Abstract

One of the biggest problems in irrigation management in vineyards is the lack of information about actual evapotranspiration (ETa). ETa can be measured using Lysimeters, Eddy covariance (EC) and Bowen ratio systems, but these systems have a high cost and complexity. One alternative for estimating ETa under field conditions is the use of the residual energy balance (REB) method (LEREB = Rn-G-H, where LEREB is the latent heat flux estimated by REB method; Rn is the net radiation, G is the soil heat flux, and H is the sensible heat flux) with H estimated using the Surface Renewal (SR) method. Therefore, a field experiment was carried out over a drip-irrigated Merlot vineyard to evaluate the reliability of SR and REB methods to estimate ETa using as input the air temperature measured at high frequency, net radiation and soil heat flux. The experimental vineyard was located in the Talca Valley Region del Maule, Chile (35 degrees 25' S, 71 degrees 32' W; 136 m above the sea level) was trained on a vertical shoot positioned system (VSP). EC system was used to measure LE and H over the vineyard during the 2009/10 season. Comparison between H values estimated by SR method and measured by a three-dimensional sonic anemometer (CSAT3) indicated that the root mean square error (RMSE) and mean absolute error (MAE) were 38 and 26 W m(-2), respectively. Finally, corrected REB method was able to estimate ETa with a RMSE of 0.42 mm day(-1). These results indicate that the combination of REB and SR methods can be an accurate and inexpensive alternative to estimate ETa of vineyards.