Use of sap flow sensors to determine vine transpiration

Knowledge of crop evapotranspiration (ET_c) is a necessary step towards water use optimization in the vineyard. The direct measurement of crop evapotranspiration using weighing lysimeters is considered the reference method, and allows to obtain the crop coefficient by comparison with the reference evapotranspiration of the area. However, this coefficient depends on the available leaf area, and the orientation and spatial distribution of the canopy, which are modified by viticultural practices. This work presents the results of a comparison over two seasons of crop evapotranspiration measured in a vineyard weighing lysimeter (ET_cLys), and that obtained from the sum of transpiration and evaporation, under non-limiting water conditions. Transpiration was obtained from sap flow measurements (T_SF) and evaporation resulted from applying a coefficient obtained for the evaporation of the lysimeter. The results showed a good correlation between the data obtained from the lysimeter readings (ET_cLys) and from sapflow sensors (ET_cSF), as well as between T_SF and vegetative growth measurements (Leaf Area Index, Intercepted Radiation). These results suggest that sap flow measurements, together with a model for soil evaporation estimation, allow accurate determination of vineyard evapotranspiration.