Agriculture Reference
In-Depth Information
(a) the strength of the soil solution increases, with the additional cations balanced
by HCO
3
−
;
(b) the CEC of the soil solid increases;
(c) some A
+
and B
2
+
are displaced from the exchange complex by Fe
2
+
.
Given the values of
[Fe(III)]
,C
T
,
[Z] and
[HS], we have nine unknowns:
the concentrations of A
+
,
B
2
+
,
Fe
2
+
,
H
+
and HCO
3
−
in the soil solution, and the
concentrations of A
+
,
B
2
+
,
Fe
2
+
and HS in the soil solid. These may be found
from the following nine equations:
(1) from Equation (3.65)
[H
+
]
L
=
10
−
(
pH
−
[HS]
/b
HS
)
(
3
.
66
)
(2) from the carbonate equilibria,
C
T
[H
+
]
L
/K
C1
+
1
[HCO
3
−
]
L
=
(
3
.
67
)
(3) from the requirement of electrical neutrality in the solution,
[A
+
]
L
+
2[B
2
+
]
L
+
2[Fe
2
+
]
L
+
[H
+
]
L
=
[HCO
3
−
]
L
+
[X
−
]
L
+
[OH
−
]
L
(
3
.
68
)
(4) from the requirement of electrical neutrality in the solid,
[A
+
]
S
+
2[B
2
+
]
S
+
2[Fe
2
+
]
S
=
[A
+
]
S0
+
2[B
2
+
]
S0
+
[Z]
−
θ/ρ(
[H
+
]
L
−
[HCO
3
−
]
L
)
}
(
3
.
69
)
−{
[HS]
where subscript 0 indicates initial values;
(5) from monovalent-divalent cation exchange equilibria,
[A
+
]
L
[B
2
+
]
L
+
[Fe
2
+
]
L
=
K
E1
[A
+
]
S
[B
2
+
]
S
+
[Fe
2
+
]
S
(
3
.
70
)
(6) from divalent-divalent cation exchange equilibria,
[Fe
2
+
]
L
=
K
E2
[B
2
+
]
S
[B
2
+
]
L
(
3
.
71
)
[Fe
2
+
]
S
and (7), (8), (9) from conservation of mass there are three equations of the type
θ/ρ
[A
+
]
L
+
[A
+
]
S
=
[A
+
]
(
3
.
72
)
These equations can be solved simultaneously to obtain the new composition of
the soil solution. Assume
K
E1
and
K
E2
constant in spite of reductive dissolution
reactions.
