Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

FIGURE 5.30. Mean monthly daily ET of grapevines irrigated using diluted winery wastewater over four seasons. Bracket indicates the period of pearl millet growth. 0 1 2 3 4 5 6 7 8 Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug ET (mm/day) Under the prevailing conditions, irrigation of grapevines using winery wastewater diluted to a maximum COD of 3 000 mg/  did not have any detrimental effects on juice quality characters (Howell et al. , 2016). At harvest, the mean total soluble solids, total titratable acidity and pH were 23.3°B, 5.1 g/  and 3.6, respectively. Although sensorial wine quality characters were also not affected, mean overall wine quality was only 37%. This indicated that the high and frequently applied irrigation volumes were detrimental to wine quality. Since quality is an important aspect, particularly if wine needs to be exported, the poor overall quality is of great concern. However, there is ample evidence that less frequent irrigation, which allows higher levels of plant available water depletion between irrigations, will enhance wine quality (Refer to Chapter 7). This implies that the winery wastewater will probably have to be applied over large areas to allow sufficient PAW depletion between irrigations. Unfortunately, such a practice will need additional infrastructure and management, which might not be economically viable. A pilot study carried out in the field trial indicated that grapevine bunches exposed to direct contact with winery wastewater may decrease in spicy character, increase wine volatile acidity and cause a winery wastewater-like off-odour in wines (Schoeman, 2012). Furthermore, as the quality of the water decreases, these off-odours may increase. Therefore, even though wine colour and common sensory wine descriptors were not affected by the various treatments, any further increase in wine VA or wastewater off-odours may reduce wine quality. Although wastewater odours may differ from winery to winery, the risk for off-flavours cannot be excluded. The foregoing also clearly demonstrates that overhead sprinkler irrigation will not be suitable if winery wastewater is re-used for vineyard irrigation.

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