Abstract

MYBURGH, P.A.. Estimating transpiration of whole grapevines under field conditions. S. Afr. J. Enol. Vitic. [online]. 2016, vol.37, n.1, pp.47-60. ISSN 2224-7904.

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 (ET). 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 ET_o as the independent variables. However, grapevines with horizontal and vertical canopies required slightly different models.

Keywords : Canopy orientation; ET; heat pulse; leaf area; sap flow.

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