Geoscience Reference
In-Depth Information
of plants and prevents a desirable distribution of water within the soil profi le when-
ever Durisols are irrigated. This RSG was only recently introduced into the WRB
system. They are recognized in national classifi cation systems also as hardpan soils
and dorbank and in the US Taxonomy as Durids in Aridisols.
Calcisols are soils with a distinct accumulation of lime as a horizon in soil pro-
fi les in arid and semiarid climatic zones. On the occasion of the soil sometimes
being wetted by a rarely occurring rain, dissolved lime is transported by evaporation
fl ux. The calcic horizon may be hardened into a rocklike formation, i.e., a petrocal-
cic horizon. They occur at various depths from very shallow to deep levels within
the profi le, and owing to high contents of adsorbed Ca
2+
, they are quite permeable.
Their calcareous, alluvial, or wind-deposited parent materials are all further weath-
ered very slowly in the dry climate. The natural vegetation is sparse - formed by
shrubs and trees and also partly by ephemeral grasses. Generally, droughts lead to a
slowdown or even to a virtual stop of soil-forming processes such as chemical
weathering, accumulation of organic matter, and translocation of clay. If some
traces of horizons are visually apparent, they could be the result of polygenetic
evolution in a previous different climate. Calcisols are frequently rich in stones.
Their name was derived from the Latin
calcarius
meaning calcareous. If irrigated,
they are susceptible to salinization and potentially change into Solonchaks. Calcisols
are classifi ed as Desert Soils or Yermic Soils with the term derived from the Spanish
yermo
meaning desert in some national taxonomic systems. When Calcisols are
attacked by accumulation of salts in areas without surface drainage, they are also
classifi ed as Takyrs - the name derived from the Kazakh or Turkish languages for
fl at land that is occasionally inundated.
9. Set of soils with a clay-rich subsoil where the following RSGs belong:
Albeluvisols
,
Alisols
,
Acrisols
,
Luvisols
, and
Lixisols
.
Albeluvisols are soils that have a thin dark humus A horizon lying on top of a
leached subsurface horizon known as an albic horizon. The name of the horizon was
derived from the Latin
albus
meaning white, while the second part of the RSG name
“luvisols” has its roots in the Latin
eluere
meaning to wash out. The albic eluviated
E horizon is an iron-depleted material changing in a sharp undulating manner into
an underlying compact illuvial clay B horizon. The harsh climate of cold winters,
short and relatively cool summers, and high annual precipitations cause periodic
over-wetting of soil and leaching of sesquioxides together with clay particles from
the eluviated E horizon into the illuviated B horizon with features typical of peri-
odic waterlogging. The high clay content of the B horizon contributes to the origin
of those features. These soils are acidic with low nutrient content, are very shallow
for adequate root penetrability, and require drainage for crop production. Hence,
their agricultural utility remains problematic. Some national classifi cations recog-
nize them as Podzoluvisols or Orthopodzolic Soils. The US Taxonomy classifi es
them under Alfi sols like
Glossaqualfs, Glossocryalfs, and Glossudalfs
.
Alisols occur mainly in tropical and subtropical environments with high amounts
of exchangeable Al
3+
cations released due to the hydrolysis of simply weathered
primary minerals rich in Al and of secondary clay minerals, like vermiculite and
