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The common GIS-based approach to regional analyses of soil organic carbon (SOC) stocks and changes is to define geographic layers for which unique sets of driving variables are derived, which include land use, climate, and soils. These GIS layers, with their associated attribute data, can then be fed into a range of empirical and dynamic models. Common methodologies for collating and formatting regional data sets on land use, climate, and soils were adopted for the project Assessment of Soil Organic Carbon Stocks and Changes at National Scale (GEFSOC). This permitted the development of a uniform protocol for handling the various input for the dynamic GEFSOC Modelling System. Consistent soil data sets for Amazon-Brazil, the Indo-Gangetic Plains (IGP) of India, Jordan and Kenya, the case study areas considered in the GEFSOC project, were prepared using methodologies developed for the World Soils and Terrain Database (SOTER). The approach involved three main stages: (1) compiling new soil geographic and attribute data in SOTER format; (2) using expert estimates and common sense to fill selected gaps in the measured or primary data; (3) using a scheme of taxonomy-based pedotransfer rules and expert-rules to derive soil parameter estimates for similar soil units with missing soil analytical data. The most appropriate approach varied from country to country, depending largely on the overall accessibility and quality of the primary soil data available in the case study areas. The secondary SOTER data sets discussed here are appropriate for a wide range of environmental applications at national scale. These include agro-ecological zoning, land evaluation, modelling of soil C stocks and changes, and studies of soil vulnerability to pollution. Estimates of national-scale stocks of SOC, calculated using SOTER methods, are presented as a first example of database application. Independent estimates of SOC stocks are needed to evaluate the outcome of the GEFSOC Modelling System for current conditions of land use and climate.

Soil nitrogen and organic carbon stocks, to a depth of 0.3 m and 1 m respectively, were determined for the Amazon Region using the soil and terrain (SOTER-LAC) database for Latin America and the Caribbean. Mean carbon densities, to a depth of 1 m, range from 4.0 kg m−2 for coarse textured Arenosols to 72.4 kg m−2 for the poorly drained Histosols. Mean carbon density for the mineral soils, excluding Arenosols and Andosols (30.5 kg C m−2), is 9.8 kg m−2. In total, the top 1 m holds 66.9 Pg C and 6.9 Pg N. About 52% of this carbon pool is held in the top 0.3 m of the soil, the layer which is most prone to changes upon land use conversion and deforestation.