Influence of different types of Strains of Bradyrhizobium japonicum Inoculation and Phosphorus Fertilizer Rates on Nitrogen Uptake Efficiency and N₂ Fixation of Soybean (Glycine max L. (Merrill)) in Ethiopia

Soybean production in western Ethiopia particularly at Bako has remained low, partly due to soil nutrient depletion and degradation, which is considered serious threats to agricultural productivity and food security. This study was conducted to assess the effect of Bradyrhizobium japonicum strains and phosphorus rates on nitrogen uptake efficiency, N2 fixation of soybean, seed yield, yield components, yield and quality to enhance soybean production and yeild. Treatments included factorial combinations of four Bradyrhizobium japonicum strains with un-inoculated, (Soybean murodk, Soybean 12 and Soybean MAR-1495) and four phosphorus levels (0, 23, 46 and 69 kg P₂O₅ ha⁻¹) which were laid out in Randomized Complete Block Design (RCBD) with three replications. Interaction of Phosphorus and Bradyrhizobium inoculation, revealed that application of 69 kg P₂O₅ ha⁻¹ with Soybean 12 inoculation significantly resulted enhanced leaf area (64.2 cm²), and above ground biomass (8241 kg ha⁻¹), whereas Soybean MAR-1495 strain inoculation produced highest harvest index (48.77% plant⁻¹). Among all treatments, combined application of Soybean 12 along with 46 kg of P₂O₅ ha⁻¹ gave better performance of soybean with highest seed yield. While, phosphorus rates at 46 and 69 kg P₂O₅ ha⁻¹ with Soybean 12 inoculation resulted in maximum leaf area index of 0.157 plant⁻¹. Hence, 46 kg P₂O₅ ha⁻¹ phosphorus rate with Soybean 12 inoculation was found to be economical and superior in yield.

Days to 50% flowering and physiological maturity, leaf area, leaf area index, above ground biomass yield, seed yield and harvest index of soybean were increased with combined application of B. japonicum and phosphorus rates.

Combined application of soybean 12 plus 46 kg of P₂O₅ ha⁻¹ gave better performance in soybean, with maximum leaf area and seed yield.