EVAPOTRANSPIRATION PARTITIONING FROM SAP FLOW AND EDDY COVARIANCE TECHNIQUES FOR OLIVE ORCHARDS IN SEMI-ARID REGION

An eddy covariance (EC) and sap flow (SF) systems were combined for partitioning evapotranspiration (ET) into soil and plant components over olive orchards under drip and flood irrigation in semi-arid region. The EC system provides the total ET while the sap flow method measures only the transpiration. Measurements of xylem sap flow indicated that sap flow: (1) decreased rapidly with depth in xylem; and (2) correlated with the reference evapotranspiration (ET₀). Sap flow measurements were scaled up using a survey of the average ground area of the trees in order to estimate Ecosystem-scale transpiration. A comparison of sap flow with eddy covariance measurements showed that the ratio of transpiration to total evapotranspiration (T/ET) was about 0.87 over irrigated olive under drip irrigation. However, this ratio is about 1 over irrigated olive under flood irrigation in dry conditions and decreases to about 0.65 in wet conditions (during the irrigation). An amount of 35% of water was lost by direct soil evaporation due to flood irrigation, can be saved or minimized by the choice of an adequate irrigation like localized drip irrigation.