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
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