Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

A

B

A

B

A

B

A

B

A

B

A

B

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

250

Pea size Véraison Harvest FC

Budbreak

200

150

PRD - “A” line irrigation PRD - “B” line irrigation PRD - In grapevine row

100

50

PWP

Soil water content (mm/0.9 m)

0

Sep

Oct

Nov

Dec

Jan Feb

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).

IRRIGATION OF WINE GRAPES 207