Carbon and Nitrogen Isotopic Discrimination in Alfalfa for High Yield and Quality Forage

Carbon and Nitrogen Isotopic Discrimination in Alfalfa for High Yield and Quality Forage

Biological nitrogen fixation and assimilation of CO₂ can be indirectly monitored in alfalfa (Medicago sativa L.) through the variation of the stable N and C isotopes in the plant (Δ values). Such measurements result in a simple, non-destructive and reliable method for identification of alfalfa cultivars of high yield and nutritional quality. A program for selection of 12 alfalfa cultivars under field and controlled conditions (lysimeters) included determination of biomass and N accumulation. Under controlled conditions yields ranged from 1.77 to 2.47 ton/ha/month (Pioneer 5312 and WL-605) and N2-fixed varied from 77.43 to 84.01% for total N (Brazilian Creoule and Victoria). ΔC varied from 21.53 to 21.94 (Pioneer 5312 and Brazilian Creole). Significant correlations between yield and ΔC (0.57*) and N from fixation (0.77*) showed the potential of using Δ values in alfalfa germplasm evaluation for high biomass yield and atmospheric N accumulation.