ISRIC Report 2003/03: A taxotransfer rule-based approach for filling gaps in measured soil data in primary SOTER databases (GEFSOC Project)

isric_report_2003_03.pdf (pdf, 544.14 kB)
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Niels H Batjes
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ISRIC, FAO and UNEP under the aegis of IUSS are updating the information on world soil resources in the World Soils and Terrain Digital Databases (SOTER) project. Primary SOTER databases are composed of two main elements: a geographic and an attribute data component. The first shows the delineations of the SOTER units, while the second holds information on their composition in terms of main soil types described by a suite of representative profiles.
Representative soil profiles for SOTER are selected from existing soil survey reports. Often there are gaps in the associated soil analytical data. This often precludes the direct use of primary SOTER data in environmental models. This study presents a methodology for filling gaps in the primary soil analytical data. There are three main stages: 1) collating additional measured soi analytical data to consolidate the existing primary data sets; 2) filling gaps using national expertise and common sense; and 3) filling the remaining gaps using taxotransfer rules. The current report focuses on the taxotransfer scheme. It draws on the soil analytical data held in an auxiliary global soil profile database (WISE – World Inventory of Soil Emission Potentials). Soil parameter estimates by soil unit (FAO Revised Legend) are presented for fixed depths intervals of 0.2 m each (up to 1 m depth) and with reference to the soil textural class. They include organic carbon, total nitrogen, pH(H2O), CECsoil, CECclay, base saturation,
effective CEC, aluminum saturation, CaCO3 content, gypsum content, exchangeable sodium percentage (ESP), electrical conductivity of saturated paste (ECe), bulk density, sand, silt, clay, content of coarse fragments, and available water capacity. This list has been identified as being useful for agro-ecological zoning (AEZ), land evaluation, crop growth simulation, studies of soil carbon stocks and change, and analyses of global environmental change.
Results are presented digitally. This information can be linked to the soil geographic component of SOTER through the unique SOTER unit and profile identifiers. All taxotransfer rules have been flagged to provide an indication of the confidence in the derived data. The present approach is considered appropriate for studies at scales smaller than 1:250 000. Correlation of soil analytical data, however, must be done more rigorously when more detailed scientific work is considered. In the first instance, the methodology will be applied to primary SOTER databases for Brazil, India, Jordan and Kenya in the framework of the GEF co-funded project on Assessment of Soil Organic Carbon Stocks and Change at National Scale.
Keywords: soil parameter estimates; environmental modelling; soil carbon; WISE database; SOTER database; taxotransfer