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the central row of each block, providing buffer zones on all
sides, with two sensors per treatment were deployed; one
sensor in each of two adjacent vines.
Soil moisture tension sensors were located at four depths
between the two adjacent vines in which plant-based sensors
were installed at depths of 10 cms, 20 cms, 40 cms and 80
cms depths, adjacent to the active root zone of the two vines.
A three-core SDI-12 cable provided by a nearby weather
station connected all crop water stress sensors and soil
moisture sensors back to the data logger, which recorded
not only climate, soil moisture, VPD and TD data, but
also monitored various diagnostic parameters reporting
operating and error conditions within the sensors. Data
was automatically uploaded each day to an FTP server,
allowing researchers remote access to the data with all
measurements were made at a 15 minute interval.
The plant’s response was integrated over
the full 24-h diurnal cycle between the
resting phases of the plants.
Materials and methods
Thermal Diffusivity
Thermal diffusivity (TD2) is a property
of a material that describes the thermal
time of a plant, with an ideal state being
‘thermal constant” with TD2 being used
to measure
how quickly the vine’s temperature will
change in response to a sudden change
in heat input.
At work in the process of maintaining a
‘thermal constant” state are the opposing
actions of thermal conductivity (trying to
take the heat away) and thermal storage
A thermal diffusity sensor in operation
a strong
relationship
between
soil moisture
conditions
and levels of
crop water
stress in
vineyards
Figure One: ‘Crop water stress’ versus average soil moisture tension for a one-week
period: when irrigation was withheld. The steady increase in crop water stress corresponds
well with the increasingly dry soil conditions