Effects of co-inoculation with Bradyrhizobium and Trichoderma harzianum on soybean nitrogen nutrition and multispectral traits

This study evaluates the potential of co-encapsulated native Bradyrhizobium spp. strains and Trichoderma harzianum T1, delivered via biodegradable microparticles, to enhance growth, nitrogen uptake, and physiological performance in soybean ( Glycine max L.). The microbial consortium was applied to soybean roots to assess synergistic effects on biological nitrogen fixation and plant development. Native Bradyrhizobium strains exhibited high tolerance to environmental stressors, including elevated temperatures, low pH, and salinity, and all produced indole-3-acetic acid (IAA), supporting their role as plant growth-promoting rhizobacteria. The most effective strains in improving nitrogen content were S1, S2, and S3, while S5, S4, and S3 were most effective in promoting dry biomass accumulation. Inoculation with T. harzianum increased shoot nitrogen content by an average of 0.2% over rhizobial-only treatments. Co-inoculation with T. harzianum and specific rhizobial strains (S1, S4, S6) led to synergistic effects, significantly enhancing plant dry weight, nodule biomass, and multispectral traits. Multispectral imaging, combined with principal component analysis, revealed treatment-specific physiological responses that were not evident from biomass or nitrogen measurements alone, highlighting its sensitivity in detecting microbial effects on plant health. These findings support the application of encapsulated microbial consortia as a sustainable strategy to improve soybean productivity under diverse environmental conditions. • Microbial co-inoculation improved soybean nitrogen uptake and biomass accumulation • Trichoderma increased nodulation and mitigated poor rhizobial strain performance • Encapsulation enabled stable delivery of microbial consortia to soybean roots • Synergistic and strain-specific effects were observed on plant physiology • Multispectral imaging sensitively captured plant responses to microbial inoculation