Response of Faba Bean (Vicia faba L.) to Rhizobium Inoculation and Potassium Fertilizer Application on Nitisols at Wolaita Sodo, Southern Ethiopia

Lack of effective indigenous soil rhizobia and low soil fertility including potassium deficiency are the major production constraints that limit the potential yield of faba bean in the study area. Hence, field experiment was conducted to evaluate the effect of Rhizobium inoculation and potassium fertilizer application on nodulation, yield components and yield of faba bean; to determine the potassium use efficiency; and to evaluate the economic feasibility of the treatments for faba bean production during 2016 cropping season at Wolaita Sodo, southern Ethiopia. Faba bean variety “Degaga” was used as the test crop. Factorial combinations of three Rhizobium inoculation levels (HUFBR-15, EAL-110 and uninoculated control) and five potassium fertilizer levels (0, 30, 60, 90 and 120 kg KCl ha-1) were laid out in a Randomized Complete Block Design with three replications. The results of the experiment revealed that days to physiological maturity, plants height, harvest index and efficiency of K were significantly affected by the main effects of both potassium rates and Rhizobium inoculation. The highest days to physiological maturity (107.40 days), plant height (128.9 cm), harvest index (40.38%) and physiological efficiency of K (72.22 kg kg-1) were obtained from HUFBR-15 inoculation, whereas, days to physiological maturity (109.60 days), plant height (131.70 cm), harvest index (40.93%) and physiological efficiency of K (62.47 kg kg-1) were obtained from 90 kg KCl ha-1 application. Significantly highest apparent recovery of K (12.19%) and agronomic use efficiency (11.61 kg kg-1) were obtained from low K rate (30 kg KCl ha-1).Among the interaction effects, combination of Rhizobium inoculation of HUFBR-15 and 90 kg KCl ha-1 rates significantly influenced many parameters and resulted in highest total K uptake (22.14 kg ha-1), K uptake by grain (5.81 kg ha-1), K uptake by straw(16.32 kg ha-1), number of primary branches (3.87), total number of nodules (134.40), effective nodules (108.40) and nodule dry weight (305.7 mg) per plant. This treatment also resulted in significantly highest number of pods per plant (39.47), number of seeds per pod (3.41), hundred seed weight (55.65 g), aboveground dry biomass yield (9280 kg ha-1) and grain yield (4101 kg ha-1). The economic analysis also indicated that the highest net return (41190 ETB ha-1) with a marginal rate of return of 204% was obtained from combined application of HUFBR-15 and 90 kg KCl ha -1. Based on the results, it can tentatively be concluded that faba bean seed inoculation with Rhizobium isolate HUFBR-15 and application of 90 kg KCl ha-1 was found to be best soil treatment for faba bean production in the study area.