World’s Soil Resources

ALISOLS (Ultisols with an argillic horizon)
Alisols are characterized by movement and accumulation of high-activity clays (cation-exchange capacity
> 24 cmolc kg -1 clay) and a low base saturation (< 50 percent). The dominant soil processes involved in
Alisol formation include argilluviation and base-cation leaching. Alisols have high Al and very low plant
nutrients (Figure A 28).
Alisols occur under equatorial or warm climates, fully humid or winter-dry with an annual precipitation
exceeding 1 200 mm. They typically carry a tropical deciduous forest or tropical evergreen forest. They
occur where the topography is variable but often hilly or undulating, while their parent material is strongly
weathered basic rocks and unconsolidated sediments. These soils are commonly more than 200 000 years
old.
Regional distribution of the approximately 100 million ha of Alisols globally is mainly in Central and
South America, the Caribbean, west and east Africa, southeastern Asia, and northern Australia. Alisols are
used for forestry, low-volume grazing and, to a limited extent, for agriculture.
Status of the World’s Soil Resources | Main Report Annex | Soil groups, characteristics,
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distribution and ecosystem services