Handbook for Irrigation of Wine Grapes in South Africa

more water constraints in Shiraz/110 R (Table 7.4). This resulted in lower cane mass at pruning, smaller berries and lower yield, compared to high frequency irrigation. The fact that low frequency irrigation reduced juice pH and TTA (Table 7.4) indicates that leaf exposure dominated the effect on pH, whereas higher berry temperatures caused a decrease in the malic acid (Fig. 7.10). Low frequency irrigation improved sensorial wine colour, as well as the berry and spicy character (Table 7.4). These trends caused a substantial increase in sensorial overall wine quality, compared to high frequency irrigation.

Figure 7.11

100 120 140 160 180 200

A

FC

(40)

0 20 40 60 80

PWP

Soil water content (mm/60 cm) Sep Oct

Nov

Dec

Jan

Feb Mar

100 120 140 160 180 200

B

FC

0 20 40 60 80

(90) PWP

Soil water content (mm/60 cm) Sep Oct

Nov

Dec

Jan

Feb Mar

FIGURE 7.11. Seasonal soil water content where Shiraz in a fine sandy loam soil was drip irrigated (A) at 30 to 40% PAW depletion and (B) at 90% PAW depletion in the 2008/09 season in the Breede River valley (Lategan, 2011). Dashed lines indicate field capacity, permanent wilting point and PAW depletion level.

188 CHAPTER 7 – IRRIGATION STRATEGIES