Handbook for Irrigation of Wine Grapes in South Africa

300

250

200

150

100

50 Applied K (kg/ha/year)

y = 0 0563x + 9 316 R² = 0 9975

0

0

1 000

2 000

3 000

4 000

5 000

COD (mg/  )

FIGURE 5.25. Relationship between the amounts of K applied via winery wastewater and the level of dilution as indicated by the COD. The horizontal band indicates K removed by pearl millet and oats ± standard deviation. Data are means for three years.

A more viable alternative would be to intercept elements applied via winery wastewater in vineyards by means of halophytic cover crops. To investigate this possibility, fodder beet ( Beta vulgaris L. ‘Brigadier’) was irrigated with Na-enriched water in a pot experiment (Myburgh & Howell, 2014a). The water was enriched to Na levels found in winery wastewater. Visual observations revealed that the plants appeared healthy (Fig. 5.26). There were no deficiency symptoms, except nitrogen, which could be corrected by fertilizer application. Although irrigation with Na-enriched water caused Na accumulation in the fodder beet (Fig. 5.27A), it did not affect fresh, or dry matter production of fodder beet if compared to clean water. Furthermore, fodder beet absorbed 38% of the Na applied via irrigation with Na-enriched water (Fig. 5.27B). Since the bulk of the plant can be harvested for fodder, Na will be removed more effectively, compared to crops where the roots remain in the soil. Therefore, this halophyte holds promise as an interception crop to reduce Na accumulation in soils where winery wastewater is used for irrigation. However, the foregoing does not rule out the possibility that other halophytic crops could be just as effective, or even better.

138 CHAPTER 5 – IRRIGATION WATER QUALITY