Date of Award
Doctor of Philosophy
This study was concerned with the genesis of loess-derived soils in southern Iowa. Field sites were selected on flat and sloping primary divides along two linear traverses oriented to represent loess distributional patterns. Field measurements for each site included loess thickness and the vertical extent of a zone of groundwater saturation perched above the slowly permeable paleosolic surface immediately subjacent to the loess. Physical and chemical properties of the genetically related soils were evaluated with relation to horizon differentiation, natural drainage, and their potential as indices of soil development in loess-derived soils;Loess thickness on the flat and sloping primary divides decreased systematically with distance from the major source area (the Missouri River Valley). Internal drainage of the soils became poorer as loess thickness decreased and distance from the source area increased. Maximum clay content in the solum and B/A clay ratio were found to increase with distance from the source area as loess thickness decreased and as the internal drainage became poorer on the flat and sloping divides. As the loess decreased in thickness from west to east, the depth to the Yarmouth-Sangamon surface decreased as well as the depth to the water table perched above this slowly permeable paleosolic surface. Negative correlations were found between the depth to the perched water table and distance from the loess source, capillary porosity of the B and C horizons, total porosity of the B horizon, and rainfall on the flat and sloping divides. Positive correlations were found between the depth to the perched water table and total porosity of the C horizon and temperature on the flat and sloping divides;Mathematical prediction equations were formulated that adequately predict the monthly depth to the perched water table on the flat and sloping divides. The higher water tables on the eastern end of the traverses were attributed to the stratigraphic and geomorphic conditions of the divides. This high water table provided an environment conducive to accelerated weathering. This weathering was reflected in the increase in <2 micron clay with distance from the source area, higher B/A clay ratios, the depth distribution of total, inorganic, and available phosphorus and organic carbon in the loess-derived profiles;Total, inorganic, and available phosphorus values showed distinct eluvial and illuvial zones in their depth distribution. The zones were found to be more pronounced from west to east along the traverses. Organic phosphorus and organic carbon decreased vertically with increasing depth in all profiles studied. The weighted average total and organic phosphorus and organic carbon in the 10-40 inch section and the solum decreased as horizon differentiation increased and as the internal drainage of the soils became poorer.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Tommy Lee Coleman
Coleman, Tommy Lee, "The influence of stratigraphy and landscape position on the genesis of upland loess-derived soils of southern Iowa " (1980). Retrospective Theses and Dissertations. 6690.