Handbook for Irrigation of Wine Grapes in South Africa

due to irrigation increased transpiration rate of Pinot noir grapevines, compared to no irrigation (Table 2.4). It must be noted that this trend only occurred where the soil preparation depth was 80 cm or less. In the deeper soil, the higher plant available water was probably sufficient to allow transpiration at a similar rate as the irrigated grapevines (Table 2.3). These results emphasize the benefit of deep soil preparation to create well-developed root systems that can absorb adequate water. Figure 2.21

40

40

A

20 10 15 30 25 35

20 10 15 30 25 35

PW

PWP

FC

Figure 2.21

5

5

0 Stomatal resistance (s/cm) 8 10 6

0 Stomatal resistance (s/cm) 2 4 6 0

16 18 20 8 10 12 14 Soil water content (mass%)

22

40

A

B

20 10 15 30 25 35

PWP

FC

C

5

0 Stomatal resistance (s/cm)

6

22 24 26 14 16 18 20 8 10 12 Soil water content (mass%)

16 18 20

22

t (mass%)

FIGURE 2.21. Relationship between stomatal resistance of Colombar/99 R grapevines and soil water content (A) in sandy soil near Robertson and (B) in a sandy loam soil in a pot experiment (Van Zyl, 1984). Vertical lines indicate FC and PWP.

46 CHAPTER 2 – THE DYNAMICS OF WATER IN AND AROUND VINEYARDS