Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

TABLE 7.7. The effect of high and medium frequency irrigation on midday Ψ S prior to harvest, cane mass, berry mass and yield, as well as juice and wine quality characteristics of Shiraz near Robertson in the Breede River valley. Data are means for three seasons (Lategan, 2011). Irrigation frequency High Medium Irrigations per season ca. 50 ca. 7 Ψ S (MPa) -0.8 a* -1.5 b Cane mass (t/ha) 3.6 a 2.3 b Berry mass (g) 1.4 a 1.1 b Yield (t/ha) 25.6 a 19.8 b Juice pH 3.8 a 3.7 b Juice TTA (g/  ) 5.2 b 5.7 a Wine colour (%) 38.6 b 55.9 a Berry character (%) 42.0 b 50.4 a Spicy character (%) 36.7 b 45.8 a Wine quality (%) 40.2 b 50.4 a * Values followed by the same letter within a row do not differ significantly (p ≤ 0.05). HIGH FREQUENCY IRRIGATION With this strategy, more than one irrigation per week is applied. High frequency irrigation also includes daily irrigation. In the warmer, semi-arid regions such as the Lower Olifants River and Lower Orange River regions, high frequency irrigation might be necessary, particularly in shallow, sandy or gravelly soils with low plant available water. Due to the low PAW of the sandy soils, these frequencies normally induce low to moderate water constraints in grapevines. High frequency irrigation has already been compared to low and medium frequency irrigation in Sections 7.2.2 and 7.2.3. The different scenarios showed that high frequency irrigation invariably reduces water constraints, stimulates vegetative growth and increases yield (Tables 7.4 & 7.7). On the other hand, high frequency irrigation generally reduces wine colour and other quality characteristics, compared to less frequent irrigation. In the warm, dry climate of the Lower Olifants River region, high frequency irrigation reduced water constraints in three cultivars grown in the same sandy soil, compared to medium frequency irrigation (Table 7.8). Vegetative growth responded positively to the lower water constraints. However, with the exception of Shiraz, yield only tended to be higher where water constraints were lower. High frequency irrigation did not affect juice pH in any of the cultivars, compared to medium frequency irrigation. In contrast, lower water constraints resulted in higher juice TTA (Table 7.8). In the case of Sauvignon blanc, high frequency irrigation reduced the sensorial fresh vegetative character and overall wine quality, compared to medium frequency irrigation. Likewise, the berry and spicy character of the Merlot and Shiraz wines tended to be reduced by high frequency irrigation. 7.2.4

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