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.

The Russian Federation has a huge agricultural potential, possessing one of the world’s most valuable natural resources - agricultural land. Availability and efficient production. The use of land resources plays a major role in agriculture, it is important to study the current situation of changes in the area of land resources in the Russian Federation using a retrospective analysis. A retrospective analysis of the use of the land fund of the Russian Federation was carried out. A retrospective analysis allows us to conclude that during the analyzed period there was a significant reduction in arable land and other agricultural land.

Mineral and symbiotrophic types of nitrogen nutrition of plants were compared in experiments with the blue-hybrid alfalfa. Variants with seed inoculation by high-mountain strains of nodule bacteria (In-1800 and N30+In) had the maximum height of plants during all experimental years (40-70 cm), which is explained by the better nitrogen provision of plants. At the same time, the effect of the mineral forms of nitrogen appeared only in the year of sowing at the beginning of the growing season to the first mowing, in the future the differences between these options were neutralized. The foliage intensity of plants was in the range of 41.4-54.8%, increasing due to the improved availability of biologically bound nitrogen in plants. Mineral forms of nitrogen reduced plants’ foliage coverage in all experimental years, however, this decrease was noted only in the initial periods of vegetation. The maximum indicators of foliage coverage were noted in the In-1800 variant. By the end of the third year of crops use, the plant stand density was 980-1100 thousand units/ha, and the total thinning of alfalfa crops reached 45-51%. At the same time, the symbiotrophic type of nitrogen nutrition made it possible to significantly increase the competitiveness of plants, which ultimately affected the persistence of the crop density.

The issue of the use of mineral forms of nitrogen for legumes is still a source of debate among scientists. Under the environmental conditions of the foothill zone of RNO-Alania, the field experiments were laid to study the activity of the symbiotic system and the productivity of the alfalfa depending on the type of nitrogen nutrition and the presence of a virulent active strain of rhizobia. The research was carried out in 2017– 2019. Soil – chernozems leached. Objects: crops of Medicago varia Mart.; industrial strain of rhizotorphin 425a; inoculum of high-mountain strains of nodule bacteria; starting doses of nitrogen fertilizers. The dimensions of the symbiotic apparatus were studied according to the G.S. Posypanov method. The specific activity of symbiosis was 4.2 to 9.0 mg/kg. The maximum amount of air nitrogen (456.1 kg/ha) for three years of experiments was fixed by the symbiotic system of alfalfa in the variant with pre-sowing seed inoculation with high-mountain strains of nodule bacteria. This indicates their higher activity and competitiveness compared to the industrial strain of rhizotorphin 425a and indigenous strains of rhizobia from the pre-mountain zone of RNO-Alania. Mineral forms of nitrogen significantly inhibited the activity of the symbiotic system. As a result, the amount of fixed nitrogen decreased by 3.5–9.0 %. In the pre-mountain zone, under natural conditions, the growth and development of plants were provided with atmospheric nitrogen by 66 %, the rest of the need for the element (34 %) they satisfied with soil nitrogen. The maximum involvement of molecular nitrogen of the atmosphere in the biological cycle was distinguished by the variant with pre-sowing inoculation of seeds by virulent active strains of rhizobia, in which the share of air nitrogen participation in plant nutrition averaged 71–73 % over the three years of research.

Приведены результаты полевых исследований потребления азота посевами люцерны в зависимости от режима азотного питания и симбиотической активности посевов за 2017…2019 годы. Опыты с люцерной синегибридной проведены в экологических условиях предгорной зоны РСО-Алания на черноземе выщелоченном с близким залеганием галечника. Сравнивались минеральный и симбиотрофный режимы азотного питания растений люцерны. Установлено, что в год посева потребление азота посевами люцерны составило от 105,0 до 135,4 кг/га, при этом к первому укосу потребление было в 1,1…1,2 раза больше, чем ко второму укосу. На второй и третий годы пользования посевами потребление азота выросло в 1,7…1,9 раза в сравнении с показателями года посева. Показатели вариантов с естественными условиями (контроль) и внесением стартовых доз азотных удобрений (N30) были практически идентичными. Показатели вариантов с инокуляцией семян высокогорным инокулюмом (Ин-1800) и внесением стартовых доз азотных удобрений на фоне инокуляции (N30 + Ин) во второй и третий годы пользования посевами были практически идентичными. Объемы потребления азота в указанных вариантах составили свыше 235 кг/га, или на 25,6…27,1 % выше показателей контрольного варианта. В сумме за три года исследований посевы люцерны в контрольном варианте усвоили 483,3 кг/га азота. Стартовые дозы азотных удобрений (N30) увеличили данный показатель всего на 1,4 %. Предпосевная инокуляция семян способствовала увеличению потребления азота во всех вариантах: в варианте с промышленным штаммом ризоторфина (Шт. 425а) – на 17,8 %, с высокогорным инокулюмом на фоне внесения стартовых доз минеральных азотных удобрений (N30 + Ин) – на 24,6 %, с высокогорным инокулюмом в чистом виде (Ин-1800) – на 27,1 %. Ключевые слова: люцерна, режим питания, симбиотическая активность, минеральный азот, биологический азот, потребление азота. The results of field studies of nitrogen consumption in alfalfa crops depending on the nitrogen nutrition pattern and symbiotic activity of crops for 2017...2019 are presented. Experiments with the alfalfa purple were carried out in the ecological conditions of the foothill zone of the North Ossetia-Alania, on leached chernozem with a close occurrence of gravel. Mineral and symbiotrophic patterns of nitrogen nutrition of alfalfa plants were compared. It was found that in the year of planting, the nitrogen consumption of alfalfa crops ranged from 105.0 to 135.4 kg/ha, and by the first mowing, the consumption was 1.1...1.2 times bigger than by the second mowing. In the second and third years of crop use, nitrogen consumption increased by 1.7...1.9 times compared to the year of planting. The parameters of the options with natural conditions (control) and the addition of starting doses of nitrogen fertilizers (N30) were almost identical. In the second and third years of use of crops, parameters of options with inoculation of seeds with high-altitude inoculum (In-1800) and the addition of starting doses of nitrogen fertilizers within the background of inoculation (N30 + in) were almost identical. In these options, the amount of nitrogen consumption was more than 235 kg/ha, or 25.6...27.1 % higher than in the control variant. In total, over three years of research, in the control option alfalfa crops took 483.3 kg/ha of nitrogen. Starting doses of nitrogen fertilizers (N30) increased this indicator by only 1.4 %. Pre-planting inoculation of seeds contributed to an increase in nitrogen consumption in all options: in the option with the industrial strain of risotorphine (St. 425a) – by 17.8 %, with high-altitude inoculum within the background of adding starting doses of mineral nitrogen fertilizers (N30 + In) – by 24.6 %, with high-altitude inoculum in pure form (In-1800) – by 27.1 %.