Biological nitrogen fixation and growth parameters correlations of alfalfa (Medicago sativa L.) genotypes under organically managed fields with limited irrigation

To identify the effective characters and their relative importance in improvement of BNF, two separate field experiments were conducted under irrigated and rain-fed organic managements of dry, Pannonian region of east Austria. The experiments were laid out in an α-lattice design with two replications and 18 genotypes (eight Iranian ecotypes and ten European cultivars). Plant height was positively and significantly correlated with leaf area index (LAI) and shoot dry matter (DM) under both conditions. Positive correlations were found between biological nitrogen fixation (BNF) and shoot DM (r = 0.61** and 0.87**, irrigated and rain-fed management, respectively). Regarding correlation coefficients, high yielding genotypes had taller plants and denser stands, especially under rain-fed condition. In path analysis, all direct effects of BNF components were positive in both conditions, while some of the indirect effects were negative. These can be regarded in selection models to avoid undesirable negative effects. Plant height and LAI can be considered as primary selection criteria for improving shoot DM, while crop re-growth and plant height, with antonymous effects, were more important for improving root dry matter.