Greenhouse and multi-location experiments were conducted for two consecutive years to investigate the effects of rhizobium on nodulation, biomass production and partitioning of faba bean. Split-plot in randomized complete block design was used for field experiments. Treatments consisted of six rhizobium strains and three faba bean varieties. Peat carrier-based inoculant of each strain was applied at the rate of 10 g kg⁻¹ seed. Non-inoculated plants without N fertilizer and with N fertilizer served as –N and + N controls, respectively. Data on nodulation, shoot dry weight and root dry weight were collected and analyzed. Inoculation of rhizobium significantly increased nodulation of faba bean under greenhouse and field conditions. Location x strain x variety interaction had significant effects on nodulation, dry matter production and partitioning. Rhizobium inoculation increased nodulation, shoot and root dry weights of faba bean across locations. For example, inoculation with rhizobium strains NSFBR-15 and NSFBR-12 to variety Moti resulted in 206.9 and 99.3% shoot dry weight increase at Abala Gase and Hankomolicha, respectively and 133.3 and 70.7% root dry weight increase on the same variety at the same sites, respectively. Nodulation and biomass production depend on the compatibility between faba bean genotype and rhizobium strain and its interaction with soil bio-physical conditions.

This study reports the effectiveness of some selected rhizobium strains in enhancing nitrogen fixation and nutrient uptake in Vicia faba L. Multi-location field experiments were conducted for two years (2016 and 2017) using a split-plot in randomized complete block design. Treatments comprised six rhizobium strains as the main plot factor and three varieties of Vicia faba as the sub-plot factor. Non-inoculated plants with or without N fertilizer served as +N and −N controls, respectively. Peat carrier-based inoculant of each strain was applied at the rate of 10 g kg⁻¹ seed. Data on nodulation were taken at the late-flowering stage, whereas nitrogen and phosphorus concentrations in plant parts were analyzed at physiological maturity. The total nitrogen difference method was employed to quantify nitrogen fixation. Location x rhizobium strain x variety interaction had a significant effect on nodule dry weight plant⁻¹. Rhizobium strains significantly enhanced nodulation, nitrogen fixation, nutrient uptake and soil nitrogen balance. Inoculation with NSFBR-12 and NSFBR-15 resulted in the highest nitrogen fixed, nutrient uptake and soil nitrogen balance. Vicia faba inoculated with the two top performing strains, NSFBR-12 and NSFBR-15 fixed respectively 87.7% and 85.5% of the total nitrogen uptake. Non-inoculated plants fulfilled proportionately more of the total nitrogen uptake through nitrogen derived from the soil rather than fixed nitrogen. Soil available phosphorus and pH had appreciable influences on nitrogen and phosphorus uptake of inoculated Vicia faba. Inoculation with competitive and effective rhizobium strains can improve soil nitrogen balance, nitrogen fixation and nutrient uptake of Vicia faba.

This study reports the interaction of rhizobium strains and varieties on yield and yield components of faba bean and the economic feasibility of the inoculant use in faba bean production. The two years field experiments used a split-plot design that involved six elite rhizobium strains as the main plot and three faba bean varieties as sub-plot treatments. Non-inoculated plants with N fertilizer and without fertilizer were included as +N (46 kg ha−1) and −N controls, respectively. Phosphorus (P) was applied as triple super-phosphate at the time of sowing. Data on yield and yield components were collected and statistically analyzed. Partial budget, dominance, and marginal rate of return analysis were conducted to identify profitable rhizobial strain-variety combinations for each study location. Rhizobium strains NSFBR-15, TAL_1035 and NSFBR-12 increased grain and haulm yield of faba bean more than N fertilizer across the study locations. Location, rhizobium strain, and variety interaction influenced yield and yield components of faba bean. Economic analysis document that rhizobium inoculation for symbiotic N fixation is more profitable for supplying N to faba bean than N fertilizer application. Rhizobium strains NSFBR-15, TAL_1035, and NSFBR-12 with all faba bean varieties resulted in the highest revenue with a higher marginal rate of return at all study locations.