Alfisols
Encyclopedia
Alfisols are a soil order in USDA soil taxonomy
. Alfisols form in semiarid to humid areas, typically under a hardwood
forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium (Al) and iron (Fe). Because of their productivity and abundance, the 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
and Africa
are still very deficient in nitrogen
and available phosphorus
. Those in monsoon
al tropical regions, however, have a tendency to acidify when heavily cultivated, especially when nitrogenous fertilizers are used.
In the FAO
soil classification, most Alfisols are classified as Luvisols or Lixisols
, but some are classed as Nitosols.
Alfisols occupy around one-tenth of the Earth's ice-free land surface. They are dominant in many areas, such the Ohio River
basin in the United States, southern
and unglaciated Western Europe
, the Baltic region and central European Russia
, the drier parts of Peninsular India, Sudan
in Africa, and many parts of South America
.
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
, 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
. Probably owing to their fertility, they are the oldest forest soils; vegetation on weathered Oxisol
s, by contrast, is not known earlier than Middle Permian
. Fossil Alfisols remain common from the Carboniferous
and all periods since the Eocene
.
USDA soil taxonomy
USDA Soil Taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.- Example of...
. Alfisols form in semiarid to humid areas, typically under a hardwood
Hardwood
Hardwood is wood from angiosperm trees . It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.Hardwood contrasts with softwood...
forest cover. They have a clay-enriched subsoil and relatively high native fertility. "Alf" refers to aluminium (Al) and iron (Fe). Because of their productivity and abundance, the 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
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
are still very deficient in nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and available phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
. Those in monsoon
Monsoon
Monsoon is traditionally defined as 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 the asymmetric heating of land and sea...
al tropical regions, however, have a tendency to acidify when heavily cultivated, especially when nitrogenous fertilizers are used.
In the FAO
Fão
Fão is a town in Esposende Municipality in Portugal....
soil classification, most Alfisols are classified as Luvisols or Lixisols
Lixisols
Lixisols are soils with subsurface accumulation of low activity clays and high base saturation. They develop under intensive tropical weathering conditions....
, but some are classed as Nitosols.
Alfisols occupy around one-tenth of the Earth's ice-free land surface. They are dominant in many areas, such the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
basin in the United States, southern
Southern Europe
The term Southern Europe, at its most general definition, is used to mean "all countries in the south of Europe". However, the concept, at different times, has had different meanings, providing additional political, linguistic and cultural context to the definition in addition to the typical...
and unglaciated Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...
, the Baltic region and central European Russia
European Russia
European Russia refers to the western areas of Russia that lie within Europe, comprising roughly 3,960,000 square kilometres , larger in area than India, and spanning across 40% of Europe. Its eastern border is defined by the Ural Mountains and in the south it is defined by the border with...
, the drier parts of Peninsular India, Sudan
Sudan
Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...
in Africa, and many parts of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
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
Ultisols
Ultisols, commonly known as red clay soils, are one of twelve soil orders in the United States Department of Agriculture soil taxonomy. They are defined as mineral soils which contain no calcareous material anywhere within the soil, have less than 10% weatherable minerals in the extreme top layer...
, which are the more highly leached forest soils having less than 35% base saturation. In eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, Alfisols are commonly found in glaciated areas while Ultisols are restricted to the areas south of the limit of maximum glaciation.
The fossil record
Paleopedological record
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 plateau escarpments or sides of river valleys...
of Alfisols begins in the Late Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
. Probably owing to their fertility, they are the oldest forest soils; vegetation on weathered Oxisol
Oxisol
Oxisols are an order in USDA soil taxonomy, best known for their occurrence in tropical rain forest, 15-25 degrees north and south of the Equator. Some oxisols have been previously classified as laterite soils.-Formation:...
s, by contrast, is not known earlier than Middle Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
. Fossil Alfisols remain common from the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
and all periods since the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
.
Suborders
- Aqualfs — wet soils; aquic soil moisture regime
- Cryalfs — cold climate; frigid or cryic soil temperature regime
- Udalfs — humid climate; udic moisture regimeUdic moisture regimeThe 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 evapotranspiration...
- Ustalfs — subhumid climate; ustic moisture regime
- Xeralfs — Mediterranean climate; xeric moisture regime
See also
- PedogenesisPedogenesisPedogenesis is the science and study of the processes that lead to the formation of soil ' and first explored by the Russian geologist Vasily Dokuchaev , the so called grandfather of soil science, who determined that soil formed over time as a consequence of...
- Pedology (soil study)Pedology (soil study)Pedology is the study of soils in their natural environment. It is one of two main branches of soil science, the other being edaphology...
- Soil classificationSoil classificationSoil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.- Overview :...
- Soil scienceSoil scienceSoil 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 the use and management of soils.Sometimes terms which...
- Soil typeSoil typeIn terms of soil texture, soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay...