Effect of NPS Rate and <i>Rhizobium</i> Inoculation on Yield and Yield Components of Common Bean (<i>Phaseolus vulgari</i> L.) at Kellem Wollega Zone, Western Oromia, Ethiopia

Common bean (Phaseolus vulgaris L.) is one of the most important and widely cultivated pulse crops in most developing countries. However, its cultivation is constrained mainly by low soil fertility and lack of improved agronomic practices. The experiment was conducted to evaluate the effects of Rhizobium inoculation, NPS fertilizer rate, and their interaction effect on grain yield and yield components of common bean and to recommend the appropriate combination that can maximize the productivities of common bean in the study areas. Six levels of NPS rates (0, 50, 75, 100, 125 and 150 kg ha<sup>-1</sup>) and three levels of Rhizobium strains (un-inoculated, BH429 and BH-A-15) were laid out in Randomized Complete Block Design with three replications in factorial arrangement. The collected data were analyzed by SAS software. Main effect of rhizobium strain exerted significant effect on effective branch/plant, however, NPS levels significantly influenced days to 50% flowering, days to 90% maturity, nodule/plant, effective branch/plant, pod/plant and grain yield. The main effect of experimental location imposed significant effect on most of agronomic parameters including pod/plant and grain yield. Significantly higher mean grain yield was recorded at Haro Sabu Agricultural Research Center and Igu experimental locations compared to Sago, which had the lower mean value of grain yield. Application of NPS rate with rhizobium strain affected number of effective branch/planr, while the interaction of NPS rate with location influenced number of days to 90% maturity, effective branch/plant, pod/plant, seed/pod and grain yield. Significantly higher mean grain yield was obtained by applying 100, 125 and 150 Kg/ha of NPS at Haro Sabu Agricultural Research Center and Igu, by applying 125 and 150 Kg/ha of NPS at Sago. Based on partial budget analysis the highest net benefit (Birr 31792.34 ha<sup>-1</sup>) was obtained from combined application of 100 kg blended NPS ha<sup>-1</sup> with un-inoculated strain which had 811% marginal rate of return. Hence, application of 100 kg NPS ha<sup>-1</sup> without inoculation of the strain was recommended for common bean productivity enhancement in the study area.