Appraisal of the 15N-isotope dilution and 15N natural abundance methods for quantifying nitrogen fixation by flood-tolerant green manure legumes

Abstract

Quantification of biological nitrogen fixation (BNF) is fundamental to identifying potential green manure legumes for their enhanced nitrogen contribution to sustained crop production. A screenhouse experiment compared BNF by Aeschynomene afraspera L. as affected by phosphorus, using the 15Nisotope dilution and the 15N methods. Rice (Oryza sativa L.) was grown as a non-fixing plant. Phosphorus significantly increased the percent N derived from the atmosphere (% Ndfa), whereby the 15N method tended to overestimate BNF contribution on average by 20% compared to the
15 N dilution. Data confirmed rice as a non-fixing plant for estimation of BNF by flood-tolerant legumes