Comparison of Orange Orchard Evapotranspiration by Eddy Covariance, Sap Flow, and FAO-56 Methods under Different Irrigation Strategies

The study evaluates the accuracy of measured and estimated crop evapotranspiration fluxes (ETc) on Citrus in a semiarid Mediterranean climate (Sicily, Italy). Specifically, ETc rates derived from in situ techniques [eddy covariance (EC) and sap flow heat pulse velocity (HPV)] and modelling approaches [Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) single and dual crop coefficient (Kc)] were compared under deficit irrigation scenarios. Results of the comparison showed that the single and dual Kc approaches provided similar ETc estimates (292 and 324 mm), even if these approaches overestimated ETc measured by EC (ETEC) (17% and 30% respectively). HPV was able to show transpiration (T) reductions caused by deficit irrigation strategies when compared with T under full irrigation condition (ranging from 70% to 82%). Overall, the assessed methodologies were able to capture ETc trends, but the selection of the most appropriate one will depend on the specific crop and study site characteristics.