Forest soil uniformity along toposequences in the loess-mantled Driftless Area of Wisconsin
Frolking, T.A.
Forest soils in the loess-mantled ridge and ravine topography of the Driftless Area of southwest Wisconsin show minimal effects related to hillslope gradient. Twelve undisturbed Fayette silt loam profiles (Typic Hapludolf, fine silty, mixed, mesic) that developed in Peoria loess and silty colluvium on slopes of 2 to 55% were examined to ascertain systematic differences as a function of slope. Climate, vegetation, parent material, and time of development were similar for the 12 profiles. Physical and chemical properties of the A and E horizons (including texture, pH, dithionite extractable Fe and Mn, and total P) do not vary significantly as a function of slope gradient. Of the B and C horizon properties measured, only Bt horizon pH, clay accumulation, and total P distribution show statistically significant variations with slope gradient. The Bt horizon pH decreases with increasing slope gradient (r2 = 0.63). Illuvial horizons show less clay accumulation in profiles on steeper slopes (r2 = 0.37). Total P content is higher throughout the B and C horizons of profiles on steep slopes (45%) compared to soils on level and moderate slopes (2-20%). Together these results indicate slightly less leaching of the subsoil on steep slopes. Exchangeable Ca/Mg, Fe(d), Mn(d), maximum clay, and depth to maximum clay reveal no trends as a function of slope gradient. Soil conditions have favored infiltration and minimized surface erosion, leading to nearly uniform soil development in homogeneous parent materials on ridgecrests and sideslopes.
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