This major land resource area (MLRA 120) occupies 3 million ha (7.65 million acres) in western Kentucky and eastern Indiana. Much of the general information in this section was excerpted from USDA (1981).
Climate Annual precipitation in MLRA 120 averages 1,185 mm, of which approximately half falls during the growing season (Fig. 1). Snowfall is highly variable and averages 25 cm per year. The mean annual temperature is 14°C, with an average of 185 frost-free days.
Geology and Topography MLRA 120 includes the Western Kentucky Coal Field, which is smaller than its eastern counterpart, the Eastern Kentucky Coal Field. It comprises the southern edge of a larger geologic feature called the Illinois or Eastern Interior Basin, which includes the coal fields in Indiana and Illinois. As in eastern Kentucky, the border of the Western Kentucky Coal Field and the Mississippi Plateau is commonly marked by an escarpment because thick Pennsylvanian-age sandstones are resistant to erosion. However, since this coal field is not adjacent to the Appalachian Mountains, and the sandstones are less continuous, the escarpment is not as dramatic as along the Cumberland Escarpment of the Eastern Kentucky Coal Field.
Elevation ranges from 100 m on the Ohio River flood plain to about 200 m on the higher ridges. Local relief is generally 50 to 100 m between ridgetops and the flood plains of local streams. The area is mostly hilly with broad undulating ridge tops on major divides. The flood plains and terraces of the Ohio River and its tributaries are nearly level to sloping.
Landuse Most of MLRA 120 consists of small- and medium-sized farms. A large area in Indiana is in the Hoosier National Forest; some large tracts belong to coal mining companies. About 40% of the area is in cropland, but the acreage varies widely from county to county depending largely on the topography. Corn, soybeans, and wheat are the major crops, with tobacco important in some parts.
About 40% of the area is in forests of mixed hardwoods, but forest products are important in only a few parts of the area. Oak-hickory forest occurs on the rolling plateaus. Coves and cooler slopes support mixed hardwood vegetation of beech, sugar maple, yellow-poplar, white ash, and red and white oak. Eastern red cedar often grows on the shallower limestone soils. Such bottomland hardwoods as cottonwood, cherrybark oak, pin oak, Shumard oak, sweetgum, and swamp white oak occur on the flood plains.
About 17% of the area is pasture used mostly for beef cattle production. Urban development is minor. Stabilizing strip mine spoil is a major concern of management.
Water Resources Water is relatively abundant throughout the region. In most years, precipitation is adequate for crops. In some years, however, droughts reduce yields, and in others too much rainfall delays planting or interferes with harvesting operations. The large streams and constructed lakes supply most of the urban water, and waterlines carry this water to nearby rural communities. Large quantities of ground water are available in the valley of the Ohio River and its major tributaries, but only small quantities are locally available throughout the rest of the area.
Soils Most of the soils in MLRA 120 are Udalfs. They are medium to moderately fine textured, have a mesic temperature regime, a udic moisture regime, and mixed mineralogy. They formed in loess and in residuum from sandstone, shale, and siltstone. The major soil associations in MLRA 120 are: Zanesville-Frondorf, Grenada-Loring, and Belknap-Karnak (Table 1). Selected soil physical properties for these soils are given in Table 2. STATSGO soils of the region are shown in Fig. 2.
Soils of the Zanesville-Frondorf association are deep and moderately deep Fragiudalfs and Hapludalfs. They are well drained, formed in residuum from acid shales, siltstone and sandstone capped with a thin loess mantle on broad ridge tops and steep side slopes in the Western Coalfields. Soils of the Grenada-Loring association are deep, moderately well drained Fragiudalfs, formed in loess on undulating and hilly uplands of the Western Coalfields. Soils of the Belknap-Karnak association are Fluvaquents and Hapludalfs. These are deep, somewhat poorly to poorly drained soils formed in loamy and clayey alluvium on nearly level flood plains and undulating terraces in the thick loess area of the Western Coalfields.
Water and Contaminant Transport Data on water and contaminant transport in soils of this MLRA are limited. Green (1970) measured saturated hydraulic conductivity (Ksat) as a function of depth for each of three replicates of five soils (Memphis, Loring, Grenada, Calloway and Henry) in the Memphis soil catena. Regression analysis revealed that total porosity was the best predictor of saturated hydraulic conductivity for these soils with Ksat increasing as a power law function of porosity (Fig. 3). Values of Ksat for Karnak silty clay loam have been determined by the auger-hole method (Haszler, 1988). This method is an in situ procedure and is accomplished by drilling an auger hole below the watertable and recording the time for the change of head. The resulting range for Ksat was 0.028 to 0.15 cm hr-1. Additional soil hydrological properties, including the water retention curve, saturated hydraulic conductivity and unsaturated hydraulic conductivity vs. tension function, are available for the Grenada soil (see Cassel [1985] and Römkens et al., [1986]).
In terms of solute transport, Tyler and Thomas (1981) have published a break-through curve (BTC) for chloride applied as a pulse to an undisturbed partially-saturated column of Karnak soil. Chloride appeared in the first effluent fraction collected after the pulse application, and maximum Cl concentrations occurred after just 0.05 pore volumes had leached at an average flow rate of 0.45 cm/hr (see Fig. 3 in Tyler and Thomas, 1981). The shape of the Karnak BTC indicates that some of the chloride solution moved rapidly through the initially drained macropore space mixing little with resident soil water. Kluitenberg and Horton (1990) have shown similar rapid increases in chloride concentration for BTCs with initially drained undisturbed soil materials.
Literature Cited Cassel, D.K. (ed). 1985. Physical characteristics of soils of the southern region - summary of in situ unsaturated hydraulic conductivity, Southern Cooperative Series Bull. 303, Regional Research Project S-124, North Carolina State Univ., Raleigh, North Carolina, 143 pp.
Green, W.H. 1970. Relationships between hydraulic conductivity and the chemical and physical properties of the Memphis soil catena. Unpublished M.S. Thesis, University of Kentucky, Lexington.
Haszler, G.R. 1988. Drainage characteristics and nitrogen response on a tiled Karnak silty clay soil. Unpublished M.S. Thesis, University of Kentucky, Lexington.
Kluitenberg, G.J. and G. Horton. 1990. Effects of solute application method on physical transport of solutes in soil. Geoderma 46:283-297.
Römkens, M.J.M., J.M. Selim, H.D. Scott, R.E. Phillips and F.D. Whisler. 1986. Physical characteristics of soils in the southern region - Captina, Gigger, Grenada, Loring, Oliver, and Sharkey series. Southern Cooperative Series Bull. 264, Regional Research Project S-124, Mississippi Agric. and For. Exp. Stn., Mississippi State Univ., Mississippi State.
Tyler, D.D., and G.W. Thomas. 1981. Chloride movement in undisturbed soil columns. Soil Sci. Soc. Am. J. 45:459-461.
USDA. 1981. Land resource regions and major land resource areas of the United States. U.S. Department of Agriculture, Soil Conservation Service Handbook No. 296.
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