Harnessing Rhizobial Inoculation for Sustainable Nitrogen Management in Mung Bean (Vigna radiata L.)

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 (<i>Vigna radiata</i> L.) by evaluating selected strains for cowpea (<i>Vigna unguiculata</i> L.), soybean (<i>Glycine max</i> L.), and common bean (<i>Phaseolus vulgaris</i> 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 (<i>Bradyrhizobium viridifuturi</i>) increased mung bean yield by 18%, achieving results similar to a 240 kg N ha^-1 fertilizer application. The soybean strain BR 96 (<i>B. elkanii</i>) 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 <i>Bradyrhizobium</i> strains can benefit mung beans through both enhanced nitrogen fixation and additional growth-promoting mechanisms, offering a sustainable approach to improve mung beans production.