A duripan is a diagnostic

soil horizon A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...

of the USDA soil taxonomy that is cemented by illuvial

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

into a subsurface

hardpan In soil science, agriculture and gardening, hardpan or soil pan is 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 ...

. Similar to a fragipan, Petrocalcic Horizon and petrogypsic horizon, it is firmly cemented and restricts

soil management Soil management is the application of operations, practices, and treatments to protect soil and enhance its performance (such as soil fertility or soil mechanics). It includes soil conservation, soil amendment, and optimal soil health. In agricult ...

. In soil descriptions, they are most often denoted by the symbol Bqm. The closest equivalent in the Canadian system of soil classification is called a duric horizon, although it does not mean exactly the same thing as a duripan in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. They form almost exclusively in arid or

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

s, and can be as hard as

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...

, which makes

plowing A plough or plow ( US; both ) is a farm tool for loosening or turning the soil before sowing seed or planting. Ploughs were traditionally drawn by oxen and horses, but in modern farms are drawn by tractors. A plough may have a wooden, iron or ...

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 (ST) developed by the United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters (most commonly their properties) and in sev ...

, Tenth Edition, 2006" are: # The pan is cemented or indurated in more than 50 percent of the volume of some horizon; ''and'' # 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'' # 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'' # 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: # More than half the horizon is made up of cemented materials. # There is evidence that the horizon was actually formed by movement of silica into the subsoil. # The purpose of the water, HCl, and KOH tests is to separate a duripan from a Petrocalcic Horizon or fragipan. These tests are seldom conducted in a field environment and usually are performed in a lab with prepared field samples. # 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

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...

s. The

parent material Parent material is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are ...

of duripan soils usually does not contain a large amount of calcium carbonate, and if there is an abundance of calcium, a Petrocalcic 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.

References

* https://web.archive.org/web/20070610013420/https://www.soils.org/sssagloss/?check - Soil Science Society of America ''Soil Terms Glossary'' * Soil Survey staff. 1999. ''Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys''. 2nd Edition. USDA-NRCS. Washington D.C. * Soil Survey staff. 2006. ''Keys to Soil Taxonomy'', Tenth Edition. USDA-NRCS. Washington, DC. Available online at: http://soils.usda.gov/technical/classification/tax_keys/ * Research Branch, Canada Department of Agriculture. 1977. ''Soils of Canada'', First Edition. Ministry of supply and services. Ottawa, Ontario, Canada. Pedology

Characteristics

Genesis

See also

References