FAO soil classification

FAO soil classification
Name	FAO soil classification
Other names	Food and Agriculture Organization soil classification, FAO-UNESCO soil map system
Type	Soil classification system
Developer	Food and Agriculture Organization
First published	1974 (Legend), 1988 (Revised)
Scope	Global soil mapping and land evaluation

FAO soil classification is a global soil nomenclature and mapping framework developed under the auspices of the Food and Agriculture Organization (FAO) and the United Nations Educational, Scientific and Cultural Organization (UNESCO). It provided a standardized set of soil units and diagnostic criteria used in the FAO-UNESCO Soil Map of the World and later global and regional soil surveys. The system influenced national schemes and international projects in United Nations agencies, World Bank programs, and conservation initiatives.

History and development

The FAO soil classification emerged during collaborative post‑war efforts linking the Food and Agriculture Organization and UNESCO to produce the FAO‑UNESCO Soil Map of the World, a multinational project involving institutions such as the International Union of Soil Sciences and national soil surveys from United States Department of Agriculture, Soil Survey of England and Wales, and the Australian Soil and Land Survey. Early work built on precedents from the Russian soil classification tradition, the German soil classification (Boden), and the taxonomic concepts advanced by scientists like Konstantin Glinka and Vasily Dokuchaev. The 1974 legend provided a practical global legend; subsequent revision and the 1988 documentation reflected feedback from the International Soil Reference and Information Centre (ISRIC) and regional stakeholders in Africa, Asia, and the Americas. Major mapping campaigns supported by the World Soil Survey network and programs sponsored by the United Nations Development Programme propagated its use through the late 20th century.

Classification system and criteria

The FAO system organized soils into hierarchical units using diagnostic horizons, texture, chemical properties and environmental factors recognized in the FAO legend. Criteria included presence of organic horizons, salinity, alkalinity, carbonates, gleying, and cryic or permafrost indicators relevant to regions such as Siberia, Greenland, and the Andes. The scheme employed a set of categories—such as Histosols, Arenosols, and Solonchaks—that functioned as major units for mapping at continental and global scales, integrating pedogenetic concepts similar to those in the Soil Taxonomy of the United States Department of Agriculture and the World Reference Base for Soil Resources. Diagnostic features referenced stratigraphic analogues used in landscape studies by institutions like the United States Geological Survey and considerations from climatological frameworks developed by Wladimir Köppen.

Major soil groups and units

FAO major units grouped global soils into categories reflecting dominant pedogenic processes and landform associations. Examples included organic‑rich Histosols mapped in peatlands of Scandinavia, saline Solonchaks in arid zones of Sahara, vertic and swelling clay soils noted in parts of India and Australia, and cryic or permafrost‑influenced soils across Canada and Russia. The legend translated these into map units used by national agencies such as the Brazilian Agricultural Research Corporation (Embrapa) and the National Institute for Agricultural Research organizations in Europe. Mapping units were often cross‑referenced with land capability frameworks used in projects by the Food and Agriculture Organization and the European Commission rural programs.

Mapping and applications

FAO classification underpinned the FAO‑UNESCO Soil Map of the World and numerous regional maps used by entities like the World Meteorological Organization for climate‑soil interactions, the International Fund for Agricultural Development for land evaluation, and the Global Soil Partnership. Applications included land use planning in national ministries, agroecological zoning in development projects funded by the World Bank, and conservation work coordinated with Ramsar Convention wetland inventories. The system supported GIS datasets produced by research centers such as ISRIC and informed agricultural extension services in countries including Kenya, Indonesia, and Argentina.

Relationship to other classification systems

The FAO framework interfaced with other taxonomies including the USDA Soil Taxonomy, the Russian taxonomy systems, and the later World Reference Base for Soil Resources (WRB) developed under the International Union of Soil Sciences and endorsed by the FAO. Crosswalks and correlation tables were prepared by organizations like ISRIC and national soil surveys to translate FAO units to USDA orders, WRB Reference Soil Groups, and national legends used by agencies such as Agroscope in Switzerland and Agriculture and Agri‑Food Canada. These efforts facilitated global comparative studies published in journals associated with the International Union of Soil Sciences and supported by funding bodies like the European Union.

Criticisms and updates

Critiques of the FAO system addressed its coarse resolution for local land management, ambiguities in diagnostic thresholds, and challenges reconciling pedogenic process emphasis with taxonomic precision—points raised in reviews by academics at institutions such as the University of California, Davis and Wageningen University & Research. These limitations contributed to the development of the WRB and revisions by ISRIC and the FAO in subsequent decades, aiming to improve interoperability with national systems and incorporate advances in soil physics, soil chemistry, and remote sensing technologies promoted by organizations like the Committee on Earth Observation Satellites and the Group on Earth Observations. Contemporary use tends to favor WRB or harmonized legends for detailed mapping, while FAO legacy units remain important in historical datasets and global syntheses compiled by the Food and Agriculture Organization and partner institutions.

Category:Soil classification