Mollisol is a

soil type A soil type is a taxonomic unit in soil science. All soils that share a certain set of well-defined properties form a distinctive soil type. Soil type is a technical term of soil classification, the science that deals with the systematic categ ...

which has deep, high organic matter, nutrient-enriched surface soil ( A horizon), typically between 60 and 80 cm (24-31 in) in depth. This fertile surface horizon, called a mollic epipedon, is the defining diagnostic feature of Mollisols. Mollic epipedons are created by long-term addition of organic materials derived from plant roots and typically have soft, granular soil structure. Mollisols typically occur in savannahs and mountain valleys (such as Central Asia, and the North American

Great Plains The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

). These environments have historically been strongly influenced by fire and abundant pedoturbation from organisms such as ants and earthworms. It was estimated that in 2003, only 14 to 26 percent of grassland ecosystems remained in a relatively natural state (that is, they were not used for

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

due to the fertility of the horizon). Globally, they represent ~7% of ice-free land area. As the world's agriculturally most productive soil order, the Mollisols represent one of the most economically important soil orders. Though most other soil orders known today were formed at the beginning of the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

Ice Age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

280 million years ago, Mollisols are best known from the paleopedological record as early as the ''

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

''. Their development is very closely associated with cooling and drying of the global climate that occurred during the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58eluvial horizon :Aquolls—wet soils; aquic soil moisture regime :Cryolls—cold climate; frigid or cryic soil temperature regime :Gelolls—very cold climate; mean annual soil temperature < 0 °C :Rendolls—lime parent material :Udolls—humid climate; udic moisture regime :Ustolls—subhumid climate;

ustic Ustic is a class of soil moisture regime. It is one of a range of different soil moisture regimes, such as: aquic moisture regime, aridic moisture regime, udic moisture regime and xeric moisture regime. The ustic moisture regime is intermediate ...

moisture regime :Xerolls—Mediterranean climate; xeric moisture regime Soils which are mostly similar to Mollisols but contain either continuous or discontinuous

permafrost Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below ...

, consequently affected by cryoturbation are common in high mountain plateaus of

Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...

and the Andean

altiplano The Altiplano (Spanish language, Spanish for "high plain"), Collao (Quechuan languages, Quechua and Aymara language, Aymara: Qullaw, meaning "place of the Qulla people, Qulla") or Andean Plateau, in west-central South America, is the most extens ...

. Such soils are called Molliturbels or Mollorthels and provide the best grazing land in such cold climates because they are not acidic like many other soils of very cold climates. Other soils which have a mollic epipedon are classified as Vertisols because high shrink swell characteristics and relatively high clay contents dominate over the mollic epipedon. These soils are especially common in parts of South America in the

Paraná River The Paraná River ( ; ; ) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. ...

basin receiving abundant but erratic rainfall and extensive deposition of

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

-rich minerals from the

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

. Mollic epipedons also occur in some Andisols but the andic properties take precedence. In the

World Reference Base for Soil Resources The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the I ...

(WRB), Mollisols are split up into Chernozems, Kastanozems and Phaeozems. Shallow or gravelly Mollisols may belong to the Leptosols. Many Aquolls are Gleysols, Stagnosols or Planosols. Mollisols with a natric horizon belong to the Solonetz.

References

* Brady, N.C. and Weil, R.R. (1996). ‘The Nature and Properties of Soils.’ 11th edition. (Prentice Hall, New Jersey). * Buol, S.W., Southard, R.J., Graham, R.C., and McDaniel, P.A. (2003). ‘Soil Genesis and Classification.’ 5th edition. (Iowa State University Press - Blackwell, Ames.)

External links

* * * {{Soil type Pedology Types of soil

See also

References

External links