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. These low productivity in leguminous crops are as a result of declining soil fertility and reduced N2-fixation due to biological and environmental factors. Thus, study was carried out to determine the influence of lime, Bradyrhizobium inoculation and phosphorus fertilizer on soybean nodulation, 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 Randomized Complete Block Design (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 (91.1 cm), number of primary branches per plant (6.6), 100-seed weight (18.3 g), above ground biomass yield (9153 kg ha-1) and harvest index (41%). Similarly, significantly higher above ground biomass yield (8888 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 highest plant height (90.4 cm), number of primary branches (6.6), above ground biomass yield (9099 kg ha-1) and harvest index (43%). The interaction of P and Bradyrhizobium inoculation, revealed that application of 46 kg P2O5 ha-1 with TAL379 inoculation significantly resulted in the highest number of nodules per plant (62.3), number of effective nodules (62.2) and number of pods (70). Similarly, the highest number of nodules per plant (76), number of effective nodules (72.3), number of pods per plant (69.4) and grain yield (3866 kg ha-1) were recorded at the combination of 3.12 t lime ha-1 and 46 kg P2O5 ha-1. Likewise, the combination of lime (3.12 t ha-1) with TAL379 inoculation gave the highest nodule volume (3.4 ml/plant) and nodule dry weight (0.99 g/plant) of soybean. On the other hand, three ways interaction of Bradyrhizobium, lime and P rates significantly influences soil available P after harvest of the crop where the highest soil available P (12.33 mg kg-1 of soil) was recorded from the plots treated with lime + 69 kg P2O5 ha-1 supplied with Legumefix. The highest net benefit (26569.6 Birr ha-1) and MRR (784.7%) were recorded from the combination of 3.12 t lime ha-1, 23 kg P2O5 ha-1 and TAL379 strain. Thus, it can be concluded that application of 3.12 t lime ha-1 and 23 kg P2O5 ha-1 with TAL379 inoculation proved to be superior with respect to grain yield as well as economic advantage and is tentatively recommended for use. However, as this study was done for one seasons at one location, the experiment has to be repeated over years to reach at a conclusive recommendation