Inoculating legumes with nitrogen-fixing bacteria, such as Bradyrhizobium, can significantly reduce reliance on synthetic nitrogen fertilizers. To optimize this process, a suitable rhizobial strain must be carefully selected and formulated. This study aimed to develop a biopolymer blend formulation for Bradyrhizobium pachyrhizi strain BR 3262. From four commercial starches and two carboxymethylcelluloses (CMC), we developed CMC/starch blends compatibilized or not with MgO at concentrations from 0.1% to 1.0% and subjected them to autoclaving for either 30 or 60 min. The resulting inoculants were stored for 168 days. Generally, blends compatibilized with 1.0% MgO exhibited a significant decrease in cell numbers, likely due to the observed pH values of approximately 10. The best performance was observed for CMC-I/starch B blends autoclaved for 60 min, and CMC-II/starch C blends autoclaved for 30 min, both compatibilized with 0.3% MgO. These blends maintained a cell viability of 10⁸ CFU mL⁻¹ for approximately 130 days at room temperature. Blend optimization depends on the selection of specific interactions and quantities of each component in order to achieve a given functionality; in the conditions of this study, the capacity to maintain Bradyrhizobium cell viability for at least four months.

As a pulse crop, mung beans are associated with nitrogen-fixing bacteria, which can improve soil fertility, lower the need for nitrogen fertilizers, and increase yield and soil quality for subsequent harvests. This study aimed to identify effective rhizobial inoculants for mung beans (Vigna radiata L.) by evaluating selected strains for cowpea (Vigna unguiculata L.), soybean (Glycine max L.), and common bean (Phaseolus vulgaris L.) under controlled (axenic) conditions. Cowpea, soybean, and common bean strains were tested as mung beans inoculants under axenic conditions. Promising strains were then tested in the field to assess grain yield and to quantify nitrogen fixation using the ¹⁵N natural abundance method. The cowpea strain BR 3302 (Bradyrhizobium viridifuturi) increased mung bean yield by 18%, achieving results similar to a 240 kg N ha⁻¹ fertilizer application. The soybean strain BR 96 (B. elkanii) facilitated the highest nitrogen fixation (35.3 kg N ha⁻¹), significantly surpassing the contribution of indigenous diazotrophic bacteria (18.5 kg N ha⁻¹). Interestingly, BR 3302 appeared to primarily enhance nitrogen uptake from the soil (65% of plant N), indicating the presence of other potential plant growth-promoting mechanisms beyond nitrogen fixation. This research demonstrates that Bradyrhizobium strains can benefit mung beans through both enhanced nitrogen fixation and additional growth-promoting mechanisms, offering a sustainable approach to improve mung beans production.