Alfisols are a soil order in
USDA soil taxonomy. Alfisols form in semi-arid to humid areas, typically under a
hardwood forest cover. They have a clay-enriched
subsoil
Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and ...
and relatively high native fertility. "Alf" refers to aluminium (Al) and iron (Fe). Because of their productivity and abundance, Alfisols represent one of the more important soil orders for food and fiber production. They are widely used both in agriculture and forestry, and are generally easier to keep fertile than other humid-climate soils, though those in
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
and
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
are still very deficient in
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and available
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
. Those in
monsoon
A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
al tropical regions, however, have a tendency to acidify when heavily cultivated, especially when nitrogenous fertilizers are used.
In the
World Reference Base for Soil Resources (WRB), most Alfisols are classified as
Luvisols or
Lixisols, but some are classed as
Retisols or
Nitisols. Aqualfs are mainly
Stagnosols or
Planosols. Alfisols with a natric horizon are mainly
Solonetz.
Alfisols occupy around one-tenth of the Earth's ice-free land surface. They are dominant in many areas, such as the
Ohio River basin in the United States,
southern
Southern may refer to:
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and unglaciated
Western Europe
Western Europe is the western region of Europe. The region's countries and territories vary depending on context.
The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the ancient Mediterranean ...
, the Baltic region and central
European Russia
European Russia (russian: Европейская Россия, russian: европейская часть России, label=none) is the western and most populated part of Russia. It is geographically situated in Europe, as opposed to the cou ...
, the drier parts of
Peninsular India,
Sudan
Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...
in Africa, and many parts of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
.
Alfisols have undergone only moderate leaching. By definition, they have at least 35% base saturation, meaning calcium, magnesium, and potassium are relatively abundant. This is in contrast to
Ultisols, which are the more highly leached forest soils having less than 35% base saturation. In eastern
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, Alfisols are commonly found in glaciated areas while Ultisols are restricted to the areas south of the limit of maximum glaciation.
The
fossil record of Alfisols begins in the Late
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...
. Probably owing to their fertility, they are the oldest forest soils; vegetation on weathered
Oxisol
Oxisols are a soil order in USDA soil taxonomy, best known for their occurrence in tropical rain forest within 25 degrees north and south of the Equator. In the World Reference Base for Soil Resources (WRB), they belong mainly to the ferralsols, ...
s, by contrast, is not known earlier than
Middle Permian
The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
. Fossil Alfisols remain common from 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 ...
and all periods since 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'', ...
.
Suborders
*
Aqualfs – This suborder is saturated with water long enough to cause oxygen depletion. Almost all of this suborder is thought to have been forested at some point.
Redoximorphic features Redoximorphic features (RMFs) consist of color patterns in a soil that are caused by loss (depletion) or gain (concentration) of pigment compared to the matrix color, formed by oxidation/reduction of iron and/or manganese coupled with their remo ...
are present.
*
Cryalfs – This suborder occurs mainly in high elevations which tend to be cold with temperatures ranging from greater than 0 C to less than 8 C.
*
Udalfs – This suborder is located in humid or subhumid climates. All of this word is thought to have been forested at some point.
* Ustalfs – This suborder is located in semiarid climates with wet summers and dry winters.
*
Xeralfs – This suborder is located in mediterranean climates with very dry summers and wet winters.
Fossil record of Alfisols
The fossil record of Alfisols extends back to the Late Devonian. The Alfisol paleosols were woodland soils and early forest soils. The fertile Alfisols were most likely formed by Devonian forests. The oldest of the Alfisol paleosol forest soils are in the paleosols of the Aztec Siltstone in
Victoria Land, Antarctica. In the paleosols of the Aztec Siltstone, the Rosemary paleosol, there is evidence for trees from surficial tree-throwing structures and large drab-haloed root tracers. From the fossil wood and spores found in the Aztec Siltstone, there is a strong indication that the trees were
Archaeopteris
''Archaeopteris'' is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (), the oldest fossils being 385 million years old, ...
-
Callixylon.
In upper
New York State, there have been Devonian trees found in a large variety of paleosols. These Devonian trees help give clues as to what ecological tolerances for various early trees looked like. The paleosols associated with
progymnosperm trunks are interpreted to not have grown in soils similar to the type of soils modern seed plants are grown in. The
taxa of progymnosperm trunk fossils reproduced by
spores. For reproduction, they were more dependent on moisture than modern seed plants. Comparing the ''
Wattieza
''Wattieza'' was a genus of prehistoric trees that existed in the mid-Devonian that belong to the cladoxylopsids, close relatives of the modern ferns and horsetails. The 2005 (publicly revealed in 2007) discovery in Schoharie County, New York ...
'', from New York Devonian paleosols, and the ''Callixylon''
ecotones
An ecotone is a transition area between two biological communities, where two communities meet and integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and gras ...
to show this dependency on moisture it shows that the Wattieza lived in an ecotone of 571 ± 72 mm mean annual precipitation and the Callixylon lived in an ecotone of 611 ± 46 mean annual precipitation. Because the Callixylon grew taller than the ''Wattieza'' it is inferred it was because there was more mean annual moisture available to the ''Callixylon''.
In the lower
Walton Formation, near
Sidney, New York fossils of ''
Archaeopteris macilenta'', ''Callixylon zalesskyi'', and ''
Geminospora lemurata'' have been found. The tapering geometry of large woody root traces is the most likely cause of the intimate relationship between
Argillic horizons, Alfisols, and forests. The large woody root traces can transport water and clay using their large pipes. They are very efficient at moving soil into a subsurface horizon when the plant dies and the roots decay.
The
Mata Amarilla Formation
The Mata Amarilla Formation is a fossiliferous formation of the Austral Basin in southern Patagonia, Argentina. The formation consists of sediments deposited during the Middle Cenomanian, dated to 96.94 to 95.52 Ma. The middle section of the fo ...
, a formation in the
Austral Basin in southern
Patagonia, Argentina is the location known for the preservation of
podocarp-dominated
fossil forests. In the eastern area of the middle section of the Mata Amarilla Formation, there are vertic Alfisols. In these Alfisols, there is a preservation of fossil forests, whose minimum age is 337 years. The fossil forests in this section are made up of ''
in situ'' trunks. These trunks, in life position, have shallow root systems with well-developed horizontal roots, and have minimal development of vertical roots. A log of ''Podocarpxylon gargiae'' roots was found in the formation as well. The total mean
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid f ...
of these trees in the vertic Alfisol paleosol is greater than 60 cm and the smallest tree diameter is 26 cm.
While Afisol paleosols are known for their woodland soils and fossils, there have also been other types of fossils found. The
ichnofacies
An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.
Concept
Trace fossil assemblages are far from random; the range of fossils recorded in association is constra ...
of the ground-nesting bees, ''Celliforma'', was formed in well drained Alfisols as well as
Aridisols and
Oxisols. The ''Termitichnus'' ichnofacies, which included a large array of termite nests and pellets, is found in Oligocene Alfisols, Aridisols, and Oxisols. All the
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
bones and tracks from the paleosol sequences of Late Devonian and
Mississippian of New York and Pennsylvania, U.S.A. are found in Aridisols and Alfisols. The Alfisols in the Texas High Plains have evidence for fossilized pollen and beetles.
See also
*
Paleosol
*
Paleopedology
Paleopedology (palaeopedology in the United Kingdom) is the discipline that studies soils of past geological eras, from quite recent ( Quaternary) to the earliest periods of the Earth's history. Paleopedology can be seen either as a branch of s ...
*
Pedogenesis
*
Pedology (soil study)
Pedology (from Greek: πέδον, ''pedon'', "soil"; and λόγος, ''logos'', "study") is a discipline within soil science which focuses on understanding and characterizing soil formation, evolution, and the theoretical frameworks for modeling ...
*
Soil classification
*
Soil science
Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to ...
*
Soil type
References
External links
*
*
{{Soil type
Pedology
Types of soil