The source of soil information used in Global AEZ is primarily the digital version of the FAO/UNESCO Soil Map of the World (DSMW). It provides classification of soils according to the FAO/UNESCO ’74 Legend (FAO/UNESCO, 1974).
The digital soil information constitutes part of the land resources database and is kept together with other geographic information (i.e., elevation, terrain slopes, distance to coast, protected areas, land cover, and administrative divisions). Additional information, specifying the composition of the soil associations in terms of percentage occurrence of soil units, textures, terrain-slope classes and soil phases, is kept in a soil association composition database. The soil units in the FAO legends are defined in terms of measurable and observable properties of the soil itself. Many of the properties are directly relevant to agricultural production potential.
Quantification of soil unit characteristics in terms of physical and chemical properties was obtained from: (i) the DSMW CD-ROM for the soil units of FAO/UNESCO '74 Legend (FAO, 1995c), and (ii) the World Inventory of Soil Emissions Potential (WISE) database (Batjes, 1995). This latter WISE database contains a wide range of soil attributes for over 4000 soil profiles. The individual profiles were classified by International Soil Reference and Information Centre (ISRIC) for the FAO ’74 legend facilitating the linkage with the FAO/UNESCO Digital Soil Map of the World.
