Geoscience Reference
In-Depth Information
We have seen in the previous chapter (§ 10.2.4) how the iron and
aluminium oxides are characterized. It is not necessary to repeat it here.
We give only some essential references below (Table 11.4).
Characterization of iron and aluminium oxides
Table 11.4
Principal reagents used for the extraction of iron and aluminium
oxides (Page and de Kimpe 1987; van der Salm
et al
. 2000).
Symbol
Reagent
References (not included in the list of
references)
d
CBD: citrate, bicarbonate,
Mehra and Jackson (1960
)
.
Proc. 7th
dithionite
Nat. Conf. Clays Clay Miner
. 317-327.
o
Oxalic acid/ammonium
Tamm (1922).
Medd. Statens
oxalate
Skogsfôrsôkanstalt
,
19
. Schwertmann
(1964).
Z. Bodenkunde
,
105
: 194-202.
p
Sodium pyrophosphate
McKeague (1967).
Can. J. Soil Sci
.
47
Bascomb (1968).
J. Soil Sci
.
19
11.2 ECOLOGY
11.2.1 Conditions for Formation of Podzols
Here we shall focus our attention on Europe while giving some
indications on the other parts of the world.
Role of parent material
Podzolization is blocked by:
high base content because alkalinity neutralizes acidity; Podzols
occur mostly on acid rocks;
iron content higher than 3 per cent (Souchier 1971); actually, an
excess of metal ions (Al + Fe) insolubilizes humic and fulvic
acids; this is rather paradoxical since the phenomenon of pod-
zolization is identified in the profile mostly by the expression of
layers richer in iron;
high clay content that restricts downward drainage and hinders
transport of dissolved substances.
Overall, strongly podzolized soils chiefly occur on materials very
poor in bases, weathering to sands: granite with both micas, granite
with muscovite, leptynite (light-coloured gneiss), quartzose sandstone,
quartzite… However, Podzols also overlie other materials, for example
limestones, flysch or schists rich in iron. Actually, they do not form
directly on these rocks. They are established on the quartzose residues
that the rocks can provide following more or less intense depletion.
