Geoscience Reference
In-Depth Information
tion is not caused by an abrupt textural change in the profi le. Their agricultural use
is rather limited since a simple pipe drainage system is not suffi cient to improve
their lack of aeration and oxygen defi ciency. In other words, owing to their hydrau-
lic properties, a substantial increase of air-fi lled porosity, mainly of medium and
coarse pores, is simply not attainable. Many national classifi cations denote them as
Pseudogleys. The US Taxonomy incorporates them in Aqualfs, Aquents, Aquolls,
in taxons starting with the Latin
aqua
meaning water and in Inceptisols.
7. Soils evolving in steppe regions with humus-rich top horizon. Rich in base satu-
ration, their vertical transition to parent rock is gradual:
Chernozems
,
Kastanozems
, and
Phaeozems
.
Chernozems are probably the most popular soils and are ranked with the best of
them owing to their high natural fertility. The term was introduced by the founder of
the systematic studies of soil types, the Russian V.V. Dokuchaev. The soil profi le is
simple - a humus-rich A horizon having a thickness ranging from 30 to 100 cm
covers the usually silty loam to loamy loess parent material. The high content of
humus reaching to about 10 % is readily apparent from the black color. Their name
was derived from the Russian
chernij
(
chorny
) meaning black and
zemlia
meaning
earth or soil. The high content of humus is the result of two positive factors: the
dense steppe vegetation consisting mainly of grasses, especially papilionaceus
plants, and mild climate with cool winters and long warm summers with low fre-
quency of rains. Since the climate forms a continuous belt and the same is valid for
the zone of steppes, earlier classifi cations recognized Chernozems as zonal soils.
Their richness in high-quality humus causes stable aggregated soil structure and
favorable soil physical conditions for plants. These attributes with those of calcare-
ous loessial parent material provide a neutral chemical reaction needed for an ample
supply of readily available plant nutrients. Hence, Chernozems are universally
known for their high fertility and noteworthy crop productivity. The term Chernozem
was taken over in majority of national classifi cations, sometimes modifi ed like
Chernosols in Canada, or Chernossolos, and in some instances in literal translation,
like Schwartzerde and Black Earth. In the US Taxonomy we fi nd Mollisols and their
suborders.
Kastanozems are soils in many aspects similar to Chernozems, and even their
classifi cation as zonal soils was the same. Their zone, to south of the Chernozem
zone in the Northern Hemisphere, differs from the environment of Chernozems by
substantially drier climate and shorter grass steppe vegetation. With the majority of
their plants requiring less soil water, they are basically more resistant to dry climatic
periods. Kastanozems show more intensive accumulation of secondary carbonates,
since the net upward unsaturated fl ow prevails slightly over the net downward fl ow
of rainwater. Consequently, they have a dark brown surface horizon, which is less
deep and less black than that of Chernozems. They also differ from Chernozems by
having an additional horizon in their profi le - a B horizon with a cinnamon to a
more pale color. Sometimes there is an accumulation of lime or gypsum. Their
name results from dark chestnut color in A horizon, since the Latin
castanea
or the
Russian
kashtan
means chestnut and
zemlia
means earth or soil (see also Chernozem).
