Handbook for Irrigation of Wine Grapes in South Africa

7.5 CONCLUSIVE REMARKS There is no fixed irrigation recipe to achieve optimum grapevine yield and wine quality, but some trends stand out clearly. The irrigation strategy is important from the day that a new vineyard is established. Irrigation of young grapevines is critical to ensure that root systems will develop throughout the newly prepared soil. For bearing vineyards, irrigation strategies need to be adapted to achieve specific end-product objectives with respect to yield and wine quality. In most cases, less irrigation will reduce yield, but will increase wine quality and vice versa . However, by adapting trellis systems it is possible to obtain higher yield and better WUE without compromising wine quality. It is important to note that WUE can only be higher if the same yield is maintained with less irrigation water, or if the yield can be increased with the same volume of irrigation water. Wine quality will not necessarily be better if vegetative growth and berry mass are reduced by water constraints induced before véraison. Given the risk of lower yields, this strategy does not seem to be an option. Likewise, post-véraison water deficits will not necessarily ensure better wine quality. Partial root zone drying holds promise to improve wine quality. However, it does not seem to improve WUE, compared to conventional single line, drip irrigation systems. The risk of excessive water constraints during drought periods will be less if long term practices such as soil preparation and mulching are carried out properly. Short term practices include timely removal of excessive shoots, reduction in nitrogen fertilisers, complete weed control and killing cover crops with herbicides before budbreak.

234 CHAPTER 7 – IRRIGATION STRATEGIES