Editing USDA soil taxonomy (section)

== Soil Orders ==
[[File:Global soils map USDA.jpg|thumb|upright=1.5|Global distribution of Soil Orders in the USDA soil taxonomy system. [[:File:USDA soil taxonomy global map.png|A much larger version of the map]] is also available.]]

Name of soil orders in soil taxonomy with their major characteristics:
* [[Alfisols]]:  Must have argillic, natric, or kandic [[Soil horizon|horizon]]; high-to-medium base saturation; moderately weathered; commonly form under boreal or broadleaf forests; rich in iron and aluminum; common in humid areas, semi-tropics, and mediterranean climates; 9.6% of global and 14.5% of U.S. ice-free land.

* [[Andisols]]: Form from volcanic ejecta, dominated by [[allophane]] or Al-humic complexes; Must have andic soil properties: high in poorly crystalline Fe and Al minerals, high in phosphorus, low bulk density, and high proportions of glass and amorphous colloidal materials, such as allophane, [[imogolite]] and [[ferrihydrite]]; high organic matter content, sometimes melanic [[Soil horizon#Diagnostic Surface Horizons of Mineral Soils|epipedon]]; 0.7% of global and 1.7% of U.S. ice-free land.

* [[Aridisols]]: Dry soil (i.e., must have aridic moisture regime); ochric [[Soil horizon#Diagnostic Surface Horizons of Mineral Soils|epipedon]] is common; Sometimes argillic or natric horizon; must have some [[Soil horizon#Diagnostic Subsurface Horizons|diagnostic subsurface horizon]]; commonly in deserts; 12.7% of global and 8.8% of U.S. ice-free land.

* [[Entisols]]: Least soil profile development; ochric epipedon is common; no B horizons; most common order by surface area (16.3% of global and 12.2% of U.S. ice-free land).

* [[Gelisols]]: Soils with permafrost within 100&nbsp;cm or cryoturbation (frost churning) within 100&nbsp;cm plus permafrost within 200&nbsp;cm; commonly at high latitudes and elevations; 8.6% of global and 7.5% of U.S. ice-free land.

* [[Histosols]]: Must have histic epipedon; usually aquic soil moisture regime; no diagnostic subsurface horizons; rapid decomposition when aerated;  peat or bog; >20% organic matter; organic soil materials extending down to an impermeable layer or with an organic layer that is more than 40&nbsp;cm thick and without andic properties; commonly in wetlands (swamps, marshes, etc.); 1.2% of global and 1.3% of U.S. ice-free land.

* [[Inceptisols]]: Similar to entisol, but beginning of a B horizon is evident; no diagnostic subsurface horizons; on landscapes continuously eroded or young deposits; cambic, sulfuric, calcic, gypsic, petrocalcic, or petrogypsic horizon, or with a mollic, umbric, or histic [[Soil horizon#Diagnostic Surface Horizons of Mineral Soils|epipedon]], or with an exchangeable sodium percentage of >15% or fragipan; 9.9% of global & 9.1% of U.S. ice-free land.

* [[Mollisols]]: Must have mollic epipedon; high base saturation of >50%; dark soils; some with argillic or natric horizons; common in grasslands; 6.9% of global and 22.4% of U.S. ice-free land.

* [[Oxisols]]: Most soil profile development; must have [[oxic]] horizon within 150&nbsp;cm of soil surface; low nutrient availability; no argillic horizon; highly weathered; dominated by end-member clays, Al and Fe oxides; commonly in old landscapes in tropics; 7.6% of global and <0.01% of U.S. ice-free land.

* [[Spodosols]]: Must have spodic horizon within 2 m of soil surface and without andic properties; Usually have albic horizon; high in Fe, Al oxides and humus accumulation; acidic soils; common in coniferous or boreal forests; 2.6% of global and 3.3% of U.S. ice-free land.

* [[Ultisols]]: Must have argillic or kandic horizon; Low base saturation of <35% at 2 m depth or 75&nbsp;cm below a fragipan; common in subtropical regions; often known as red clay soils; 8.5% of global & 9.6% of U.S. ice-free land.

* [[Vertisols]]: Usually mollic epipedon; high in shrinking and swelling clays; >30% clay to a depth of 50&nbsp;cm; deep cracks (called gilgai) form when soil dries; form from parent material high in clay (e.g., shales, basins, exposed Bt horizons of old soils); 2.4% of global and 1.7% of U.S. ice-free land.