The FAO developed a supra-national classification, also called World Soil Classification, which offers useful generalizations about soils pedogenesis in relation to the interactions with the main soil-forming factors. It was first published in form of the Unesco Soil Map of the World (1974) (scale 1 : 5 M.). Many of the names offered in that classification are known in many countries and do have similar meanings.
Originally developed as a legend to the Soil Map of the World, the classification has been applied by United Nations sponsored projects. Many countries have modified this system to fit their particular needs.
The Soil Units (106) are mapped as Soil Associations, designated by the dominant soil unit,
- with soil phases (soil properties, such as saline, lithic, stony),
- with three textural classes (coarse, medium, and fine)
- three slopes classes superimposed (level to gently undulating, rolling to hilly, and steeply dissected to mountainous)
Soil Units form 26 World Classes. The FAO soil map is a very simple classification system with units very broad, but it is the only truly international system, and most soils can be accommodated on the basis of their field descriptions. The FAO soil map is intended for mapping soils at a continental scale but not at local scale.
Since 1998 this system has been replaced by the World Reference Base for Soil Resources, a much-improved classification.
FAO Soil Units
- Acrisols
- Andosols
- Arenosols
- Cambisols
- Chernozems
- Ferralsols
- Fluvisols
- Gleysols
- Greyzems
- Histosols
- Kastanozems
- Lithosols
- Luvisols
- Nitosols
- Phaeozems
- Planosols
- Podzols
- Podzoluvisols
- Rankers
- Regosols
- Rendzinas
- Solonchaks
- Solonetz
- Vertisols
- Yermosols
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