Effects of phosphorus fertilizer rate and Rhizobia inoculation on growth, nodulation and yield of Soybean [Glycine max (L.) Merrill] varieties under nitisol of South-Western Ethiopia

Soybean is high quality protein source for resource poor families and oil crop in Ethiopia, but low phosphorus levels and soil acidity limit yields in the BunoBedele area. Therefore, the aim of this study is to investigate the effect of phosphorus fertilizer and different rhizobia strains on soybean performance in terms of growth, nodulation, and yield in Nitisol of southwestern Ethiopia. The experiment was conducted at BunoBedele, Ilkekerero sub site of Bedele Agricultural Research Center in 2023 main cropping season. The experiment included 16 treatment combinations four phosphorus levels (0, 10, 20 and 30 kg P ha-1), with and without inoculation MAR-1495 rhizobia, and two soybean varieties (Ketta and Cheri). The experimental design was Randomized Complete Block Design RCBD) in factorial arrangement with three replications. The Analysis of variance showed very high significant (P<0.0001) interactions between rhizobia inoculation and phosphorus levels, as well as variety (P<0.0001) effects on growth, nodulation, and yield. The highest yields were achieved (3.45 ton ha-1) with 30 kg P ha-1 and Rhizobium inoculation, particularly with the Ketta variety, while the lowest grain yield was observed 0.33 ton ha-1 under un-inoculated rhizobia and control plot of P application. The combined application of MAR-1495 rhizobia and 30 kg P ha-1 significantly improved nodulation and yield. This approach also resulted in the highest net benefits (113231.2 ETB) and marginal rate of return (541.6%), making it a profitable strategy for enhancing soybean production and farmer income in the region. The findings from this research provide several practical recommendations for optimizing soybean cultivation in environments similar to the one studied: Cultivar Selection and Fertilizer Management. By implementing these practical recommendations, farmers in similar environments can optimize their soybean cultivation practices and improve the productivity and profitability of their operations.