Hand-feel soil texture observations to evaluate the accuracy of digital soil maps for local prediction of particle size distribution. A case study in central France

International audienceDigital maps of soil properties are now widely available. End-users now can access several digital soil mapping (DSM) products of soil properties, produced using different models, calibration/training data, covariates and at various spatial scales from global to local. Therefore, there is an urgent need to provide easy-to-understand tools to communicate map uncertainty and help end-users assess the reliability of DSM products for use at local scales. In this study, we used a large number of hand-feel soil texture data (HFST) to assess the performance of various published DSM products on the prediction of particle-size distribution in Central France. We tested four DSM products of texture prediction developed at various scales (Global, continental, national, and sub-national) by comparing their predictions with ca 3,200 HFST observations realised on a 1:50,000 soil survey conducted after the release of these DSM products. We used both visual comparisons and quantitative indicators of matching DSM predictions and HFST. The comparison between low-cost observed HFST and DSM predictions clearly showed the applicability of various DSM products, with prediction accuracy increasing from global to sub-national predictions. This simple evaluation can decide which products can be used at the local scale and if more accurate DSM products are required