Handbook for Irrigation of Wine Grapes in South Africa

Na (cmol (+) /kg

Bray 2 - K (mg/kg)

0 00

0 10

0 20

0

50

100

150

200

0 30 60 90

0 30 60 90

River water 3000 mg  C2D

River 3000

C o n r a d i e

120 150 180 210 240 270 300 330

120 150 180 210 240 270 300 330

Depth (cm)

Depth (cm)

A

Na (cmol (+) /kg)

Bray 2 - K (mg/kg)

0 00

0 10

0 20

0 30

0 40

50

100

150

200

0 30 60 90

River water 3000 mg  C2D

River water 3000 mg  C2D

C o n r a d i e

120 150 180 210 240 270 300 330

3 0

3 0

Depth (cm) Stellenbosch shale - 21% clay Stellenbosch granite - 13% clay Rawsonville sand - 3.3% clay Lutzville sand - 0.4% clay

2 5

2 5

2 0

2 0

1 0 K ex (cmol (+) /kg) 1 5

1 0 Na ex (cmol (+) /kg) 1 5

B

FIGURE 5.19. Soil K (Bray II) and extractable Na contents over 3 m depth in a sandy soil in September 2013 following irrigation with river water and winery wastewater diluted to 3 000 mg/  for four seasons. 0 5 0 5

0 0

0 0

0

500

1 000

1 500

0

200

Although irrigation with winery wastewater had relatively little effect on element accumulation in the sandy soil under field conditions, considerable amounts of K and Na accumulated in the absence of rainfall (Mulidzi et al. , 2015b). It must be noted that these elements accumulated, irrespective of clay content (Fig. 5.20). Since the pot experiment was carried out under a rain shelter, it reflects a worst case scenario, i.e. where no leaching due to rainfall occurred. As expected, leaching occurred when the soils were subjected to simulated rainfall (Mulidzi, 2016). However, the leaching appears to depend on the clay content and the amount of rainfall as illustrated in Figure 5.21. This implies that salts applied via 2 0 2 5 3 0 Appli d K (kg/ )

Applied Na

- 3.3% clay 4% clay le - 21% clay ite - 13% clay

0 5 1 0 Na ex (cmol (+) /kg) 1 5

132 CHAPTER 5 – IRRIGATION WATER QUALITY