The effect of biopreparations on the adaptive properties of soybean in organic farming under hydrothermal stress

In the context of organic farming and hydrothermal stress, the use of biopreparations – particularly arbuscular mycorrhiza, rhizobial bacteria, and phytohormonal treatments – has gained special significance as a means of enhancing the adaptive properties of soybean. Their application helps to mitigate the negative effects of abiotic factors and maintain crop productivity. This study aimed to assess the adaptive potential of soybeans under organic farming conditions through the application of mycorrhizal, bacterial, and phytohormonal biopreparations during periods of hydrothermal stress. Based on a field study conducted in the Poltava Region, the influence of biopreparations of various origins on the biochemical, physiological-morphological, and stress-indicative parameters, as well as the productivity of the Khorol soybean variety, was analysed. The application of biopreparations significantly improved biochemical and physiological-morphological indicators, as well as the productivity of soybeans, indicating an improvement in the overall physiological condition of the plants. The highest concentrations of chlorophylls a and b were recorded in 2023 under the three-component treatment (Mycofriend with Profix and Violar), where the average increase in Chl a over the years of research was 42.3%, and Chl b was 26.7% compared with the control. The assimilative leaf area reached an average of 29.24 thousand m²/ha, while yield was recorded at 3.23 t/ha, exceeding the control by 28.9% and 49.0% respectively. In the drought affected 2024 season, the adaptive application of biopreparations contributed to a reduction in leaf surface area loss within the range of 16.4-20.0% and yield reduction of 17.1-20.0%, compared with the control, where losses amounted to 22.1% and 24.4%, respectively. The use of biopreparations under hydrothermal stress in 2024 also resulted in an increase in proline concentration (up to 7.27 mg/g) and a decrease in MDA content (down to 7.14 mg/g), indicating reduced oxidative stress and improved osmoregulation. This effect is attributed to the synergistic action of mycorrhiza formation, nitrogen fixation, and phytohormonal activity. The practical significance of the findings lies in demonstrating the potential of integrated biological treatments to enhance the yield and stress tolerance of soybeans under the conditions of organic farming and climate-related challenges.