Page 30 - Soil Degradation, Conservation and Remediation

1.6 Classification of World Soils 15
1.6.4 Entisols

Entisols are defined as soils that have little or no sign of horizon differentiation. Most
Entisols are basically unaltered from their parent materials. Actually they are affected
to a limited extent by translocation processes. However, there is considerable darken-
ing of the surface soil by organic matter. The presence of unweatherable parent mate-
rials, removal of soil materials by continuous erosion, continuous deposition of silts

with floodwater in active floodplains, cold and dry climates, and insuffi cient time
after rock exposure or sediment deposition are the causes of delayed soil develop-
ment in Entisols. These soils are distributed over a wide geographic area and can be
found in any climate and under any vegetation. Entisols along river fl oodplains are
often intensively farmed and are some of the most agriculturally productive soils in
the world. Most Entisols are used for pasture, rangeland, and forests. Entisols occupy
about 16 % of the global ice-free land surface. (The WRB equivalents of Entisols are
Anthrosols, Arenosols, Fluvisols, Regosols, Stagnosols, and Umbrisols.) Entisols
have four suborders. They are:

Aquents: These are the wet Entisols. They may be found in tidal marshes, on deltas,

on the margins of lakes where the soils are continuously saturated with water, on
fl oodplains along streams where the soils are saturated at some time of the year,
or in areas of wet, sandy deposits. Many Aquents have gleying with bluish or
grayish colors and redoximorphic features. They may have any temperature
regime. Most are formed in recent sediments and support vegetation that tolerates
permanent or periodic wetness. Vast areas of alluvial Aquents are used for rice
cultivation in South and Southeast Asia, including Bangladesh. Some Aquents

have sulfidic materials (former acid sulfate soils).

Arents: Arents are the Entisols that do not have horizons because they have been
deeply mixed by plowing, spading, or other methods of moving by humans.
Arents may have 3 % or more, by volume, fragments of diagnostic horizons in one
or more subhorizons at a depth between 25 and 100 cm below the soil surface.

Fluvents: Fluvents are mostly brownish to reddish soils that are formed in recent

alluvial sediments, mainly on floodplains, fans, and deltas of rivers and small
streams but not in back swamps where drainage is poor. Strata of clayey or loamy
materials commonly have more organic carbon than the overlying, more sandy

strata. Fluvents are often found associated with Aquents in floodplains. Rice and
jute are grown in many Fluvents.
Psamments: Psamments are Entisols that are very sandy at all layers. Some

Psamments form in poorly graded but well-sorted sands on shifting or stabilized
deposits, in cover sands, or in sandy parent materials that were sorted in an ear-
lier geologic cycle. Psamments occur under any climate without permafrost
within 100 cm of the soil surface. They can have any vegetation and can be
cropped with irrigation. Psamments on old stable surfaces commonly consist of
quartz sand. These soils are poorly fertile and dry and often show nutrient

deficiencies.