Technical Reference
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59
Permittivity is commonly used as a means of measuring water
content, because the real permittivity of water is ~80 at 20 MHz,
25°C, whereas the permittivity of most soil particles is typically in
the range 3 to 8.
Dielectric
Best used as
a descriptive term, e.g. “
dielectric
materials”
usually refers to insulating materials with a high relative
permittivity.
Dielectric constant
Sometimes used interchangeably for
permittivity
but may be
more rigorously defined as the real part of the
permittivity
in a
static electric field.
Saturation
The moisture content at which all the air within the pores has
been replaced by water. It’s not a stable situation because the
water will immediat
ely start to drain through. It’s a property of
soil type only.
Field Water Capacity (or Field Capacity)
The moisture content obtained when a saturated soil has been
allowed to drain (sometimes taken as 2 days later, sometimes
when drainage has become “negligible”).
It’s a property of soil type only, and typically varies between 0.1
m
3
.m
-3
for sandy soils up to about 0.45m
3
.m
-3
for clay soils.
