Handbook for Irrigation of Wine Grapes in South Africa

TABLE 7.9. The effect of high frequency irrigation and two DI strategies on midday Ψ S prior to harvest, cane mass, berry mass, yield and sensorial wine quality of Shiraz near Robertson in the Breede River valley (Lategan, 2011). Data are means for three seasons.

Irrigation strategy

High frequency

DI 1

DI 2

Seasonal irrigation (mm)

422

137*

77*

Ψ S

(MPa)

-0.8 a**

-1.6 b

-1.8 c

Cane mass (t/ha)

3.6 a

2.6 b

2.3 c

Berry mass (g)

1.4 a

1.1 b

0.9 c

Yield (t/ha)

25.6 a

20.1 b

16.0 c

Juice pH

3.80 a

3.70 b

3.55 c

5.2 b

5.1 b

6.2 a

Juice TTA (g/  )

Wine colour (%)

38.6 c

54.2 b

72.4 a

Berry character (%)

42.0 b

45.6 b

54.7 a

Spicy character (%)

36.7 b

40.4 b

47.1 a

Wine quality (%)

40.2 b

45.4 b

59.4 a

* In the case of DI 1 , the soil water content was restored to field capacity at véraison. ** Values followed by the same letter within a row do not differ significantly (p ≤ 0.05).

7.2.7

DIFFERENT PRE- AND POST-HARVEST IRRIGATION FREQUENCIES

The primary objective for combining different irrigation frequencies is to improve wine quality without severe yield losses. This strategy can basically be approached in two ways. The one approach is to induce water constraints before véraison to reduce vegetative growth and obtain smaller berries for better wine quality. From véraison onwards, adequate irrigation is applied to prevent water constraints during berry ripening. The other approach is to avoid water constraints before véraison to optimize yield, followed by the induction of water constraints during berry ripening to improve wine quality. Low frequency irrigation before or after véraison tended to reduce vegetative growth and reduced berry mass of Sauvignon blanc in a sandy loam soil near Robertson in the Breede River valley, compared to medium frequency irrigation throughout the season (Table 7.10). Low frequency irrigation after véraison reduced yield, which suggested that the sudden subjection to water constraints was probably a shock to the grapevines. Under the prevailing conditions, juice pH and TTA, as well as wine characteristics and overall quality of Sauvignon blanc seems to be insensitive to water constraints induced before or after véraison (Table 7.10). This was probably because the water constraints did not reduce vegetative growth significantly, compared to more frequent irrigation. In contrast, where Pinotage was

198 CHAPTER 7 – IRRIGATION STRATEGIES