LOCATION BUNKUM             IL

BUNKUM SERIES

The Bunkum series consists of very deep, somewhat poorly drained, moderately slowly permeable soils on dissected till plains. They formed in loess; or in loess and the underlying silty water-worked sediments (pedisediment). Slope ranges from 2 to 18 percent. Mean annual precipitation is about 38 inches, and mean annual temperature is about 55 degrees F.

TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Aquic Hapludalfs

TYPICAL PEDON: Bunkum silty clay loam - on a severely eroded west-facing back slope with a gradient of 9 percent in a cultivated field at an elevation of about 510 feet. (Colors are for moist soil unless otherwise stated.)

Ap--0 to 8 inches; mixed brown (10YR 4/3) and yellowish brown (10YR 5/4) silty clay loam, pale brown (10YR 6/3) dry; moderate very fine subangular blocky structure; friable; many very fine roots; common fine and medium constricted tubular pores; common fine rounded black (7.5YR 2.5/1) iron-manganese nodules with sharp boundaries; about 30 percent clay; neutral; abrupt smooth boundary. (3 to 9 inches thick)

Bt1--8 to 16 inches; yellowish brown (10YR 5/4) silty clay loam; moderate fine and medium subangular blocky structure; firm; common very fine roots; few fine constricted tubular pores; common distinct brown (10YR 5/3) clay films on faces of peds; few fine distinct light brownish gray (10YR 6/2) iron depletions and common fine distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium rounded black (7.5YR 2.5/1) iron-manganese nodules with sharp boundaries; about 34 percent clay; slightly acid; clear smooth boundary.

Bt2--16 to 26 inches; yellowish brown (10YR 5/4) silty clay loam; weak fine prismatic structure parting to weak fine and medium subangular blocky; firm; common very fine roots; few very fine constricted tubular pores; common distinct brown (10YR 4/3) clay films on faces of peds; common fine distinct light brownish gray (10YR 6/2) iron depletions and common fine and medium prominent strong brown (7.5YR 5/6) masses of iron accumulation in the matrix; common medium and coarse irregular black (7.5YR 2.5/1) masses of iron-manganese accumulation with clear strong brown (7.5YR 4/6) boundaries; about 31 percent clay; slightly acid; clear smooth boundary.

Btg1--26 to 32 inches; grayish brown (2.5Y 5/2) silty clay loam; weak medium prismatic structure parting to weak medium angular blocky; firm; few very fine roots; few fine and medium constricted tubular pores; common distinct dark grayish brown (10YR 4/2) clay films on faces of peds; few fine distinct light olive brown (2.5Y 5/4) and common medium prominent strong brown (7.5YR 5/6) masses of iron accumulation in the matrix; few medium and coarse irregular black (7.5YR 2.5/1) masses of iron-manganese accumulation with clear strong brown (7.5YR 4/6) boundaries; about 28 percent clay; moderately acid; clear smooth boundary.

Btg2--32 to 40 inches; light brownish gray (2.5Y 6/2) silt loam; weak coarse angular blocky structure; friable; few very fine roots; few fine and medium constricted tubular pores; few prominent dark grayish brown (10YR 4/2) clay films on vertical faces of peds; common medium and coarse prominent strong brown (7.5YR 5/6) masses of iron accumulation in the matrix; few medium irregular black (7.5YR 2.5/1) masses of iron-manganese accumulation with clear strong brown (7.5YR 4/6) boundaries; about 26 percent clay; moderately acid; gradual smooth boundary. (Combined thickness of the Bt horizon is 27 to 52 inches.)

CBg--40 to 58 inches; light brownish gray (2.5Y 6/2) silt loam; massive; friable; few very fine roots; few fine and medium constricted tubular pores; few medium and coarse prominent strong brown (7.5YR 5/6) masses of iron accumulation in the matrix; few fine and medium irregular black (7.5YR 2.5/1) masses of iron-manganese accumulation with diffuse strong brown (7.5YR 4/6) boundaries; about 21 percent clay; slightly acid; abrupt smooth boundary. (0 to 24 inches thick.)

2CB--58 to 80 inches; brown (7.5YR 5/4) silt loam; massive; friable; few fine and medium constricted tubular pores; few fine distinct pinkish gray (7.5YR 6/2) iron depletions; few medium rounded very dark brown (7.5YR 2.5/3) iron-manganese concretions with clear strong brown (7.5YR 4/6) boundaries; about 25 percent clay and 8 percent sand; slightly acid.

TYPE LOCATION: St. Clair County, Illinois; about 1 mile west of Smithton in St. Clair County, Illinois; approximately 1,740 feet south and 160 feet east of the center of sec. 29, T. 1 S., R. 8 W.; USGS MILLSTADT, ILL. topographic quadrangle; lat. 38 degrees 24 minutes 47 seconds N. and long. 90 degrees 00 minutes 37 seconds W. NAD 27.

RANGE IN CHARACTERISTICS: The depth to the base of the argillic horizon is 24 to 60 inches. Loess thickness typically is 24 to about 60 inches. The particle-size control section averages 25 to 35 percent clay and contains less than 7 percent sand. Typically about one-third to one-half of the sand is very fine.

The Ap, A, and E horizons have value of 4 or 5 (6 or 7 dry) and chroma of 2 to 4. It is silt loam or silty clay loam. Clay content is 18 to 35 percent and sand content is less than 7 percent. Reaction is strongly acid to slightly acid except in pedons that have been limed range to neutral.

In most eroded pedons the E horizon has been mixed into the Ap horizon.

The Bt and Btg horiozns have value of 4 to 6 and chroma of 2 to 4 in the upper part. In the middle and lower part it has hue of 10YR, 2.5Y, or less commonly 5Y; value of 4 to 6; and chroma of 1 or 2. Redoximorphic features have hue of 7.5YR or 10YR, value of 4 to 6, and chroma of 1 to 8. Clay films commonly have chroma of 2 or 3 in the upper part and 1 to 4 in the lower part. The Bt horizon is silty clay loam or silt loam. Clay content is 25 to 35 percent. Reaction is very strongly acid to moderately acid in the upper part and strongly acid to slightly acid in the lower part.

The BCg or CBg has hue of 10YR, 2.5Y or 5Y, value of 4 to 6, and chroma of 1 to 4. Colors of redoximorphic features are in the range as defined for the Bt horizon and also includes 5YR hue. Texture is silt loam. Clay content is 18 to 27 percent and sand content is less than 7 percent. Reaction is strongly acid to neutral.

The 2CB, and 2C horizons, where present have hue of 7.5YR, 10YR, 2.5Y, or 5Y; value of 4 to 6; and chroma of 1 to 4. Texture is commonly silt loam, or less commonly, silty clay loam, loam or clay loam. Clay content is 15 to 30 percent and sand content is 5 to 30 percent. Reaction is strongly acid to neutral.

COMPETING SERIES: These are the Appleriver, Blair, Fishhook, Freeburg, Geff, Glenford, Keene, Lykens, Muren, Reesville, Sugarvalley (T), Torox, Travilah, and Xenia series. Appleriver soils have a paralithic contact between a depth of 45 and 60 inches. Blair soils have some part of the series control section above a depth of 24 inches that averages more than 7 percent sand and averages more than 1 percent rock fragments in the lower part of the series control section. Fishhook soils average more than 35 percent clay in the lower part of the series control section. Freeburg soils contain more than 7 percent sand in the upper part of the series control section. Geff soils average more than 7 percent sand within a depth of 40 inches. Glenford soils have a mean annual soil temperature of less than 54 degrees F. Keene soils have weathered bedrock in the lower part of the series control section. Lykens, Reesville, Sugarvalley (T), Torox, and Xenia soils contain carbonates within a depth of 60 inches. Muren soils have less than 7 percent sand throughout the series control section. Travillah soils have a lithic contact between a depth of 20 and 40 inches.

GEOGRAPHIC SETTING: Bunkum soils are on gently sloping to moderately steep parts of dissected Illinoian till plains. Slope ranges from 2 to 18 percent. These soils formed in loess; over silty, water-worked pedisediment and the underlying paleosol. Mean annual air temperature is 54 to 57 degrees F., mean annual soil temperature is 56 to 59 degrees F., mean annual precipitation is 36 to 40 inches, frost-free period is 170 to 200 days, and elevation is 350 to 800 feet above sea level.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Atlas, Darmstadt, Grantfork, Homen, Marine, Ruma, and Ursa soils. The somewhat poorly drained Atlas and Grantfork soils and the well drained Ursa soils formed in the strongly developed paleosol in the till and are on lower backslopes and footslopes downslope from the Bunkum soils. Also, the Grantfork soils contain a concentration of exchangeable sodium in the subsoil. The somewhat poorly drained Coulterville soils are on summits and in upland drainageways nearby and contain a concentration of exchangeable sodium in the subsoil. The somewhat poorly drained Darmstadt and Marine soils are on summits above the Bunkum soils. Darmstadt soils have a natric horizon. The fine-textured Marine soils have an abrupt textural change. The moderately well drained Homen and well drained Ruma soils are on summits, shoulders, and backslopes above the Bunkum soils.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained. The potential for surface runoff is medium or high. Permeability is moderately slow. Saturated hydraulic conductivity is moderately high (1.41 to 4.23 micrometers/sec). In drained areas, depth to an intermittent apparent high water table is 1.0 foot to 2.0 feet from December to April in most years.

USE AND VEGETATION: Most areas are cropped. Corn, soybeans, milo, and small grain are the principal crops. More sloping areas are in forages for hay or pasture, or in woodland. Native vegetation is deciduous forest.

DISTRIBUTION AND EXTENT: Southwestern Illinois. Extent is moderate, and mainly in MLRA 114.

MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana

SERIES ESTABLISHED: St. Clair County, Illinois, 1997. The Bunkum series was named for Bunkum Road in St. Clair County.

REMARKS: Bunkum soils formerly were included with variants of Alford and Muren series.

Diagnostic horizons and features in this pedon include: Ochric epipedon - from the surface of the soil to a depth of 8 inches (Ap horizon). Argillic horizon - from a depth of approximately 8 inches to 40 inches (Bt1, Bt2, Btg1, and Btg2 horizons). Aquic conditions - endosaturation and reduction indicated by redoximorphic features such as soft masses and concretions of iron manganese, and iron depletions or reduced chroma matrix. Redoximorphic features - throughout the soil.

ADDITIONAL DATA: For lab analysis refer to a pedon from the St. Clair County Glacial Lake Kaskaskia Study, Part II. (S93IL-163-015; NSSL pedon number: 94P-273-1720-1730), sampled about a 0.5 mile southeast of typical pedon.