Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean conditions: Effect of tillage system

Abstract

A field experiment was conducted during a 2-year period (2001–2002 and 2002–2003) in Córdoba (Southern Spain) on a rainfed Vertisol, within the wheat-faba bean rotation framework of a long-term experiment started en 1986, to determine the effects of tillage systems [no tillage (NT) and conventional tillage (CT)], on faba bean N 2 fixation. Fixation was calculated using the 15N dilution and 15N natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N 2 fixed between 39 and 144 kg N ha −1. The N balance was positive for all years and treatments, with a mean value of 18.3 kg N ha −1 and a maximum of 40 kg N ha −1, in terms of above-ground biomass only. No significant difference was recorded between faba bean N 2 fixation values as calculated by the 15N enriched (ID) method and the 15N natural abundance (NA) method. The effect of tillage system on %Ndfa and the amount of N 2 fixed was not significant, possibly due to the negligible difference in soil NO 3 −–N content between the two systems.