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

A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Cordoba (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 N-15 dilution and N-15 natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N, 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, fixation values as calculated by the N-15 enriched (ID) method and the N-15 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 NO3--N content between the two systems. (c) 2006 Elsevier B.V. All rights reserved.