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Global estimates of soil organic carbon stocks have been produced in the past to support the calculation of potential emissions of CO2 from the soil under scenarios of change land use/cover and climatic conditions (IPCC, 2006), but very few global estimates are presented as spatial data. For global spatial layers on soil parameters, the most recent and complete dataset is available as the Harmonized World Soil Database (HWSD) (Fisher et al. , 2008). The HWSD represents a step forward towards a spatially more detailed and thematically more refined set of global soil data. the evaluation of the data for generating estimates of global SOC stocks Version 1. 1 of the HWSD revealed also some rough edges. Consequential are the values of bulk density attributed to soils high in organic carbon. In the evaluation the database was completed and suitable substitutions for bulk density for soil high in organic carbon were investigated. For the amended data the global SOC stock to 100cm soil depth is estimated at 1, 417 Pg C, although this estimate very much dependent on the ancillary data used. amended HWSD was compared to data from 4 other global data sets on SOC stocks. The comparative evaluation has demonstrated that bulk density is the most important factor for estimating SOC stocks and mainly responsible for the differences between estimates. Moist affected from the variability in bulk density are SOC stocks in areas with soils which are high in organic carbon.
Hiederer et al. (Sat,) studied this question.