The influence of fertilizers on plant growth and symbiotic capacity of lupin crops

To determine the influence of various fertilizers on plant growth and the symbiotic potential of lupine crops, field experiments were conducted between 2022 and 2024 in the foothill zone of the Central Ciscaucasia, characterized as a forest-steppe with a moderately humid climate. The experimental plot featured leached chernozem soils of medium thickness and medium loam texture. The topsoil contained 5.4% of humus, 75 mg/kg of easily hydrolyzable nitrogen, 90 mg/kg of available phosphorus, 150 mg/kg of mobile potassium, and the acidity level of pH 5.8. The study employed classical methods of experimental design, phenological observations, and statistical data analysis. Research subjects included varieties of white lupine (Lupinus albus L.) Desnyansky and Gamma and narrow-leaved lupine (Lupinus angustifolius L.) Snezhet. The symbiotic apparatus of lupine reached maximum size during the flowering phase. The synergistic effect of combined treatments (Rhizotorfin + P₂O₅ + Mo) increased nodule mass by 173–195% during budding, 153–170% during flowering, and 120– 136% during the shiny pod phase. Seed inoculation with active Rhizotorfin enhanced active symbiotic potential (ASP) by 7.2–22.5%, while optimized phosphorus nutrition further increased ASP by 8.4–24.6%. The greatest improvement in ASP (38–40% compared to controls) was observed under the combined application of all factors. Maximum atmospheric nitrogen fixation (173.2–240.6 kg/ha) across lupine genotypes occurred with phosphorusmolybdenum optimization coupled with Rhizotorfin inoculation, exceeding control values by 45.1–58.1%. The Desnyansky variety demonstrated the highest adaptability to the ecological conditions of the foothill zone of North Ossetia-Alania, achieving biological nitrogen fixation ranging from 152.2 kg/ha in control plots to 240.6 kg/ha under combined macromicroelement fertilization and rhizobial strain inoculation.