12 Soil Orders In Depth

Alfisols
-semi arid to moist areas
-weathering leaches clay minerals and other constituents into subsoil
-formed primarily under forest or mixed vegetation
-usually productive
Andisols
-cool areas with moderate to high ppt
-especially associated with volcanic PM
-weathering generates minerals with little crystalline structure
-high water and nutrient holding capacity
-highly productive
Aridisols
-soils that are too dry for mesophytic plant growth
-common in deserts
-lack of moisture restricts weathering and limits development
-accumulates gypsum, CaCO3, and other soluble materials
Entisols
(polygenetic)
-many environments
-little to no pedogenic horizon development
-recently deposited PM or erosion/deposition is faster than soil development
Gelisols
-higher latitudes and elevations
-soils with permafrost or cryoturbation or ice segregation
Histosols
-usually saturated year round (bogs and moors)
-high content of O matter (peat or muck)
-decomposed plant matter accumulates in water
Inceptisols
-semi arid to humid areas
-moderate degrees of soil weathering and development
-wide range of characteristics in a wide variety of climates
Mollisols
-moderate to pronounced seasonal moisture deficit areas
-dark colored surface horizon
-relatively high O matter content
-base rich throughout
-characteristically form under grass in appropriate climates (Steppes)
Oxisols
-tropical and subtropical areas
-highly weathered
-dominated by low activity minerals (quartz, kaolinite, iron oxides)
-indistinct horizons
-low natural fertility and low capacity to retain additions
Spodosols
-humid areas
-coarse-textured deposits under coniferous forests in humid regions
-weathering processes strip O matter combined with Al (and sometimes Fe) from surfaces and deposit in subsoil
-gray eluvial horizon and dark subsoil sometimes
-tend to be acidic and infertile
Ultisols
-humid areas
-fairly intense weathering and leaching resulting in clay-enriched subsoils dominated by minerals (i.e. quartz, kaolinite and iron oxides)
-typically acid soils, most nutrients in upper few inches
-moderately low capacity to retain additions
Vertisols
-high content of expanding clay minerals
-undergo pronounced volume changes with change in moisture
-cracks that open and close, show movement in soil profile
-swell when wet (transmit water slowly, little leaching)
-high natural fertility