Converting Bulk Ec To Pore Ec - Decagon Devices 5TE Operator's Manual

5TE Operator's Manual
3. Theory

Converting Bulk EC to Pore EC

For many applications, it is advantageous to know the electri-
cal conductivity of the solution contained in the soil pores
(σ ), which is a good indicator of the solute concentration in
p
the soil. Traditionally, σ
water from the soil and measuring σ
expect, this is a time consuming and labor intensive process.
The 5TE measures the electrical conductivity of the bulk soil
surrounding the probes (σ
research has been conducted to determine the relationship
between σ and σ
b
advantage of the linear relationship between the soil bulk
dielectric permittivity (ε
from σ to σ
b
σ
nearly simultaneously in the same soil volume. It is there-
b
fore well suited to this method.
The pore water conductivity can be determined from (see Hil-
horst, 2000 for derivation):
'
ε σ
p
=
σ
p
−
'
ε ε
b
where σ is the pore water electrical conductivity (dS/m); ε
p
the real portion of the dielectric permittivity of the soil pore
water (unitless); σ
which is measured directly by the 5TE; ε
of the dielectric permittivity of the bulk soil (unitless); is the
real portion of the dielectric permittivity of dry soil (unitless).
has been obtained by extracting pore
p
. Recent work by Hilhorst (2000), has taken
p
) and σ
b
if the ε is known. The 5TE measures ε
p b
b
'
=
σ 0
b
is the bulk electrical conductivity, (dS/m),
b
directly. As one would
p
). A considerable amount of
b
to allow accurate conversion
p
b
8
b
(1)
is the real portion
and
is
P