CS616 and CS625 Water Content Reflectometers
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Collecting measurements of CS616/CS625 period and core samples from
the location where the probe is to be used will provide the best soil-specific
calibration. However, intentionally changing water content in soil profiles
can be difficult.
A vertical face of soil can be formed with a shovel. If the CS616/CS625 is
to be used within about 0.5 metres of the surface, the probe can be inserted
into the face and water added to the surface with percolation. After adding
water, monitor the CS616/CS625 output period to determine when the soil
around the rods is at equilibrium.
With soil at equilibrium, record the CS616/CS625 period value.
Soil hydraulic properties are spatially variable. Obtaining measurements
that are representative of the soil on a large scale requires multiple readings
and sampling. The average of several core samples should be used to
calculate volumetric water content. Likewise, the CS616/CS625 should be
inserted at least 3 times into the soil recording the period values following
each insertion and using the average.
Remove the CS616/CS625 and take core samples of the soil where the
probe rods were inserted. This is necessary for measurement of bulk
density. Copper tubing of diameter
1inch and length about 2 inches
works well. The tubes can be pressed into the soil surface.
It is good to take replicate samples at locations around the tray surface.
Three carefully handled samples will provide good results.
The sample tubes should be pushed evenly into the soil surface. Remove
the tube and sample and gently trim the ends of excess soil. Remove
excess soil from outside of tube.
Remove all the soil from tube to a tray or container of known weight that
can be put in oven or microwave. Weigh and record the wet soil weight.
Water is removed from the sample by heating with oven or microwave.
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 weigh is constant.
Gravimetric water content is calculated after the container weight is
accounted for.
g
wet
dry
dry
m
m
m
For the bulk density,
bulk
dry
cylinder
m
volume
the dry weight 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
