Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Accelerated erosion poses several problems for soil classification. Removal of surface soil can result in the thinning or removal of a mollic epipedon and can alter the clay distribution, an essential feature, of an argillic horizon. Erosional processes and soil properties vary across the landscape. This study examines the distribution of clay, total phosphorus, organic carbon, pH, clay mineralogy, and soil micromorphology in a small, first-order loess watershed. Twenty pedons from five different hillslope elements were used to study the relationship between soil properties, landscape position, and erosion;Soils on the summit and shoulder positions are similar in their clay, total phosphorus, organic carbon, and pH distributions. Shoulder soils are slightly more eroded than soils on the summit. Clay distributions on both positions are marginal to the argillic requirement. Thin section analysis, however, shows sufficient illuvial clay to meet the argillic criteria. Total phosphorus distributions resemble curves for forest or transition soils. Summit and shoulder soils are best classified as eroded Alfisols;Backslope soils display little profile development. Clay maximums and total phosphorus minimums occur at the surface. Illuvial clay is not evident in thin section. Accelerated erosion has truncated at significant portion of these soils. Evidence suggests that soils on the backslope were Inceptisols prior to cultivation;Footslope soils are a result of cumulic additions. A well-defined zone of phosphorus depletion exists in these soils. The organic carbon content in the footslope soils varies with aspect within the watershed. These soils are Mollisols;Toeslope soils are composed predominantly of post-cultural erosion sediments and inherit their properties from this material. Lighter colored sediments at the soil surface place these soils in the Entisol order;Clay mineralogy is consistent between landscape positions. Smectite content increases with depth while hydroxy interlayer minerals have a maximum in the surface and decrease with depth. Minor amounts of kaolinite, quartz, and vermiculite make up the remainder of the clay suite. Soils on younger geomorphic surfaces contain more vermiculite in the lower horizons. Smectites at all positions appear to have a mix of both tetrahedral and octahedral charge.



Digital Repository @ Iowa State University,

Copyright Owner

Douglas A. Wysocki



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253 pages