Energy exchange and evapotranspiration over irrigated seed maize agroecosystems in a desert-oasis region, northwest China

Abstract

Investigating the dynamics of energy and water vapor exchange in oasis agroecosystems is important to improve scientific understanding of land surface processes in desert-oasis regions. In this study, water vapor and energy fluxes were obtained by using an eddy covariance technique for two similar irrigated seed maize fields at Yingke and Pingchuan, in northwest China. Seasonal variabilities of evapotranspiration (ET) and relevant environmental and biophysical factors were explored. Results showed that the energy balance closures were reasonable, with energy balance ratio of 0.99 and 0.79 for a half-hourly time scale at Yingke and Pingchuan, respectively. The seasonal changes in net radiation (Rn), latent heat flux (LE), and sensible heat flux (H) of Yingke and Pingchuan were similar. Net radiation was 11.27MJm−1day−1 during the growing season. Latent heat flux accounted for 67.5% of net radiation, sensible heat flux was 25.0%, and soil heat flux was 7.5%. A reverse seasonal change was found in partitioning energy flux into LE and H. The seasonal variation in energy flux partitioning was significantly related to the phenology of maize. During the growing season, ET was 467 and 545mm, and mean daily ET 2.84 and 3.35mmday−1 at Pingchuan and Yingke, respectively. “Non-growing” season ET was 15% of the annual ET in the bare field (during October–March) and 85% of the annual ET for maize (during April–September). Daily ET was mainly controlled by net radiation and air temperature, and was significantly affected by leaf area index (<3.0m2m−2) and canopy conductance (<10mms−1). Furthermore, irrigation promoted daily ET greatly during the growing season. Accurate estimation of seed maize ET and determination the controlling factors helps to develop exact irrigation scheduling and improve water resource use in desert-oasis agroecosystems.