Variation in Nitrogen Fixation among Three Bush Bean Cultivars Grown in Kenya when Inoculated with Three Rhizobia Strains

Nitrogen deficiency is a major factor limiting bean production in Africa. This problem can be alleviated by the use of nitrogen fertilizers which on the other hand adversely affect the environment. The problem can also be alleviated by the use of environmental friendly biological nitrogen fixation technology. In this study, growth experiments were designed to investigate biological nitrogen fixation in three determinate (bush) beans namely Ayenew, GLP 24, and Ecab 0807. Greenhouse and field studies were carried out to determine the most efficient bean cultivar and rhizobia strain in nitrogen fixation. Each bean cultivar was inoculated with the rhizobia strains CIAT 899, USDA 2674, USDA 2676, the three rhizobia strains combined and one was not inoculated. Results from greenhouse studies showed significant statistical differences in nodulation within the bean cultivars. The bush bean cultivar GLP24 was poorly nodulated (40.0 nodules on average) as compared to Ayenew (52.0 nodules on average) and Ecab 0807 (58.0 nodules on average). It was also observed that bush beans inoculated with USDA 2674 strain of rhizobia in the greenhouse produced the highest nodule number although in the field, it was those inoculated with strain CIAT 899. Bush beans inoculated with USDA 2674 gave the highest total plant dry weight. Treatments within each of the cultivars showed differences in total plant dry weight yield in response to rhizobia strain used. Field experiments showed that plant dry weight differed statistically between cultivars at P<0.05. Bush beans inoculated with USDA 2674 gave the highest total plant dry weight but there were no significant differences in yield.