Can Azospirillum brasilense compensate part of the phosphate fertilizer in soybean crop by promoting plant growth?

Bioinoculants are widely used in Brazil, based on their efficiency and low cost, in addition to increase in grain yield and lower use of fertilizers in agriculture. In this context, we investigated the use of Azospirillum brasilense to compensate part of phosphate fertilization in soybean crop by promoting plant growth. The field trials were carried out in 2020/21 crop season in four locations in Brazil. The treatments consisted of control (no P application and no microbial inoculation); complete fertilization (100% of the recommended P for the crop and no microbial inoculation); standard commercial inoculant + 75% of the recommended P for the crop; Azosphera® (inoculant based on A. brasilense, strains Ab-V5 and Ab-V6) + 75% of the recommended P for the crop. The effects were assessed on grain yield, thousand grain weight, nodulation, root and shoot dry weight, N and P content in grains and leaves. The results obtained show that inoculation of soybean crop with Azosphera® inoculant, combined with 75% of the recommended phosphate fertilization, in general, provided higher nodulation and plant dry weight and increased grain yield compared to control, and these parameters also did not differ from treatment with complete phosphate fertilization. Thus, the results show that the use of Azosphera® inoculant promoted soybean plant growth and it was possible to compensate the 25% reduction in phosphate fertilization, without impairing the development and yield of soybean crop.