Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

TABLE 7.4. The effect of high and low frequency irrigation on Ψ S , cane mass, berry mass and yield, as well as juice and wine quality characteristics of Shiraz in the Breede River valley. Data are means for three seasons (Lategan, 2011). Irrigation frequency High Low Irrigations per season ca. 50 ca. 3 Ψ S (MPa) -0.8 a* -1.7 b Cane mass (t/ha) 3.6 a 2.6 b Berry mass (g) 1.4 a 1.1 b Yield (t/ha) 25.6 a 21.3 b Juice pH 3.8 a 3.7 b Juice TTA (g/  ) 5.2 a 5.1 b Wine colour (%) 38.6 b 65.0 a Berry character (%) 42.0 b 55.4 a Spicy character (%) 36.7 b 47.3 a Wine quality (%) 40.2 b 56.6 a * Values followed by the same letter within a row do not differ significantly (p ≤ 0.05). MEDIUM FREQUENCY IRRIGATION Medium frequencies, i.e. one to four week intervals between irrigations, are generally applied to wine grape vineyards in heavier soils with high plant available water. These frequencies normally induce low to moderate water constraints in grapevines. However, medium irrigation frequencies can be adapted to suit the end product objective, e.g. more frequent irrigation if maximum yield is required, and vice versa if high wine quality is the objective. Near Robertson in the Breede River valley, weekly micro-sprinkler irrigation resulted in ca. 50% RAW depletion, compared to ca. 75% depletion where irrigations were less frequently applied. The soil water matric potentials were ca. -30 and -65 kPa, respectively, when the irrigations were applied (Fig. 7.12). Less frequent irrigation induced more water constraints, compared to weekly irrigation in Pinotage/99 R, as well as Sauvignon blanc/99 R (Table 7.5). In the case of the Pinotage, less water did not reduce vegetative growth, but resulted in smaller berries and lower yield. Although berry mass of Sauvignon blanc responded in a similar way, less frequent irrigation did not reduce yield. This suggested that the higher water constraints were detrimental to vegetative growth, whereas yield seemed to be less sensitive. Less frequent irrigation did not affect the Sauvignon blanc juice pH and TTA (Table 7.5). In the case of Pinotage, higher juice pH and a tendency towards lower TTA indicated that berry exposure due to less vigorous vegetative growth dominated under the prevailing conditions (Fig. 7.10). For both cultivars, higher water constraints improved overall wine quality (Table 7.5). In general, the response to different levels of medium frequency irrigation tended to be similar for the two cultivars. 7.2.3

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