Page 84 - Microsoft Word - 20120528 Unesco study

Appendix 2: Soil classifications of

Tabasco

Acrisols
Origin:
Product of the weathering of the acid rocks, the acrisols are acid soils, heavily weathered with
low saturation of the base in some depth.

The acrisols show a marked clay accumulation horizon and a low saturation of the bases (less
than 50%). These are soils with higher clay content in the subsoil which in surface soil as a
result of pedogenetic processes (especially clay migration).

Environment:
Mainly old surfaces with topography with hills or hollows. Regions with a humid
tropical/monsoonal, subtropical and warm temperate. The type of natural vegetation in these
soils is jungle.

Regional distribution of Acrisols: The acrisols are found in humid tropical regions, humid
subtropical and temperate warm. There are about 1.000 million hectares of Acrisols
worldwide.

Comparison:
By origin, environment and geographical distribution, the acrisols belong to groups of clays,
the primary (source) and secondary (migratory). In both cases the particle diameter is less than
0.002 mm.

Therefore, acrisols are defined in any of the following groups for the Unified Soil Classification
System (USCS):
CH - Inorganic clays of high plasticity, frank clays.
OH - Organic clays of medium or high plasticity.
PT - Peat and other highly organic soils.

Arenosols
Origin:
The arenosols not distinguish the horizons of the soil profile and consist entirely of material or
coarse sandy loam. Basically there are unconsolidated deposits of sand dunes frequently found
in dunes and also in areas of very thick parent material subject to millions of years of
weathering.

Environment:
They are found worldwide and are especially abundant in the deserts and in some humid
regions. Have very low water retention capacity, because the sand in the soil is not graded, so
that is not grain size variations. In humid environments tend to be very acidic, but not in arid
climates.

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