Soil Genesis and Variability Along a Benchmark Soil Toposequence In North Alabama.

Variability of soil properties across distances of even a few meters on the landscape is a well recognized phenomenon in soil formation and classification. Soils that show differences profile characteristics that reflect the influence of local topography are called toposequences. Soil toposequences developed on elevated gently rolling stable hillslopes are ideal for studying changes in soil-forming processes with time. In the extreme north Alabama region, much of the physiography is the Highland Rim Section of the Interior Low Plateaus Province, the landscapes are characterized by flat or gently rolling terrain. Geologically, this region is a cuesta surrounding the Central Basin, and characterized by ridges and valleys with a few fairly low hills. Ultisols and Inceptisols are generally found on the different hillslope positions of a typical Highland Rim Landscape, but no detailed investigations of the characteristics of the soils profiles on the toposequences in the area have ever been conducted. The objective of this study was to integrate field soil morphology investigations, physiochemical, characterization, and soil mineralogical interpretations to describe the occurrence and variability of these soils on a benchmark toposequence in North Alabama. Five soil pedons were selected on five hillslope positions. The initial morphological analysis showed that very deep, well drained, reddish strongly developed angular and subangular blocky structures were more common in higher hillslope positions than in lower landscape positions. Reddish colors, depth to the parent material, solum thickness, and thickness of the Bt horizons decreased in the lower landscape positions. Soil profiles on the hillslope positions will be characterized with respect to pH, organic carbon, CEC, contents of Fed, Feo, and Mnd to determine the range of changes in soil characteristics with the landscape positions. X-ray diffraction analysis of the clay-size fraction, will be used to characterize the mineralogy of soils at the landscape positions.