Effect of Rhizobium Inoculation and Nitrogen Fertilization on Nodulation and Yield Response of Common Bean (Phaseolus vulgaries L.) at Boloso Sore, Southern Ethiopia

The cost of chemical fertilizer is high and their use efficiency especially nitrogen fertilizer is low. Use of biological nitrogen fixation as source of N and determining the optimum level of N as starter fertiliser are important option to increase productivity of legumes. A field experiment was conducted to assess the effect of rhizobium inoculation and N fertilizer application on nodulation and yield of common bean varieties in 2014 cropping season.  Two common bean varieties (Omo-95 and Red Wolaita) were treated by three level of N (0, 23 and 46 kgNha -1 ) and two rhizobium strains (BH129 and BH113). The treatments were arranged using randomized complete block design with three replications. The result of this study indicated that application of N fertilizer significantly suppressed the number of nodules while inoculation of rhizobium bacteria increased the number of nodules per plant significantly for the two varieties. Furthermore, both application of N fertilizer and inoculation of rhizobium increased hundred seed weight and seed yield ha -1 . Om-95 gave significantly higher number of seeds per pod and seed yield ha -1 than Red Wolaita. From this result, it can be conclude that inoculation of rhizobium enhanced nodulation of haricot bean varieties with better response of Omo-95 while application of N fertilizer had suppressing effect. Furthermore, both application of chemical fertilizer and inoculation of rhizobium increased yield of common bean with better performance of  Omo-95 variety (2416.1 kgha -1 ) treated by rhizobium strain called  BH129. For better health of the soil and reducing cost of production, it is better to use seeds treated by bacteria but further study should be done  by considering other soil and crop factors. Keywords : Rhizobium, nitrogen, nodulation and yield