2 11 Abstract 12 Rhizobia inoculation can increase soybean yield, but its performance is influenced by soybean 13 genotype, rhizobia strains, environment, and crop management among others. The objective of 14 the study was to assess soybean response to rhizobia inoculation when grown in soils amended 15 with urea or Vermicompost to improve nitrogen levels. Two greenhouse experiments and one 16 field trial at two sites were carried out. The first greenhouse experiment included soils from sixty 17 locations, sampled from smallholder farms in Western Kenya. The second greenhouse 18 experiment consisted of one soil selected from soils used in the first experiment where 19 inoculation response was poor. The soil was amended with Vermicompost or urea. In the two 20 greenhouse experiments, Legumefix® (inoculant) + Sympal (legume fertilizer blend) were used 21 as a standard package. Results from the second greenhouse experiment were then validated in the 22 field. In the first greenhouse trial, soybean response to inoculation was significantly affected by 23 soil fertility based on nodule fresh weight and shoot biomass. Soils with low nitrogen had low to 24 no response to inoculation. After amendment, nodule fresh weight, nodule effectiveness, nodule 25 occupancy, and shoot dry biomass were greater in the treatment amended with Vermicompost 26 than those amended with urea (Legumefix® + Sympal + Vermicompost and Legumefix® + 27 Sympal + urea). Under field conditions, trends were similar to the second experiment for 28 nodulation, nodule occupancy, and nitrogen uptake resulting in significantly greater grain yields 29 (475, 709, 856, 880, 966 kg ha -1 ) after application of Vermicompost at 0, 37, 74, 111, and 148 kg 30 N ha -1 , respectively. It was concluded that soybean nodulation and biological nitrogen fixation in 31 low fertility soils would not be suppressed by organic amendments like Vermicompost up to 148 32 kg N ha -1 . 33 Keywords: Rhizobia inoculation, nodule occupancy, nodule effectiveness, Vermicompost, grain 34 yield. 3 36 Introduction 37 Soybean (Glycine max L. Merr) is one of the world's most important legumes in terms of 38 production and trade and has been a dominant oilseed since the 1960s [1]. The crop is well 39 known for its high protein content (about 40%) [2]. Additionally, it can improve soil properties 40 and soil biological health by soil nitrogen enrichment through N 2 fixation and subsequent 41 mineralization of shoot and root biomass [3]. It therefore represents a significant opportunity in 42 sub-Saharan Africa (SSA), where over 80% of the soils are nitrogen deficient [85], and over 39% 43 of the children under 5 years are stunted because of malnutrition caused by nutrient deficiency, 44 particularly proteins [4], contributing to over one third of child deaths [5]. Integration of soybean 45 in smallholder farming systems would thus not only improve human nutrition when the crop is 46 included in diets but also soil productivity. Such benefits would materialize when good 47 agronomic practices...
