Soil parameter estimates for the soil types of the world for use in global and regional modelling (WISE-IFPRI study)
This study was commissioned by the International Food Policy Research Institute (IFPRI), as Research Agreement Contract No. 2001X020.ISR, using funds from the European Economic Commission (2000-2001). It was a sequel to ealier taxotransfer-related work, carried out in 1997, using version 1.0 of the ISRIC-WISE database with the International Institute for Applied Systems Analysis (IIASA) and the Food and Agriculture Organization (FAO). This study identified several geographic, taxonomic and soil physico-chemical gaps, showing the persisting need for expanding the set of soil profile data available for this type of analyses.
Important gaps in the soil profile data were filled and the initial methodology was reviewed and refined during the follow-up study in order to generate a revised set of physical and chemical parameter estimates for the soils units of the world, as described by the two FAO soil legends (version 1974 and 1988).
The current study used all profiles held in WISE, version 1.1, to which have been added profiles extracted from currently available soil and terrain (SOTER) databases as well as new data from the literature.
Soil unit, topsoil textural class, and depth zone (0-30 cm and 30-100 cm) were used to cluster the horizon data. Criteria used are in accordance with conventions developed by FAO for use with the Soil Map of the World. Upon a screening on data ‘integrity’ and application of a statistical outlier rejection scheme, derived statistics were generated for 28 soil chemical and physical attributes. These attributes were identified as being useful for AEZ studies, crop growth simulation, and analyses of global environmental change.
Derived parameters are presented for: organic carbon; total nitrogen; C/N ratio; pH(H2O), pH(KCl), pH(CaCl2); sum of exchangeable Ca, Mg, Na and K (TEB); the ratio of exchangeable Ca/Mg and exchangeable (Ca + Mg)/K; the cation exchange capacity of the fine earth fraction (CECsoil), the effective cation exchange capacity (ECEC), apparent cation exchange capacity of the clay fraction (CECap), and cation exchange capacity of the clay fraction corrected for the contribution of organic matter (CECclay); base saturation; aluminium saturation; CaCO3 content; gypsum content; exchangeable sodium percentage (ESP); electrical conductivity (ECe); bulk density; total porosity; weight percent of sand, silt and clay; gravel content; available water held between –5 kPa and -1500 kPa, –10 kPa and -1500 kPa, and –33kPa and -1500 kPa, respectively; and, effective soil depth. For each of these parameters, the following are listed: number of observations, means, coefficients of variation, 95% confidence intervals, medians, and medians of absolute deviations. Simple taxotransfer rules are introduced to fill gaps that remained in the derived data, notably where sufficient measured data were lacking for particular attributes and soil units. The type of rule used has been flagged in the data set.
The set of derived soil parameters should be seen as the best possible estimates, based on the present selection of soil profiles and adopted data clustering procedure. The derived data set is considered appropriate for use in studies at a regional to global scale (< 1:250,000). Correlation of soil analytical data, however, must be done more accurately when more precise scientific research is considered.
- Batjes NH, 2002. Soil parameter estimates for the soil types of the world for use in global and regional modelling (Version 2.1). ISRIC Report 2002/02c [Available on-line at http://www.isric.org ], International Food Policy Research Institute (IFPRI) and International Soil Reference and Information Centre (ISRIC), Wageningen. (download)
- Batjes, 2002. Revised soil parameter estimates for the soil types of the world. Soil Use and Mangement18, 232-235 (download)