Duripan
Encyclopedia
A duripan is a diagnostic soil horizon
Soil horizon
A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...

 of the USDA soil taxonomy that is cemented by illuvial silica into a subsurface hardpan
Hardpan
In soil science, agriculture and gardening, hardpan or ouklip is a general term for a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water...

. Similar to a fragipan
Fragipan
A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations...

, petrocalcic horizon
Petrocalcic Horizon
A petrocalcic horizon is a diagnostic horizon in USDA soil taxonomy. They are formed when secondary Calcium Carbonate or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan. Petrocalcic horizons are similar to a duripan and a petrogypsic horizon...

 and petrogypsic horizon, it is firmly cemented and restricts soil management. In soil descriptions, they are most often denoted by the symbol Bqm. The closest equivalent in the Canadian system of soil classification
Canadian system of soil classification
The Canadian system of soil classification is more closely related to the American system than any other. They differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with a sub-order hierarchical level. Solonetzic and Gleysolic soils are...

 is called a duric horizon, although it does not mean exactly the same thing as a duripan in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. They form almost exclusively in arid or Mediterranean climate
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...

s, and can be as hard as concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, which makes plowing very difficult or impossible. Soils that include duripans are generally used for grazing or wildlife habitat, and are seldom cultivated.

Characteristics

The required characteristics for a duripan, according to the "Keys to USDA soil taxonomy
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...

, Tenth Edition, 2006" are:
  1. The pan is cemented or indurated in more than 50 percent of the volume of some horizon; and
  2. The pan shows evidence of accumulation of opal or other forms of silica, such as laminar caps, coatings, lenses, partly filled interstices, bridges between sand-sized grains, or coatings on rock or pararock fragments; and
  3. Less than fifty percent of the volume of air-dry fragments slakes in 1 N HCl even during prolonged soaking, but more than 50 percent slakes in concentrated KOH or NaOH or in alternating acid and alkali; and
  4. Because of lateral continuity, roots can penetrate the pan only along vertical fractures with a horizontal spacing of 10 cm or more.


What this means in plain English is:
  1. More than half the horizon is made up of cemented materials.
  2. There is evidence that the horizon was actually formed by movement of silica into the subsoil.
  3. The purpose of the water, HCl, and KOH tests is to separate a duripan from a Petrocalcic Horizon
    Petrocalcic Horizon
    A petrocalcic horizon is a diagnostic horizon in USDA soil taxonomy. They are formed when secondary Calcium Carbonate or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan. Petrocalcic horizons are similar to a duripan and a petrogypsic horizon...

     or fragipan
    Fragipan
    A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations...

    . These tests are seldom conducted in a field environment and usually are performed in a lab with prepared field samples.
  4. The main purpose of describing a duripan is to denote limitations for land management. If plant roots are able to penetrate the duripan then there is no significant limitation and there would be little point in describing a duripan.

Genesis

Duripans occur mostly in arid or semiarid climates, where the soil is usually dry or seasonally dry. Soils with duripans are often geographically associated with areas of volcanic activity, and show evidence of ash or volcanic glass deposition. Volcanic glass weathers rapidly, providing an ample supply of soluble silica to cement the underlying soil. Other common sources of the silica cementing agent are Iron-Magnesium minerals and feldspars. The parent material
Parent material
In soil science, parent material is the underlying geological material in which soil horizons form...

 of duripan soils usually does not contain a large amount of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

, and if there is an abundance of calcium, a Petrocalcic Horizon
Petrocalcic Horizon
A petrocalcic horizon is a diagnostic horizon in USDA soil taxonomy. They are formed when secondary Calcium Carbonate or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan. Petrocalcic horizons are similar to a duripan and a petrogypsic horizon...

 can form in conjunction with the duripan. The weathered silica is mostly transported by water into the subsoil, where it precipitates and forms microaggregates that gradually grow into a full-fledged duripan. It cannot be considered a duripan until the cracks and gaps that allow roots to penetrate are 10 cm or more apart. A duripan can sometimes be broken up by earthquakes or periods of alternate wetting and drying that cause small volume changes.

See also

  • USDA soil taxonomy
    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...

  • Petrocalcic Horizon
    Petrocalcic Horizon
    A petrocalcic horizon is a diagnostic horizon in USDA soil taxonomy. They are formed when secondary Calcium Carbonate or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan. Petrocalcic horizons are similar to a duripan and a petrogypsic horizon...

  • Fragipan
    Fragipan
    A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations...

  • Petrogypsic horizon
  • Canadian system of soil classification
    Canadian system of soil classification
    The Canadian system of soil classification is more closely related to the American system than any other. They differ in several ways. The Canadian system is designed to cover only Canadian soils. The Canadian system dispenses with a sub-order hierarchical level. Solonetzic and Gleysolic soils are...

  • Hardpan
    Hardpan
    In soil science, agriculture and gardening, hardpan or ouklip is a general term for a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water...



More information on soils in specific areas of the United States can be found on Web Soil Survey at: http://websoilsurvey.nrcs.usda.gov/app/
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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