Genotypic variation in nitrogen fixation characteristics in faba bean (Vicia faba L.) under contrasting phosphorus fertilizer regimes

Assessment of the genetic variability is an important step in improving nitrogen (N₂) fixation potential of faba bean (Vicia faba L.) genotypes. The study was conducted to evaluate the genotypic variation for symbiotic N₂ fixation traits of faba bean under contrasting phosphorus (P) fertilizer regimes. Twenty and 12 genotypes in the field and greenhouse, respectively, were planted under two P fertilizer regimes (P− and P+ corresponding to 0 and 46 kg/ha) using a randomized complete block design with three replications. Analysis of variance indicated highly significant (p < 0.01) variation among genotypes for all N₂ fixation traits under both P regimes, indicating the availability of genotypic variation. Genotypes Obse, Dosha, Didea, Gebelcho, Gora, Moti, and Hachalu had better performance for N₂ fixation traits and higher grain yield (GY) across all study conditions. Performances of all N₂ fixation traits, except nitrogen harvest index, were better under P+ than under P−. P fertilizer application in the field resulted in 12.3, 12.9%, 18.9%, and 24.2% increase in the number of nodules per plant, nodule dry weight per plant (NDWP), N₂ yield (NY), and the amount of N₂ fixed (NF), respectively. In the greenhouse, 18.9%, 22.5%, and 27.2% increment was obtained for NDWP, NY, and NF, respectively, due to fertilizer application. Biplot analysis revealed that NF, NY, percentage of nitrogen derived from atmosphere (%Ndfa), shoot nitrogen concentration (ShN), and GY were the traits responsible for large genetic variation for N₂ fixation. NF had higher heritability and formed a significant positive correlation with most nitrogen fixation traits, suggesting the potential of the trait to be improved through breeding.