Assessing evapotranspiration and single crop coefficients of common crops by eddy covariance measurement at multi-sites

Abstract

The assessment of evapotranspiration and crop coefficients is essential for water-saving irrigation. The evapotranspiration and single-crop coefficient (K_c) values of 22 crops were identified based on eddy covariance measurements at 50 flux sites. The mean K_c values of all crops during the entire growing season ranged from 0.71 to 1.07, with most crops (18/22) within 0.77–0.98. Ten crops were with multiple sites and growing seasons data. The rice, soybean, and spring barley K_c values showed concentration distributions among sites and within growing seasons at the same site. Significant variations in K_c values for maize, winter wheat, and sugar beets were found among the sites or within the different growing seasons at the same site, with maximum differences ranging from 17 % to 32 %. The variations in winter rapeseed and winter barley K_c values among the sites were greater than those within different growing seasons at the same site. Contrary results were observed for alfalfa and potatoes. Large variations in the sugar beet and winter rapeseed K_c values were observed within growing seasons at each growth stage, with standard deviations ≥ 0.11. The proportion of inconsistencies between the local and FAO-tabulated K_c values was 32 % (16/50) and was 30 % (3/10), 25 % (5/20), and 40 % (8/20) during the early, middle, and late growth stages, respectively. Overall, the local K_c values of common crops must be improved based on future studies. The K_c values identified in this study provide valuable references for researchers who require precise Kc values for evapotranspiration assessment.