Field evaluation of Bacillus -based consortium biofertilizer for rhizosphere zinc availability, grain biofortification and paddy yield

The zinc (Zn) deficiency in submerged rice limits productivity and nutritional quality. This study evaluated the potential of zinc-solubilizing plant growth-promoting rhizobacteria (PGPR) to enhance Zn availability and uptake in rice under submerged conditions. Field experiments were conducted over two years using five Bacillus-based biofertilizer formulations: three single-strain inoculants (B. megaterium AN24 as BF-1, B. aryabhattai AN30 as BF-2, B. megaterium AN31 as BF-3) and two combined formulations (B. megaterium AN24 + B. aryabhattai AN30 as BF-4, B. megaterium AN24 + B. megaterium AN31 as BF-5), standardized with optimized inoculum-carrier compositions. Among these, BF-4 significantly increased soil Zn availability by 16% compared to the control, resulting in higher Zn uptake, grain Zn content (30%), plant dry matter (36%), and grain yield (19%) along with improvement in soil micronial activity and nutrients dynamics. Superior performance of BF-4 is associated with microbial functions increasing rhizosphere nutrient mobilization and support root activity. Multivariate analysis also confirmed the superiority of co-inoculation over control, indicating coordinated changes in soil and plant. These findings demonstrate Bacillus-based biofertilizers as a microbial strategy for improving grain-Zn and nutritional quality under submerged cultivation. Further multi-location and long-term evaluation is required to establish consistency across soil types and agroecological environments.