Podzolic Soils - Major Soil Groups of the World - page 338

In practice, the formulation is more complex and requires the use of
a calculator: all the horizons of the profile are included and the bulk
densities are considered for calculating percentages of displaced material
in weight. For Podzols of the mountains in France, REDIS is less than 25
per cent displaced through the soil mass above the C horizon for iron
as well as for aluminium.

11.3.2 The Classic Model of Podzolization and its
Refutation
The classic model is known by the name ' fulvate theory ', i.e., involvement
of fulvic acids in degradation of the minerals and transport of their
metallic constituents.

The pH is lower than 5, and only quartz is resistant. There is rapid
and total decomposition of silicates. The Si, Al and Fe extracted by
podzolization are totally exported from the E horizons that get depleted.
Silica is mostly removed from the profile in the drainage water, and Al is
blocked in the B. But the great insolubility of aluminium (Chap. 3, Fig. 3.8)
makes its movement surprising. An explanation has been found. Some
soluble organic acids capture the aluminium and form complexes or
chelates mentioned earlier. This mechanism is named cheluviation (from
chel = chelate, and eluviation = depletion). The complexed aluminium
becomes mobile and can easily be transported. It is precipitated in the
B horizon at the same time as the organic matter for reasons given
above. Just like aluminium, iron can be transported as a mineral-organic
complex . Moreover it is mobile in the ferrous form. Iron can be reduced
in podzolizing environments for many reasons: direct action of certain
organic acids, winter rain (especially under snow in silty soils) or lastly,
and above all, saturation with groundwater (if any) and involvement of
microorganisms (Chap. 12).
This traditional model of podzolization (Righi and Chauvel 1987) is
not recent. Apart from the odd detail, it had been formulated in 1856
by the Norwegian scientist J.B. Barth (Läg 1987). It expresses a kind of
evidence: what is in excess at the level of the B (humus, oxides of iron
and aluminium…) appears to have come from what is missing from the
E (the same substances)!
We should note in passing that the water-soluble phase of the organic
matter corresponds in totality to the Dissolved Organic Matter (DOM) or
to the Dissolved Organic Carbon (DOC).

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