Handbook for Irrigation of Wine Grapes in South Africa

Since overhead pulse irrigation requires a fair amount of irrigation water, as well as an additional irrigation system, it is not a viable option. The best growers can do in regions where winter rainfall is normally low, or where abnormally dry winters occur, is to apply irrigations at a low frequency, i.e. 80 to 90% PAW depletion, depending on the soil texture and root depth (Fig. 7.25). Irrigation at these frequencies will suppress physiological activity that could cause re-growth of shoots in the post- harvest period. It will also allow proper ripening of the canes. Furthermore, irrigation will prevent unnecessary drying out of the canes, spurs and roots during winter and the period before budbreak. At this stage, it can only be speculated that the low bud fertility and poor bunch differentiation are either caused by hormones not being produced in roots if the soil is extremely dry, or insufficient hormone translocation to the dormant buds if the cane water content falls below a critical level.

PHOTO: M. CORNELISSEN.

FIGURE 7.25. Vineyards being flood irrigated during winter in the Lower Olifants River region.

212 CHAPTER 7 – IRRIGATION STRATEGIES