PHOTOSYNTHETIC PARAMETERS OF ALFALFA CROPS IN RELATION TO THE TYPE OF NITROGEN NUTRITION

The paper shows the results of field experiments conducted in 2017-2019. The experiments were devoted to photosynthetic indices of alfalfa in relation to the type of nitrogen nutrition and symbiotic activity of crops. The experiments with alfalfa blue-hybrid were carried out in environmental conditions of the piedmont zone of RNO-Alania on chernozem leached soil with close occurrence of gravel. The researchers compared mineral and symbiotrophic types of nitrogen nutrition of alfalfa plants; they applied mineral nitrogen fertilizers and biospecimens on the basis of rizobium. In natural conditions (control group) the crops formed photosynthetic potential from 1701.3 thousand m²-days/ha per year of sowing to 3624.3 thousand m²-days/ha in the second year of sowing. Crop rates in the third year had intermediate values between the first and second years of crop use. The effect of starting doses of nitrogen fertilizers was observed during the sowing year in its early stages, when the symbiotic system is still underdeveloped and inactive. When estimating the annual average photosynthetic potential, starting nitrogen doses gave an advantage of only 1.6%. Presowing inoculation of seeds by active strains of strawberry bacteria provided the maximum positive effect, while high mountain strains of rizobium were more effective. Average annual parameter of photosynthetic potential varied from 2699.1to3189.4 thousand m² days/ha, increasing with the improvement of nitrogen nutrition. Inoculation of seeds by high-altitude strains of tuber bacteria increased photosynthetic potential to its maximum values or by 18.2%. In the same variant, as well as in the variant with the starting dose of nitrogen, the maximum values of net productivity of photosynthesis were achieved, which exceeded the values of the control variant by 0.09-0.11 g/m²- day.