Effects of inoculation and phosphorus nutrition on yield and seed quality of soybean varieties in the Central Forest-Steppe Zone

Background. The relationship between the seed yield of soybean (Glycine max (L.) Merrill) and nitrogen (N) has been well studied, whereas the effect of other elements, particularly phosphorus (P), remains insufficiently explored. Phosphorus, the second most important element after nitrogen, is crucial for obtaining high-quality soybean yields. At the same time, despite numerous studies on the effects of phosphate-mobilizing and nitrogen-fixing microorganisms on sustainable agricultural development, the effectiveness of these scientific efforts is insignificant. Materials and Methods. General scientific and specialized methods were used, inclu­ding field, laboratory, chemical and statistical methods. The research was conduc­ted in the Forest-Steppe Zone from 2019 to 2021 at the experimental field of the LLC “Institute of Agrobiology” (Velykyi Mytnyk village, Khmilnyk district, Vinnytsia region). In this experiment, three foreign-bred soybean varieties were used: Mentor (early-matu­ring), Cordoba, and Moravia (mid-early varieties), using mineral phosphorus fertilization (P30) and biofertilization based on a ternary composition of phosphate-mobilizing strains – Bacillus megaterium de Bary, 1884 (eko/207), B. amyloliquefaciens (ex Fukomoto, 1943) Priest, Goodfellow, Shute & Berkeley, 1987 (eko/205), and Trichoderma harzianum Rifai, 1969 (eko/101). These treatments were applied both without inoculation and with seed inoculation with three strains of Bradyrhizobium japonicum (Kirchner, 1896) Jordan, 1982 from the LLC “Institute of Agrobiology” (active ingredients of the applied formulations). Results and Discussion. All studied soybean varieties responded positively to the application of phosphorus fertilization and biofertilization based on phosphate-mobilizing strains, both without inoculation and with seed inoculation using nitrogen-fixing bacterial strains. Overall, the grain yield increase (%) in the experimental variants ranged from +7.70 % to +18.28 %. The best yield performance (compared to the control) was recorded in the variant combining inoculation with bacterial-micromycete (BM) biofertilization, resulting in a grain yield increase of +0.31 t/ha or 11.27 % (Mentor), +0.31 t/ha or 13.58 % (Cordoba), and +0.48 t/ha or 18.28 % (Moravia). The protein content (%) in soybean seeds ranged from 38.75 % to 42.75 %, depending on the variety, treatment variant, and fertilization background. The mid-early Moravia variety was the only one that showed an increase in protein percentage across all experimental variants (P30 and BM), both without inoculation and with seed inoculation. In contrast, the Mentor and Cordoba varieties exhibited a quantitative reduction in protein content in the P30 and BM variants (compared to the control) only in the absence of seed inoculation. Conclusion. In the Central Forest-Steppe Zone of Ukraine, the combination of seed inoculation with phosphorus fertilization and biofertilizers based on phosphate-mobilizing microorganisms significantly improved soybean yield and seed protein content. In the overall variance, the factorial share of influence (%) on yield was lower than on protein content, amounting to 34 % and 67 %, respectively. The greatest impact on protein content was from inoculation (29 %), while yield was most affected by inoculation (17 %) and phosphorus supply (14 %). Variety-related factors were less influential for yield but contributed 17 % to protein variation. Factor interactions were mostly insignificant for yield but notable for protein.