Campbell Hydrosense, Instruction Manual

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HydroSense
9
prompt is displayed. With CAL 0 displayed, the probe rods are inserted and
the READ button is pressed. This stores the measured value in HydroSense
memory as the lower reference level for the chosen site.
After irrigating to the desired upper reference level, the HydroSense is set to
CAL 100 and a measurement taken by inserting the probe rods and pressing
READ. This value is stored as the upper reference level for the chosen site.
HydroSense is now calibrated for the chosen site.
0
20
40
60
80
100
10 15 20 25 30 35
volumetric water content (%)
rel
ati
ve water
co
n
ten
t
0
5
10
15
20
25
30
water
d
e
fi
ci
t (mm)
relative water content water deficit
FIGURE 5-3. Relative water content and deficit for example application
Figure 5-3 presents the relationship between relative water content and water
deficit for the chosen reference levels. A measurement taken at this site when
water content is 20% would give a relative water content (RWC) value of
approximately 33% and a water deficit value of 20 mm. Adding 20 mm of
water would bring the water content to 30% for a soil depth equal to the probe
rod length.
6. Proper Measurement Technique and Method
Limitations
Detailed instructions for making measurements with HydroSense are given in
Sections 4 and 5 and are specific for the
Water Deficit Mode and Water
Content Measurement Mode . The following information applies to
HydroSense measurements in general and provides operational information that
will optimize measurement quality.