Eleroy and Derinda soils (Typic Hapludalfs) and Keltner and Schapville soils (Typic Argiudolls) were studied. Weathering of silt‐size minerals is not advanced in these relatively youthful soils. Iron is the most sensitive indicator of weathering, being particularly labile in the Hapludalf profiles. Iron weathers from silt‐size minerals and is localized in concretions and in the clay fraction. Clay‐mineral weathering involves formation of chloritized vermiculite and montmorillonite from illite and montmorillonite precursors. The stage of weathering of these soils approximates that in Clinton, Fayette (Hapludalfs), and Tama (Argiudoll) soils that occur along the Mississippi River. Soil test values for K and P and amounts of exchangeable K and total P are high. Productivity is related more to depth of underlying shale and attendant physical effects than to nutrient status.
Corn roots (Zea mays L.) did not penetrate calcareous Maquoketa shale (IIC) horizons appreciably in four soils derived from thin loess on shale in northwestern Illinois. Alfalfa roots (Medicago sativa L.), in contrast, penetrated the shale horizons to considerable depths. This difference in rooting behavior of the two plants probably explains the better adaptation of a perennial taprooted plant such as alfalfa to these soils than an annual plant such as corn. The shale (IIC) horizons had low total porosities «38%), very low noncapillary porosities «1.5'%), high bulk densities (>1.69 g/cc), and were impermeable to water. Bulk density slightly greater than 1.80 g/cc and intraped porosity of slightly less than 32% of discrete peds in the IIC horizons appear to be limiting to corn root penetration. Seepage and erosion problems on these soils are related to the impermeable nature and depth to the underlying shale.
Exhumed paleosols and modern soils formed in Illinoian and/or Kansan till occur in a complex pattern in many places on the sides of incised valleys in predominantly loess covered regions in western Illinois and adjacent states. The paleosols studied in western Illinois are thicker, finer textured, grayer and more poorly drained, and more impermeable than the modern soils formed during late Pleistocene and Recent weathering. However, the paleosols and modern soils do not differ greatly in chemical properties.The presence of highly contrasting paleosols and modern till soils on the same slope not only cause problems in soil mapping, but because of side‐hill seepage, and the fine texture and poor physical condition of the paleosols, difficult problems in soil management also exist. The use of soil complexes, undifferentiated units, or the inclusion of strongly contrasting soils in given mapping units is necessary to show these soil conditions on many slopes.
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