Integrated use of Consortia-based Microbial Inoculants and Nutrient Complex Stimulates the Rhizosphere Microbiome and Soybean Productivity

Background: The effectiveness of soybean inoculants in field conditions may be improved through the joint application of rhizobia and plant growth-promoting bacteria (PGPB). Plant nutrients may also contribute to the higher efficacy of microbial inoculants as well as the growth and development of plants. Methods: A field experiment was performed to evaluate the responses of the rhizomicrobiome and soybean to seed treatments with multiple bacterial strains (Bradyrhizobium japonicum, Bacillus subtilis, Bacillus megaterium and Azotobacter chroococcum), applied individually or in consortia, with and without nutrient complex (S, Mg, Mn, Fe, Zn, Cu, B and Mo). Result: Seed treatments with microbial consortia of Br. japonicum, B. subtilis/B. megaterium, A. chroococcum strains and nutrients had the highest effect on the abundance of total bacteria, nitrogen-fixing bacteria, actinomycetes and activity of dehidrogenase in the soybean rhizosphere. The highest effect on plant height, plant weight, pod number, pod weight, seed number and seed weight was obtained from treatment with Br. japonicum strains with nutrients, followed by co-inoculation with B. megaterium and A. chroococcum. In comparison with the control and Bradyrhizobium single inoculation, a statistically significant increase in the seed yield was recorded in treatment with Br. japonicum, B. megaterium, A. chroococcum and nutrients, reflecting the highest increase in protein and oil yield. The interactive effects of microbial consortia and nutrients could be used as promising seed technology for sustainable soybean cropping.