Differential Response of Three Legume Crops to Integrated Nutrient Management: Synergistic Effects of Reduced Nitrogen and Bradyrhizobium-Based Biofertilizer

This study investigates the impact of selected soil parameters and integrated fertilizer formulations on the productivity of three legume crops – mungbean, soybean, and cowpea – in order to identify the optimal strategies to maximize yields through reduced Nitrogen and bio-augmentation. A five-year experiment composed of 2-year pot trials (2019 – 2020) and 3-year field trials (2022 – 2024) were conducted to assess the changes in some soil parameters (N, P, K, OM, pH) and yield response of the crops with varying amounts (1, 2, 4kg) of Bradyrhizobium-based biofertilizer combined with 25-50% reduction in mineral N fertilizer. The biofertilizer is composed of locally-isolated strains which were genetically identified in our previous reports as B. elkanii NE1-6, NE2-1, B. diazoefficiens NE1-65, Bradyrhizobium sp. NE1-19, NE1-34, and NE2-3. Results indicated that among the soil parameters, the amount of K strongly influenced yield increase for soybean (r = 0.85, p>0.05) and mungbean (r = 0.67, p>0.05) while the amount of N has the highest influence on cowpea (r = 0.60, p=0.05). Soybean yield was maximized with 50% reduction in N fertilizer (20kgN) combined with 2-4kg biofertilizer while cowpea and mungbean achieved increased yields at 25% reduced N fertilizer combined with 2-4kg biofertilizer. This study confirms the viability of integrating Bradyrhizobium-based biofertilizer with 25-50% reduction in mineral N fertilizer without yield loss by harnessing the efficient N-fixation ability of the strains in the consortium.