Geoscience Reference
In-Depth Information
The present masses of the index mineral and of iron in the horizon
i
studied are given by:
vol
(
i
)
.da
(
i
)
.MI
(
i
)/100
(1)
vol
(
i
)
.da
(
i
)
.Fe
(
i
)/100
In the same horizon, the initial masses of the index mineral and of
iron before weathering and pedogenesis were
volor
(
i
)
.da
(
r
)
.MI
(
r
)/100
(2)
volor
(
i
)
.da
(
r
)
.Fe
(
r
)/100
Then the loss of iron in
i
, except that we do not know
volor
(
i
), is
given by
vol
(
i
)
.da
(
i
)
.Fe
(
i
)
- volor
(
i
)
.da
(
r
)
.Fe
(
r
)
________________________________
volor
(
i
)
.da
(
r
)
.Fe
(
r
)
The two terms of the numerator could indeed be reversed. But the
proposed method has the advantage of indicating the losses by negative
values and gains by positive values.
Again, we have
Loss Fe
(
i
)
=
vol
(
i
)
.da
(
i
)
.Fe
(
i
)
________________
volor
(
i
)
.da
(
r
)
.Fe
(
r
)
- 1
(3)
What remains now is to determine the value of
volor
(
i
)
.
For this,
there are two methods, presented below.
In
isovolumetric
reasoning, we calculate the losses on the assumption that
the soil has not undergone changes in volume (Fig. 1.5).
Isovolumetric reasoning
Horizon
studied
Comparison of
quantities of
substances present
in the same volume
Parent
material
(R or C)
Fig. 1.5
Explanation of isovolumetric reasoning.
In this case,
volor
(
i
)
= vol
(
i
)
and the losses in horizon
i
become, by simplification of equation (3):
Loss Fe
(
i
)
=
Fe
(
i
)
.da
(
i
)
_________
Fe
(
r
)
.da
(
r
)
- 1
(4)
