Harmonization of Digital Soil Survey Information Across the Canada-US Border.

Efforts are underway to create a seamless raster based world soil map of 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). Development of this new digital soil map relies on existing soil maps from various regional and national soil survey programs. These maps are of different scales and different ages, and were created for different purposes using different mapping concepts. Consequently, the harmonization of soil information across country borders will be required. We are investigating methods for overcoming the difference in soil information related to different spatial and temporal scales as well as type and completeness of information collected by the US and Canada. Spatial soil information for US and Canada is provided as polygon maps at coarse scales (greater than 1:250,000) and finer scales (less than 1:250,000). A case study for an area along the North Dakota-Manitoba border has provided opportunities to apply digital mapping techniques to produce more detailed, spatially-continuous soil information. The preliminary results indicate that geomorphic land surface classifications based on elevation derivatives are a good approximation of the soil landscape relationships for both countries and the subsequent spatial correlation at coarse scales. Scale differences, especially related to the level of detail within soil map units remained and required further investigations of soil map unit compositions and their soil components in order to taxonomically correlate similar soils based on their geomorphology. Similar soils were further disaggregated based on soil properties that showed spatial patterns at scales different from the soil polygon maps.