Can re-inoculation with Bradyrhizobium and Azospirillum in soybean crops be a strategy to increase productivity?

In this study we tested the hypothesis of increasing the yield potential of soybean crops based on the use of two specific microorganisms together, Bradyrhizobium japonicum and Azospirillum brasiliense. The study was conducted in a producer area, in two municipalities in Rio Grande do Sul, during the 2023/2024 harvest. The experimental design was defined in two treatments, co-inoculation of seeds before sowing (2 doses of Bradyrhizobium + 1 dose of Azospirullum) and re-inoculation in part of the area during the beginning of the reproductive stage of the R1 culture (10 doses of Bradyrhizobium + 4 doses of Azospirullum). The results showed an increase in productivity of up to 7.4%, 420 kg ha-1 in study site 1 and 17.5%, 780 kg ha-1 for site 2, through re-inoculation. These results were related to the quality of the soil, which showed a difference in organic matter content on the surface of 33.9% more in site 1, in addition, the distribution of rainfall had a significant influence, site 2 had a period close to 20 days without the presence of rain in the R3 – R4 reproductive stage (full pod formation). Re-inoculation is an alternative to increasing the productive potential of soybeans in crops in southern Brazil, and it is essential to increase the doses of Bradyrhizobium and Azospirillum.