ABSTRACT
Soil moisture content is measured using the time domain reflectometry (TDR) technique, which is based on the change in dielectric constant of a material with a change in moisture content. The dielectric constant of dry soil can range from three to eight (whereas that of free water is 81). A TDR probe is shown in Figure 22.2. This probe (CS615; Campbell Scientific) has two parallel conducting rods held on one end by an epoxy head, containing a bistable multivibrator. A suitable oscillation frequency of the vibrator is used for measurement of dielectric constant and to determine moisture content with the help of a data acquisition system.
