e. Weigh the container holding the wet soil, and subtract the container weight from this
value to get the wet soil mass.
f. Record the wet soil mass.
g. Use oven or microwave to remove water from soil. Oven drying requires 24 hours at
105 °C. Microwave drying typically takes 20 minutes depending on microwave power
and sample water content. ASTM Method D4643-93 requires heating in microwave
for 3 minutes, cooling in desiccator then weighing and repeating this process until
measured mass is constant (
(p. 34)).
h. Weigh the container holding the dry soil, and subtract the container weight from this
value to get the dry soil mass.
i. Record the dry soil mass.
j. Repeat process to take replicate samples. Three carefully handled samples provide
good results.
13. Calculate gravimetric water content from wet mass of sample (m
wet
) and dry mass of
sample (m
dry
):
For the bulk density
the dry mass of the sample is divided by the sample tube volume.
The volumetric water content is the product of the gravimetric water content and the bulk
density
The average water content for the replicates and the recorded CS650 permittivity are one
datum pair to be used for the calibration curve fit.
8.4.4 Collecting field data for calibration
Required equipment:
l
CS650 connected to data logger programmed to measure sensor permittivity
l
Cylindrical sampling devices to determine sample volume for bulk density, such as copper
tubing with diameter of ≥ 1 inch and length about 2 inches.
l
Oven or microwave safe container of known weight
CS650 and CS655 Water Content Reflectometers
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