Agriculture Reference
In-Depth Information
Soil A
Soil B
Mixed
Soil
FIGURE 9.14
Mixed media as a mixture of two soils having different properties.
We now extend the MRTM formulation to a mixed soil system with two
or more geologic media or soil where each medium has distinct physical,
chemical, and microbiological properties (see Figure 9.14). Such parameters
include θ, the soil water content (cm
3
cm
-3
), ρ
,
the soil bulk density (g cm
-3
),
soil-hydraulic conductivity, and soil-water and solute retention parameters.
If one assumes that each medium competes concurrently for retention sites for
a specific ion species present in the solution phase,
S
T
can thus be expressed as:
Sf Sf Sf S
=
+
22 33
+
+
+
f
S
(9.17)
T
11
T
T
T
mTm
Here
S
T
1
, S
T
1
, S
T
1
, S
T
1
,
and
S
Tm
represent the sorption capacity for geologic
medium 1, 2, 3, and
n
, respectively. For simplicity, we assume the mixed sys-
tem is composed of
n
media and the dimensionless parameter
f
(omitting
subscripts) represents the fraction of medium 1, 2, 3, etc., to that of the entire
mixed medium (on a mass per unit bulk volume basis). This parameter is
necessary in order to account for the proportion of each geologic medium
per unit bulk volume of the mixed soil system.
Based on the MRTM formulation, we can express
S
T
for each respective
medium such that for medium 1, we have:
SSSS
T
=++
(9.18)
1
e
1
k
1
i
1
And the respective
S
T
for the
m
th medium can expressed as
SSSS
Tm
=++
(9.19)
em
km
im
Consequently, the amount sorbed by the equilibrium sites of the mixed
soil
m
∑
S
=
f
[]
S
(9.20)
e
l
el
l
=
1
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