[From Philippe Lagacherie]
Another very relevant challenge. I let the soil physicists react about the right model at the right scale. Our job, as Digital Soil Mappers, is to provide estimations of soil properties and of the associated uncertainties for any required geographical support whereas we stick at working at the horizon or pedon level. My experience is that most of the users do not ask for such a fine support for making decisions. Delivering soil prediction at larger support is not only relevant for users but also would avoid discouraging the users with the large uncertainties that are often obtained when working at the pedon level. Spatial aggregation techniques exist, including those provided by geostatistics. As often, the main limiting factor for applying these techniques is the input data, in particular a minimum knowledge of the short-range soil spatial variabilities. Ad-hoc spatial sampling, collection of legacy proximal and high-resolution remote sensing data, or meta-analysis of the literature should be explored as possible solutions for obtaining this information.