In northwestern China,there has been a change from traditional cultivation system (TC) with no mulching and flood irrigation to a more modern cultivation system (MC) using plastic film mulching with drip irrigation.A field study was conducted to compare soil CO 2 concentrations and soil surface CO 2 fluxes between TC and MC systems during a cotton growing season.CO 2 concentrations in the soil profile were higher in the MC system (3 107-9 212 μL L-1) than in the TC system (1 275-8 994 μL L-1) but the rate of CO 2 flux was lower in the MC system.Possible reasons for this included decreased gas diffusion and higher soil moisture due to the mulching cover in the MC system,and the consumption of soil CO2 by weathering reactions.Over the whole cotton growing season,accumulated rates of CO2 flux were 300 and 394 g C m-2 for the MC and TC systems,respectively.When agricultural practices were converted from traditional cultivation to a plastic film mulching system,soil CO 2 emissions could be reduced by approximately 100 g C m-2 year-1 in agricultural lands in arid and/or semi-arid areas of northern and northwestern China. In northwestern China, there has been a change from traditional cultivation system (TC) with no mulching and flood irrigation to a more modern farming system (MC) using plastic film mulching with drip irrigation. A field study was conducted to compare soil CO 2 concentrations and soil surface CO 2 fluxes between TC and MC systems during a cotton growing season. CO 2 concentrations in the soil profile were higher in the MC system (3 107-9 212 μL L -1) than in TC system (1 275- 8 994 μL L-1) but the rate of CO 2 flux was lower in the MC system. Possible reasons for this included decreased gas diffusion and higher soil moisture due to the mulching cover in the MC system, and the consumption of soil CO2 by weathering reactions. Over the whole cotton growing season, accumulated rates of CO2 flux were 300 and 394 g C m-2 for the MC and TC systems, respectively. When agricultural practices were converted from traditional cultivation to a plastic film mulching system, soil CO 2 emissions could b e reduced by approximately 100 g C m-2 year-1 in agricultural lands in arid and / or semi-arid areas of northern and northwestern China.