INFLUENCE OF BLENDED NPS FERTILIZER, VERMICOMPOST, AND SEED INOCULATION WITH RHIZOBIUM BACTERIA ON YIELD PERFORMANCE OF SOYBEAN AND SELECTED SOIL CHEMICAL PROPERTIES AT BAKO, WESTERN ETHIOPIA

Soil acidity is the main production constraint that reduces nodulation and productivity of soybean crop in Bako district, western Ethiopia. This study was carried out to determine the influence of blended NPS fertilizer, Vermicompost (VC), and Seed inoculation with Rhizobium bacteria on productivity of soybean (Glycine max. (L.)Merrill) and selected soil chemical properties. Factorial combinations of two Rhizobium strain (TAL-379) levels: uninoculated, inoculated, three vermicompost (VC) levels (0, 1 and 2 t ha-1) and three NPS levels (50%, 75% and 100% of 100 kg NPS ha-1) were laid out in Randomized Complete Block Design (RCBD) with three replications. Nodulation parameters, agronomic parameters, yield and yield related data were collected and analyzed. Analysis of the results revealed that soybean nodulation, yield components and yield were significantly affected by the main as well as interactions effects of NPS fertilizer, Rhizobium inoculation and vermicompost application. The highest number of effective nodules per plant (31.4) was recorded in response to the application of combined 2 tons VC ha-1 and 75 kg NPS ha-1 while the highest aboveground biomass (8953 kg ha-1) yield was recorded in response to the combining 2 tons VC ha-1 and 100 kg NPS ha-1. Combination of VC at 2 tons ha-1 with Rhizobium inoculation produced the highest number of effective nodules per plant (26.3). The three-factor interactions of Rhizobium inoculation, VC and NPS rates significantly influenced number of primary branches (NPB), number of pods per plant, seed yield and harvest index. The highest number of pods per plant (87.6), maximum seed yield (3762kg ha-1) and maximum harvest index (41%) were recorded from the plots treated with 100 kg NPS ha-1 + 2 t VC ha-1 inoculated with Rhizobium. The interaction of 100 kg NPS ha-1 with Rhizobium strain (TAL-379) inoculation resulted in the highest available P (12.34 mg kg-1) and available sulfur (21.41 mg kg-1) after crop harvest. The partial budget analysis showed that the highest net benefit (23537.2 Birr ha-1) and marginal rate of return (339.4%) were recorded for the combined application of 100 kg NPS ha-1+ 2 t VC ha-1 + inoculated with Rhizobium strain TAL-379. Combined application of 100 kg NPS ha-1+ 2 t VC ha-1 + inoculated with Rhizobium strain TAL-379 was superior with respect to grain yield as well as economic advantage. Therefore, the result could be verified for practical recommendation to be enhancing soybean production and income of farmers in the region.