Agriculture Reference
In-Depth Information
Figure 4.18 Pressure chamber and accompanying gas cylinder for measuring leaf water
potential.
Othertechniquestomeasurevinewaterstatusincludeuseofadendrometerto
continuously record small changes in trunk diameter, which enables prompt deci-
sions to be made about when to irrigate. Changes in the rate of trunk growth and
diurnal changes in trunk diameter correlate well with changes in LW P . Another tech-
niqueusesinfraredthermographytomeasurethecanopyandberrytemperature,
which increases as the vines experience water stress. However, at present, only LW P
is used routinely in commercial vineyards, as in California's Central Valley region.
Research there has shown that shoot growth starts to slow when the midday LW P falls
to −0.6 MPa or less, but photosynthesis is not affected until −1 MPa is reached. Vines
in the range of −1 to −1.2 MPa are only mildly stressed. The normal threshold to trig-
ger RDI is when LW P dropsbelow−1.2MPa,whichisapproximatelyequivalentto
supplying60%offullwaterdemandintheCalifornian“volumebalance”approach.
Comparison of Methods
Table 4.5 provides a summary of the advantages and disadvantages of soil,
weather, and plant-based measurements for assessing vine water status and sched-
uling irrigation.
Partial Root Zone Drying
Partialrootzonedrying(PRD)isatechniquethataimstoregulatevinegrowth
whilesavingirrigationwaterwithoutsacriicinggrapeyieldandquality.hebasic
principle of PRD is to keep part of a vine's root system moist while the remainder
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