Soils of the Southeastern USA: LRRs O, P, and T

Abstract

Land Resource Regions (LRRs) O, P, and T encompass the southeastern USA with the exception of the Florida peninsula (LRR U). Although climate is uniformly warm and humid, the region has a wide variety of soil parent materials and topographies that give rise to a broad range of soils. Soils in LRR O have primarily developed in Holocene and Pleistocene alluvium associated with floodplains and terraces of the Mississippi, Arkansas, and Red Rivers. The region has fertile soils, smooth topography, abundant moisture, and a long growing season, which favor agricultural production. The relatively flat topography gives rise to a preponderance of somewhat poorly and poorly drained Vertisols, Inceptisols, and Alfisols. Only on topographically high convex landforms are moderately well- and well-drained soils found. LRR P is dominated by two types of soil parent materials: saprolite from Precambrian to late Paleozoic acid igneous and metamorphic rocks (Southern Piedmont), and Tertiary and younger fluviomarine sediments that comprise the Atlantic and Gulf Coastal Plains. In the Southern Piedmont, most upland soils are Ultisols that are deep, well drained, and moderately permeable. Loamy surface horizons are thin and overly red clayey subsoils dominated by kaolinite and other low-activity clays. Although the area was historically used for crop production, it is currently dominantly forest and pasture. The Southern and Western Coastal Plains are underlain by sediments ranging in age from Cretaceous at the interior margin to Holocene in coastal areas and alluvial valleys. Topography varies from rolling hills in the interior to broad swampy flats at low elevations. Most upland soils are Ultisols that are deep and acidic and have low base saturation. Crops, forests, and pasture are dominant land covers across the region. LRR T is the lowest elevation part of the Southern Coastal Plain. As elevations decrease toward the sea, relief decreases, and upland interfluves become wider with large areas of poorly and very poorly drained soils interspersed with swamps , estuaries, and lagoons. Along the Atlantic and Gulf coasts east of the Mississippi River, soils are dominantly Ultisols similar to those in the inland part of the coastal plain although Spodosols and Histosols are common. The region west of the Mississippi River (Louisiana and Texas) has similar landscapes, but soils have thicker surface horizons, more fertile subsoils with active clays, and are dominantly Mollisols, Alfisols, and Vertisols.

L.T. West retired from USDA-NRCS