Handbook for Irrigation of Wine Grapes in South Africa

(MPa)

Ψ P D

-1 2

-1 0

-0 8

-0 6

-0 4

-0 2

0 0

in Merlot (after Myburgh, 2011a). -2 0 -1 8 -1 6 -1 4 -1 2 -1 0 -0 8 -0 6 -0 4 -0 2 0 0 Ψ S Class I (no)

Class II (low)

Class III (moderate)

(MPa)

Class IV (high)

Class V (severe)

FIGURE 6.28. The relationship between midday Ψ S

and Ψ PD

TABLE 6.3. Thresholds for water constraint classes for midday Ψ L

and Ψ S

water potential in

Merlot (Myburgh, 2011a). Class Water constraints

Water potential (MPa)

Ψ L

Ψ S

Ψ L

Ψ S

≥ -1.1

≥ -0.5

I

No

-0.5 > Ψ S -1.0 > Ψ S -1.4 > Ψ S

-1.1 > Ψ L -1.4 > Ψ L -1.6 > Ψ L

≥ -1.4

≥ -1.0

II

Low

≥ -1.6

≥ -1.4

III

Moderate

≥ -1.8

≥ -1.6

IV Strong

Ψ S

Ψ L

< -1.8

< -1.6

V Severe

170 CHAPTER 6 – GRAPEVINE WATER STATUS