Handbook for Irrigation of Wine Grapes in South Africa

Figure 6.20

Chapter 6

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0 0

VSP - 50% RAW water depletion 2-Tier - 50% RAW water depletion VSP - 75% RAW water depletion 2-Tier - 75% RAW water depletion

-0 2

-0 4

-0 6

Ψ L ( M P a )

-0 8

-1 0

-1 2

FIGURE 6.20 . Variation of Ψ L in Pinotage/99 R trained onto a 6-strand VSP and a 2-Tier vertical trellis, and irrigated at two levels of RAW depletion near Robertson (after Myburgh, 2011d). -1 4 6.3.6 CANOPY MANAGEMENT Canopy management can determine the extent to which grapevine leaves will be exposed to radiation. Consequently, manipulation of the canopy will affect the level of transpiration, which in turn, will play a role in grapevine water status. For example, in the case of grapevines with sprawling canopies and box pruned grapevines more leaves will be exposed to radiation, compared to VSP grapevines (Fig. 6.21). Therefore, water constraints in grapevines with more exposed leaves will be higher, compared to grapevines where less leaves are exposed (Fig. 6.22). This trend seems to occur irrespective of cultivar, soil or prevailing atmospheric conditions.

IRRIGATION OF WINE GRAPES 163