Classifying Soils

Classification systems are essential for us to be able to study and communicate information about soils. While classification systems for plants and other organisms are quite old, a comprehensive soil classification system was only recently developed. (Table 1.1).

Table 1.1. Classification scheme for soils (Soil Survey Staff, 1975)

Taxonomic Level

Number of Classes

Examples (Abbreviations)



Alfisol (alf) — deciduous forest

Aridisol (id) — dry/arid, desert

Entisol (ent) — beginning: no horizon

Histosol (ist) — organic; boggy

Inceptisol (ept) — young; few horizons

Mollisol (oll) — soft; grasslands

Oxisol (ox) — oxide; tropical

Spodosol (od) — mineral; coniferous

Ultisol (ult) — last; hot, humid

Vertisol (vert) — invert; swelling



Saprist — sphagnum

Humod — organic

Andept — volcanic

Great Group


Borosaprist — frigid

Cryohumod — colder than frigid

Dystradept — low base saturation



Fluvaquentic — flood plain

Borosaprist — wetness

Lithic — weathered Rock


Aquic — wetness




Coarse-silty — texture, mineralogy

Mixed, mesic — temperature regime

Series Texture


McCook loam — surface Soil


This system may appear to be relatively complex. However, it is much like giving names to people that reflect­ their heritage or which describe them in a way that makes them different from everyone else. For instance­, we might identify a person as Nancy Marie Wilson­ Johnson. We could also describe her as having blonde hair, blue eyes, a high forehead and being long-waisted, round-faced and short. Classifying soils is similar to using these descriptions to identify Nancy Johnson.

For our purposes we need to establish some general concepts which allow us to use and understand soil classification at a practical level. 

Soils are classified according to the number of horizons in the soil profile and the soil properties of each horizon. Well developed soils are old and contain all three master horizons (A, B, and C) as well as several subdivisions of the master horizons. Young soils, or soils that have not developed extensively because of the lack of formation factors (climate, topography, vegetation, parent material, time), may have only two horizons — the surface soil or A horizon and the parent materials or C horizon. The presence of a B horizon indicates an older mature soil.