Response of Soybean (Glycine max L. (Merrill)) to Bradyrhizobium Inoculation, Lime, and Phosphorus Applications at Bako, Western Ethiopia

Soil acidity and poor soil fertility are the major soil chemical constraints which limit crop productivity in western Ethiopia. In leguminous crops, low productivity is not only a result of declining soil fertility but also reduced N2 fixation due to biological and environmental factors. Thus, this study was carried out to determine the influence of lime, Bradyrhizobium inoculation, and phosphorus fertilizer on soybean yield components and yields and to identify economically feasible treatments that can maximize the productivity of soybean. Factorial combinations of three Bradyrhizobium strains (uninoculated, TAL379, and Legumefix), two lime levels (0 and 3.12 t ha−1), and four P levels (0, 23, 46, and 69 kg P2O5 ha−1) were laid out in RCBD with three replications. The results showed that the application of lime (3.12 t ha−1) significantly increased soil pH (5.6), plant height (77.2 cm), number of primary branches per plant (6.6), 100-seed weight (17.5 g), grain yield (3431 kg ha−1), and harvest index (41%). Similarly, significantly higher grain yield (3228 kg ha−1) and harvest index (41%) were obtained with inoculation of TAL379 whereas Legumefix inoculation recorded the highest number of primary branches (6.7). The effect of P at 69 kg P2O5 ha−1also gave significantly higher plant height (75.5 cm), number of primary branches (6.6), grain yield (3277 kg ha−1), and harvest index (43%). The interaction of P and Bradyrhizobium inoculation significantly influenced days to physiological maturity and number of pods per plant. Similarly, the interaction of phosphorus and lime significantly influenced days to 50% flowering. Likewise, the combination of lime (3.12 t ha−1) with TAL379 inoculation gave the highest aboveground biomass. On the other hand, the interaction of Bradyrhizobium × lime × phosphorus revealed that application of 69 kg P2O5 ha−1 without TAL379 inoculation under limed condition significantly resulted in the highest number of nodules per plant (79.4) and number of effective nodules (67.9). Thus, it can be concluded that, particularly in the western part of Ethiopia where soil acidity is a major problem, application of phosphorus with Bradyrhizobium and lime is an alternative option to enhance biological nitrogen fixation and grain yield of soybean in smallholder farming system.