Improving Soybean Development and Grain Yield by Complementary Inoculation with Growth-Promoting Bacteria Azospirillum, Pseudomonas, Priestia, and Bacillus

Bioinputs are natural products applied to crops that contribute to more sustainable agriculture by boosting yields and reducing environmental impacts. In Brazil, the use of bioinputs such as Bradyrhizobium in soybean has been consolidated, but the expansion of on-farm bioinput production is currently initiating a new revolution. Furthermore, applications of bioinputs to cash crops in Brazil have shed light on the great potential of such growth-promoting microorganisms (GMPs) to improve nutrient uptake and increase productivity. This study explores the effect of the complementary inoculation with growth-promoting bacteria of post-emergence soybean, previously inoculated with Bradyrhizobium spp. Five treatments with growth-promoting bacteria were evaluated: T1—Control (no inoculation); T2—Azospirillum brasilense; T3—Pseudomonas fluorescens and Azospirillum brasilense; T4—Priestia aryabhattai, Bacillus haynesii, and Bacillus circulans; and T5—Priestia megaterium and Bacillus subtilis. In comparison with the control, all treatments with growth-promoting bacteria of the genera Azospirillum, Pseudomonas, Priestia, and Bacillus, applied after soybean emergence, induced 4–7% higher grain yields. Co-inoculation with Priestia megaterium and Bacillus subtilis (treatment T5) resulted in a higher 1000-grain weight, while Priestia aryabhattai, Bacillus haynesii, and Bacillus circulans (treatment T4) increased the number of pods and shoot dry weight. Our conclusion is that bioinputs increase soybean productivity and make agriculture more sustainable and efficient.