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Introduction
Using thermal imaging in calculating crop water stress
index (CWSI) has not been always considered an easy
task, with the limitations of its use as a routine tool
generally stemming from its high sensitivity to climate
factors, among them radiation, wind speed, and humidity,
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water-stressed baselines for different agroclimate zones.
Statistical analysis has consistently revealed that the
relationship between CWSI and leaf water potential
(LWP) has been found to be more stable than the relation
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of which may be attributed to the difference between sunlit
and shaded leaves.
Researchers have been known to use a variety of methods
to determine soil moisture content (SMC) in orchards.
Some of the methods employed have been found to be
both time consuming and expensive due to the equipment
density required by the soil spatial variability.
For that reason, less expensive methods need to be
tried and used if found reliable, with, among others, the
use of thermal images of tree leaves to determine CWSI
in fruit cultivation.
In recent years, researchers in Romania, one of the
major centers of fruit cultivation in Eastern Europe have
been involved in the investigation of the best methods
of establishing and calculating a crop water stress index
and estimate soil moisture status in order to use the date
accumulated for irrigation scheduling.
Material and Methods
A series of experiments were carried out over a typical
summer growing season, at a Research Station situated
in the Constanta region of Romania, located on the Black
Sea coastline, at a latitude of 44º 05’ North and longitude
of 28º 37’ East.
The experimentation was carried out in an orchard
specializing in the the cultivation of peaches, which are
grown on a wide scale across the region.
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tree rows with the central row containing six trees for
various measurements and observations, trained in a
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canopy volumes occupy all the space in the row.
The climate conditions at the semi-arid experimental site
are characterized by a mean annual temperature (Ta)
of 11.4°C and a mean annual precipitation (P) of 382
mm, not uniformly distributed across the year; reference
evapotranspiration (PM-ETo) for the year of the test
totaled 788 mm, with an average of 121, 137 and 124
mm per month-1 during the months of the test (June, July
and August, respectively (See Tables 1a and 1b)).
The relationship between soil water potential measured
with the Watermark sensors and SMC measured
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data, with the established relationship was then applied to
the soil water potential readings during the experiment in
order to estimate SMC values, averaged over the normal
active rooting depth of 80 cm.
Estimating soil moisture status in
peach tree orchards through
a crop water stress index
Using thermal imaging in calculating
crop water stress index (CWSI) has
not been always considered an easy
task, with the limitations of its use as
a routine tool generally stemming from
its high sensitivity to climate factors