Decagon Devices 5TE Operator's Manual page 14

5TE Operator's Manual
3.Theory
soil matrix and that water was collected and tested for EC.
Solution EC is the electrical conductivity of pore water
removed from a saturated paste. In this case, the soil is wet-
ted with distilled water until the soil saturates, then the soil
is placed on filter paper in a vacuum funnel and suction is
applied. An electrical conductivity measurement on the
water removed from the sample will give the solution elec-
trical conductivity. Theoretically, the two are related by the
bulk density. An example calculation will illustrate this rela-
tionship: A soil is at 0.1 m
of 0.7 dS/m, and a bulk density of 1.5 Mg/m
culate the solution EC as follows.
ρ
φ
= − =
b
1 1
ρ
s
Solution EC
In this example, ø is the porosity,
density of the minerals (assumed to be 2.65 Mg/m
script d is distilled water, and θ is volumetric water content.
We assume that the EC of the distilled water is 0 dS/m. In
practice, solution EC calculated from this method and solu-
tion EC taken from a laboratory soil test may not agree well
because wetting soil to a saturated paste is very imprecise.
Reference
Hilhorst, M.A. 2000. A pore water conductivity sensor.
Soil Science Society of America Journal 64:6 1922-
1925
1 5 .
− =
. 0 43
. 2 65
(
σ θ σ φ
+
=
p d
φ
3 3
/m VWC, has a pore water EC
)
( )
θ
−
0 7 . 0 1 .
=
0.43
ρ
is bulk density,
b
10
3
. We can cal-
+
0
=
. 0 162 dS/m
3
), sub-
ρ
is
s