Evaluation of methods for inoculating soybean seeds with Bradyrhizobium spp. and Azospirillum brasilense in the plant nodulation and productivity

Besides replacing the mineral fertilization, the biological nitrogen fixation promoted by bacteria from genus Bradyrhizobium provides enough nitrogen to enable high yields in the soybean crop. The objective of this study was to compare the standard inoculation of a product containing Bradyrhizobium spp., either applied alone or associated to Azospirillum brasilense, to the preinoculation by seed treatment in the plant nodulation and productivity of soybean crop grains. The trial was implanted in November, 2020 in four locations (Mandaguaçu/PR, Marialva/PR, Paranavaí/PR, and Itaquiraí/MS) with different edaphoclimatic features. The design with randomized blocks was used, with seven treatments and five repetitions. The evaluated variables were number and dry mass of nodules in the beginning of flowering, dry biomass of the aerial portion, N content and total N in the aerial portion and grains, and grain yield. The results obtained in the four tests enabled to conclude that the inoculation with Bradyrhizobium spp. + Azospirillum brasilense by seed treatment of leaf spraying with Azospirillum showed to be technically feasible in the soybean crop.