Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

Figure 7.48

A

B

C

FIGURE 7.48. Pinotage/99 R irrigated with micro-sprinklers at 50% PAW depletion on (A) a six-wire vertical trellis and (B) a two-tier vertical trellis, as well as (C) grapevines irrigated at 75% PAW depletion on a two-tier vertical trellis near Robertson.

Research results have shown that the yield of micro-sprinkler irrigated Pinotage/99 R grapevines on a two-tier vertical trellis in the Breede River valley near Robertson was approximately 40% more, compared to grapevines on a six-wire vertical trellis (Myburgh, 2011f). It is important to note that the yield increased without any reduction in wine quality (Table 7.19). Where grapevines were irrigated at 50% PAW depletion, the WUE improved from 3.6 kg/m 3 for the six-wire vertical trellis, compared to 5.1 kg/m 3 for the two-tier vertical trellis. This conforms to the norm that more grapes were produced with the same volume of irrigation water without compromising on wine quality. On the other hand, where irrigation was applied at 75% PAW depletion, approximately 25% more grapes were produced, compared to grapevines on the six-wire vertical trellis irrigated at 50% PAW depletion (Table 7.19). Since the WUE increased to 6.6 kg/m 3 , it shows that more grapes can indeed be produced with less water if the trellis and/or pruning systems are adapted. Furthermore, wine quality improved concomitantly with the higher WUE where irrigation was applied at 75% PAW depletion (Table 7.19). TABLE 7.19. Combined effects of trellis system and PAW depletion on yield and overall sensorial wine quality micro-sprinkler irrigated Pinotage/99 R near Robertson. Data are means for three seasons (Myburgh, 2011c & f). Trellis system Irrigation frequency PAW depletion (%) Irrigation (mm) Yield (t/ha) Wine quality (%)

Six-wire vertical

Weekly

50

584 21.1 b*

49.4 b

Two-tier vertical

Weekly

50

584 30.1 a

49.7 b

Two-tier vertical 407 26.7 ab 58.7 a * Values followed by the same letter within a column do not differ significantly (p ≤ 0.05). Fortnightly 75

IRRIGATION OF WINE GRAPES 231