The research is aimed to study the effect of liquid organic fertilizer on the yield, productivity elements, and grain quality of regional soybean varieties. The work was carried out in the dark gray forest soil of Oryol Oblast in 2022–2024. The reaction of the Leader-1 and Mezenka varieties to the pre-sowing seed treatment and spraying of the crops in the 1–3 trifoliate leaf and budding phases with the Bioklad fertilizer has been studied. The experiment includes variant with fertilizer application dosages of 1.0 L/t or 1.0 L/ha and 2.0 L/t or 2.0 L/ha. The water treatment (fertilizer-free) application has been used for the control variant. In both studied varieties and all experimental variants, the treatment with the organic fertilizer increases the mass of nodules and their number on the soybean root system in the flowering phase by an average of 183.7 and 505.3%, respectively. Additionally, application of the Bioklad fertilized affects the legume-rhizobial symbiosis: nitrogen-fixing activity of the Leader-1 and Mezenka varieties increases by 114.6–136.2% and 102.9–109.1%, respectively. Depending on the variety, fertilizers increased grain yield (by 0.23–0.42 t/ha or 10.1–17.7%), number of seeds per bean (by 0.04–0.59 or 1.6–27.6%), and weight of 1000 seeds (by 4.85–10.4 g or 3.0–7.2%), relative to control. The quality of soybean grains improved significantly: the protein content increased by 0.2–0.68%. The highest efficiency of the liquid organic fertilizer has been detected for the application dose of 2.0 liters on the determinate variety Leader-1 and 1.0 liters on the indeterminate variety Mezenka. The maximum grain yield increases over the years of research are 0.42 and 0.27 t/ha for the Leader-1 Mezenka varieties, respectively. The highest protein yield per unit of cultivated area is 1178 and 1040.9 kg/ha, respectively.
Zotikov et al. (Mon,) studied this question.