Growth-promoting bacteria in coinoculation in soybean

Growth-promoting bacteria play a crucial role in sustainable soybean production, prompting research into the application of microbiological interactions to optimize their functions. This study aimed to assess the impact of coinoculation with growth-promoting bacteria on soybean grain productivity. Five experiments were conducted over two harvest seasons, employing a randomized block design with four replications. The first and second experiments, conducted during the 2020/21 and 2021/22 harvests, respectively, included eight treatments: (i) control without microorganism application; (ii) Bradyrhizobium japonicum (Bj); (iii) Bj + Azospirillum brasilense (Ab); (iv) Bj + Bacillus aryabhattai (Ba); (v) Bj + Bacillus megaterium (Bm); (vi) Bj + Biobokashi (Bi); (vii) Bj + Pseudomonas fluorencens (Pf); and (viii) Bj + Ab + Ba + Bm + Bi + Pf. The third and fourth experiments employed a factorial design, considering irrigation and the eight previously described treatments. The fifth experiment, conducted during the 2020/21 harvest, featured a factorial design considering fertilization levels (no fertilization, 50%, and 100% of recommended fertilization) and the eight aforementioned treatments. Evaluated variables included productivity, mass of thousand grains, number and dry mass of nodules, soil coverage rate, and various root parameters such as length, diameter, surface area, and volume per plant. Overall, optimal results were observed with the coinoculation of Bradyrhizobium japonicum and Pseudomonas fluorencens, as well as the coinoculation of Bradyrhizobium japonicum and Bacillus aryabhattai. These combinations significantly increased the number and mass of nodules, stimulated root growth, and enhanced soybean productivity across diverse locations. Additionally, the study suggests the potential for partial replacement of mineral fertilizers due to increased root volume and nutrient absorption. This research underscores the efficacy of growth-promoting bacteria coinoculation, particularly the synergistic effects of Bradyrhizobium japonicum with Pseudomonas fluorencens and Bacillus aryabhattai. These findings contribute valuable insights into sustainable agricultural practices, demonstrating the potential for improved soybean productivity and reduced reliance on traditional fertilization methods.