Twelve Soil Orders

Well-developed mineral soils

alfisols, aridisols, mollisols, oxisols, ultisols, spodosols, vertisols

Weakly developed soils

andisols, entisols, inceptisols

Characterized by maturity (6)

entisols, inceptisols, alfisols, ulitisols, spodosols, oxisols

organic soils

gelisols, histosols

Characterized by climate (3)

mollisols, aridisols, gelisols

ultisols

Highly weathered soils in tropical and subtropical environments that have low base content and a subsurface horizon rich in eluviated clay.

oxisols

Highly weathered soils in tropical environments that have low base status and subsurface horizon that has a high oxide concentration.

entisols

Horizonless soils usually formed within recently deposited sediments.

gelisols

Largely organic soils that form in extremely cold environments where permafrost is thick. Due to repeated freezing and thawing, soil horizons and surface expression are chaotic.

spodosols

Soils in cool, moist environments that thave a B horizon rich in eluviated sesquioxides.

aridisols

Soils in dry climates that are low in organic matter and frequently have subsurface horizons rich in calcium carbonate or soluble salts.

mollisols

Soils in semi-arid/subhumid grasslands in midlatitudes that have humus-rich A horizon and a B horizon that has a high base status.

alfisols

Soils with high-base-content B horizon rich in eluviated clay. Found from low to subarctic latitudes.

inceptisols

Soils with poorly developed horizons, but which may evolve further.

vertisols

Tropical and subtropical soils with high base status that contain an abundant amount of expandable clay that swells when wet and shrinks when dry.

histosols

Very dark soils consisting mostly of organic matter. Typically found in cool/moist environments where organic decompostiton is slow.

andisols

Weakly developed soils formed within glassy volcanic sediments ejected by active volcanoes.

Characterized by parent material (3)

vertisols, andisols, histosols