Inter-comparison Between Different Techniques for Evapotranspiration Partitioning: Eddy Covariance-, Sap Flow-, Lysimeter- and FAO-Based Methods

A precise estimate of the evapotranspiration (ET) partitioning is fundamental for determining the crop water needs and optimizing irrigation management. The plant transpiration (T) is generally considered to be the most desirable component, increasing the flow of T within the ET could be one of the most important actions to save water in semi-arid agricultural regions. Given the lack of reference method to estimate the E/T partitioning of wheat crop, this study inter-compares four different methods based on eddy covariance, sap flow and lysimetry measurements and FAO modeling. The objectives are: i) quantify T and ET flows using different approaches and ii) evaluate the response of the FAO dual approach model to different periods of stress. Results indicate that despite the small surface sensed by mini-lysimeters, the partitioning ratio is evaluated more precisely (19% relative error) with lysimetry than with the other systems (any combination of eddy covariance, lysimetry and sap flow measurements). Moreover, stem-scale T measurements from sap flow sensors are subject to representativeness issues at the field scale, and to systematic errors during water-stress and senescence periods.