LOCATION HARCO ILEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Aquic Argiudolls
TYPICAL PEDON: Harco silt loam. (Colors are for moist conditions unless otherwise stated.)
Ap--0 to 9 inches; very dark gray (10YR 3/1) silt loam, gray (10YR 5/1) dry; weak fine granular structure; friable; many very fine roots and fresh worm casts are common; neutral; abrupt smooth boundary.
A--9 to 14 inches; black (10YR 2/1) silt loam; very dark gray (10YR 3/1) crushed, gray (10YR 5/1) dry; moderate medium granular structure; friable; many very fine roots; few concretions (iron oxides); neutral; gradual smooth boundary. (The combined thickness of the A horizon is 10 to 18 inches)
BA--14 to 17 inches; very dark gray (10YR 3/1) silt loam, grayish brown (10YR 5/2) dry; weak fine and medium subangular blocky structure; firm; many very fine roots; common fine distinct olive brown (2.5Y 4/3) masses of iron and manganese oxide accumulation; few fine concretions (iron oxides); neutral; clear smooth boundary. (0 to 4 inches thick)
Bt1--17 to 23 inches; olive brown (2.5Y 4/3) silty clay loam; moderate medium subangular blocky structure; firm; many distinct and prominent very dark gray (10YR 3/1) clay films on faces of ped and in root channels; common very fine roots; common fine distinct yellowish brown (10YR 5/4 and 5/6) masses of iron and manganese oxide accumulation; common concretions (iron and manganese oxides); neutral; clear smooth boundary.
Bt2--23 to 31 inches; olive brown (2.5Y 4/3) silty clay loam; weak medium prismatic structure parting to moderate medium to coarse subangular blocky; firm; many distinct very dark gray (10YR 3/1) clay films on faces of ped and in root channels; common roots; common fine distinct yellowish brown (10YR 5/6) and light olive brown (2.5Y 5/6) masses of iron and manganese oxide accumulation; few fine concretions (iron and manganese oxides); neutral; gradual smooth boundary. (6 to 12 inches thick)
Bt3--31 to 39 inches; olive (5Y 5/3) clay loam; weak medium prismatic structure parting to weak medium subangular blocky; firm; few distinct dark grayish brown (2.5Y 4/2) clay films on vertical faces of ped and few faint dark grayish brown (2.5Y 4/2) clay films on the horizontal faces of peds; common faint very dark gray (10YR 3/1) coatings in root channels; few roots; common medium distinct dark yellowish brown (10YR 4/4) and yellowish brown (10YR 5/6) masses of iron and manganese oxide accumulation; few fine concretions (iron and manganese oxides); neutral; gradual smooth boundary. (Combined thickness of the Bt horizon is 14 to 31 inches.)
C1--39 to 49 inches; mixed grayish brown (2.5Y 5/2) light olive brown (2.5Y 5/3) and yellowish brown (10YR 5/6) silt loam; massive; friable; common fine very dark gray (10YR 3/1) coatings in root channel; few fine concretions (iron and manganese oxides); slightly effervescent; slightly alkaline; diffuse smooth boundary.
C2--49 to 61 inches; yellowish brown (10YR 5/6) silt loam; massive; friable; common medium distinct light olive brown (2.5Y 5/3) iron depletions; strongly effervescent; moderately alkaline.
TYPE LOCATION: Gallatin County, Illinois; about 2 miles southeast of Cottonwood; 300 feet east and 1,420 feet north of the southwest corner of sec. 35, T. 7 S., R. 9 E.
RANGE IN CHARACTERISTICS: The thickness of the mollic epipedon ranges from 10 to 18 inches. The depth to the base of soil development ranges from 25 to 45 inches. The depth to carbonates ranges from 30 to 40 inches. The series control section averages between 5 and 20 percent total sand and less than 5 percent rock fragments.
The Ap or A horizon has value of 2 or 3 and chroma of 1 or 2. It is silt loam. Reaction is slightly acid or neutral.
The Bt horizon has hue of 10YR, 2.5Y, or 5Y, value of 4 to 6, and chroma of 1 to 4. It is silt loam or silty clay loam. Average clay content ranges from 24 to 35 percent. Reaction ranges from slightly acid to neutral.
Some pedons have a BC horizon.
The C horizon has hue of 10YR, 2.5Y, or 5Y, value of 4 to 6, and chroma of 1 to 6. It is silt loam with average clay content ranging from 20 to 27 percent. Reaction ranges from slightly alkaline to moderately alkaline.
COMPETING SERIES: These are the Arrowsmith, Bearpen, Brenton, Edwardsville, Elburn, Grundelein, Hacreek, Higginsville, Keller, Lafayette, Lawndale, Lisbon, Lismod, Loran, Mundelein, Muscatune, Nevin, Raub, Rooks, Rowley and Shannondale soils in the same family and the Frankenmuth soils in a closely related family (cation exchange activity class not assigned). Bearpen, Brenton, Elburn, Frankenmuth, Grundelein, Keller, Lawndale, Lisbon, Lismod, Mundelein, Raub, Rowley and Shannondale soils average more than 20 percent sand in the lower part of the control section. Edwardsville and Hacreek soils are more than 40 inches to carbonates. Higginsville, Loran, and Rooks soils average more than 27 percent clay in the lower part of the control section. Lafayette soils contain more than 5 percent rock fragments in the lower part of the control section. Nevin soils have mollic epipedons greater than 18 inches thick and are more than 40 inches to carbonates.
GEOGRAPHIC SETTING: The Harco soils are on nearly level stream terraces. The soils formed in texturally uniform silty sediments (of Wisconsin Age?) which has a mixed mineralogy and contains free carbonates between depths of 30 and 40 inches. Slope gradients range from 0 to 3 percent. Climate consists of hot summers and cold winters with mean annual air temperature between 46 and 57 degrees F and precipitation between 30 and 45 inches per year.
GEOGRAPHICALLY ASSOCIATED SOILS: Soils commonly in association with the Harco soils are the Patton and Marissa soils. Marissa soils have an E horizon, higher average clay content in the Bt horizon, and are on similar positions nearby. The poorly drained Patton soils have more clay in the upper part of the control section and are on somewhat lower elevations.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained. Potential for surface runoff is low. Permeability is moderate. The depth to the top of an apparent seasonal high water table ranges from 1 to 2 feet in the spring in normal years.
USE AND VEGETATION: Most areas are cultivated. Corn, soybeans, small grain, and pasture are the principal crops. Native vegetation is prairie grasses.
DISTRIBUTION AND EXTENT: Southeastern Illinois. Extent is small.
MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Saline County, Illinois, November 29, 1974.
REMARKS: Diagnostic horizons and soil features recognized in this pedon are:
mollic epipedon -- the zone from the surface to a depth of 17 inches (Ap, A, and BA horizons);
argillic horizon -- the zone from 17 inches to 39 inches (Bt horizons).