Chickpea and faba bean nitrogen fixation in a Mediterranean rainfed Vertisol: Effect of the tillage system

Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N-2 fixation. A field experiment was conducted during a 6-year period (2001-2002 to 2006-2007) in Cordoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect of tillage systems [no tillage (NT) and conventional tillage (CT)] on chickpea and faba bean N-2 fixation. Fixation was calculated using the N-15 isotopic dilution (ID) and N-15 natural abundance (NA) methods with the reference being the wheat crop. The strong inter-annual rain variation caused great differences in the behaviour of both leguminous plants with regard to grain yield, nodule biomass and N-2 fixation. The NT system showed more nodule biomass than the CT system in both legumes. The ID method was more accurate than the NA method in determining N-2 fixation. The average amount of fixed N in faba bean (80 kg ha(-1) year(-1)) was much greater than that in chickpea (31 kg ha(-1) year(-1)). The Vertisol under the NT system offered more favourable conditions for the stimulation of the N-2 fixation, with fixed N values that were significantly higher than under CT. The N added to the system through N-2 fixation was low in faba bean and virtually nonexistent in chickpea, only in terms of above-ground biomass. (C) 2011 Elsevier B.V. All rights reserved.