Digital Soil Mapping and SSURGO Data: A Case Study From Louisiana.

Soil Survey Geographic (SSURGO) Database, previously archived and distributed by the Natural Resources Conservation Service (NRCS) - National Cartography and Geospatial Center (NCGC), has been increasingly used by a variety of groups recently. With mapping scales range from 1:12,000 to 1:63,360, the SSURGO database is the most detailed level of soil mapping available for large areas in the United States. Designed for use by landowners, townships, and natural resource planning and management specialists, the SSURGO database was developed based on soil maps constructed from field mapping methods using national standards. The quality of these maps, and by extension the SSURGO database, depends largely on the knowledge and experience level of the field surveyors. Soil maps across large areas were often constructed by multiple field surveyors with varying pedological ideas. This could potentially lead to man-made spatial discontinuity within the database. Digital soil mapping, “the creation and the population of a geographically referenced soil databases at a given resolution by using field and laboratory observation methods coupled with environmental data through quantitative relationships”, provides a methodology to construct soil maps in a way distinct from the traditional soil survey. It applies models that combine information from soil observations with information contained in correlated environmental variables and remote sensing images and thus offers the ability to synthesize this information into a uniform SSURGO product. This study aims 1) to develop a detailed soil map for the state of Louisiana using digital soil mapping based on pedon data registered in the National Soil Characterization Database and correlated environmental variables, 2) to cross-validate the quality of digital soil mapping products with the currently available SSURGO data, and 3) to discuss the limits and problems in digital soil mapping application for large areas.