Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

sandy soil in the Lower Orange River region near Upington (Fig. 7.22). This practice improved grapevine fertility (Fig. 7.24A), and subsequently the yield (Fig. 7.24B), compared to no irrigation during the dry winter. However, it must not be confused with “hydro cooling”, which is overhead irrigation applied to reduce ambient air temperature. The lower temperature is necessary to increase the cold units required by grapevines in winter. Being a summer rainfall region, hydro cooling is primarily applied to table grape vineyards in the Lower Orange River region. Figure 7.23

Figure 7.23 Figure 7.23

100 120 140 160

1997

10 120 140 160

100 120 140 160

19 7

1997

1995

0 20 40 60 80

19 5

1995

0 20 40 60 80

0 20 40 60 80

1999

19

1999

1998

1996

19 8

1998

19 6

1996

Bunches per grapevine Bunches per grapevine Bunches per grapevine

y = 3.35x - 120 (R 2 = 0.937) y = 3. 5x - 120 (R 2 = 0.937) y = .35x - 120 (R 2 = 0.937)

40 45 50 55 60 65 70 75 80 40 45 50 5 60 65 70 75 80 40 45 50 55 60 65 70 75 80

RH (%)

RH (%)

RH (%)

FIGURE 7.23. Relationship between grapevine fertility of Sultanina in a sandy soil and mean relative humidity (RH) in the Lower Orange River region over five seasons (Myburgh, 2003b).

50

50

25

25

A

B

40

40

20

20

50

25

30

30

15

15

40

20

20

20

10

10

Yield (t/ha)

Yield (t/ha)

30

15

10

10

5

5

Bunches per grapevine Bunches per grapevine

y = 0.538x - 3.061 (R 2 = 0.8413) y = 0.538x - 3.061 (R 2 = 0.8413)

y = 6.808x - 321 (R 2 = 0.9486) y = 6.808x - 321 (R 2 = 0.9486)

0

0

0

0

20

0 10

48

48

50

50

52

52

54

54

56

56

0

20

20

40

40

60

60

Cane water content (%) Cane water content (%)

Bunches per grapevine Bunches per grapevine

Yield (t/ha)

FIGURE 7.24. Relationships between (A) bunches per grapevine and cane water content at pruning, as well as (B) yield and bunches per grapevine of Sultanina in the Lower Orange River region (after Myburgh & Van der Walt, 2005). 5

10

Bunches per grapevine

y = 0.538x - 3.061 (R 2 = 0.8413)

y = 6.808x - 321 (R 2 = 0.9486)

0

0

48

50

52

54

56

0

20

40

6

Cane water content (%)

Bunches per grapevine

IRRIGATION OF WINE GRAPES 211