Podzolic Soils - Major Soil Groups of the World - page 343

It does not involve the very hypothetical migration of proto-imogolite in
a humic medium, but presumes migration of silica in monomeric form,
which is quite conceivable. In short, it is, in our view, a major advance.
It is supported by Macías-Vásquez et al . (1986).

11.3.4 Model Involving Descent of Weathering Fronts
We do not claim here to invalidate the established facts, that is to say the
laboratory experiments and field observations made by many competent
investigators. We only want to show that, based on these data, there is
another way of resolving the puzzle of the worldwide phenomenon of
podzolization. Our opinion, expressed long ago (Legros 1982), has been
discussed in the first edition of this topic in 2007. It totally agrees with
the view of Buurman and Jongmans (2005) and is reinforced by many
authors whose key phrases are sometimes quoted below. For example,
' the proto-imogolite and the fulvate theories are both inadequate to explain the
Podzol's water characteristics ' (Patel-Sorrentino et al . 2007).

For us, Podzols are not an exception to the general rule and their
differentiation is in line with the descent of weathering fronts. It is
written as follows:

Principle

C Æ Bs Æ Bh Æ E

Weathering Interception Maturation of Degradation Depletion

of complexes complexes of complexes

￿ At the bottom of the Bs, the organic matter is precipitated because
the C/metal ratio is low. More precisely, acid weathering of sili-
cates yields poorly ordered minerals of the generic imogolite or allo-
phane type. These substances develop considerable surface area
(Karltun et al . 2000), giving rise to high reactivity. The ability to
fix organic anions (fulvic acids and other short-chain complex-
ing acids) is high. Released protons (see Fig. 11.3) participate in
the attack on new silicates. Consequently weathering progresses
downwards.

￿ The transformation Bs Æ Bh is undoubtedly the most difficult to
admit because it is the farthest from classic concepts. However,
when the Bs is in pockets, the Bh totally envelops them. The Bh
can thus be found below the Bs, in certain soils of Amazonia
particularly (Bravard 1988). Freeland and Evans (1993) observed:
the development of the Bs horizon precedes that of the Bhs . Above all,
the upper Bs horizons can easily be transformed to Bhs horizons… if