Page 86 - Microsoft Word - 20120528 Unesco study

And in the deeper layers (> 50cm):
CL - Inorganic clays of low to medium plasticity sandy clay, silty or poor.
MH - Inorganic silts, micaceous or diatomaceous silts, more elastic.
CH - Inorganic clays of high plasticity frank clays.

Fluvisols

Origin:
The Fluvisols are soils developed in alluvial deposits (river, lakes and marines) that
accommodate genetically young azonal soils.

Environment:
Observed in alluvial plains, river deltas, valleys and coastal marshes in all climate zones,
particularly in the tropics. Many fluvisols under natural conditions are periodically flooded.
Most of the Fluvisols have a good natural fertility: lowland rice cultivation is widespread in
tropical Fluvisols with satisfactory irrigation and drainage. In dry periods is also stimulated
microbial activity that promotes the mineralization of organic material.

Comparison:
In its migratory origin because the water flows that move their water-bearing components to a
alluvial deposits, we see the formation of material with low particle size that falls into the
range of clays and silts with a little or any amount of sand, because of this, we classify them in
the USCS within these groups.
SP - Sands poorly graded sand with gravel, with little or no fines.
SC - Sands clay, sand and clay mixtures.
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.

Gleysols
Origin:
Gleysols are soils of a wide range of unconsolidated materials, mainly fluvial, marine and lake,
with basic to acidic mineralogy.

Environment:
Tropical soils with clear signs of influence of groundwater that is saturated with water for long
periods. They are found in depressed areas and low landscape positions with shallow
groundwater.

Comparison:
In addition to their organic quality, the textures of the Gleysols are sandy and loamy and
sometimes clay, so they are defined as:
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.

84