Alisols

 
Distribution of Alisols (click to view larger picture)

Alisols

Alisols occur in the tropics and subtropics, and in the warm temperate regions of the world in relatively young landscapes. The high level of exchangeable aluminium in these soils is caused by rapid weathering of secondary high-activity clays such as vermiculite and smectite.

Characteristics

Soils having an argic horizon (a subsurface horizon with distinct higher clay content than the overlying horizon), which has a cation exchange capacity of 24 cmolc per kg clay or more, and which starts either within 100 cm from the soil surface, or within 200 cm from the soil surface if the argic horizon is overlain by loamy sand or coarser textures throughout. They have "alic" properties (high content of exchangeable aluminium) in the major part between 25 and 100 cm from the soil surface; moreover, only such diagnostic horizons as an ochric, albic, andic, ferric, nitic, plinthic, or vertic horizon are present.

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Yellowish and imperfectly drained Alisol, China, characterized by a high content of exchangeable aluminium (Hyperdystri-Stagnic Alisol; ISRIC reference soil CN022)

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Red Alisol, China; the oblique stoneline between 60 and 110 cm depth separates colluvial from residual material derived from granite
(Chromi-Hyperdystric Alisol; ISRIC reference soil CN028)