Evaluation of single and dual crop coefficients over a drip-irrigated Merlot vineyard (Vitis vinifera L.) using combined measurements of sap flow sensors and an eddy covariance system

Abstract

Background and Aims Irrigation is one of the most important viticultural practices in semi-arid regions. For this reason, the Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 single and dual crop coefficient approaches were evaluated to estimate actual evapotranspiration (ETa) over a drip-irrigated Merlot vineyard. Methods and Results Vine transpiration was measured using sap flow sensors, and ETa was measured by an eddy covariance system. Soil evaporation was calculated as the difference between ETa and sap flow sensors. Reference evapotranspiration (ETo) was calculated using the Penman–Monteith equation. This information was used to evaluate single (Kc) and dual crop coefficients [Kcb and Ke] approaches during the 2007/08 and 2008/09 grapevine growing seasons. Conclusions Results indicated that vine transpiration is the most important component of ETa for a drip-irrigated Merlot vineyard trained on a vertical shoot-positioned system. In midseason, the observed values of single crop coefficients and Kcb were lower by 11 and 19% than those recommended by the Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 for grapevines, respectively. The application of site-specific Kcb values reduced the error in the estimation of ETa by about 10%. Significance of the Study The study indicates that the use of sap flow sensors could be an alternative method for obtaining site-specific Kcb values for vineyards under field conditions.