Soil
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Soil".

Loess field in Germany
Loess field in Germany
Surface-water-gley developed in glacial till, Northern Ireland
Surface-water-gley developed in glacial till, Northern Ireland
For other uses, see Soil (disambiguation).

Soil is the naturally occurring, unconsolidated or loose covering of broken rock particles and decaying organic matter (humus) on the surface of the Earth, capable of supporting life.[1] In simple terms, soil has three components: solid, liquid, and gas. The solid phase is a mixture of mineral and organic matter. Soil particles pack loosely, forming a soil structure filled with voids.[2] The solid phase occupies about half of the soil volume. The remaining void space contains water (liquid) and air (gas).[3] Soil is also known as earth: it is the substance from which our planet takes its name.

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Characteristics

Darkened topsoil and reddish subsoil layers are typical in some regions.
Darkened topsoil and reddish subsoil layers are typical in some regions.

Soil color is the first impression one has when viewing soil. Striking colors and contrasting patterns are especially memorable. The Red River in Louisiana carries sediment eroded from extensive reddish soils like Port Silt Loam in Oklahoma.

Soil color results from chemical and biological weathering. As the primary minerals in parent material weather, the elements combine into new and colorful compounds. Iron forms secondary minerals with a yellow or red color; organic matter decomposes into brown compounds; and manganese, sulfur and nitrogen can form black mineral deposits. [4]

Soil structure is the arrangement of soil particles into aggregates. These may have various shapes, sizes and degrees of development or expression.[5]

Soil texture refers to sand, silt and clay composition. Sand and silt are the product of physical weathering while clay is the product of chemical weathering. Clay content is particularly influential on soil behavior due to a high retention capacity for nutrients and water.[6]

Formation

Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological, and anthropogenic processes on soil parent material resulting in the formation of soil horizons. Soil is always changing. The long periods over which change occurs and the multiple influences of change mean that simple soils are rare. While soil can achieve relative stability in properties for extended periods of time, the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion. Little of the soil continuum of the earth is older than Tertiary and most no older than Pleistocene.[7] Despite the inevitability of soils retrogression and degradation, most soil cycles are long and productive. How the soil "life" cycle proceeds is influenced by at least five classic soil forming factors: regional climate, biotic potential, topography, parent material, and the passage of time.

An example of soil development from bare rock occurs on recent lava flows in warm regions under heavy and very frequent rainfall. In such climates plants become established very quickly on basaltic lava, even though there is very little organic material. The plants are supported by the porous rock becoming filled with nutrient bearing water, for example carrying dissolved bird droppings or guano. The developing plant roots themselves gradually breaks up the porous lava and organic matter soon accumulates but, even before it does, the predominantly porous broken lava in which the plant roots grow can be considered a soil.

In nature

Geologists have a particular interest in the patterns of soil on the surface of the earth. Soil texture, color and chemistry often reflect the underlying geologic parent material and soil types often change at geologic unit boundaries. Buried paleosols mark previous land surfaces and record climatic conditions from previous eras. Geologists use this paleopedological record to understand the ecological relationships in past ecosystems. According to the theory of biorhexistasy, prolonged conditions conducive to forming deep, weathered soils result in increasing ocean salinity and the formation of limestone.

Geologists use soil profile features to establish the duration of surface stability in the context of geologic faults or slope stability. An offset subsoil horizon indicates rupture during soil formation and the degree of subsequent subsoil formation is relied upon to establish time since rupture.

Soil examined in shovel test pits is used by archaeologists for relative dating based on stratigraphy (as opposed to absolute dating). What is considered most typical is to use soil profile features to determine the maximum reasonable pit depth than needs to be examined for archaeological evidence in the interest of cultural resources management.

Soils altered or formed by man (anthropic and anthropogenic soils) are also of interest to archaeologists. An example is Terra preta do Indio.

Uses

 Please help improve this section by expanding it
with: examples of uses of soil as a material and uses involving soil as a natural resource.
Further information might be found on the talk page or at requests for expansion.
A homeowner tests soil to apply only the nutrients needed.
A homeowner tests soil to apply only the nutrients needed.
Due to their thermal mass, rammed earth walls fit in with environmental sustainability aspirations.
Due to their thermal mass, rammed earth walls fit in with environmental sustainability aspirations.
A homeowner sifts soil made from his compost bin in background. Composting is an excellent way to recycle household and yard wastes.
A homeowner sifts soil made from his compost bin in background. Composting is an excellent way to recycle household and yard wastes.

Soil material is a critical component in the mining and construction industries. Soil serves as a foundation for most construction projects. Massive volumes of soil can be involved in surface mining, road building, and dam construction. Earth sheltering is the architectural practice of using soil for external thermal mass against building walls.

Soil resources are critical to the environment, as well as to food and fiber production. Soil provides minerals and water to plants. Soil absorbs rainwater and releases it later thus preventing floods and drought. Soil cleans the water as it percolates. Soil is the habitat for many organisms.

Waste management often has a soil component. Septic drain fields treat septic tank effluent uses aerobic soil processes. Landfills use soil for daily cover.

Organic soils, especially peat, serve as a significant fuel resource.

Both humans in many cultures and animals occasionally eat soil.

See also

Wikiquote has a collection of quotations related to:
Wikimedia Commons has media related to:

References

  1. ^ Voroney, R. P., 2006. The Soil Habitat in Soil Microbiology, Ecology and Biochemistry, Eldor A. Paul ed. ISBN=0125468075
  2. ^ James A. Danoff-Burg, Columbia University The Terrestrial Influence: Geology and Soils
  3. ^ Taylor, S. A., and G. L. Ashcroft. 1972. Physical Edaphology
  4. ^ The Color of Soil. United States Department of Agriculture - Natural Resources Conservation Service. Retrieved on 2007-11-25.
  5. ^ Soil Survey Division Staff (1993). Soil Structure. Handbook 18. Soil survey manual. Retrieved on 2006-04-11.
  6. ^ R. B. Brown (September 2003). Soil Texture. Fact Sheet SL-29. University of Florida, Institute of Food and Agricultural Sciences. Retrieved on 2007-12-02.
  7. ^ Buol, S. W.; Hole, F. D. and McCracken, R. J. (1973). Soil Genesis and Classification, First, Ames, IA: Iowa State University Press. ISBN 0-8138-1460-X. .

Further reading

  • Adams, J.A. 1986. Dirt. College Station, Texas : Texas A&M University Press ISBN 0890963010
  • Soil Survey Staff. (1975) Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. USDA-SCS Agric. Handb. 436. U.S. Gov. Print. Office. Washington, DC.
  • Soil Survey Division Staff. (1999) Soil survey manual. Soil Conservation Service. U.S. Department of Agriculture Handbook 18.
  • Logan, W. B., Dirt: The ecstatic skin of the earth. 1995 ISBN 1-57322-004-3
  • Faulkner, William. Plowman's Folly. New York, Grosset & Dunlap. 1943. ISBN 0-933280-51-3
  • Jenny, Hans, Factors of Soil Formation: A System of Quantitative Pedology 1941
  • Why Study Soils?
  • Soil notes
  • 97 Flood. USGS. Retrieved on 2006-05-31. Photographs of sand boils.
  • Oregon State University's Soils (wiki)
  • Soil-Net.com A free schools-age educational site teaching about soil and its importance.
  • LandIS Soils Data for England and Wales a pay source for GIS data on the soils of England and Wales and soils data source; they charge a handling fee to researchers.
  • LandIS Free Soilscapes Viewer Free interactive viewer for the Soils of England and Wales
  • Geo-technological Research Paper, IIT Kanpur, Dr P P Vitkar - Strip footing on weak clay stabilized with a granular pile http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cgj_t78-066_15_ns_nf_cgj4-78

External links
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