Land use: Most of this area consists of small and medium-size farms. Urbanization is relatively small. Extensive forests are on the deeply dissected hills surrounding the Nashville Basin and along the western edge joining the Coastal Plain. Elsewhere, the forests consist mostly of small farm woodlots. Hay and pasture for beef cattle are the principal crops. Corn and soybeans, grown mostly on narrow strips of bottom land and on upland flats, are important locally. Tobacco, especially burley, is an important cash crop.
Elevation and topography: Elevation is 200 to 300 m, ranging from about 100 m along the deepest valley floors to about 400 m on the crest of isolated hills. The area is greatly diversified with low rolling hills, upland flats, and narrow valleys. Steep slopes occur where the encircled Nashville Basin cuts into the area and along the western edge bordering the Coastal Plain. Elsewhere, except for steep walls and hillsides along deeply cut stream channels, the topography is predominantly gently rolling to strongly rolling with a few interruptions by broad upland flats and shallow basins. In many places the land surface is pitted by limestone sinks.
Climate: Average annual precipitation-1,125 to 1,375 mm. Maximum precipitation is in winter and early in spring, and the minimum is in fall. Average annual temperature-13 to 16 C, decreasing from south to north. Average frost-free period-180 to 205 days, decreasing from south to north.
Water: In most years, precipitation is adequate for crops, but in some years, yields are reduced by short dry periods early in summer. The numerous perennial streams and lakes supply abundant water to much of the area. Several medium to large lakes constructed by the U.S. Corps of Engineers provide flood control, power production, recreation, and water for municipalities. In some parts where surface water is scarce, the water comes mainly from wells, large springs, and farm ponds. In many places, waterlines from metropolitan areas extend far into the countryside.
Soils: Most of the soils, southward from about the Kentucky-Tennessee border, are Udults that have a thermic temperature regime, an udic moisture regime, and siliceous and kaolinitic mineralogy. Udalfs and Udulfs of mesic temperature regime, udic moisture regime, and mixed mineralogy are dominant in Kentucky and in Indiana. The soils generally are very deep to cherty limestone and strongly acid and highly leached and have a subsoil rich in clay. In the southern part, well drained, cherty Paleudults (Baxter, Bodine, and Fullerton series) are on hillsides, and moderately well drained Fragiudults (Dickson and Sango series) are on upland flats. Fragiaquults (Guthrie series) are in small basins and depressions, and Dystrochrepts (Ennis and Lobelville series) are in narrow strips of bottom land. In the northern part, well drained Paleudults (Baxter and Frederick series) are on hill slopes, well drained Paleudalfs (Crider and Pembroke series) are on broad smooth areas capped with loess, and moderately well drained Fragiudults and Fragiudalfs (Bedford, Nicholson, and Lawrence series) are on upland flats. On the narrow strips of bottom land are mainly Hapludolls (Huntington series), Udifluvents (Haymond series), and Eutrochrepts (Nolin series). In the extreme northernmost part in Indiana, a sizable area is underlain by shale, sandstone, and limestone; loamy-skeletal Dystrochrepts (Weikert and Berks series) and Hapludults (Gilpin series) are on the slopes, and Hapludalfs (Wellston series) and Fragiudalfs (Zanesville series) are on upland flats capped with loess.
Potential natural vegetation: This area supports oak-hickory forests.
Yellow-poplar is common on the deeper soils. Understory plants include a
variety of grasses, forbs, vines, and shrubs. Little bluestem and broomsedge
are dominant grass species.
(From "Land Resource Regions and Major Land Resource Areas of the United
States". United States Department of Agriculture Soil Conservation Service
Handbook 296. Dec. 1981. page 88.)