Mitigating soil drought effects in soybean with Bradyrhizobium Japonicum inoculants

Soybean is valued for its high protein content and its symbiosis with the nitrogen-fixing bacterium Bradyrhizobium japonicum. This study evaluated whether commercial inoculants could mitigate drought effects in soybean grown in pots at 20% (drought) and 70% (control) field water capacity. Inoculation with Rhizobium Bio-Gen improved photosystem II efficiency under water deficit, while Nitragina IUNG prevented drought-induced losses in water status, biomass, nodulation, and yield. Nitragina Biofood promoted the highest share of biologically fixed nitrogen under optimal watering (leaves: 65.5%; seeds: 57.0%) and further enhanced N₂ fixation during drought (leaves: 79.9%; seeds: 57.8%). Across watering regimes, δ¹³C values were highest in leaves and lowest in pods and seeds, indicating drought-driven recycling of respired CO₂. Overall, application of Nitragina IUNG in soybean cultivation can effectively mitigate the adverse effects of soil drought on yield, whereas Nitragina Biofood appears particularly well suited for crops intended as green manure or as preceding crops for winter cereals.