (In-1800). About 43% of dry matter was formed in leaves, about 35% - in stems and about 22% - in roots. In the following years of experiments, alfalfa crops formed 3 full-fledged harvests; the accumulation of dry matter was significantly more - by 75-88% on the second year and by 62-74% more on the third year of the crop use. It was found that the accumulation of dry matter both by individual organs and by the whole plant of alfalfa depended to a critical extent on the regime of nitrogen nutrition and, in particular, on the availability of biologically fixed nitrogen. The activation of symbiotic activity of crops with high-mountain strains of nodule-forming bacteria both in pure form and against the background of starting doses of mineral nitrogen fertilizers (variants “In-1800” and “N<sub>30</sub>+In”) allowed the plants to accumulate by 18-20% more dry matter at each harvest than in the control variant.