Geoscience Reference
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The mechanisms presented above act effectively. One of the proofs of
the importance of organic matter in podzolization is that the phenomenon
is attenuated below the higher latitudes and below high altitudes where
the amount of organic matter produced by plants decreases. We find
Arctic Brown Soils (vernacular language) under tundra or Alpine Brown
Soils in the mountains. Then, even if acidification takes place, chelation
is impeded, as are transport and vertical differentiation of the profile
(Campbell and Claridge 1992). So, we do not object to the numerous
laboratory experiments demonstrating that complexing organic acids
can transport iron and aluminium, then precipitate them, especially if
the system is not sterile and permits biological decarboxylation to take
place (Berthelin et al . 1974).
But scientists are still working on the question after 150 years of
investigation. This proves that it has not been satisfactorily resolved! The
model, therefore, deserves to be refined. We list the major difficulties
below:
Refutation of the model
1. Experimental work (Vincente and Robert 1979; Robert et al . 1979)
has shown that, contrary to ideas propounded by many writers,
short-chain complexing organic acids (oxalic, citric, tartaric)
prove to be the most effective in decomposing silicates, especially
because these acids are the most abundant in soils. Fulvic acids
will not have an exclusive role.
2. More than 75 per cent of the iron present in the Bs horizon is
not complexed but exists in the form of oxides or hydroxides;
according to Anderson et al . (1982), the same proportion of Al is
also in the mineral form (allophane, and imogolite or proto-imog-
olite); it is therefore necessary to think of processes of systematic
decomposition of mineral-organic complexes operating in the B
horizon… soon after their formation in the A or the E.
3. The fulvate theory does not properly account for the superposition
of two different kinds of B horizons in Podzols. Most writers
imagine some sort of chromatographic separation whereby
carbon, iron and aluminium do not reach the same depth in the
profile. But then, how do we reconcile this with the fact that they
are presumed to migrate together in the form of complexes?
4. If aluminium migrates with carbon, a correlation must be found
between the contents of C and Al across horizons. But this is
rarely so (Freeland and Evans 1993).
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