Evaluation of Different Rhizobial Strains of Faba Bean (V. Faba) for Yield and Yield Components in Acid-Prone Areas: South Gondar Zone, Northwest Ethiopia

Abstract Aims Soil acidity constrains faba bean (Vicia faba L.) productivity in the Ethiopian highlands by increasing aluminum toxicity and suppressing biological nitrogen fixation. Although liming is a well-established amendment, its interaction with elite rhizobial inoculants under farmers' field conditions remains poorly documented. This study aimed to evaluate the performance of nine rhizobial strains under limed and unlimed conditions on nodulation, growth, biomass, and grain yield of faba bean. Methods A split-plot trial with three replications was conducted over three cropping seasons in Farta and Guna Begemidir districts, South Gondar Zone, Ethiopia. Lime served as the main-plot factor and rhizobial inoculation as the subplot factor. Results Lime application significantly increased grain yield by 17.6% (2329 vs. 1980 kg ha⁻¹), along with biomass yield, plant height, nodule number, and nodule dry weight. Rhizobial strains differed significantly in symbiotic effectiveness, with strain FB-15 giving the highest grain yield (2467 kg ha⁻¹), biomass yield (6846 kg ha⁻¹), nodule number (51.9 plant⁻¹), and nodule dry weight (1.90 g plant⁻¹). Significant lime × strain interactions for grain yield, plant height, nodulation, and nodule dry weight indicated that inoculant performance depended on soil acidity status: FB-15 performed best under limed conditions (2889 kg ha⁻¹), while FB NS-03 outperformed other strains without lime (2536 kg ha⁻¹). The negative control consistently gave the lowest values across all parameters. Conclusions Combining lime with efficient rhizobial inoculation substantially enhances biological nitrogen fixation and faba bean productivity in acidic soils. FB NS-03 offers farmers a viable alternative where lime is unavailable.