Page 88 - Microsoft Word - 20120528 Unesco study

Comparison:
Luvisols are soils with higher clay content in the subsoil than in surface soil, so they fall within
the clay groups:
SC - Sand clay, sand and clay mixtures.
GC - Clayey gravels, mixtures of gravel, sand and clay
CL - Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty
clays, clays poor.

Plinthosols
Origin:
They are mineral soils of warm regions without human influence in their genesis and low
activity clays. Are soils with plinthite. The plinthite is more common in material weathered
from basic rocks in acidic weathering of rocks. In any case, it is crucial that sufficient iron was
present, originating from either the parent material itself or incorporated by filtration of water
or groundwater upward from somewhere else. A high proportion is ferruginous of red clay
brick color.

Environment:
The formation of plinthite is associated with flat to gently sloping areas with fluctuating
groundwater or stagnating surface water. A widely accepted concept is that plinthite is
associated with areas of rainforest.

Comparison:
The major fraction of this type of soil rests in the group of clays.
CL - Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty
clays, clays poor.
CH - Inorganic clays of high plasticity frank clays.

Solonchaks
Origin:
The original material that forms these kinds of soils it is virtually any unconsolidated material.
Are soils that have high concentration of soluble salts in some time of the year, with a
vegetation of grasses and/or salt-resistant grasses.

Environment:
Solonchaks are distributed in saline coastal plains associated with marshes, deltas, beaches
and bars, also in vessels lakes and desert plains.

Comparison:
Due to the biotic environment where they develop, these kinds of soils often hold elements
from organic decomposition.
OL - Organic silts and organic silty clays of low plasticity.
OH - Organic clays of medium or high plasticity, organic silts medium plasticity.
PT - Peat and other highly organic soils.

86