Tuesday, November 14, 2006

Landscape Evolution and Soil Pedogenesis in a MLRA Benchmark Catena.

M.A. Wilson1, S.J. Indorante1, B.D. Lee2, Leon Follmer3, D.R. Williams1, B.C. Fitch1, Kara Kleinschmidt4, J.D. Bathgate1, W.M. McCauley1, and R. Burt1. (1) USDA-NRCS, 100 Centennial Mall N, Rm 152; MS 41, Lincoln, NE 68522, (2) Purdue Univ, 915 W State St, West Lafayette, IN 47907, (3) Illinois State Geological Survey, 204 Natural Resources Building, 615 E. Peabody Drive, Champaign, IL 61820, (4) USDA-Forest Service, 148 E Pleasant Hill Rd, Suite 105, Carbondale, IL 62903

Soils in Major Land Resource Area 115 (Central Mississippi Valley Wooded Slopes) in southern Illinois, Indiana, and Missouri are developed from a thick mantle of loess in a udic soil moisture regime.  Distinct differences in soils exist based on landform position resulting from hydrologic influences.  Soils in a representative 10 ha watershed in Union County, Illinois were studied to evaluate properties and determine dominant processes influencing pedogenesis and soil-landform distribution.  Soils develop from 12-25 ka (late Wisconsianan-aged) Peoria loess overlying the 28-55 ka (middle Wisconsinan-aged) Roxana silt.   A terra-rosa geosol and karsted Mississippian-aged limestone underlies the Roxana material.  The site has been in fescue for about 15 yr, but was row cropped previously.  Deep, well drained soils of the Menfro series (Typic Hapludalfs) compose convex ridge top and shoulder slope positions.  These soils have pH ranging from 5.0 to 7.4 and thick argillic horizons.  Bisequal soils (Oxyaquic Fragiudalfs) with a fragipan at depths ranging from 50-100 cm develop in soils on shoulder and backslope positions.  Fragipans develop at the contact between the Peoria and underlying Roxanna loess.  Depth to pan is also influenced by soil erosion.  Amount of topsoil loss is 25-50 cm across the study area based on depth to clay maximum for soils in this landscape position.  Redox concentrations are present above the pan indicating the hydrologic discontinuum.  Fragipans are >100 cm or absent in lower backslope/upper footslope positions and soils classify as Oxyaquic or Aquic Hapludalfs.  The pH in the lower argillic horizons of this position are >8.0 suggesting lateral groundwater discharge associated with underlying stratigraphic discontinuities.