Page 85 - Microsoft Word - 20120528 Unesco study

Comparison:
The arenosols are definitely sandy soils, highly siliceous and very poor in nutrients.
Because of these properties the arenosols are defined within any of the following groups of
the Unified Soil Classification System Classification:
SP - Sands poorly graded with little or no fines
SM - Salty sands mixed of sand and silt.

Cambisols
Origin:
Are composed of media parent materials and of finely textured and non-migrants, so, they are
originate and evolve in the same place derived from various kinds of rocks. Most are from
colluvial deposits accumulation by gravitational processes, for example: slopes), alluvial
(associated with large rivers with silt grading to gravel) and wind (associated with wind
erosion: sand and silt).

Environment:
Flat to mountain terrains in all climates and under a wide range of vegetation types, with no
appreciable amounts of “iluviada” clay (accumulation in a horizon of the soil of elements from
other) organic matter, aluminum and/or iron compounds.

Comparison:
Because the grading of these soils ranges goes from gravel to silt, their classification in the
USCS is located in the following groups:
GW - Gravel well graded, sand and gravel mixtures with little or no fines
GM - Silty gravels, mixtures of gravel, sand and silt
SW - Well graded Sand, sand and gravel, with little or no fines
SM - Silty sands, mixed sand and silt.
ML - Inorganic silts, rock dust, clayey slightly sandy silt or plastics.

Ferralsols
Origin:
Ferralsols represent the classical soil and are often associated with Acrisols. Stem from the
decomposition of the silicates by strong weathering of basic rocks. They are red or yellow soils
of the humid tropics. These soils are formed by sets of clays dominated by a low activity clays
(mainly kaolinite) and high content of sesquioxides.

Environment:
Ferralsols are restricted to regions with basic rocks easily weatherables and a warm and humid
weather, typical of flat to undulating lands of humid tropics. Usually has much natural
vegetation typical of the tropics, whatever the nutrients are taken up by the roots at a depth
and are eventually returned to the soil surface with leaves and other plant debris that falling so
are typifies as infertile because of its lack of organic materials and the complete absence of
soluble minerals, washed or leached to lower horizons by very wet weather.

Comparison:
The Ferrasoles correspond to a wide range of particle size and its organic content depends on
the plant material deposits that falling on its surface. Thus, in the sense of the use of a surface,
its USCS nomenclature corresponds to the following groups:
OL - Organic silts and organic silty clays of low plasticity.
OH - Organic clays of medium or high plasticity, organic silts with medium plasticity.
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