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 categori ...

which has deep, high organic matter, nutrient-enriched surface soil ( a horizon), typically between 60 and 80 cm 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 also occur in savannahs and mountain valleys (such as Central Asia, and the North American

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, a ...

). These environments have historically been strongly influenced by fire and abundant

pedoturbation Perturbation (from Latin: ''perturbare'' "to confuse, disorder, disturb", from ''per''- "through" + ''turbare'' "disturb, confuse," from ''turba'' "turmoil, crowd") is a set of pedology (soil study) and sedimentary geology processes relating to ch ...

from organisms such as ants and earthworms. It was estimated that in 2003, only 14 to 26 percent of grassland ecosystems still remained in a relatively natural state (that is, they were not used for

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...

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 period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferou ...

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 gre ...

280 million years ago, Mollisols are best known from the

paleopedological record {{inline citations, date=June 2013 The paleopedological record is, essentially, the fossil record of soils. The paleopedological record consists chiefly of paleosols buried by flood sediments, or preserved at geological unconformities, especially p ...

as early as the ''

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

''. 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 of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

Miocene The Miocene ( ) is the first 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 means "less recen ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million 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 The udic moisture regime is common to soils of humid climates which have well-distributed rainfall, or which have enough rain in summer so that the amount of stored moisture plus rainfall is approximately equal to, or exceeds, the amount of evapotr ...

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

permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...

, consequently affected by

cryoturbation In gelisols ( permafrost soils), cryoturbation (frost churning) refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing. Cryoturbation occurs to varying degrees in most gelisols. The c ...

are common in high mountain plateaus of

Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...

and the Andean

altiplano The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau, in west-central South America, is the most extensive high plateau on Earth outside Tibet. The plateau is located at ...

. 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 ( es, Río Paraná, links=no , pt, Rio Paraná, gn, Ysyry Parana) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Br ...

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. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

-rich minerals from the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

. Mollic epipedons also occur in some

Andisols In USDA soil taxonomy, Andisols are soils formed in volcanic ash and defined as soils containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite. In the World Reference Base for Soil Re ...

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 In ...

(WRB), Mollisols are split up into

Chernozem Chernozem (from rus, чернозём, p=tɕɪrnɐˈzʲɵm, r=chernozyom; "black ground"), also called black soil, is a black-colored soil containing a high percentage of humus (4% to 16%) and high percentages of phosphorus and ammonia compou ...

s, Kastanozems and

Phaeozem A Phaeozem in the World Reference Base for Soil Resources (WRB) is a dark soil with a high base status, but without a secondary carbonates within one metre of the soil surface. Phaeozems correlate with the Udolls and Aquolls ( Mollisols) of the ...

s. Shallow or gravelly Mollisols may belong to the

Leptosol A Leptosol in the World Reference Base for Soil Resources (WRB) is a very shallow soil over hard rock or a deeper soil that is extremely gravelly and/or stony. Leptosols cover approximately 1.7 billion hectares of the Earth's surface. They are ...

s. Many Aquolls are

Gleysol A gleysol is a wetland soil ( hydric soil) that, unless drained, is saturated with groundwater for long enough to develop a characteristic colour pattern. The pattern is essentially made up of reddish, brownish, or yellowish colours at surfaces ...

Stagnosol A Stagnosol in the World Reference Base for Soil Resources (WRB) is soil with strong mottling of the soil profile due to redox processes caused by stagnating surface water. Stagnosols are periodically wet and mottled in the topsoil and subsoil, ...

s or Planosols. Mollisols with a natric horizon belong to the

Solonetz Solonetz ( uk, Солонець, rus, Солоне́ц, p=səlɐˈnʲɛts) is a Reference Soil Group of the World Reference Base for Soil Resources (WRB). They have, within the upper 100 cm of the soil profile, a so-called "natric horizon" ( ...

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