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The Twelve Soil Orders

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Department of Soil and Water Systems

University of Idaho

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Rm 242
606 S Rayburn St

Mailing Address:
875 Perimeter Drive MS 2340
Moscow, ID 83844-2340

Email: rheinse@uidaho.edu

Web: uidaho.edu/cals/sws

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College of Agricultural & Life Sciences
Twelve Soil Orders
Andisols

Andisols

Andisols (from Japanese ando, "black soil") are soils that have formed in volcanic ash or other volcanic ejecta. They differ from those of other orders in that they typically are dominated by glass and short-range-order colloidal weathering products such as allophane, imogolite and ferrihydrite. As a result, Andisols have andic properties — unique chemical and physical properties that include high water-holding capacity and the ability to "fix" (and make unavailable to plants) large quantities of phosphorus. They are divided into eight suborders: Aquands, Gelands, Cryands, Torrands, Xerands, Vitrands, Ustands and Udands.

Globally, Andisols are the least extensive soil order and only account for approximately 1% of the ice-free land area. They occupy approximately 1.7% of the U.S. land area, including some very productive forests in the Pacific Northwest region.

Andisols have andic soil properties in layers either: (1) with a cumulative thickness of 36 cm within 60 cm of the mineral soil surface; or (2) comprising at least 60 percent of the depth between the mineral soil surface and a root-restrictive horizon. (USDA-NRCS image)

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A map showing the global distribution of Andisols. Source: USDA-NRCS

A map showing the percent of land in Andisols. Source: USDA-NRCS

Diagram and description of Andisols suborders

Map of Andisols dominant suborders. Source: USDA-NRCS

Xerands, Vitrands (Idaho)

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Vitrixerand Landscape, Bonner County, Idaho — This landscape incurred repeated flooding from glacial Lake Missoula during the last Ice Age and outwash deposits are extensive in the valleys. These outwash deposits and surrounding mountains have been mantled with volcanic ash from the eruption of Mount Mazama approximately 7,700 years ago. Mean annual precipitation is approximately 635-900 mm (25-35 inches) and mean annual temperature is approximately 6°C (43°F). The soils are used for timber production, pastureland, wildlife habitat and limited crop production. (Image from University of Idaho)

Typic Vitrixerand (ashy over sandy-skeletal, aniso, glassy over isotic, frigid), Idaho — This soil is a member of the Bonner series. The profile has formed in two parent materials and is typical of many of the Andisols of northern Rocky Mountains. The upper 40 to 50 cm of the profile contains volcanic ash, the majority of which came from the eruption of Mount Mazama. A cambic Bw horizon containing 5-10 percent clay has formed as the ash has weathered over the past 7,700 years. The lower portion of the profile is formed in glacial outwash materials from the last Ice Age. Scale is in decimeters. (Image from University of Idaho)

Udivitrand Landscape, northern Idaho — Andisols are the dominant soils of north Idaho forests. Mean annual precipitation ranges from approximately 635 to 1,270 mm (25-50”). These forests are among the most productive in the region, in part because of the additional water-holding capacity associated with the mantle of weathered volcanic ash. Studies indicate that the presence of a 36-cm-thick ash mantle can increase the 50-year grand fir (Abies grandis) site index by approximately 4.5 m (15 ft) (Kimsey et al., 2008. Forest Science 54: 356-366). (Image from University of Idaho)

Oxyaquic Udivitrand, northern Idaho — This soil is a member of the Threebear series, Idaho’s state soil, and has formed in two parent materials. The upper 40-50 cm has formed in volcanic ash from the eruption of Mount Mazama. Textures of the ash mantle are typically silt loam and clay content is low, approximately 5-10 percent. Underlying horizons have formed in older loess and reworked silty sediments. A dense, root-restrictive, very slowly permeable horizon (2Btxb) referred to as a fragipan has formed in the lower part of the profile. The fragipan greatly restricts vertical water movement, resulting in the presence of a perched water table for approximately 6-8 months of the year. Scale increments are decimeters. (Image from University of Idaho)

Cryands (Iceland)

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Eroded Andisol Landscape, Iceland — This highland landscape once consisted of deep Andisols overlying glacial till. However, centuries of overgrazing by sheep and the high susceptibility of these soils to wind erosion has resulted in the landscape seen here. In the foreground, rocky glacial till has been exposed by erosion of the overlying Andisol, thereby promoting desertification. Only sparse vegetation is supported by the glacial till despite annual precipitation of approximately 1,100 mm (43 inches). An Andisol approximately 1.5 m thick can be seen (left side of photo) supporting healthy vegetation. It has been estimated that the vegetative cover of Iceland has been reduced by greater than 60 percent since settlement because of overgrazing and soil erosion. (Image from University of Idaho)

Typic Haplocryand medial, amorphic), Iceland — This deep Andisol profile (Thingvallasveit soil) has formed in volcanic ash and eolian material in southwestern Iceland. The soil lacks distinct horizonation. Soil structure is weak and the volcanic ash particles are mostly silt- and sand-sized, making these soils highly susceptible to wind erosion. However as is the case with many Andisols, organic matter levels are relatively high — the top 60 cm of this profile contains 70-80 g/kg organic carbon. Scale is in decimeters. (Image from University of Idaho)

Vitrands (New Zealand)

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Udivitrand Landscape, New Zealand — This landscape occurs within the Taupo Volcanic Zone on the North Island of New Zealand. This area includes the Taupo caldera volcano, which is the most frequently active rhyolitic volcano on Earth. Much of the native podocarp/ hardwood forest was destroyed by the approximately 233 AD Taupo eruption, which produced a violent pyroclastic flow that spread over an area of 20,000 sq km in approximately 7 minutes. Mean annual precipitation is approximately 1,100-1,200 mm (43-47 inches). Current land uses include dairy, sheep and beef production, and plantation forest (seen in background). (Image from University of Idaho; information courtesy of Dr. David Lowe, University of Waikato)

Typic Udivitrand (ashy/pumiceous, mesic), New Zealand — The upper 50 cm of this soil has formed in non-welded ignimbrite from the Taupo eruption around 233 AD. This material has undergone relatively little weathering and has sandy textures with many pumice fragments. Clay content is generally low, less than 10 percent. Underlying horizons to a depth of almost 2 m have formed in numerous intermixed tephra layers deposited over the past 27,000 years or so. The dark color of the A horizon is due to shrub-bracken fern vegetation and burning by pre-European Maori (Polynesian) inhabitants since approximately 1300 AD. Scale is in centimeters. (Image from University of Idaho)

Udands (Costa Rica)

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Melanudand Landscape, Costa Rica — Melanudands are found on the upper slopes of volcanoes in the central highlands of Costa Rica. They have relatively high organic matter content and excellent physical properties. Because of this, they are highly sought after for production of specialty crops and pasture. (Image from University of Idaho)

Melanudand, Costa Rica — This soil is formed in layers of volcanic ash from the Volcan Turrialba. The upper part of this soil provides a good example of a melanic epipedon, which is a dark, organic matter-rich surface layer that has andic properties. In this profile, it extends to depth of approximately 75 cm. The A1 horizon contains 16.4 percent organic matter by weight. The water content at 1500 kPa ranges from 147 percent in the A1 horizon to 226 percent in the Bw horizon. These are excellent agricultural soils and are used locally for production of cilantro, peppers, coffee and other specialty crops. Scale is in decimeters. (Image from University of Idaho)

Andic soil properties, Mazama eruption

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Andic Soil Properties — Andic soil properties are defined in Soil Taxonomy by a combination of criteria. A common component of many Andisols is volcanic glass (left), which weathers to form a variety of Si-, Fe- and Al-containing products. These weathering products include metal-humus complexes (extracted by pyrophosphate) and allophane, imogolite and ferrihydrite, which are quantified using an ammonium oxalate extraction. Together, the percentages of glass and oxalate-extractable Fe and Al are used to define andic properties, which is indicated by orange shading in the figure above. Other criteria used to define andic properties include the ability to retain large quantities of applied P and relatively low bulk density (<0.90 g/cm3). (Images from University of Idaho)

Mount Mazama Eruption — Top left: Mount Mazama was a 12,000 foot volcano in the Cascade Mountains of southwestern Oregon. Approximately 7,700 years ago a huge, explosive eruption deposited volcanic ash across the Pacific Northwest (brown shading on map). The eruption resulted in the collapse of the volcano, forming a 8 x 10 km (5 x 6 mile) caldera. The caldera filled with water to give rise to Crater Lake (bottom left), which is the deepest lake in the United States at 594 m (1,949 ft). (Information from https://volcanoes.usgs.gov/volcanoes/crater_lake/)

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Department of Soil and Water Systems

University of Idaho

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Rm 242
606 S Rayburn St

Mailing Address:
875 Perimeter Drive MS 2340
Moscow, ID 83844-2340

Email: rheinse@uidaho.edu

Web: uidaho.edu/cals/sws

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The Twelve Soil Orders

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Department of Soil and Water Systems

Andisols

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Xerands, Vitrands (Idaho)

Cryands (Iceland)

Vitrands (New Zealand)

Udands (Costa Rica)

Andic soil properties, Mazama eruption

Contact

Department of Soil and Water Systems