Carbon Dioxide Exchange in an Irrigated Agricultural Field within an Oasis, Northwest China

Abstract

ontinuous eddy covariance measurements of CO2, water vapor, and heat fluxes were obtained from a maize field within an oasis in northwest China from 1 May 2008 to 30 April 2009. The experimental setup used was shown to provide reliable flux estimates on the basis of cross-checks made using various quality tests of the flux data. Results show that the highest half-hourly CO2 fluxes (Fc) were ?55.7 and 6.9 ?mol m?2 s?1 during the growing and nongrowing seasons, respectively. The daily net ecosystem exchange of carbon (NEE) ranged from ?14.7 to 2.2 g C m?2 day?1 during the growing season; however, the daily NEE fell to between 0.2 and 2.1 g C m?2 day?1 during the nongrowing season. The annual NEE calculated by integrating flux measurements and filling in missing and spurious data was about ?487.9 g C m?2. The total NEE during the growing season (?692.9 g C m?2) and the annual NEE were in the middle of the range, when compared with results obtained for maize fields in different studies and regions, whereas the differences between the off-season NEE from this study (205.0 g C m?2) and those defined in previous studies were very small. In addition, the seasonal variations in energy balance and evapotranspiration over the maize field were also addressed.