Nitrous oxide is a greenhouse gas contributing to global warming. Biocrops have been proposed as an alternative for energy production. Nevertheless, the use of biofuels could be a counterproductive approach to mitigate global warming, as the fuel energy gained from biofuel crops might be offset against the nitrogen inputs and associated N2O emissions. The objective of this work was to determine the warming potential of a rapeseed crop in northern Spain caused by direct N2O emissions and CO2 emitted during farm machinery operations. Mineral fertilizer was applied at a rate of 180 kg N ha(-1) Fluxes of N2O were measured year round. The emission factor of direct N2O losses was determined, together with the relative warming with regard to plant N content and the CO2 emissions from farm equipment operation. The emission factor from direct N2O losses from rapeseed crop was 2.54%. Emissions of CO2 produced by farm machinery in rapeseed crop represented 8.5% of the CO2 equivalents in terms of N2O emitted by the crop. Thus, rapeseed grown in our conditions leads to N2O emissions whose warming effect is compensated by the "saved fossil CO2" of biofuel production. (C) 2012 Elsevier B.V. All rights reserved.
