Estimating Transpiration of Whole Grapevines under Field Conditions

yield, growth and quality. Diurnal whole-plant transpiration, to be used in combination with a soilevaporation model to estimate vineyard evapotranspiration, was quantified by measuring sap flow ingrapevines. Sap flow was measured in grapevine trunks by means of the heat pulse velocity technique.Diurnal sap flow ranged from almost zero to c. 5 L/d per grapevine under various atmospheric, viticulturaland soil conditions. Sap flow showed good linear correlation with leaf area per grapevine and referenceevapotranspiration (ETo). Grapevines with similar leaf area trained onto horizontally orientatedtrellis systems transpired more than those on vertical trellises under the same atmospheric conditions.Approximately 90% of the variation in daily transpiration could be explained by means of multiple linearregression, with leaf area and daily ETo as the independent variables. However, grapevines with horizontaland vertical canopies required slightly different models.