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When compared to Chernozems, they dry out to greater depth in dry summer sea-
sons and are not as completely wetted by rains. Their structural stability, mainly that
of microaggregates, is weaker, and their hydraulic conductivity is less favorable.
Suffi ciently high yields are reached only if they are irrigated. Their synonyms in
national systems are either translations or names that are derived from colors such
as Chestnut Soils, Kalktchernozems, or Brown Soils. They belong to various taxo-
nomic levels of Mollisols (Borolls, Ustolls, Xerolls) in the US Taxonomy.
Phaeozems are soil in the zone north of the Chernozem zone in the Northern
Hemisphere. They were formed in a wet steppe or prairie zone. Being more inten-
sively percolated and leached, their humus horizon is less rich in bases when com-
pared with the topsoil of Chernozems and Kastanozems. Moreover, we don't fi nd
secondary carbonates in the top 1 m of their profi le. The name was derived from the
Greek phaios which means dusky. The Russian zemlia was explained earlier, it
means earth or soil. We fi nd in their profi le the cambic or argic B horizon that is
slightly more rich in clay than the A horizon and usually has a distinct polyhedral
structure with aggregates having more than 6 slightly irregular walls. This B hori-
zon is between the humus A horizon and parent material formed by loess or loessial
loam and other unconsolidated basic fi ne-grained materials (C horizon). Phaeozems
are fertile, excellent farm soils, well reacting to additional irrigation. They are usu-
ally identifi ed with the color brown in many national classifi cations, like Brunizems
derived from the French brun meaning brown and Parabraunerde derived from the
German braun meaning brown or Fahlerde. The US Taxonomy keeps them as
Udolls and Albolls in Mollisols.
8. The next set comprises soils from drier regions with accumulation of a certain
material. If it is gypsum, the RSGs are called accordingly Gypsisols . If it is silica,
the RSGs are Durisols . And if the accumulated material is calcium carbonate,
the soils are Calcisols .
Gypsisols are soils existing in dry areas of semiarid regions or even in desert
areas. Due to the climate with precipitations substantially lower than evapotranspi-
ration, carbonates and sulfates are transported immediately below the thin top hori-
zon where gypsum (CaSO 4 . 2H 2 O) accumulates and precipitates during long-lasting
hot and rainless summers. This accumulation was the logic for the name of the soils
having common roots with the Greek gypsos meaning gypsum. The parent material
is formed by unconsolidated alluvial and wind deposits of base-rich material, i.e.,
materials with an alkaline reaction. Their natural vegetation is rather sparse and
dominated by thorny shrubs. Their agricultural use is conditioned by cautiously
managed irrigation to avoid the secondary salinization during long periods of crop
production. The national classifi cations use the terms Desert Soils, Yermosols
(Spanish yermo meaning desert), and Xerosols. Among the soils of the US
Taxonomy, the most frequent are Gypsids in Aridisols.
Durisols occur mainly on old arid and semiarid surfaces with a relatively perme-
able material, but this positive feature is frequently disturbed by a hardpan of sec-
ondary cemented silica (SiO 2 ). The name was derived just to indicate this property,
since the Latin durus means hard. The hard horizon (hardpan) disturbs the rooting
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