Effects of rhizobial inoculant and nitrogen fertilizer on yield and nodulation of common bean

A two-year field experiment was conducted to determine if using mixed strai ns of Rhizobium inoculant and starter nitrogen (N) fertilizer could improve yield and nodulation of four common bean varieties on a Vertisol at Alemay a, Ethiopia. A granular mixed inoculant of CIAT isolates 384, 274, and 632 and a starter N fertilizer at a rate of 23 kg N ha(-1) (50 kg urea ha(-1)) were applied separately at planting. Inoculation with mixed strains and sta rter N fertilizer gave a significantly higher grain yield, nodule number, a nd dry matter yield for most varieties used. Both grain yield and dry matte r yield showed a significant correlation (r=0.93 and r=0.87; P less than or equal to 3.05 for grain yield and dry matter yield, respectively, for 1991 crop season and r=0.90 and r-0.86; P less than or equal to 0.05 for grain yield and dry matter yield, respectively, for 1992 crop season) with nodule number. It is recommended that resource-poor farmers adopt the practice of using a Rhizobium inoculant or starter N to improve common bean yields in the Hararghe highlands, Ethiopia.