To evaluate faba bean Rhizobia strains from the USDA collection for effective nodulation of selected cultivars.
To evaluate faba bean Rhizobia strains from the USDA collection for effective nodulation of selected cultivars; to compare the nitrogen (N) fixation ability of the best selected faba bean strains to three commercial pea/lentil inoculants.
Faba bean is a relatively newly emerging crop in Saskatchewan agriculture. It is reported to be an excellent nitrogen (N) fixing pulse crop, able to fix 70% to more than 90% of its N from biological nitrogen fixation. Despite its excellent N-fixation abilities, there is not currently a commercial Rhizobium inoculant available for this crop. This study screened 42 strains of Rhizobium , originally isolated from faba bean nodules, for their ability to nodulate and fix N in two varieties of faba bean. The two faba bean varieties included a large seeded variety (FB9-4) and a small-seeded variety (FB34-2; CDC Snowdrop). Faba bean inoculated with the different strains were measured for nodulation, productivity, and N content. The five Rhizobium strains that were ranked the best for these parameters for both faba bean varieties were selected for more extensive study in a greenhouse study. In addition, the three Rhizobium strains that performed well with FB9-4 (but not FB34-2) and the two Rhizobium strains that performed well with FB34-2 (but not FB9-4) were also selected for the greenhouse study.
All but one of the original 42 strains improved nodulation, biomass production, and N content in the faba bean varieties to different extents. Inoculating the faba bean seed with the ten strains of Rhizobium approximately doubled the percentage of N-fixation which increased the overall biomass production by an average of 33%. Percentages of N derived from fixation averaged about 60% in the greenhouse. This study demonstrates the large improvements in productivity and biological N-fixation that can be achieved by inoculating faba bean at seeding. In addition, the two top performing Rhizobium strains for the FB34-2 variety were identified and are currently being evaluated in field studies. The small, fairly uniform seed size of the FB34-2 variety (CDC Snowdrop) makes it much easier to seed with traditional seeders and more likely to be adopted by producers in Saskatchewan.