Field pea (Pisum sativum) is widely cultivated in Ethiopia as a source of protein and integrated in crop rotation to improve soil fertility for it fixes nitrogen with rhizobia. However, effectiveness in nitrogen fixation depends upon the selection of symbiotically effective rhizobia to enhance production. Thus, a study was conducted to evaluate the performance of three inoculants (isolates); FBR 11, FBR 15, FBR 23 on growth, nitrogen fixation and yield under field conditions in relation to a commercial rhizobial strain 1018 at Kulumsa Agricultural Research Center during 2015/16 growing seasons. Inoculation of field pea showed a highly significant (p≤0.001, p≤0.01 and p≤0.05) effect on all parameters compared to the un-inoculated plants in the field trial. Accordingly, plants inoculated with isolate FBR15 and Strain 1018 showed a significant increase in nodule number 84-112NN/plant (10 times), NDW 77-94mg/plant (12 times) against the un-inoculated control plants, and they also showed a 20-25% increase in both parameters in comparison to FBR11 and FBR23 inoculated plants. The treatments with FBR15 and the reference strain 1018 also showed significant difference in grain total nitrogen and N uptake and straw N uptake, and seed protein with 50-100% and 12-20% difference from the un-inoculated control plants and other Rhizobium treatments, respectively. Positive correlations were observed with respect to the number of nodule and shoot dry weight (r = 0.49, p<0.05), number of nodule and number of pod (r = 0.59, p<0.01), number of nodules and total grain yield (r = 0.56, p<0.05), and shoot dry weight and N content (r = 0.73, p<0.001). Although the MPN count of rhizobia in the soil at the experimental site was 1.5 x 104 and contained sufficient number of indigenous rhizobia, they were not effective that was indicated by the nodulation and yield parameters of the un-inoculated treatments. The data in general, showed that the rhizobial inoculants, particularly FBR 15 isolate was nutritionally versatile, ecologically competent, and symbiotically effective rhizobia compared to the commercial inoculant (strain 1018) that could be used as commercial inoculants for pea production after it is tested (validated) at different agro-ecological conditions.

Keywords: Biological yield, Grain yield, inoculation, nodule occupancy, N uptake