Estimation of Dual Crop Coefficients over a Drip-Irrigated Merlot Vineyard Using Sap Flow Sensors and Eddy Covariance System

A study was carrying out to develop a dual crop coefficient (soil evaporation (Ke) plus canopy transpiration (Kcb) coefficients) for a drip-irrigated Merlot vineyard located in the Talca valley. In this study, the transpiration (Tsap) and actual evapotranspiration (ETa) were measured using compensation heat-pulse sap flow sensors (SF) and Eddy covariance system (EC), respectively. Soil evaporation (Es) was estimated as a residual of the actual evapotranspiration (Es = ETa - Tsap), and reference evapotranspiration (ETo) was calculated using FAO-56 standardized Penman-Monteith. Using these information, basal (ratio of Tsap to ETo) and soil (ration of Es to ETo) coefficients were estimated for key phenological stages. Results indicate that the ratios of Tsap to ETo were about 0.38 for initial conditions, 0.60 for middle season and 0.54 for the end of vine growing season. Also, the ratios of Es to ETo under the conditions of this study were very similar for the three periods with average values around to 0.12.