Geoscience Reference
In-Depth Information
Man himself could also be an agent of degradation of structure and
therefore of Ferralsols. Overall, the Xanthic soils are important because
they represent the beginnings of degradation of the typical soil cover
of the intertropical zone.
The mechanism of podzolization is manifested by the destruction of
silicate minerals, including clay minerals, and leads to the relative
concentration of quartz in the form of a very white and very sandy
E horizon. Ferrallitic materials are liable to undergo such evolution and
Podzols represent one of the final stages of the evolution of pedological
materials in the hot and humid regions of the world (Chap. 11). However,
their presence in the tropical environment has long remained unnoticed,
especially in Amazonia. And yet they are huge! Their E horizon, seen on
the surface, can be up to 6 metres thick. But it has long been taken for
a special alluvial deposit because it was believed Podzols were confined
to cold climates of the mountains and of the high latitudes…
Transformation of Ferralsols and Acrisols to Podzols
5.6 LAND USE
We can only touch upon the question. Much more can be learnt by
referring to specialized topics (Phiri
et al
. 1994; Bertrand and Gigou
2000). The soils of the intertropical zone are naturally infertile for the
following reasons:
insufficient base retention capacity: low for kaolinite and almost
nonexistent for oxides and hydroxides of iron and aluminium,
deficiency of major (N, P, K, Ca, Mg) and secondary (sulphur)
nutrient elements that have been removed by millions of years
of depletion of the soil,
frequent deficiency of micronutrients (boron, molybdenum,
zinc),
aluminium toxicity. Aluminium, more soluble in acid medium, is
present in the soil solution of tropical soils, which is also very rich
in aluminium compounds. Aluminium represents 80 per cent of
the exchangeable ions. Root growth is affected, thereby limiting
the nutrition of the plant and its water uptake. Blocking of
nodulation and reduction of absorption of atmospheric nitrogen
also occurs in legumes. Agronomic trials have shown that crop
yields decrease almost linearly with increase in the proportion of
Al present on the exchange complex. Many species grown in the
