Benefits of soybean co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense: Large-scale validation with farmers in Brazil
André Mateus Prando, Julierme Zimmer Barbosa, Arnold Barbosa de Oliveira, Marco Antônio Nogueira, Edivan José Possamai, Mariangela Hungría
Abstract
The global contribution of biological nitrogen fixation (BNF) to soybean production ranks Brazil as the leading country. In 2013/2014, a new technology based on soybean co-inoculation with Bradyrhizobium spp. and Azospirillum brasilense strains Ab-V5 and Ab-V6 was released, and here we report a five-year set of extension activities in Paraná state, southern Brazil, to demonstrate the benefits of co-inoculation. In total, 273 technical reference units (TRUs) were installed in two main soybean macro-regions, all showing naturalized populations of soybean bradyrhizobia. In each TRU, side-by-side plots consisting of soybean seeds non-inoculated or co-inoculated with Bradyrhizobium spp. and A. brasilense were installed, and 260 TRUs were evaluated for nodulation and 242 for grain yield. Consistent nodulation increases, of up to 350% were observed in every cropping season, with an average significant (p < 0.01) increase of 35% in the five-year period. Similarly, grain yield increased up to 80% due to co-inoculation, with an average significant (p < 0.01) increase of 8%, corresponding to 273 kg ha−1. The increases were confirmed in the two macro-regions and different levels of grain yield, from low (<3000 kg ha−1) to high (>4000 kg ha−1). In the five-year period, 3299 small farmers were reached (farms of ∼50 ha) and the average profit due to co-inoculation was estimated at US$ 111.5 ha−1 per cropping season. In addition, we discuss environmental benefits associated with the mitigation of greenhouse gases emissions, estimated at 350 kg ha−1 of CO2-e, in addition to soil N enrichment.