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Estimating Transpiration of Whole Grapevines under Field Conditions

P.A. Myburgh

The accurate estimation of vineyard water use is important for irrigation scheduling in order to optimise
yield, growth and quality. Diurnal whole-plant transpiration, to be used in combination with a soil
evaporation model to estimate vineyard evapotranspiration, was quantified by measuring sap flow in
grapevines. 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, viticultural
and soil conditions. Sap flow showed good linear correlation with leaf area per grapevine and reference
evapotranspiration (ETo). Grapevines with similar leaf area trained onto horizontally orientated
trellis 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 linear
regression, with leaf area and daily ETo as the independent variables. However, grapevines with horizontal
and vertical canopies required slightly different models.

Canopy orientation, ETo, heat pulse, leaf area, sap flow

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