Evapotranspiration Partitioning and Estimation Based on Crop Coefficients of Winter Wheat Cropland in the Guanzhong Plain, China.

Accurate estimation and effective portioning of actual evapotranspiration ( ET a ) into soil evaporation (E) and plant transpiration (T) are important for increasing water use efficiency (WUE) and optimizing irrigation schedules in croplands. In this study, E/T partitioning was performed on ET a rates measured using the eddy covariance (EC) technique in three winter wheat growing seasons from October 2020 to June 2023. The variation in the crop coefficients ( K c , α, and K Hc ) were quantified by combining the ET a and reference evapotranspiration rates using the Penman–Monteith, Priestley–Taylor, and Hargreaves equations. In addition, the application of models based on the modified crop coefficient ( K c , α, and K Hc ) was proposed to estimate the ET a rates. According to the obtained results, the average cumulative ET a , T, and E rates in the three winter wheat growth seasons were 471.4, 265.2, and 206.3 mm, respectively. The average T/ ET a ratio ranged from 0.16 to 0.72 at the different winter wheat growth stages. Vapor pressure deficit (VPD) affected the ET a rates at a threshold of 1.27 KPa. The average K c , α, and K Hc values in the middle stage were 1.34, 1.54, and 1.21, respectively. The measured ET a rates and ET a rates estimated using the adjusted K c , α, and K Hc showed regression slope coefficients of 0.96, 0.99, and 0.96, and coefficients of determination (R2) of 0.92, 0.93, and 0.90, respectively. Therefore, the Priestley–Taylor-equation-based adjusted crop coefficient is recommended. The adjusted crop-coefficient-based models can be used as valuable tools for local policymakers to effectively improve water use. [ABSTRACT FROM AUTHOR]