ISRIC Report 2015/01 World soil property estimates for broad-scale modelling (WISE30sec)

isric_report_2015_01.pdf (pdf, 8.68 MB)
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Niels H. Batjes
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This report describes a harmonized dataset of derived soil properties for the world that is comprised of a soil-geographical and a soil attribute component (supplement to paper: ). The GIS dataset was created using the soil map unit delineations of the broad scale Harmonised World Soil Database, version 1.21, with minor corrections, overlaid by a climate zones map (Köppen-Geiger) as co-variate, and soil property estimates derived from analyses of the ISRIC-WISE soil profile database for the respective mapped ‘soil/climate’ combinations. The dataset considers 20 soil properties that are commonly required for global agro-ecological zoning, land evaluation, crop growth simulation, modelling of soil gaseous emissions, and analyses of global environmental change. It presents ‘best’ estimates for: organic carbon content, total nitrogen, C/N ratio, pH(H2O), CECsoil, CECclay, effective CEC, total exchangeable bases (TEB), base saturation, aluminium saturation, calcium carbonate content, gypsum content, exchangeable sodium percentage (ESP), electrical conductivity, particle size distribution (content of sand, silt and clay), proportion of coarse fragments (> 2 mm), bulk density, and available water capacity (-33 to -1500 kPa); also the dominant soil drainage class. These estimates are presented for fixed depth intervals of 20 cm up to a depth of 100 cm, respectively of 50 cm between 100 cm to 200 cm (or less when appropriate) for so-called ‘synthetic’ profiles’ (as defined by their ‘soil/climate’ class). The respective soil property estimates were derived from statistical analyses of data for some 21,000 soil profiles managed in a working copy of the ISRIC-WISE database; this was done using an elaborate scheme of taxonomy-based transfer rules complemented with expert-rules that consider the ‘in-pedon’ consistency of the predictions. The type of rules used was flagged to provide an indication of the possible confidence (i.e. lineage) in the derived data.
Best estimates for each attribute are given as means and standard deviations (STD), as calculated for the sample populations that remained upon application of a robust data outlier detection scheme. Results of the analyses can be linked to the spatial data through the unique map unit (grid cell) identifier, which is a combination of the soil unit and climate class code. Most map units are comprised of up to ten different components; each of these with their own range of derived soil properties and associated statistical uncertainties.
The present soil property values are ‘best estimates’ based on the current selection of soil profiles in WISE, and criteria and procedures for clustering the measured data in the taxotransfer scheme. They may be used for assessments at a continental and global level (scale < 1:1M) upon due consideration of the underlying generalisations and assumptions. These assessments should consider the full map unit composition, i.e. calculate first for each ‘soil/climate cluster, depth layer and attribute’, and then aggregate the results. Estimates of global soil organic carbon (SOC) stocks are presented as an example. According to this study, some 30% (607 ± 87 Pg C) of the total SOC stock (2060 ± 215 Pg C) to 2 m depth is held in the Northern Circumpolar Region, which is considered most sensitive to climate change.
Studies at (sub)national level should be based on regionally more detailed soil data sets.

Related publication:
Batjes NH 2016. Harmonised soil property values for broad-scale modelling (WISE30sec) with estimates of global soil carbon stocks. Geoderma 269, 61-68,