Campbell Scientific CS650 and CS655 Water Content Reflectometers User Manual

Page 40

CS650 and CS655 Water Content Reflectometers

A vertical face of soil can be formed with a shovel. If the CS650 is to be used

within about 0.5 meters of the surface, the probe can be inserted into the face

and water added to the surface with percolation. After adding water, monitor

the CS650 permittivity to determine if the soil around the rods is at

equilibrium.

With soil at equilibrium, record the CS650 permittivity.

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 CS650 should be inserted at least 3

times into the soil recording the permittivitys following each insertion and

using the average.

Remove the CS650 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 ≥ 1 inch and length about 2 inch works well. The tubes can

be pressed into the soil surface.

It is good to take replicate samples at locations around the soil 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 mass that can be

put in oven or microwave. Weigh and record the wet soil mass. If samples

must be stored prior to weighing, seal the container with tape or inside a plastic

bag to prevent water loss and store away from direct sunlight.

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 mass is constant.

Gravimetric water content is calculated after the container mass is accounted

for.

wet

dry

−

For the bulk density,

bulk

dry

cylinder

volume

the dry mass of the sample is divided by the sample tube volume.