Nitrogen-fixing capacity of variegated alfalfa and red clover on sod-podzolic-sandy soil

Abstract

Currently, with rising energy prices and difficulties in obtaining certain material and technical resources due to numerous sanctions, scientists and agricultural specialists have developed recommendations for replacing expensive agrochemicals, and there has also been a shift towards developing and using biologically-based technologies that rely on legumes, which have nitrogen fixing abilities. This problem can be solved by introducing perennial legume grasses into field fodder production. During the study, it was found that the amount of nitrogen fixed from the atmosphere by variegated alfalfa in the control setup exceeds the amount taken from the soil by an average of 22%. For red clover, control values  were exceeded by 20%. Under favorable growing conditions (2022–2023), increasing doses of potassium in phosphorus-potassium fertilizers ensured the growth of nitrogen fixation by 31–51 and 28–41%, respectively. In terms of ammonium nitrate in physical weight, the share of alfalfa in the soil in these years accounted for 115–280 kg/ha and red clover for 80–186 kg/ha. The level of nitrogen fixation of alfalfa on sod-podzolic sandy soils turned out to be 1.1–1.4 times higher than the level of nitrogen fixation of clover. The moisture deficit observed in 2024 reduced the symbiotic activity of nitrogen fixation from the air in alfalfa by 3.5–6.6 times, and in clover by 2–3 times. Based on data from 2022 and 2023, it was found that alfalfa has a better capacity to nitrogen fixation (19–66 kg/ha) than clover (18–47 kg/ha). The amount of nitrogen left in the soil due to assimilation from the air was 55–196 kg/ha after alfalfa and 52–138 kg/ha after red clover, in physical weight converted to ammonium nitrate. The scatter of data on the nitrogen-fixing capacity of alfalfa and clover in the control are moderately variable (13.3 and 16.6%). With the introduction of phosphorus-potassium fertilizers, they stabilized to low variability. The range of normal distribution of the data was 62.5%. The problem of studying biological nitrogen fixation by perennial leguminous grasses is relevant, since the introduction of a wedge of perennial leguminous grasses and other most promising crops into the structure of crop areas is one of the elements of improving resource-saving agricultural technologies.