Digital Raster Grid Property Maps Versioning for North America.

Many disciplines utilize the soil information that is spatially provided mostly as polygon maps. There is a need for continuous raster soil property maps that represent spatial variability at different scales and level of detail. Spatial soil information for US and Canada is provided as polygon maps at both coarse scales (US - State Soil Geographic Data Base - STATSGO - 1:250,000; CANADA - Soil Landscapes of Canada - SLC – 1:1,000,000) and finer scales (US - Soil Survey Geographic Database - SSURGO – 1:12,000- to 1:65,000; CANADA – SLC + Canada Land inventory – CLI - Detailed Soil Surveys - 1:10,000-1:250,000). Due to the diverse soil information related to different spatial and temporal scales as well as type and completeness of information collected; several versions have been suggested for development of raster soil property maps from soil polygon maps that will utilize legacy data and digital mapping techniques. The raster maps will be in accordance with Harmonized World Soil Database and meet the specifications set by GlobalSoilMap.net for major soil properties (soil organic carbon-SOC, pH, clay, silt, sand, coarse fragments, bulk density, available water capacity, ECEC, and soil depth) at 90 m resolution for standard depth increments (0-5,  5-15, 15-30, 30-60, 60-100, 100-200 cm). The objective of this research is to discuss the versioning approach for the North America node and present the preliminary results of selected soil property maps for the US. Raster property maps from both scales of data inherit the inconsistencies related to various spatial and temporal scales as well type and completeness of information. The spatial distribution of soil properties for coarser scale maps showed patterns related to major events of geologic time scale. The US SOC (g kg-1) spatial distribution shows higher values for the north central region (Wisconsin, Minnesota and North Dakota) and south central Florida as well Mississippi Delta. Silt content is higher in mid-west portion of then US that has undergone the most recent glaciations and western portions of Washington state and central Idaho from volcanic ash deposits. Sand content is higher for south east US related to coastal plains deposits, sand hills region in Nebraska and Michigan State related to wind and glacial fluvial deposits. Clay content is generally higher for south Texas and parts of Montana and South Dakota related to old landscapes dominated by palosols. While these trends and patterns are useful for general information and planning at regional scales, the finer scale raster soil property maps will be more beneficial for local planning. Subsequent versions of these maps will use advanced digital soil mapping techniques to develop continuous raster grids of soil properties.