Decagon Devices 5TE Operator's Manual page 12

5TE Operator's Manual
3.Theory
the soil. Traditionally, σ
pore water from the soil and measuring σ
would expect, this is a time consuming and labor intensive
process.
The 5TE measures the electrical conductivity of the bulk
soil surrounding the sensors (σ
research has been conducted to determine the relationship
between σ and σ
b
taken advantage of the linear relationship between the soil
bulk dielectric permittivity (ε
conversion from σ
sures ε and σ
b
ume. It is therefore well suited to this method.
The pore water conductivity can be determined from (see
Hilhorst, 2000 for derivation):
σ
=
p
where σ is the pore water electrical conductivity (dS/m); ε
p
is the real portion of the dielectric permittivity of the soil
pore water (unitless); σ
(dS/m), which is measured directly by the 5TE; ε
portion of the dielectric permittivity of the bulk soil (unit-
ε
less); is the real portion of the dielectric permittivity
σb=0
of the soil when bulk electrical conductivity is 0 (unitless).
ε
can be calculated from soil temperature using:
p
ε
= 80.3 - 0.37 * (T
p
where T is the soil temperature (C) measured by the 5TE.
soil
has been obtained by extracting
p
. Recent work by Hilhorst (2000), has
p
to σ if the ε
b p
nearly simultaneously in the same soil vol-
b
ε σ
p b
-------------------------- -
ε ε
–
σb
b = 0
is the bulk electrical conductivity,
b
- 20)
soil
p
). A considerable amount of
b
) and σ
to allow accurate
b b
is known. The 5TE mea-
b
8
directly. As one
(1)
is the real
b
(2)
P