SUMMARYThe effect of elevated carbon dioxide (CO₂) concentration on greenhouse gas (GHG) emission from semi-arid cropping systems is poorly understood. Closed static chambers were used to measure the fluxes of nitrous oxide (N₂O), CO₂and methane (CH₄) from a spring wheat (Triticum aestivumL. cv. Yitpi) crop-soil system at the Australian grains free-air carbon dioxide enrichment (AGFACE) facility at Horsham in southern Australia in 2009. The targeted atmospheric CO₂concentrations (hereafter CO₂concentration is abbreviated as [CO₂]) were 390 (ambient) and 550 (elevated) μmol/mol for both rainfed and supplementary irrigated treatments. Gas measurements were conducted at five key growth stages of wheat. Elevated [CO₂] increased the emission of N₂O and CO₂by 108 and 29%, respectively, with changes being greater during the wheat vegetative stage. Supplementary irrigation reduced N₂O emission by 36%, suggesting that N₂O was reduced to N₂in the denitrification process. Irrigation increased CO₂flux by 26% at ambient [CO₂] but not at elevated [CO₂], and had no impact on CH₄flux. The present results suggest that under future atmospheric [CO₂], agricultural GHG emissions at the vegetative stage may be higher and irrigation is likely to reduce the emissions from semi-arid cropping systems.