Hydrology of a Southeastern Coastal Plain Plinthic Soilscape.

The National Cooperative Soil Survey (NCSS) is nearing completion of soil inventories and is emphasizing landscape scale map unit (termed soilscape) interpretations.  Interpretations associated with soil hydraulic properties are of particular importance (e.g. irrigation management, on-site waste disposal, animal waste applications).  Studies evaluating hydrology and hydraulic properties of “benchmark soils” on representative landscapes are thereby essential to soil survey advancement.  Soils with plinthite (plinthic soils) constitute appreciable acreage of the Southeastern US Coastal Plain.  Plinthite is a soil hydromorphological feature; however, its genesis, relationship with contemporary soil saturation and effect on soil hydraulic properties are not well understood.  Therefore, a study was initiated in the Alabama Coastal Plain on a plinthic soil catena (Plinthic Kandi- and Paleudults) in an attempt to: 1) develop improved relationships between plinthite development, soil hydromorphology and seasonal saturation and 2) evaluate vadose zone hydrology in plinthic soilscapes.  Site characterization included high-resolution digital elevation modeling and terrain attribute development, an Order 1 (1:5000) soil survey, and soil morphological and hydraulic characterization.  A transect was established consisting of three nests of instrumentation (piezometers, wells, soil water content) for monitoring both unsaturated and saturated conditions.  Plinthite quantities along the catena ranged from <1 to 50% plinthite in subsoil horizons.  Significant correlation (α=0.05) between soil hydromorphic features, plinthite and contemporary saturation was observed.  Data also suggested a polygenetic formation pathway for these soils coinciding with the depth of maximum plinthite content.  No significant differences between NCSS saturated hydraulic conductivity (K_sat) estimates and measured values were found, although measured values were generally in a lower K_sat class than NCSS estimates.