Extragrade Formative Elements (Partly updated to 1998 Soil Taxonomy Revisions)

Formative Element Derivation Connotation Abruptic L. - abruptum, torn off Abrupt textural change Aeric Gr. - aerios, air Aeration Anthropic Gr. - anthropos, man Anthropic epipedon Arenic L. - arena, sand Arenic surface horizon Cumulic L. - cumulus, heap Thickened epipedon Epiaquic Gr. - epi, over, and aquic Surface wetness Glossic Gr. - glossa, tongue Tongued horizon boundaries Grossarenic L. - grossus, thick and arena, sand Grossarenic surface horizon Hydric Gr. - hydor, water Presence of water Leptic Gr. - leptos, thin Thin soil Limnic Gr. - limn, stone Limnic materials present Lithic Gr. - lithos, stone Shallow lithic contact present Pachic Gr. - pachys, thick A thick epipedon Paralithic Gr. - para, beside and lithic Shallow paralithic contact present Pergelic L. - per, throughout; gelare, freeze Permanently frozen Petrocalcic Gr. - petra, rock and calcic Petrocalcic horizon present Petroferric Gr. - petra, rock and liferrum, iron Petroferric contact present Plinthic Gr. - plinthos, brick Plinthite present Ruptic L. - ruptum, broken Intermittent horizon Superic L. - superare, to overtop Plinthite at surface Terric L. - terra, earth Mineral substratum Thapto Gr. - thapto, buried A buried soil

Soil Order General Features

AlfisolsAlfisols develop in humid and subhumid climates, have average annual precipitation of 500-1300 mm. They are frequently under forest vegetation. Characteristic features: Clay accumulation in a Bt horizon, thick E horizon, available water much of the growing season, slightly to moderately acid.

AndisolsAndisols are soils with over 60 % volcanic ejecta (ash, cinder, pumice, basalt) with bulk densities below 900 kg/m 3. Characteristic features: Dark A horizon, early-stage secondary minerals (allophane, imogolite, ferrihydrite clays), high adsorption and immobilization of phosphorus, very high cation exchange capacity.

AridisolsAridisols exist in dry climates. Characteristic features: horizons of lime or gypsum accumulation, salty layers, and/or A and Bt horizons.

EntisolsEntisols have no profile development except a shallow marginal A horizon. Many recent river floodplains, volcanic ash deposits, unconsolidated deposits with horizons eroded away, and sands are Entisols.

Gelisols Gelisols are soils that contain within 200 cm of the ground surface the condition known as permafrost.

HistosolsHistosols are organic soils (peat and mucks) consisting of variable depths of accumulated plant remains in bogs, marshes, and swamps.

InceptisolsInceptisols, especially in humid regions, have weak to moderated horizon development. Horizon development have been retarded because of cold climate, waterlogged soils, or lack of time for stronger development. Characteristic feature: Texture has to be finer than loamy very fine sand.

MollisolsMollisols are frequently under grassland, but with some broadleaf forest-covered soils. Characteristic features: Deep, dark A horizons, they may have B horizons and lime accumulation.

OxisolsOxisols are excessively weathered, whereas few original minerals are left unweathered. They develop only in tropical and subtropical climates. Characteristic features: Often Oxisols are over 3 m deep, have low fertility, have dominantly iron and aluminum clays, and are acid.

SpodosolsSpodosols are typically the sandy, leached soils of cold coniferous forests. Characteristic features: O horizons, strongly acid profiles, well-leached E horizons, Bh or Bs horizons of accumulated organic material plus iron and aluminum oxides.

UltisolsUltisols are extensively weathered soils of tropical and subtropical climates. Characteristic features: Thick A horizon, clay accumulation in a Bt, strongly acid.

VertisolsVertisols exist most in temperate to tropical climate with distinct wet and dry seasons. They have a high content of clays that swell when wetted and show cracks when dry. Characteristic features: Deep self-mixed A horizon , top soil falls into cracks seasonally, gradually mixing the soil to the depth of the cracking.

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Soil Orders and SubordersThis page is nothing more than a splicing of pages found at the Natural Resources Conservation Service's page on Soil Orders athttp://soils.usda.gov/technical/classification/orders/

Gelisols

The central concept of Gelisols is that of soils that have permafrost within 100 cm of the soil surface and/or have gelic materials within 100 cm of the soil surface and have permafrost within 200 cm.

Gelic materials are mineral or organic soil materials that have evidence of cryoturbation (frost churning) and/or ice segeration in the active layer (seasonal thaw layer) and/or the upper part of the permafrost.

Gelisols are known to occur only in Alaska. Most of the soils have a layer of gelic materials that is underlain by permafrost. Permafrost influences pedogenesis through its effect on the downward movement of the soil solution and on the soil forming processes.

Dominant Suborders

Histels

Histels are the Gelisols with large amounts of organic carbon. They are in Alaska. The

vegetation is mostly mosses, sedges, and shrubs. The soils are used as wildlife habitat.

Orthels

Orthels are the Gelisols that show little or no evidence of cryoturbation. They occur throughout the Gelisol area in Alaska. The vegetation is mostly lichens, mosses, sedges, shrubs, black spruce, and white spruce. The soils are used mostly as wildlife habitat.

Turbels

Turbels are the Gelisols show cryoturbation in the form of irregular, broken, or distorted horizon boundaries, involutions, an accumulation of organic matter on top of the permafrost, ice or sand wedges, or oriented rock fragments. They occur throughout the Gelisol area in Alaska. The vegetation is mostly mosses, sedges, shrubs, and black spruce. The soils are used mostly as wildlife habitat. The Cryepts occur on slopes that receive more solar radiation or in areas where fire or land

clearing has changed the thermal properties of the soils enough to allow the permafrost to thaw.

Histosols

 

The central concept of Histosols is that of soils that are dominantly organic. They are mostly soils that are commonly called bogs, moors, or peats and mucks.

A soil is classified as Histosols if it does not have permafrost and is dominated by organic soil materials.

Histosols are forming in organic soil materials. The general rule is that a soil is classified as a Histosol if half or more of the upper 80 cm is organic.

Dominant Suborders

Fibrists

Fibrists are the wet, slightly decomposed Histosols. The largest extent is in southern Alaska. Most of the soils support natural vegetation of widely spaced, small trees, shrubs, forbs, and grasses and grass-like plants.

Folists

Folists are the more or less freely drained Histosols that consist primarily of horizons derived from leaf litter, twigs, and branches resting on bedrock or on fragmental materials. The largest extent is in Hawaii and Alaska. Some Folists developed in the mountains and the most humid parts of the conterminous United States. Most of these soils support forest vegetation. Some of the soils in Hawaii mainly support grass. A few of the soils in Hawaii are used for specialty crops or for urban or recreational development.

Hemists

Hemists are the wet Histosols in which the organic materials are moderately decomposed. The largest extent is in Minnesota and Alaska. Most Hemists support natural vegetation and are used as woodland, rangeland, or wildlife habitat. Some have been cleared and drained and are used as cropland.

Saprists

Saprists are the wet Histosols in which the organic materials are well decomposed. The largest extent is in Michigan, Florida, Wisconsin, Minnesota, and Alaska. Small areas are common on the Atlantic and gulf coasts. Many Saprists support natural vegetation and are used as woodland, rangeland, or wildlife habitat. Some of the soils, mostly those with a mesic or warmer temperature regime, have been cleared and drained and are used as cropland.

Spodosols

The central concept of Spodosols is that of soils in which amorphous mixtures of organic matter and aluminum, with or without iron, have accumulated. In undisturbed soils there is normally an overlying eluvial horizon, generally gray to light gray in color, that has the color of more or less uncoated quartz.

Most Spodosols have little silicate clay. The particle-size class is mostly sandy, sandy-skeletal, coarse-loamy, loamy, loamy- skeletal, or coarse-silty.

Spodosols a spodic horizon or spodic materials, both of which consist of accumulated amorphous mixtures of organic matter and aluminum, with or without iron. Spodosols are most extensive in areas of cool, humid or perhumid climates in the Northeastern States, southern Alaska, the Great Lakes States, and the high mountains of the Northwestern States. Spodosols are naturally infertile soils, but they can be highly responsive to good management.

Dominant Suborders

Aquods

Aquods are the wet Spodosols. They are characterized by a shallow fluctuating water table. They are in Florida and along the Atlantic coast. The vegetation is water-loving plants, ranging from moss, shrubs, and trees in cold areas to mixed forests and palms in the warmest areas. Most Aquods are used as forest or wildlife habitat. Some, mostly in Florida and New Jersey, have been cleared and are used as cropland or pasture. Aquods are naturally infertile, but they can be highly responsive to good management.

Cryods

Cryods are the cold Spodosols of high latitudes and/or high elevations. They are mostly in southern Alaska and in the mountains of Washington and Oregon. Some are in the high mountains of New York and northern New England. The vegetation is mostly coniferous forest. Most Cryods are used as forest or wildlife habitat.

Humods

Humods are the relatively freely drained Spodosols that have a large accumulation of organic carbon in the spodic horizon. They are mostly in Washington State, but a few are known to occur on tropical islands and in the Northeastern and Southeastern States. Most Humods formed under coniferous forest vegetation. These soils are used mainly as forest.

Orthods

Orthods are the relatively freely drained Spodosols that have a moderate accumulation of organic carbon in the spodic horizon. They are most extensive in the Northeastern United States and the Great Lakes States. Most Orthods are used as forest or have been cleared and are used as cropland or pasture. Orthods are naturally infertile, but they can be highly responsive to good management. The spodic horizon can be destroyed under cultivation, particularly if lime and nitrogen are applied.

Andisols

 

The central concept of Andisols is that of soils dominated by short-range-order minerals. They include weakly weathered soils with much volcanic glass as well as more strongly weathered soils. Hence the content of volcanic glass is one of the characteristics used in defining andic soil properties.

Materials with andic soil properties comprise 60 percent or more of the thickness between the mineral soil surface or the top of an organic layer with andic soil properties and a depth of 60 cm or a root limiting layer if shallower.

Andisols are dominated by short-range-order minerals or Al-humus complexes. Many Andisols developed in volcanic ejecta and/or in volcaniclastic materials.

Dominant Suborders

Aquands

Aquands, which have aquic conditions, occur mostly in western Washington and Oregon, in the lower landscape positions and under forest or grass vegetation. Some of the soils have been drained and are used as cropland or pasture.

Cryands

Cryands, which have a cryic temperature regime, dominate some areas in Alaska and in the mountains of the Pacific Northwest. Most of the soils formed under coniferous forest vegetation. Most Cryands are used as forest.

Torrands

Torrands, which have an aridic (or torric) moisture regime and a temperature regime warmer than cryic, are in very few areas in western Oregon and in Hawaii. Most of the soils formed under grassy or shrub vegetation. They are used as rangeland or as irrigated cropland.

Udands

Udands, which have a udic moisture regime, a temperature regime warmer than cryic, and a relatively high content of water held too tightly for plants to use, dominate mostly in western Washington and Oregon and in Hawaii. Most of the soils formed under forest vegetation. Udands are used mostly as forest, but some have been cleared and are used as cropland or pasture.

Ustands

Ustands, which have an ustic moisture regime, a temperature regime warmer than cryic, and a relatively high content of water held too tightly for plants to use, are of very small extent in the United States. They are mostly in Hawaii. They formed mostly under forest or savanna vegetation. Ustands are used mostly as forest, cropland, or pasture or for urban development.

Vitrands

Vitrands, which are the more or less well drained, coarse textured Andisols that have a udic or ustic moisture regime, a temperature regime warmer than cryic, and a low content of water held too tightly for plants to use, occur mostly in Idaho, Oregon, and Washington. Most of the soils formed under coniferous forest vegetation. They are used mostly as forest, but some are used as rangeland and some have been cleared and are used as cropland or pasture.

Xerands

Xerands, which have a xeric moisture regime and a frigid, mesic, or thermic temperature regime, are mostly in Washington, California, Oregon, and Idaho. Most

of the Xerands that have a frigid or mesic temperature regime formed under coniferous forest vegetation. Some Xerands, mostly those with a thermic temperature regime, formed under grass and shrub vegetation. They are used mostly as forest, but some have been cleared and are used as cropland or pasture.

Oxisols

The central concept of Oxisols is that of soils of the tropical and subtropical regions. They have gentle slopes on surfaces of great age. They are mixtures of quartz, kaolin, free oxides, and organic matter. For the most part they are nearly featureless soils without clearly marked horizons. Differences in properties with depth are so gradual that horizon boundaries are generally arbitrary.

Oxisols are only on tropical and subtropical islands. Most are infertile. The natural vegetation ranges from tropical rain forests to desert savannas.

Dominant Suborders

Aquox

Aquox are the wet Oxisols. They are rare in the United States and are known to occur only in Puerto Rico or in Hawaii. Curing many seed crops and storage of produce are difficult on these soils.

Torrox

Torrox are the Oxisols of arid regions. Torrox are very rare in the United States.

Udox

Udox are well drained Oxisols with a udic soil moisture regime. They are known to occur only in Hawaii, Puerto Rico, and Guam. They have a year-round growing season. The dry period is short enough for rainfed crops to be grown continuously in normal years.

Ustox

Ustox are the Oxisols that have an ustic moisture regime. They are known to occur only in Hawaii, Puerto Rico, and Guam. They are moist long enough for one rain-fed crop. Crops are not grown continuously on these soils because there is inadequate moisture for at least 90 days in normal years.

Vertisols

 

The central concept of Vertisols is that of soils that have a high content of expending clay and that have at some time of the year deep wide cracks. They shrink when drying and swell when they become wetter.

Vertisols are are clayey soils that have deep, wide cracks for some time during the year. They shrink as they dry and swell as they become moist. The natural vegetation is predominantly grass, savanna, open forest, or desert shrub. Most Vertisols are well suited to mechanized farming if there is plenty of rainfall or irrigation water. Vertisols are well known among engineers because their unique properties limit engineering uses.

Dominant Suborders

Aquerts

Aquerts are the wet Vertisols. They have aquic conditions at or near the soil surface for extended periods during the year but also are dry enough in normal years for cracks to open during some periods. These soils are mostly in Texas, the lower Mississippi River Valley, and the valley of the Red River of the North. The natural

vegetation is predominantly forest, grass, or savanna. These soils are used mostly as rangeland, cropland, or forest. Drainage of cropland presents special problems since the saturated hydraulic conductivity of these soils is very low.

Cryerts

Cryerts are not known to occur in the United States. They are the Vertisols that have a cryic temperature regime. They are cold, but they periodically shrink and swell, forming the diagnostic characteristics of Vertisols. Cracks commonly open once a year, late in summer.

Torrerts

Torrerts are the Vertisols of arid climates. They are in western Texas and in Arizona and New Mexico. The cracks in these soils commonly stay open for most of the year but close for at least part of the winter in normal years. The native vegetation is mostly grasses and forbs. These soils are used mainly as rangeland. The use of Torrerts as irrigated cropland presents special problems since the saturated hydraulic conductivity is very low. Bypass flow through open cracks is common. Because the permeability of these soils is so slow, irrigation may result in waterlogging and a buildup of salinity unless an adequate artificial drainage system can be installed.

Uderts

Uderts are the Vertisols of humid areas. They have cracks that open and close, depending on the amount of precipitation. In some years the cracks may not open completely. These soils are mostly in Texas, in the lower Mississippi River Valley, in the valley of the Red River of the North, and in Alabama and Mississippi. At one time many of these soils supported grass and widely spaced trees, although some supported hardwood forest vegetation. Uderts are used mostly as pasture, cropland, or forest. Because the saturated hydraulic conductivity of these soils is very low, a surface drainage system is commonly used to remove excess water from cropland. Rice is grown on some Uderts that have a thermic or warmer temperature regime.

Usterts

Usterts are mostly in Texas, South Dakota, and Montana. They receive low amounts of rainfall during the summer, and cracks open and close once or twice during normal years. The native vegetation is mostly grasses and forbs. Usterts are used mainly as rangeland or cropland. The use of Usterts as irrigated cropland presents special problems since the saturated hydraulic conductivity is very low. Bypass flow through open cracks is common. Because the permeability of these soils is so slow, irrigation

may result in waterlogging and a buildup of salinity unless an adequate artificial drainage system can be installed.

Xererts

Xererts are the Vertisols of Mediterranean climates, which are typified by cool, wet winters and warm, dry summers. Xererts are mostly in California, Oregon, and Idaho. They have cracks that regularly close and open each year. Because these soils become dry every summer and moisten in winter, damage to structures and roads is very significant. The native vegetation is mostly grasses and forbs. Xererts are used mainly as rangeland or cropland. Irrigated rice is grown on some Xererts that have a thermic temperature regime.

Aridisols

 

The central concept of Aridisols is that of soils that are too dry for mesophytic plants to grow. They have either:

(1) an aridic moisture regime and an ochric or anthropic epipedon and one or more of the following with an upper boundry within 100 cm of the soil surface: a calcic, cambic, gypsic, natric, petrocalcic petrogypsic, or a salic horizon or a duripan or an argillic horizon, or

(2)A salic horizon and saturation with water within 100 cm of the soil surface for one month or more in normal years.

An aridic moisture regime is one that in normal years has no water available for plants for more than half the cumulative time that the soil temperature at 50 cm below the surface is >5� C. and has no period as long as 90 consecutive days when there is water available for plants while the soil temperature at 50 cm is continuously >8� C.

Aridisols are in the Western States. For long periods, they are too dry for mesophytic plants to grow. The concept of Aridisols is based on the limited availability of soil

moisture for sustained plant growth.. The redistribution and accumulation of soluble materials in some layer of the soils are common.

Dominant Suborders

Argids

Argids have an argillic or natric horizon, but not a duripan or a gypsic, petrocalcic, petrogypsic, or salic horizon.. Most Argids are used as rangeland or wildlife habitat. Some are used as irrigated cropland.

Calcids

Calcids have a calcic or petrocalcic horizon and have calcium carbonate in the layers above. The parent materials are high in content of carbonates, or carbonates were added as dust, or both. Precipitation has been insufficient to remove the carbonates or even move them to great depths. These soils are in the Western States. Most are used as rangeland or wildlife habitat. Some are used as irrigated cropland.

Cambids

Cambids are characterized by the least degree of soil development. They are mostly in Washington State. Most are used as rangeland or wildlife habitat. Some are used as irrigated cropland.

Cryids

Cryids are the Aridisols of cold areas. They have a cryic temperature regime. The growing season is short. The short growing season and arid conditions severely limit the use of these soils. The soils are at high elevations in mountain valleys and basins in Idaho. Most of these soils are used as rangeland or wildlife habitat.

Durids

Durids are the Aridisols that have a duripan. They are in the Western States. The largest extent is in Nevada and Idaho. Most of the soils are used as rangeland or wildlife habitat. A few are used as irrigated cropland.

Gypsids

Gypsids are the Aridisols that have a gypsic or petrogypsic horizon. They are mostly in the Southwestern States. They are on many segments of the landscape. The gypsic

horizon limits many soil uses. A petrogypsic horizon is an even greater limitation. Most of these soils are used as rangeland or wildlife habitat.

Salids

Salids are the Aridisols that have a salic. They are commonly in depressions (playas). They are mostly in Utah and Nevada. As a rule, Salids are unsuitable for agricultural uses unless they are leached of salts. Leaching the salts is an expensive undertaking, particularly if there is no natural outlet for the drainage water. Most of these soils are used as rangeland or wildlife habitat.

Ultisols

 

The central concept of Ultisols is that of soils that have a horizon that contains an appreciable amount of translocated silicate clay (an argillic or kandic horizon) and few bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases with depth.

Ultisols an ochric epipedon and an argillic or kandic horizon that has few bases and commonly is calcium deficient. Most of these soils supported mixed coniferous and hardwood forest vegetation at the time of settlement. Some are now used as cropland or pasture.

Dominant Suborders

Aquults

Aquults are the Ultisols in wet areas where ground water is very close to the surface during part of each year, usually in winter and spring. They are on the coastal plains, particularly along the Atlantic Ocean and the Gulf of Mexico. Slopes are gentle. Most of the soils formerly supported forest vegetation. Many still support forest vegetation.

Humults

Humults are the more or less freely drained, humus-rich Ultisols. They are in Oregon and Washington and also occur in California and Puerto Rico. They commonly receive high rainfall but also have a moisture deficit during some season. The vegetation was mostly coniferous forest in the Northwest and rain forest in the tropics. Most of these soils are used as forest or have been cleared and are used as cropland or pasture.

Udults

Udults are the more or less freely drained, relatively humus poor Ultisols that have a udic moisture regime. They are in southern and eastern parts of the country. Most of these soils currently support or formerly supported mixed forest vegetation. Many have been cleared and are used as cropland, mostly with the use of soil amendments.

Ustults

Ustults are the more or less freely drained Ultisols that have an ustic soil moisture regime and have a relatively low content of organic carbon. They occur in the extreme western part of the Ultisol delineation in Texas. Some are in California and on tropical islands. The vegetation is commonly forest or savanna. Some of the soils have been cleared and are used as cropland or pasture.

Xerults

Xerults are the more or less freely drained Ultisols of Mediterranean climates. They are in California and Oregon. The vegetation formerly was and currently is mostly coniferous forest. Most of these soils are used as forest, but some have been cleared and are used as cropland or pasture.

Mollisols

 

The central concept of Mollisols is that of soils that have a dark colored surface horizon and are base rich. Nearly all have a mollic epipedon. Many also have an argillic or natric horizon or a calcic horizon. A few have an albic horizon. Some also have a duripan or a petrocalic horizon.

Mollisols on the Great Plains and in the Western States. Nearly all Mollisols have a mollic epipedon. Most have supported grass vegetation at some time, although many apparently have been forested at times. Mollisols are used mainly as cropland. Generally, grains and sorghum are grown in the drier regions and maize (corn) and soybeans in the warmer, humid regions.

Dominant Suborders

Albolls

Albolls are the Mollisols that have both an albic horizon and fluctuating ground water. They are mostly on the Great Plains, in eastern Washington, and in Oregon and Idaho. Most supported grass or grass and shrub vegetation. In early stages of development,

some are thought to have supported forest vegetation that was later succeeded by grass. Most of the soils have gentle slopes and are used as cropland.

Aquolls

Aquolls are the wet Mollisols. They are most extensive in glaciated areas of the Midwestern States, mainly Iowa, Minnesota, North Dakota, and Indiana. Most have supported vegetation of grasses, sedges, and forbs, but some supported forest vegetation. Most have been artificially drained, and are used as cropland.

Cryolls

Cryolls are the cool or cold, more or less freely drained Mollisols. Most are in the high mountains of the Western States. Some are in Alaska. They support forest, grass, or grass and shrub vegetation. In Alaska forests of spruce, birch, and aspen trees are common. Cryolls are used mostly as rangeland. Some are used as forest and some as pasture.

Rendolls

Rendolls are the Mollisols that are of humid regions and formed in highly calcareous parent materials, such as limestone, chalk, and drift composed mainly of limestone, or on shell bars. They are in Florida, on tropical islands, and in a few areas in the mountains of the Western States. They formed mostly under forest vegetation or under grass and shrubs. Most are used as cropland or pasture, but some are used as rangeland or forest.

Udolls

Udolls are the more or less freely drained Mollisols of humid climates. They are in the eastern part of the Great Plains and east of the Great Plains. They are most extensive in Minnesota, Illinois, Iowa, and North Dakota. The vegetation at the time of settlement was dominantly tall grass prairie. Where slopes are not too steep, nearly all of these soils are used as cropland. Some are used as pasture or rangeland.

Ustolls

Ustolls are the more or less freely drained Mollisols of subhumid to semiarid climates. They are mostly on the western Great Plains. They also are common throughout the Rocky Mountain States. Most of the Ustolls on the Great Plains supported grass vegetation when the country was settled. Some Ustolls, mostly those in the mountains of the Western States, supported forest vegetation. Rainfall comes mainly during a

growing season, often in heavy showers, but is erratic. Drought is frequent and may be severe. Without irrigation, the low supply of moisture usually limits crop yields. During a drought, soil blowing can be a problem. Most of these soils are used as cropland or rangeland.

Xerolls

Xerolls are the more or less freely drained Mollisols of regions that have Mediterranean climates. They are in the Pacific Northwest, California, Idaho, Nevada, and western Utah. Xerolls are dry for extended periods in summer, but moisture moves through most of the soils in winter and is stored above the deep layers or above bedrock in normal years. The vegetation at the time of settlement was dominantly bunchgrass and shrubs or trees in the areas that have a mesic or frigid temperature regime, a savanna of perennial grasses and oak and Douglas-fir in the Willamette Valley of Oregon, and a savanna of annual grasses and oak species on the Xerolls in California that have a thermic temperature regime. Many irrigated crops are grown on the Xerolls in the United States, especially where the temperature regime is thermic or mesic. Most of the soils that have gentle or moderate slopes are used as cropland. The very steep soils are used mainly as rangeland, but some are used as forest.

Alfisols

 

The central concept of Alfisols is that of soils that have an argillic, a kandic, or a natric horizon and a base saturation of 35% or greater. They typically have an ochric epipedon, but may have an umbric epipedon. They may also have a petrocalcic horizon, a fragipan or a duripan.

Alfisols are extensive in the United States. They make up about 13.9 percent of the surface area. In normal years water they are dry when the soils are warm enough for plants to grow.

Dominant Suborders

Aqualfs

Aqualfs, which have warm and aquic conditions, primarily are found in an area bordering the southern part of the Mississippi River, in southern Illinois, and in Indiana and Ohio. Most Aqualfs have some artificial drainage or other water control and are used as cropland for corn, soybeans, and rice. Nearly all Aqualfs are believed to have supported forest vegetation in the past.

Cryalfs

Cryalfs, which are the cold Alfisols, occur mostly at high elevations, mainly in the Rocky Mountains in the Western United States. Most of the Cryalfs in the United States are used as forest because of their short, cool growing season.

Udalfs

Udalfs, which have a udic moisture regime, are of large extent in the United States. They form a belt extending from Minnesota through Wisconsin, Michigan, Indiana, and Ohio and ending in New York State. Another large area of Udalfs begins in southern Iowa and extends through Missouri, Illinois, and the States to the south bordering the Mississippi River. All Udalfs are believed to have supported forest vegetation at some time during development.

Ustalfs

Ustalfs, which have an ustic soil moisture regime, occur on the southern Great Plains, mostly in Texas and Oklahoma. They also occur throughout the Rocky Mountain States from Montana to Arizona and New Mexico and in the Black Hills of South Dakota. The dry season is pronounced. Many Ustalfs support savanna vegetation, and some supported grassland vegetation. Most are used as cropland or grazing land.

Xeralfs

Xeralfs, which have a xeric soil moisture regime, are mostly in California, but small areas are in Oregon, Washington, Idaho, and Utah. The natural vegetation was a mixture of annual grasses, forbs, and woody shrubs on the warmest and driest Xeralfs and coniferous forest on the coolest and most moist Xeralfs. Xeralfs are used mostly as cropland, forest, or grazing land. Small grains, mostly winter wheat, are the most common crops..

Inceptisols

 

The central concept of Inceptisols is that of soils of humid and subhumid regions that have altered horizons that have lost bases or iron and aluminum but retain some weatherable minerals. They do not have an illuvial horizon enriched with either silicate clay or with an amorphous mixture of aluminum and organic carbon.

The Inceptisols may have many kinds of diagnostic horizons, but argillic, natric kandic, spodic and oxic horizons are excluded.

Inceptisols are soils of cool to very warm, humid and subhumid regions. The largest area is one that includes the southern New England States and the Appalachian Mountains. Other areas are on the southern Great Plains; in the Rocky Mountains; in eastern Montana; in the coastal and Cascade Mountains of California, Oregon, and Washington; and in northeastern Minnesota. Inceptisols have many kinds of diagnostic horizons and epipedons.

Dominant Suborders

Anthrepts

Anthrepts are the more or less freely drained Inceptisols that have either an anthropic or plaggen epipedon. These soils are not known to occur in the United States.

Aquepts

Aquepts are the wet Inceptisols. Their natural drainage is poor or very poor, and, if the soils have not been artificially drained, ground water is at or near the soil surface at some time during normal years but typically not in all seasons. Many formed under forest vegetation, but they can have almost any kind of vegetation. Aquepts are used mostly as cropland, pasture, forest, or wildlife habitat.

Cryepts

Cryepts are the cold Inceptisols of high mountains or high latitudes. They are mostly in the high mountains of the West as well as southern Alaska. The vegetation is mostly conifers or mixed conifers and hardwoods. Most are used as forest or wildlife habitat. Some of the soils, mostly those in Alaska, are used as cropland.

Udepts

Udepts are mainly freely drained Inceptisols that have a udic or perudic moisture regime. They are most extensive in the Appalachian Mountains, on the Allegheny Plateau, in northeastern Minnesota, and in Oregon. Most of the soils currently support or formerly supported forest vegetation, but some support shrub or grass vegetation. The vegetation was mostly coniferous forest in the Northwest and mixed or hardwood forest in the Eastern States. Most are used as forest or have been cleared and are used as cropland or pasture.

Ustepts

Ustepts are freely drained Inceptisols that have an ustic moisture regime. They are most common on the Great Plains, mostly in Montana, Texas, and Oklahoma. The native vegetation commonly was grass, but some of the soils supported trees. Most Ustepts are used as cropland or pasture. Some are used as rangeland, forest, or wildlife habitat.

Xerepts

Xerepts are mainly freely drained Inceptisols that have a xeric moisture regime. They are in the western part of the United States, mostly in California, Oregon, and Washington. The native vegetation commonly was coniferous forest on the soils with a frigid or mesic temperature regime and shrubs, grasses, and widely spaced trees on

the soils with a thermic temperature regime. Most Xerepts are used as forest, cropland, or pasture. Some are used as rangeland or wildlife habitat.

Entisols

 

The central concept of Entisols is that of soils that have little or no evidence of development of pedogenic horizons. Many Entisols have an ochric epipedon and a few have an anthropic epipedon. Many are sandy or very shallow.

Entisols have no diagnostic horizons. Some Entisols have steep, actively eroding slopes, and others are on flood plains or glacial outwash plains that receive new deposits of alluvium at frequent intervals.

Dominant Suborders

Aquents

Aquents, or the wet Entisols, are widely distributed. They dominate some of the delineations along the southern Atlantic and gulf coasts and on the flood plains along the Mississippi River and along other rivers and streams. Some Aquents are forming, mostly in sandy deposits, in other parts of the country. Most of the soils are forming in recent sediments. They support vegetation that tolerates permanent or periodic wetness. They are used mostly as pasture, cropland, forest, or wildlife habitat.

Arents

Arents do not have diagnostic horizons because they have been deeply mixed by plowing, spading, or other methods of moving by humans. They are important soils for irrigated crop production in California. Small areas also occur throughout the country. Arents are used mostly as cropland, urban land, or pasture. Some are used as wildlife habitat.

Fluvents

Fluvents are the more or less freely drained Entisols that formed in recent water-deposited sediments on flood plains, fans, and deltas along rivers and small streams throughout the country. Some of the largest areas are on the flood plains along the Mississippi River. Most Fluvents are frequently flooded, unless they are protected by dams or levees. Stratification of the materials is normal. Most Fluvents are used as rangeland, forest, pasture, or wildlife habitat. Some are used as cropland.

Orthents

Orthents are mainly in the Western States. They are commonly on recent erosional surfaces. Orthents are used mostly as rangeland, pasture, or wildlife habitat.

Psamments

Psamments occur throughout the country. Some of the largest areas are in Nebraska, California, Minnesota, Wisconsin, Michigan, Arizona, and Florida. These soils are sandy in all layers. They are among the most productive rangeland soils in some arid and semiarid climates. Some Psamments that are nearly bare are subject to soil blowing and drifting and provide poor support for wheeled vehicles. Psamments are used mostly as rangeland, pasture, or wildlife habitat.