Handbook for Irrigation of Wine Grapes in South Africa

0 1 2 3 4 5 6 7 8 9

Philadelphia

Malmesbury

0 2 4 6 8

10 12 14 16 18

0-30 cm 30-60 cm 60-90 cm

A

Level in water

pH

EC

SAR

Fe

B

Mn

0 2 4 6 8

50 100 150

-8 -6 -4 -2

ESP (%)

Change in ESP (%)

Y = -0.0802 + 13.87 (R 2 = 0.92

Rainfall (m

06 07 08 09 10 11 12 13 14 15 16

0 2 4 6 8

B

50 100 150 200 250

-8 -6 -4 -2

Change in ESP (%)

Y = -0.0802 + 13.87 (R 2 = 0.9206)

Rainfall (mm)

09 10 11 12 13 14 15 16

Irrigation with treated municipal wastewater almost doubled the vegetative growth of drip irrigated grapevines, compared to no irrigation near Philadelphia (Table 5.12). On average, the annual irrigation amounted to ca. 300 mm. Except for rainfall, the vineyards received no other water. This confirmed that re-using treated wastewater could be beneficial to vineyards where no other irrigation water is available. However, it still needs to be determined whether irrigation with treated municipal wastewater will have any negative effects on wine quality, e.g. taste or aroma, or induce any other atypical characteristics. Although leaching of salts from the root zone could be positive in terms of grape growing, over-irrigation with any wastewater should be avoided at all times to reduce the risk of negative impacts on the ecology, particularly natural water resources and soils. Irrigation with treated wastewater will reduce the pressure on existing water resources used for irrigation. Furthermore, 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 treated municipal wastewater has no detrimental effects on wine quality. FIGURE 5.14. Temporal variation in ESP in the soil at budbreak (A) and the effect of winter rainfall from May to September on the change in ESP (B), where vineyards near Philadelphia have been irrigated using treated municipal wastewater from the Potsdam scheme. The encircled value was regarded as an outlier.

126 CHAPTER 5 – IRRIGATION WATER QUALITY