Agriculture Reference
In-Depth Information
(soil, sky or wood) within the field of view of the device. Such errors are common
when using a device with a small field of view. The principal advantage of the use
of plant canopy temperature to estimate stomatal conductance is that an increase in
leaf surface temperature reflects a physical change in stomatal opening regardless
of the cause of the change (Cifre et al.
2005
), which is not the case in the leaf wa-
ter potential-stomatal conductance relationship. Canopy temperature can relatively
easily differentiate between well irrigated grapevines and vines submitted to deficit
irrigation. Clawson et al. (Clawson and Blad
1982
) showed that leaf temperature
variability within the field of view may be a more sensitive indicator of water stress
than leaf temperature itself.
Micromorphometry
Diurnal variation in water movement through the vine induces a temporary, revers-
ible change in shoot and trunk diameter (Goldhamer et al.
2000
). Measurement
of such changes is termed micromorphometry, dendometry or phytomonitoring.
The differential between the maximum and minimum trunk (or shoot) diameter is
termed Daily Contraction Amplitude (DCA) or Maximum Daily Shrinkage (MDS).
Although micromorphometry is reported as appropriate for irrigation scheduling in
vineyards, Loveys (
2005
) noted the need for further improvements if growers are to
take up the technology.
Leaf Area
Grape leaf area was measured daily by Bindi et al. (
2005
), who found a close rela-
tionship between leaf area growth rate and soil water depletion, thus demonstrating
the potential use of leaf area measurements for irrigation scheduling. Several re-
searchers have found measurement of leaf area in the field, using allometric relation-
ships, easy to carry out (Guisard
2004
; Carbonneau
1976
; Sepulveda and Kliewer
1983
). This method is however limited to the phenological stages associated with
leaf growth and could not be applied after veraison. Gómez del Campo et al. (
1999
)
proposed that crop coefficients used in irrigation scheduling from evapotranspira-
tion be formulated using measures of leaf area through the growing season. Long
term studies would provide a methodology to engineer leaf area targets to match site
specific evaporative constraints.
Carbon Isotope Discrimination (δ
13
C)
Atmospheric CO
2
is mostly composed of
12
C (about 99%) and
13
C (about 1%)
stable isotopes. The lighter and more mobile isotope
12
C is most abundant in opened
stomatal cavities and is preferentially assimilated in the photosynthetic pathway.
