S-World: An Operation Methodology to Map Soil Properties At the Global Scale.

There is an increasing call for high resolution soil data at the global level. Although a better insight in the spatial distribution of soil types would be useful, soil types often present wide ranges in soil properties. For many modelling exercises, it is important to get better insight in the spatial distribution of soil properties. Global soil maps like the Harmonized World Soil Database and databases with soil profiles like the WISE database provide an excellent starting point. In the last decades a wide array of additional global environmental data on e.g., topography, land use and climate has become available. This study aimed to develop a methodology that takes stock of available data to create a global map of soil properties. Four important soil properties were studied: organic matter in the topsoil, depth of the topsoil, soil texture of the soil profile, and soil depth. The ranges of the soil properties per soil type were assessed using the soil profile data. The research focused on the basic conceptual question where we are within this range at a particular location within that soil type. Four landscape properties, i.e., slope, annual rainfall, average annual temperature, and land use intensity, are selected that were considered to be the main driving factors behind the variability in soil properties within the soil types. The ranges of the landscape properties were also determined for the different soil types. A number of model parameters were determined on the basis of a literature review that indicate the correlation between the landscape properties and the  soil properties. Finally, the global distribution of the soil properties was determined. The methodology, denominated S-world (Soils of the World), resulted in four global soil property maps.