I studied the effects of erosion on pore size distributions and corn root ramification with depth, using Hg intrusion porosimetry. In particular, I examined the paired erosion phases of two fine-textured Illinois soils, one dominated by smectite and the other by hydrous mica. Total porosites of each moist, clayey soil sample were reduced as much as 8% when oven-dried, having the potential to alter pore size classes and corresponding volumes. The proposed method requires sampling fine-textured soils in the field when the profiles are moist (approximately at field capacity) and transporting them to the laboratory in moisture tins. In the laboratory, soil samples are rapidly frozen in liquid N and freeze-dried prior to being intruded with Hg using a porosimeter. The freeze-dried method was selected so measured soil pore sizes approximated those that the corn root tips would encounter when growing into soils at a similar moisture content. The water retention differences (WRD) measured by water-release methods appeared to correlate well with the freeze-dried (50 to 0.5 μm in equivalent diameter) pore class volumes that were not subjected to shrinkage upon drying or swelling associated with unconfined soil sample saturation and equilibration methods. The pore size classes and corresponding volumes varied with soil series, clay mineralogy, and depth. For both the subsoil and parent material, the fine-textured Clarence soils dominated by hydrous mica had much smaller transmission pore volumes and water storage volumes. Topsoil loss resulted in a greater reduction in rooting volume and water-storage capacity of the Clarence soils and resulted in greater corn yield reductions. Efforts to restore the soil productivity of the Clarence and Hoyleton soils will require an increase in the total soil porosity, water-storage pore volumes, transmission pore volumes, and rooting depth.
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