18
Rod Length Water
8 inches (20 cm) 60 - 65%
4.8 inches (12 cm) 70 - 75%
3 inches (7.5 cm) 75 - 80%
1.5 inches (3.8 cm) 65 - 70%
Note: The meter does not read 100% in water because the soil moisture
calibration equations were created to be most accurate in the volumetric
water contents typically found in mineral soils.
Appendix 2
Checking VWC Readings
There are two tests that can be performed to check if the meter is operat-
ing properly.
Test 1 (No rods): Disconnect the rods from the probe block. Press the
MODE button until the LCD is displaying the Period. With no rods con-
nected, the meter should read 1920 ± 30.
Test 2 (Rods attached): Readings can be taken in three standard environ-
ments; air, distilled water, and playground sand saturated with distilled
water. It is important that any troubleshooting be done with distilled wa-
ter. Readings taken in tap water can differ greatly from the expected re-
sults observed in distilled water. When readings are taken in water and
saturated sand, the container should have a diameter of, at least, 3 inches
(7.5cm) and should be tall enough so the rods can be completely im-
mersed or inserted.
Readings should be taken with the meter in "Stndrd VWC" mode. Be sure
that the correct rod length is selected. The meter should read VWC=0% in
air. In saturated sand, it should read between 35% and 45%. The table
below shows the approximate ranges of volumetric water content that are
expected for the different rod lengths in distilled water.
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