Rhizobium leguminosarum bv. viciae sp. inoculation improves the agronomic efficiency of N of common bean (Phaseolus vulgaris L.)

Due to common bean derives lower nitrogen (N) from symbiotic N2-fixation, it requires N either from inorganic fertilizer or soil N. Field experiments were conducted at four locations to evaluate the effect of Rhizobium leguminosarum bv. phaseoli inoculation on agronomic efficiency of N of common bean var. Dursitu major growing areas of eastern Ethiopia. Six levels of inorganic N (0, 20, 40, 60, 80 and 100 kg N ha−1) and two inoculation treatments (uninoculated and inoculated) were factorially combined and laid out in randomized completely block design, replicated three times. AE-N, nodule number per plant (NN) and nodule dry weight per plant (NDW) decreased with N rates of application beyond 20 kg N ha−1. The highest AE-Ns at Babillae, Fedis and Haramaya sites were obtained from 20 kg N ha−1 applied with Rhizobium inoculation while 40 kg N ha−1 supplied with Rhizobium inoculation at Hirna site. Regardless of experimental sites, inoculation improved AE-N. A positive relationship between AE-N and NDW was also observed in all experimental sites. Significant increase in grain yield with increasing rates of N application was also observed. Hence, it can be concluded that inoculation is recommendable to increases the efficient utilization of applied Mineral N.