The geography of fragipan soils in the eastern United States

The Soil Taxonomy definition for the brittle, compact subsoil horizons known as fragipans is vague and processes responsible for fragipan formation are poorly understood. Ambiguities in the fragipan definition have resulted in a lack of consistency in the interpretation of fragipan characteristics. These ambiguities may be attributed to difficulties encountered in establishing a precise definition broad enough to encompass the wide range of fragipan soils known to occur. This study approaches the problems of defining and identifying fragipans from a geographic perspective; emphasizing distribution of fragipan soils in the United States, and interpretation of fragipan characteristics across this range. A series of maps based on data gathered from county soil surveys are presented to estimate the areal distribution of fragipan soils in the United States and explore the regional variability of several fragipan characteristics. This study demonstrates that a "universal" definition of fragipans may not be realistic.