Estimating Field Evapotranspiration Using Soil Water Determined with Time Domain Reflectometry

The principles and methodology for measuring soil water content by time domain reflectometry (TDR) are described. Based on the determined soil moisture of different irrigation plots, the evapotranspiration (ET) of winter wheat is calculated with a field soil water budget model. The impact of the different insertion ways of TDR probes on measuring soil water storage and estimating ET is also discussed. According to the maximum passible ET values obtained in the fully-wetted root zone, actual ET under water stress root zone and ET of reference crop from meteorological data, the crop coefficient Kc and soil moisture stress factor Ks for various growth stages of winter wheat are calculated, respectively.