Eddy covariance flux measurements were performed at a cotton crop site of an oasis in northern Xinjiang, northwest China from 2008 to 2010 in order to study ecosystem evapotranspiration (ET). The soil surface area was approximately 80% covered by plastic film mulch and a cotton crop was grown with a mean population density of around 24 plants m-2 under drip irrigation. The total annual ET was measured to be 560 mm, which was 350 mm more than the average annual mean precipitation for the time period 19632006. Due to the low vapor pressure deficit associated with low temperatures, the ET was low from November to March. The ET totaled 538 mm during the cotton crop growing season, generally from early-April through mid-October. Mean daily ecosystem ET was 1.41.6 mm day-1 in April and May, 3.44.7 mm day-1 from June through August, 1.82.3 mm day-1 in September and 0.70.8 mm day-1 in October. The diurnal variations of ET in all months were consistent with those of net radiation, although the leaf area index (LAI) and climate conditions changed substantially. Soil water content was not a limiting factor for ET during the period from April through September, as the crop was regularly irrigated. Therefore, ET was mainly controlled by the available energy in April and May, and by leaf area from June through September. Due to a complete lack of irrigation, ET was constrained by soil water in October. These results of ET variability are helpful for improved allocation of water resources and agricultural water use practices in the region. Copyright (c) 2011 John Wiley & Sons, Ltd.
