23
stant than air (
ε
= 1) or soil solids (
ε
= 3-7) is exploited to
determine the VWC of the soil. The VWC measured by
TDR is an average over the length of the waveguide.
Electronics in the TDR 300 generate and sense the return
of a high energy signal that travels down and back,
through the soil, along the waveguide composed of the
two replaceable, stainless steel rods. The sampling vol-
ume is an elliptical cylinder that extends approximately 3
cm out from the rods. The high frequency signal informa-
tion is then converted to volumetric water content. High
amounts of clay or high electrical conductivity
(EC>2 dS/m) will attenuate the high-frequency signal and
affect the reading displayed by the meter. Very high or-
ganic matter content will similarly affect the VWC read-
ing.