Dynamics of alfalfa (Medicago varia Mart.) leaf area depending on nitrogen feeding type
The results of field studies for 2017-2019 of dynamics of assimilation surface of alfalfa crops depending on the type of nitrogen nutrition and symbiotic activity of crops are given. Tests with Medicago varia Mart. were carried out in environmental conditions of the pre-mountain zone of RNO-Alania (540 meters above sea level) on the black earth leached with close occurrence of pebbles. Mineral and symbiotrophic types of nitrogen nutrition of alfalfa plants were compared. The experience scheme included options: control - natural soil fertility; In-1800 - treatment of seeds with inoculum of strains of nitrogen-fixing bacteria selected in high mountain conditions (1800 m above sea level); Strain 425a - inoculation of seeds with industrial strain rhizotorphin (strain 425a); N30 - starting nitrogen dose; N30+In is the joint use of highland strains of bacteria and starting doses of nitrogen. Seeds were treated with the strains studied before sowing. Mineral nitrogen fertilizers were introduced annually early in spring in the form of starting doses. It has been established that the minimum areas of leaves on all variants are observed in the first year of life, in the second year of use of crops the maximum assimilation surface is formed in plants, in the third year - indicators gradually decrease. Every year, the maximum assimilation surface is formed by perennial leguminous herbs to the budding stage - the beginning of flowering (bevel has fallen). The dynamics of leaf surface build-up is directly proportional to the activity of symbiotic relationships with rhizobias. In variants with the highest symbiotic activity (In-1800 and N30+In) the area of leaves reaches maximum values and exceeds 40 thousand m2/ha in certain years.