Characteristics of Solonetzic Soils in Illinois

Abstract

Solonetzic soils, commonly termed “slick-spots,” occupy more than 381,000 acres on nearly level uplands in south-central Illinois and to limited extent in western Illinois. These loess-derived soils, high in exchangeable Na, occur as irregular-shaped areas varying in size from < 1 to > 100 acres. They are intimately associated with rather strongly developed planosolic soils. The climate of this area is humid with mean annual isohyets and isotherms ranging from 36 to 42 inches and 54° to 57°F., respectively. Compared morphologically to associated Planosols, solonetzic soils have similar horizon sequences, but lighter colored surface horizons; thinner subsurface horizons; less well developed, columnar-prismatic B horizons; and contain carbonate concretions randomly distributed throughout their B horizons. The solonetzic soils have higher pH values and greater extractable (water-soluble plus exchangeable) Na regimes than associated soils. In B horizons, solonetzic soils have pH values > 7.5 and extractable Na contents of 4 to 6 me. per 100 g., whereas associated soils usually have pH values < 6.5 and extractable Na contents < 1.0 me. per 100 g. Extractable Na content declines with depth below the B horizon in the solonetzic soils, and is relatively low in the underlying Illinoian till paleosol and Pennsylvanian bedrock, suggesting that these two underlying materials are not the source of Na in solonetzic soils of Illinois.