Measurement and modelling of evapotranspiration of irrigated citrus orchard under Mediterranean conditions

The evapotranspiration (E) of an irrigated citrus (Clementine) orchard in the Mediterranean region was measured throughout a growing season. Transpiration (T) was determined by the sap flow method. Since the measurement took place on several selected branches of the citrus trees, a statistical analysis for determining the "mean tree" has been carried out before the set up of the sap gauges. In this study the daily T measured by the sap flow method has been compared with E measured by the eddy covariance method, with very good results. In addition a model of the citrus E using a Penman-Monteith-type model is presented, where the canopy surface resistance is determined from standard microclimatic variables. The calibration coefficients of the proposed model depend only on the crop and they have general validity with respect to the site. The model's performance was evaluated by comparison with the sap flow data. The results were satisfactory and therefore this simple model allows determination the E of a Clementine orchard grown under a Mediterranean climate. In contrast to reports by the FAO no. 56 paper, and this has practical implications, the crop growth coefficient of this Clementine orchard was not constant throughout the growing season. The highest values occurred during the vegetative stage.