title: SoilGrids1km--global soil information based on automated mapping.
abstract: BACKGROUND
  Soils are widely recognized as a non-renewable natural resource and as biophysical carbon sinks. As such, there is a growing requirement for global soil information. Although several global soil information systems already exist, these tend to suffer from inconsistencies and limited spatial detail.
  
  
  RESULTS
  We present SoilGrids1km--a global 3D soil information system at 1 km resolution--containing spatial predictions for a selection of soil properties (at six standard depths): soil organic carbon (g kg-1), soil pH, sand, silt and clay fractions (%), bulk density (kg m-3), cation-exchange capacity (cmol+/kg), coarse fragments (%), soil organic carbon stock (t ha-1), depth to bedrock (cm), World Reference Base soil groups, and USDA Soil Taxonomy suborders. Our predictions are based on global spatial prediction models which we fitted, per soil variable, using a compilation of major international soil profile databases (ca. 110,000 soil profiles), and a selection of ca. 75 global environmental covariates representing soil forming factors. Results of regression modeling indicate that the most useful covariates for modeling soils at the global scale are climatic and biomass indices (based on MODIS images), lithology, and taxonomic mapping units derived from conventional soil survey (Harmonized World Soil Database). Prediction accuracies assessed using 5-fold cross-validation were between 23-51%.
  
  
  CONCLUSIONS
  SoilGrids1km provide an initial set of examples of soil spatial data for input into global models at a resolution and consistency not previously available. Some of the main limitations of the current version of SoilGrids1km are: (1) weak relationships between soil properties/classes and explanatory variables due to scale mismatches, (2) difficulty to obtain covariates that capture soil forming factors, (3) low sampling density and spatial clustering of soil profile locations. However, as the SoilGrids system is highly automated and flexible, increasingly accurate predictions can be generated as new input data become available. SoilGrids1km are available for download via http://soilgrids.org under a Creative Commons Non Commercial license.
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Tomislav
authors.initials: T
authors.lastname: Hengl
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Jorge Mendes
authors.initials: JM
authors.lastname: de Jesus
authors.affiliation: LandMapper Environmental Solutions Inc., Edmonton, Canada.
authors.forename: Robert A
authors.initials: RA
authors.lastname: MacMillan
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Niels H
authors.initials: NH
authors.lastname: Batjes
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands; Wageningen University, Wageningen, the Netherlands.
authors.forename: Gerard B M
authors.initials: GB
authors.lastname: Heuvelink
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Eloi
authors.initials: E
authors.lastname: Ribeiro
authors.affiliation: Federal Rural University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Samuel-Rosa
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Bas
authors.initials: B
authors.lastname: Kempen
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Johan G B
authors.initials: JG
authors.lastname: Leenaars
authors.affiliation: The Earth Institute, Columbia University, New York, New York, United States of America, and Selian Agricultural Research Inst., Arusha, Tanzania.
authors.forename: Markus G
authors.initials: MG
authors.lastname: Walsh
authors.affiliation: ISRIC - World Soil Information, Wageningen, the Netherlands.
authors.forename: Maria Ruiperez
authors.initials: MR
authors.lastname: Gonzalez
mesh_terms: D000465:Algorithms; D002244:Carbon / Q000032:analysis*; D057965:Carbon Sequestration; D002412:Cations / Q000032:analysis; D003247:Conservation of Natural Resources / Q000379:methods / Q000706:statistics & numerical data*; D017753:Ecosystem; D004777:Environment; D040362:Geographic Information Systems / Q000706:statistics & numerical data*; D005843:Geography; D006863:Hydrogen-Ion Concentration; D016015:Logistic Models; D008962:Models, Theoretical; D012987:Soil / Q000737:chemistry*
chemical_list: D002412:Cations; D012987:Soil; D002244:Carbon