Synergistic effects of organic amendments and dual microbial inoculation on morphophysiological traits, nutrient uptake, and microbial symbiosis of black soybean (Glycine max) in Inceptisol

Background Sustainable intensification of soybean production requires strategies that simultaneously enhance plant growth, nutrient acquisition, and microbial symbiosis, particularly in nutrient-limited soils. Methods This experiment investigated the combined effects of organic amendments (Biochar, Vermicompost) and microbial biofertilizers [encapsulated Rhizobium and arbuscular mycorrhizal fungi (AMF)] on the morphophysiological performance of black soybean ( Glycine max ). Results All treatments, the integration of Vermicompost and Biochar with dual inoculation (encapsulated Rhizobium + AMF) consistently produced the most pronounced improvements. Leaf area index and height–diameter ratio were significantly enhanced from 21 days after planting onward, with the strongest canopy expansion and structural growth observed at 28 days. Biomass of shoots and roots production was maximized under Biochar + dual inoculation, surpassing all other treatments. Phosphorus uptake was significantly elevated, and AMF root colonization reached 80%, the highest across treatments. This treatment also supported the greatest nitrogen-fixing bacterial population (7.63 × 105 CFU g⁻1 soil), indicating synergistic microbial interactions. Data analyses confirmed that improvements in morphophysiology, nutrient acquisition, and microbial activity were strongly interrelated, with the majority of variance explained by coordinated responses under the Biochar + dual inoculation system. Conclusion The integration of Biochar with encapsulated Rhizobium and AMF represents a highly effective strategy to enhance black soybean productivity and microbial symbiosis in Inceptisol, offering a promising pathway toward sustainable crop management.