Handbook for Irrigation of Wine Grapes in South Africa

16 18 20 22 24 26 28 30 32 34 Temperature (°C)

Figure 1.11

250

a

Lutzville

Wagga Wagga

200

ab

b

100 Stomata per mm 2 150

a

b

b

50

0

Shiraz/99 R

Merlot/99 R Sauvignon blanc/99 R

FIGURE 1.11. Comparison of stomatal density of three grapevine cultivars near Lutzville in the Lower Olifants River region (unpublished data) and Wagga Wagga in Australia (Rogiers et al ., 2009). For each locality, columns designated by the same letter do not differ significantly (p ≤ 0.05).

If climate change results is less water being available for irrigation, alternative water resources need to be exploited. Expanding urbanization is increasingly producing large volumes of treated sewage. Likewise, wineries produce between 2 m 3 and 5 m 3 wastewater per tonne of grapes crushed (Myburgh & Howell, 2014b and references therein). Therefore, irrigating vineyards with treated municipal or winery wastewater could be a useful way to re-use the water. Re-using treated wastewaters could be beneficial to vineyards for which no other irrigation water is available. Furthermore, irrigation with treated wastewater will reduce the pressure on existing water resources used for irrigation. Sustainable re-use of treated wastewater for irrigation of vineyards or other crops will contribute towards environmentally sound wastewater management. This will enhance the image of the wine industry, particularly if it can be proved that it has no detrimental effects on wine quality. Using treated municipal wastewater for irrigation is not an uncommon practice. Currently ca. 2 000 ha vineyards are being irrigated with treated municipal wastewater in the Coastal region of the Western Cape. Refer to Chapter 5, Section 5.6 for more details concerning the effects of irrigation with treated municipal and diluted winery wastewater on soils and grapevines. 1.6 CONCLUSIVE REMARKS Since the climate is so important for viticulture, it is essential to have accurate and reliable weather data. This applies to long term data banks, as well as real time weather information. Therefore, the wine industry must invest in a weather station network that covers all the wine producing regions. However, the investment should

28 CHAPTER 1 – CLIMATE