Understanding nitrous oxide (N2O) and methane (CH4) fluxes from agricultural soils in semi-arid climates is necessary to fully assess greenhouse gas emissions from bioenergy cropping systems, and to improve our knowledge of global terrestrial gaseous exchange. Canola is grown globally as a feedstock for biodiesel production, however, resulting soil greenhouse gas fluxes are rarely reported for semi-arid climates. We measured soil N2O and CH4 fluxes from a rain-fed canola crop in a semi-arid region of south-western Australia for 1 year on a subdaily basis. The site included N fertilized (75 kg N haâ??1 yrâ??1) and nonfertilized plots. Daily N2O fluxes were low (â??1.5 to 4.7 g N2O-N haâ??1 dayâ??1) and culminated in an annual loss of 128 g N2O-N haâ??1 (standard error, 12 g N2O-N haâ??1) from N fertilized soil and 80 g N2O-N haâ??1 (standard error, 11 g N2O-N haâ??1) from nonfertilized soil. Daily CH4 fluxes were also low (â??10.3 to 11.9 g CH4-C haâ??1 dayâ??1), and did not differ with treatments, with an average annual net emission of 6.7 g CH4â??C ha-1 (standard error, 20 g CH4-C ha-1). Greatest daily N2O fluxes occurred when the soil was fallow, and following a series of summer rainfall events. Summer rainfall increased soil water contents and available N, and occurred when soil temperatures were >25 °C, and when there was no active plant growth to compete with soil microorganisms for mineralized N; conditions known to promote N2O production. The proportion of N fertilizer emitted as N2O, after correction for emissions from the no N fertilizer treatment, was 0.06%; 17 times lower than IPCC default value for the application of synthetic N fertilizers to land (1.0%). Soil greenhouse gas fluxes from bioenergy crop production in semi-arid regions are likely to have less influence on the net global warming potential of biofuel production than in temperate climates.
