ABSTRACT
A field experiment in a clay loam soil was conducted to evaluate the interaction between seven soybean cultivars and three Rhizobium japonicum strains. The associations of soybean cultivars with strain USDA 110 were more efficient compared to those with strain USDA 138 or TAL 379. The more efficient symbiosis was observed between strain USDA 110 with Cumberland and Pella cultivars. However, strain USDA 138 gave the best nodulation and N2 fixation with Williams 79 and Calland cultivars. Whereas strain TAL 379 was better with Corsoy and Sprite than with other cultivars. A positive yield response to inoculation was noted with strain USDA 110, being the superior strain all tested cultivars followed by strain USDA 138. The Calland, Pella and Williams 79 cultivars gave the highest yield production. The competition studies revealed that strain USDA 110 was more competitive than either USDA 138 or TAL 379. Strain USDA 110 showed higher competitive ability with Cumberland, Pella and Calland cultivars and comparatively lower competitive ability with Corsoy and Sprite cultivars. Strain USDA 138 occupied 40 and 45% of nodules formed on Calland and Williams 79 cultivars, respectively versus 20% of nodules formed on Corsoy and Pella cultivars. The total nodule occupancy of strain TAL 379 amounted 40% on Sprite and Corsoy cultivars versus 20% on other soybean cultivars