N2 fixation by faba bean (Vicia faba L.) in a gypsum-amended sodic soil

Abstract

The response of faba bean to the application of four rates of gypsum (0, 2.5, 5.0, 10.0 t ha-1) to a non-saline, alkaline sodic soil was measured in terms of grain yield, dry matter (DM) production, N accumulation and the proportional dependence of the legume on symbiotic N2 fixation (P atm). A yield-independent, time-integrated 15N-dilution model was used to estimate symbiotic dependence. A significant decrease in the exchangeable sodium percentage and significant increases in exchangeable Ca ++ and the Ca++:Mg++ ratio in the 0-10-cm soil layer were measured 30 months after application of 10 t ha-1 gypsum. Despite low and erratic rainfall during crop growth, faba bean DM and N uptake respon..