Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

TABLE 7.18. The effect of different flood irrigation systems on the yield, irrigation applied and WUE of Sultanina grapevines in the Lower Orange River region (Myburgh, 2003a). Irrigation system Irrigation cycle (days) Yield (t/ha) Irrigation applied (m 3 ) WUE (kg/m 3 )

Wide beds

14

24.5

12 718

1.9

21

25.1

12 718

2.0

Furrows

14

26.6

7 932

3.3

21

22.1

7 932

2.8

Alternating rows

14

24.6

7 386

3.3

21

19.9

7 386

2.7

7.2.11.2 REDUCING EXCESSIVE TRANSPIRATION Transpiration losses increase with grapevine leaf area as shown in Chapter 2. Consequently, unnecessary vigorous vegetative growth (Fig. 7.34), particularly during the first part of the season, will cause unnecessary water losses. Therefore, canopy management, e.g. removal of excessive shoots by means of suckering, as well as timely tip and top actions must be carried out to reduce transpiration losses. Only apply the recommended amounts of fertilisers, particularly nitrogen, to prevent stimulation of excessive vegetative growth that will increase transpiration losses.

PHOTO: M. CORNELISSEN.

Vine row

Work row

Vine row

A

B

FIGURE 7.34. Examples of excessive vegetative growth (A) near Stellenbosch and (B) in the Lower Olifants River region.

Figure 7.35 Since transpiration by grape berries is insignificantly small, high crop loads per se are unlikely to cause excessive transpiration losses. The possibility that crop reduction in grapevines bearing high crop loads, may indirectly increase ET is discussed in Chapter 2, Section 2.4.2.1.1 (Table 2.2). However, grapevines growing in sandy soil might not be able to absorb adequate water during the night as the soil dries out. Consequently, grapevines bearing high crop loads in sandy soil could experience more water constraints, compared to grapevines without grapes, as discussed in Chapter 6, Section 6.3.7. Given that bunch removal had

IRRIGATION OF WINE GRAPES 221