Seasonal dynamics of soil CO2 efflux in a conventional tilled wheat field of the Loess Plateau, China

An automated chamber system was employed to measure the soil CO2 efflux (SCE) in situ for 2 years in a conventional wheat field of the Loess Plateau, China under semi-arid conditions. The annual mean SCE values were 2.44 +/- 2.52 mu mol m(-2) s(-1) in 2006 and 2.37 +/- 2.33 mu mol m(-2) s(-1) in 2007. Distinct seasonality in the SCE was observed, with significant differences occurring among four periods divided by harvesting, tillage and sowing. In the period from tillage to sowing, the mean SCE values were 2.82 and 2.69 times the annual mean values in 2006 and 2007, respectively, and SCE accounted for 39% and 48% of the annual total within 14% and 18% of the days of the years. Although there were significant exponential correlations between the SCE and soil temperature, and significant linear correlations between the SCE and soil moisture for measurements conducted in the periods before tillage and after sowing each year, the SCE from tillage to sowing was significantly beyond the correlation curves. These findings indicated that seasonal variation in the SCE in a conventional field was controlled not only by soil temperature and moisture, but also by tillage practice. The confounding effects of climate and practice on SCE should be considered when developing ways to mitigate soil carbon loss in conventional cropland in semi-arid regions.