Locally enhanced digital soil mapping in support of a bottom-up approach is more accurate than conventional soil mapping and top-down digital soil mapping

This study presents a regional digital soil mapping (DSM) product that used a locally enhanced method in support of a bottom-up approach to create spatial soil predictions that were more accurate than one of the most accurate and detailed conventional soil mapping (CSM) products in the world, the Soil Survey Geographic (SSURGO) map from the United States Department of Agriculture, Natural Resources Conservation Service. Prior to this work, DSM products had yet to definitively outperform CSM products, except in locations where existing CSM maps were based on low investment (e.g., generalized national soil maps). While DSM has had established advantages, such as quantitative property prediction and cost efficiency, remaining challenges for widespread adoption include obtaining accuracy and practicality that exceed CSM-based maps in areas with histories of strong soil survey programs. In comparison with SSURGO, multiple top-down DSM products (SoilGrids 2.0, POLARIS, and Soil Properties and Class 100 m Grids of the USA) were evaluated along with the locally enhanced DSM product called LE-DSM (locally enhanced digital soil map). These maps were compared for their predictions of clay, silt, sand, and organic matter content at standard depth intervals to 200 cm. SSURGO outperformed the national and global top-down DSM products for 75 % of the soil properties and depths. In contrast, LE-DSM demonstrated appreciably higher accuracy than SSURGO 46 % of the time. These results indicate that bottom-up DSM products are needed for superseding the accuracy of CSM products, which themselves are constructed from a locally enhanced bottom-up approach.