Handbook for Irrigation of Wine Grapes in South Africa

irrespective of the climate or soil. Generally, more irrigation will produce more grapes with a concomitant decline in wine quality and vice versa if less irrigation is applied (Fig. 1.9). These effects of irrigation on wine quality at the various localities are discussed in more detail in Chapter 7. It is also interesting that the Merlot wine quality seems to better where the grapes were harvested earlier (Fig. 1.9). This was probably due to higher HI and CI ′ near Wellington (Fig. 1.7).

Figure 1.9

60

27 Feb

8 Feb

21 Feb

55

50

Wine quality (%)

45

40

Wellington

Ashton

Lutzville

FIGURE 1.9. The sensorial overall quality of Merlot generally tends to decrease where the harvest date is later at a specific locality. The arrows illustrate how less irrigation will improve wine quality, and vice versa if more irrigation is applied.

1.5 CLIMATE CHANGE Climatic changes have occurred in the history of the Earth and are bound to happen again. Various mathematical models indicate towards global warming which goes hand in hand with lower rainfall. Higher air temperatures and lower rainfall will have a huge negative impact on the sustainability of viticulture, particularly in terms of water supply to the grapevine. The dilemma will be aggravated if lower rainfall reduces the available irrigation resources. Furthermore, climate change will most probably result in reduced irrigation water allocations and increased water tariffs. Since mankind is unlikely to prevent or stop possible climate change(s), certain adaptations need to be made, particularly with respect to vineyard irrigation. Firstly, vineyards should not be established in low potential soils, i.e. with low water holding capacity and low cation exchange capacity. Secondly, soil preparation must be carried out properly to ensure deep, well-developed root systems that can absorb water from the largest possible soil volume. Since large volumes of irrigation water are lost to evaporation in the case of full surface wetting, growers will have

26 CHAPTER 1 – CLIMATE