Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

Avena sativa L. cv. Pallinup (oats) established in the work rows during winter tended to increase the dry matter production when irrigated with diluted winery wastewater, compared to clean river water irrigation (Fig. 5.24). However, this trend only occurred if the oats was not preceded by Pennisetum glaucum L. cv. Babala (pearl millet) as a summer interception crop (Myburgh & Howell, 2014b). Oats continuously produced acceptable amounts of dry fibre. The different levels of winery wastewater dilution had no effect on the Ca, Mg and K in the above-ground growth. Although differences in N and Na occurred, it was not related to the level of dilution. However, the Na levels increased over time. Sowing pearl millet on 10 January allowed its growth to peak while approximately 90% of the diluted winery wastewater was applied. The latter improved the DMP of pearl millet. The diluted winery wastewater did not affect the levels of N, P, Ca and Mg in the above-ground growth, but increased the level of Na slightly over time. Although the levels of K differed between treatments, it was not related to the level of wastewater dilution. By planting both species in sequence, too much of the nutrients applied via the wastewater were intercepted, particularly K (Fig. 5.25). Furthermore, the amounts of Na removed by the cover crops were insignificant. This is a matter of concern, since Na is one the most problematic elements in many winery wastewaters. The slash and removal costs will also contribute to the already high production costs of vineyards. Based on the foregoing, the sustainability of using cover crops to intercept elements applied via winery wastewater is questionable. 1 10 100 1 000 0 500 1 000 2 000 2 500 3 000 K (mm/h) 1 500 COD (mg Ɛ) Lutzville sand - 0.4% clay (R 2 = 0.8459) Rawsonville sand - 3.3% clay (R 2 = 0.7685) Stellenbosch shale - 21% clay (R 2 = 0.8706) Stellenbosch granite - 13% clay (R 2 = 0.0317)

12

Pearl millet

Oats

10

8

6

4

DMP (t/ha)

2

0

5 100 250 500 1 000 1 500 2 000 2 500 3 000

COD (mg/  )

FIGURE 5.24. Effect of irrigation with winery wastewater containing different levels of COD on the DMP of pearl millet grown in summer and oats grown in winter. Pearl millet and oats data are means for three and four years, respectively.

IRRIGATION OF WINE GRAPES 137