The National Cooperative Soil Survey identifies and maps over 20,000 different kinds of soil in the United States. Most soils are given a name, which generally comes from the locale where the soil was first mapped. Named soils are referred to as soil series.
Soil survey reports include the soil survey maps and the names and descriptions of the soils in a report area. These soil survey reports are published by the National Cooperative Soil Survey and are available to everyone.
Soils are named and classified on the basis of physical and chemical properties in their horizons (layers). "Soil Taxonomy" uses color, texture, structure, and other properties of the surface two meters to key the soil into a classification system to help people use soil information. This system also provides a common language for scientists.
Soils and their horizons differ from one another, depending on how and when they formed. Soil scientists use five soil factors to explain how soils form and to help them predict where different soils may occur. The scientists also allow for additions and removal of soil material and for activities and changes within the soil that continue each day.
Parent material. Few soils weather directly from the underlying rocks. These "residual" soils have the same general chemistry as the original rocks. More commonly, soils form in materials that have moved in from elsewhere. Materials may have moved many miles or only a few feet. Windblown "loess" is common in the Midwest. It buries "glacial till" in many areas. Glacial till is material ground up and moved by a glacier. The material in which soils form is called "parent material." In the lower part of the soils, these materials may be relatively unchanged from when they were deposited by moving water, ice, or wind.
Sediments along rivers have different textures, depending on whether the stream moves quickly or slowly. Fast-moving water leaves gravel, rocks, and sand. Slow-moving water and lakes leave fine textured material (clay and silt) when sediments in the water settle out.
Climate. Soils vary, depending on the climate. Temperature and moisture amounts cause different patterns of weathering and leaching. Wind redistributes sand and other particles especially in arid regions. The amount, intensity, timing, and kind of precipitation influence soil formation. Seasonal and daily changes in temperature affect moisture effectiveness, biological activity, rates of chemical reactions, and kinds of vegetation.
Topography. Slope and aspect affect the moisture and temperature of soil. Steep slopes facing the sun are warmer, just like the south-facing side of a house. Steep soils may be eroded and lose their topsoil as they form. Thus, they may be thinner than the more nearly level soils that receive deposits from areas upslope. Deeper, darker colored soils may be expected on the bottom land.
Biological factors. Plants, animals, micro-organisms, and humans affect soil formation. Animals and micro-organisms mix soils and form burrows and pores. Plant roots open channels in the soils. Different types of roots have different effects on soils. Grass roots are "fibrous" near the soil surface and easily decompose, adding organic matter. Taproots open pathways through dense layers. Micro-organisms affect chemical exchanges between roots and soil. Humans can mix the soil so extensively that the soil material is again considered parent material.
The native vegetation depends on climate, topography, and biological factors plus many soil factors such as soil density, depth, chemistry, temperature, and moisture. Leaves from plants fall to the surface and decompose on the soil. Organisms decompose these leaves and mix them with the upper part of the soil. Trees and shrubs have large roots that may grow to considerable depths.
Time. Time for all these factors to interact with the soil is also a factor. Over time, soils exhibit features that reflect the other forming factors. Soil formation processes are continuous. Recently deposited material, such as the deposition from a flood, exhibits no features from soil development activities. The previous soil surface and underlying horizons become buried. The time clock resets for these soils. Terraces above the active floodplain, while genetically similar to the floodplain, are older land surfaces and exhibit more development features.
The soil forming factors continue to affect soils even on "stable" landscapes. Materials are deposited on their surface, and materials are blown or washed away from the surface. Additions, removals, and alterations are slow or rapid, depending on climate, landscape position, and biological activity.
When mapping soils, a soil scientist looks for areas with similar soil-forming factors to find similar soils. The colors, texture, structure, and other properties are described. Soils with the same kind of properties are given taxonomic names. A common soil in the Midwest reflects the temperate, humid climate and native prairie vegetation with a thick, nearly black surface layer. This layer is high in organic matter from decomposing grass. It is called a "mollic epipedon." It is one of several types of surface horizons that we call "epipedons." Soils in the desert commonly have an "ochric" epipedon that is light colored and low in organic matter. Subsurface horizons also are used in soil classification. Many forested areas have a subsurface horizon with an accumulation of clay called an "argillic" horizon.
Soil taxonomy at the highest hierarchical level identifies 12 soil orders. The names for the orders and taxonomic soil properties relate to Greek, Latin, or other root words that reveal something about the soil. Sixty-four suborders are recognized at the next level of classification. There are about 300 great groups and more than 2,400 subgroups. Soils within a subgroup that have similar physical and chemical properties that affect their responses to management and manipulation are families. The soil series is the lowest category in the soil classification system.
| Soil Order | Formative Terms | Pronunciation |
|---|---|---|
| Alfisols | Alf, meaningless syllable | Pedalfer |
| Andisols | Modified from ando | Ando |
| Aridisols | Latin, aridies, dry | Arid |
| Entisols | Ent, meaningless | Recent |
| Gelisols | Latin gelare, to freeze | Jell |
| Histosols | Greek, histos, tissue | Histology |
| Inceptisols | Latin, incepum, beginning | Inception |
| Mollisols | Latin, mollis, soft | Mollify |
| Oxisols | French oxide | Oxide |
| Spodosols | Greek spodos, wood ash | Odd |
| Ultisols | Latin ultimus, last | Ultimate |
| Vertisols | Latin verto, turn | Invert |
Maps
The distribution of these soil orders in the United States corresponds with the general patterns of the soil forming factors across the country. A map of soil orders is useful in understanding broad areas of soils. Detailed soil maps found in soil survey reports, however, should be used for local decision making. Soil maps are like road maps, for very general overview, a small scale map in an atlas is helpful, but for finding a location of a house in a city, a large scale detailed map should be used.
More detailed information on soil orders is available in "Soil Taxonomy" pp. 837-850, Chapter 22.
Formative Elements in Names of Soil Suborders
Formative Element |
Derivation |
Sounds Like |
Connotation |
| Alb | L, albus, white | Albino | Presence of albic horizon |
| Anthr | Modified from Gr. anthropes, human | Anthropology | Modified by humans |
| Aqu | L. aqua, water | Aquifer | Aquic conditions |
| Ar | L. Arare, to plow | Arable | Mixed horizons |
| Arg | Modified from argillic horizon; L. argilla, white clay | Argillite | Presence of argillic horizon |
| Calc | L. calcis, lime | Calcium | Presence of a calcic horizons |
| Camb | L. cambiare, to exchange | Am | Presence of a cambic horizon |
| Cry | G. kryos, icy cold | Cry | Cold |
| Dur | L. durus, hard | Durable | Presence of a duripan |
| Fibr | L. fibra, fiber | Fibrous | Least decomposed stage |
| Fluv | L. fluvius, river | Fluvial | Flood plain |
| Fol | L. folia, leaf | Foliage | Mass of leaves |
| Gyps | L. gypsum, gypsum | Gypsum | Presence of a gypsic horizon |
| Hem | Gr hemi, half | Hemisphere | Intermediate stage of decomposition |
| Hist | Gr. histos, tissue | Histology | Presence of organic materials |
| Hum | L. humus, earth | Humus | Presence of organic matter |
| Orth | Gr. orthos, true | Orthodox | The common ones |
| Per | L. Per, throughout in time | Perennial | Perudic moisture regime |
| Psamm | Gr. psammos, sand | Sam | Sandy texture |
| Rend | Modified from Rendzina | End | High carbonate content |
| Sal | L. base of sal, salt | Saline | Presence of a salic horizon |
| Sapr | Gr. sapros, rotten | Sap | Most decomposed stage |
| Torr | L. torridus, hot and dry | Or | Torric moisture regime |
| Turb | L. Turbidis, disturbed | Turbulent | Presence of cryoturbation |
| Ud | L. udus, Humid | You | Udic moisture regime |
| Vitr | L. vitrum, glass | It | Presence of glass |
| Ust | L. ustus, burnt | Combustion | Ustic moisture regime |
| Xer | Gr. xeros, dry | Zero | Xeric moisture regime |
Formative Elements in Names of Soil Great Groups
Formative Element |
Derivation |
Sounds Like |
Connotation |
|---|---|---|---|
| Acr | Modified from Gr. Akros, at the end | Act | Extreme weathering |
| Al | Modified from aluminum | Algebra | High aluminum, low iron |
| Alb | L. Albus, white | Albino | An albic horizon |
| Anhy | Gr. anydros, waterless | Anhydrous | Very dry |
| Anthr | Modified from Gr. anthropos, human | Anthropology | An anthropic epipedon |
| Aqu | L. aqua, water | Aquifer | Aquic conditions |
| Argi | Modified from argillic horizon; L. argilla, white clay | Argillite | Presence of an argillic horizon |
| Calci, calc | L. calcis,lime | Calcium | A calcic horizon |
| Cry | Gr. kryos, icy cold | Cry | Cold |
| Dur | L. durus, hard | Durable | A duripan |
| Dystr, dys | Modified from Gr. dys, ill; dystrophic infertile | Distant | Low base saturation |
| Endo | Gr. endon, endo, within | Endothermic | Implying a ground water table |
| Epi | Gr. epi, on, above | Epidermis | Implying a perched water table |
| Eutr | Modified from Gr. eu, good; euthrophic, fertile | You | High base saturation |
| Ferr | L. ferrum, iron | Fair | Presence of iron |
| Fibr | L. fibra, fiber | Fibrous | Least decomposed stage |
| Fluv | L. fluvius, river | Fluvial | Flood plain |
| Fol | L. folia, leaf | Foliage | Mass of leaves |
| Fragi | Modified from L. fragilis, brittle | Fragile | Presence of fragipan |
| Fragloss | Compound of fra (g) and gloss | See the formative elements "frag" and "gloss" | |
| Fulv | L. fulvus, dull brownish yellow | Full | Dark brown color, presence of organic carbon |
| Glac | L. glacialis, icy | Glacier | Ice lenses or wedges |
| Gyps | L. gypsum, gypsum | Gypsum | Presence of gypsic horizon |
| Gloss | Gr. glossa, tongue | Glossary | Presence of a glossic horizon |
| Hal | Gr. hals, salt | Halibut | Salty |
| Hapl | Gr. haplous, simple | Haploid | Minimum horizon development |
| Hem | G. hemi, half | Hemisphere | Intermediate stage of decomposition |
| Hist | Gr. histos, tissue | History | Presence of organic materials |
| Hum | L. humus, earth | Humus | Presence of organic matter |
| Hydr | Gr. hydo, water | Hydrophobia | Presence of water |
| Kand, kan | Modified from kandite | Can | 1:1 layer silicate clays |
| Luv | Gr. louo, to wash | Ablution | Illuvial |
| Melan | Gr. melasanos, black | Me + Land | Black, presence of organic carbon |
| Moll | L. mollis, soft | Mollusk | Presence of a mollic epipedon |
| Natr | Modified from natrium, sodium | Date | Presence of natric horizon |
| Pale | Gr. paleos, old | Paleontology | Excessive development |
| Petr | Gr. comb. form of petra, rock | Petrified | A cemented horizon |
| Plac | Gr. base of plax, flat stone | Placard | Presence of thin pan |
| Plagg | Modified from Ger. plaggen, sod | Awe | Presence of plaggen epipedon |
| Plinth | Gr. plinthos, brick | In | Presence of plinthite |
| Psamm | Gr. psammos, sand | Sam | Sandy texture |
| Quartz | Ger. quarz, quartz | Quarter | High quartz content |
| Rhod | Gr. base of rhodon, rose | Rhododendron | Dark red color |
| Sal | L. base of sal, salt | Saline | Presence of salic horizon |
| Sapr | Gr. saprose, rotten | Sap | Most decomposed stage |
| Somb | F. sombre, dark | Somber | Presence of sombric horizon |
| Sphagn | Gr. sphagnos, bog | Sphagnum | Presence of Sphagnum |
| Sulf | L. sulfur, sulfur | Sulfur | Presence of sulfides or their oxidation products |
| Torr | L. torridus, hot and dry | Torrid | Torric moisture regime |
| Ud | L. udus, humid | You | Udic moisture regime |
| Umbr | L. umbra, shade | Umbrella | Presence of umbric epipedon |
| Ust | L. ustus,burnt | Combustion | Ustic moisture regime |
| Verm | L. base of vermes, worm | Vermilion | Wormy, or mixed by animals |
| Vitr | L. vitrum, glass | It | Presence of glass |
| Xer | Gr. xeros, dry | Zero | Xeric moisture regime |