Geoscience Reference
In-Depth Information
5
Ferralsols and other Soils of
the Hot Regions
INTRODUCTION
We shall begin the review of the great soil groups with Ferralsols because
they are the oldest and most mature soils of the world. They correspond
to the intertropical zone. They owe their exceptional depth to three
factors: (i)
high
rainfall and temperature
that accelerate rock weathering;
(ii)
feeble surface erosion
because of their topographic position on stable,
nearly horizontal shields under forest vegetation which slows down
removal of surface soil; (iii)
absence of glaciations
that, in higher latitudes,
have scraped off old soils.
The mechanisms of formation of Ferralsols will clarify the concept
of the weathering-front model. They will also help understand the great
pedological diversity that passage of time results in!
Ferralsols cover nearly 750 million hectares in the world, mainly in
Amazonia, Central Africa and Oceania.
5.1 GENERALITIES
The word 'laterite' (from L.
later
= brick) was introduced in 1807 in a
topic by Francis Buchanan, physician and naturalist, who had explored
the south-western part of India in 1800 on behalf of the East India
Company. Buchanan had observed, in a quarry at Angadipuram, a
kind of
indurated clay
that the people used to extract by cutting it into
parallelepipeds. It was possible to use it for construction because the
material hardened in air and turned black through rapid oxidation of
ferrous compounds (Bourgeon and Gunnell 2005). But the name laterite,
initially given to a specific material, has seen its meaning broadened to
