Handbook for Irrigation of Wine Grapes in South Africa
Chapter 7
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FIGURE 7.19. Schematic presentation of the PRD strategy where irrigation is being applied through the ”A” set of subsurface dripper lines while the soil around the “B” lines is allowed to dry out.
Figure 7.20
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FIGURE 7.20. Variation in SWC where PRD irrigations were applied subsurface in the middle of the work rows, compared to SWC in the grapevine rows (Myburgh, 2011a). Dashed lines indicate field capacity and permanent wilting point.
Field trials with Merlot near Ashton in the Breede River region and Wellington in the Coastal region have shown that the PRD strategy required more irrigation water, and had no advantage regarding yield and wine quality, compared to conventional single line drip irrigation (Tables 7.14 & 7.15). In the Ashton trial, the time intervals between the PRD switches also had no effect on grapevine performance. Near Wellington, the PRD strategy only required less irrigation during one season when it was compared to conventional drip irrigation where the grapevines received unnecessarily large volumes of irrigation water (Table 7.16).
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