Optimizing Common Bean Symbiosis via Stage-Specific Reinoculation and Co-Inoculation

The common bean relies on biological nitrogen fixation to meet part of its nitrogen requirements. This study aimed to evaluate the effect of reinoculation with <i>Rhizobium tropici</i>, alone or combined with <i>Azospirillum brasilense</i>, at different phenological stages. The experiments were conducted in the winter of 2023 and the rainy season of 2023/24, and significant differences were observed between seasons, mainly due to temperature and water stress, which impacted nodulation, plant growth and grain yield. However, appropriate water management mitigated these limitations, allowing reinoculation combined with co-inoculation at the V4 stage to improve nodular and morphophysiological traits, ensuring adequate nutrition through biological nitrogen fixation. This strategy promoted nodulation and plant development, resulting in an 8.5% increase in yield compared to nitrogen fertilization (80 kg ha^-1), reaching 2197.87 kg ha^-1. These results suggest that reinoculation with co-inoculation at the V4 stage can enhance biological nitrogen fixation, reduce dependence on synthetic fertilizers and serve as a sustainable and economically viable alternative.