Handbook for Irrigation of Wine Grapes in South Africa

Chapter 6

(MPa)

Ψ PD

Ψ S y = -[ (1.60736- 0.190138/x) 2 ] (n = 24; R 2 = 0.9711; s.e. = 0.04; p ” 0 00 ) Ψ L y = -[ (1.55074- 0.090622/x) 2 ] (n = 15; R 2 0 9474 s e 0 0 p ” 0 00 )

Class I (no)

Class II (mild)

Class III (moderate)

Ψ L / Ψ S

(MPa)

Class IV (strong)

Class V (severe)

FIGURE 6.29. The relationships between midday Ψ S

and Ψ S

water potential and Ψ PD

in Shiraz

(Lategan, 2011).

TABLE 6.4. Thresholds for water constraint classes for midday Ψ L

and Ψ S

water potential in

Shiraz (adapted from Lategan, 2011). Class Water constraints

Water potential (MPa)

Ψ L

Ψ S

Ψ L

Ψ S

≥ -1.2

≥ -0.45

I

No

-0.45 > Ψ S

-1.2 > Ψ L

≥ -1.75

≥ -1.1

II

Low

-1.1 > Ψ S

-1.75 > Ψ L -1.95 > Ψ L

≥ -1.95

≥ -1.65

III

Moderate

-1.65 > Ψ S

≥ -2.1

≥ -1.9

IV High

Ψ S

Ψ L

< -2.1

< -1.9

V Severe

IRRIGATION OF WINE GRAPES 171