LOCATION COBBSFORK IN

Established Series
Rev. BGN
11/2021

COBBSFORK SERIES

The Cobbsfork series consists of very deep, poorly drained soils on broad level summits of till plains. They formed in loess and the underlying till-derived paleosol. They are moderately deep or deep to a horizon with fragic soil properties. Slope ranges from 0 to 1 percent. Mean annual precipitation is about 1092 mm (43 inches), and mean annual temperature is about 13 degrees C (55 degrees F).

TAXONOMIC CLASS: Fine-silty, mixed, active, mesic Fragic Glossaqualfs

TYPICAL PEDON: Cobbsfork silt loam, on a 0.5 percent slope in a cultivated field at an elevation of about 273 meters (895 feet) above MSL. (Colors are for moist soil unless otherwise stated.)

Ap1--0 to 15 cm (6 inches); grayish brown (10YR 5/2) silt loam, light gray (10YR 7/2) dry; weak fine granular structure; friable; many fine prominent yellowish brown (10YR 5/6) masses of oxidized iron in the matrix; few fine prominent strong brown (7.5YR 4/6) masses of oxidized iron lining tubular pores; many fine roots; common fine faint gray (10YR 6/1) iron depletions in the matrix; neutral; abrupt smooth boundary.

Ap2--15 to 30 cm (6 to 12 inches); grayish brown (10YR 5/2) silt loam, light gray (10YR 7/2) dry; weak very thick platy structure; friable; few fine roots; few fine prominent yellowish brown (10YR 5/6) masses of oxidized iron in the matrix; few fine prominent strong brown (7.5YR 4/6) masses of oxidized iron lining tubular pores; common fine faint gray (10YR 6/1) iron depletions in the matrix; slightly acid; abrupt smooth boundary. [Combined thickness of the Ap horizon is 18 to 33 cm (7 to 13 inches).]

EBg--30 to 46 cm (12 to 18 inches); light gray (10YR 7/1) silt loam; weak medium subangular blocky structure; friable; few fine roots; common medium prominent strong brown (7.5YR 5/8) masses of oxidized iron in the matrix; few fine prominent yellowish red (5YR 5/8) masses of oxidized iron lining tubular pores; few fine prominent spherical very dark brown (10YR 2/2) strongly cemented iron-manganese concretions throughout; strongly acid; gradual wavy boundary. [13 to 25 cm (5 to 10 inches) thick]

Btg--46 to 69 cm (18 to 27 inches); light brownish gray (10YR 6/2) silt loam; moderate medium prismatic structure parting to moderate medium subangular blocky; friable; few fine roots between peds; common distinct grayish brown (10YR 5/2) clay films on faces of peds (dominantly vertical); common fine prominent strong brown (7.5YR 5/8) and brownish yellow (10YR 6/6) masses of oxidized iron in the matrix; few fine prominent strong brown (7.5YR 5/8) masses of oxidized iron lining tubular pores; few fine spherical very dark brown (10YR 2/2) strongly cemented iron-manganese concretions throughout; many faint gray (10YR 6/1) clay depletions on faces of peds; very strongly acid; gradual wavy boundary. [20 to 30 cm (8 to 12 inches) thick]

Btg/Eg--69 to 97 cm (27 to 38 inches); 60 percent light brownish gray (10YR 6/2) silt loam (Btg); moderate medium and coarse prismatic structure parting to moderate medium subangular blocky; firm; few fine roots between peds; common distinct gray (10YR 6/1) clay films on vertical faces of peds; common fine prominent strong brown (7.5YR 5/8) and distinct brownish yellow (10YR 6/6) masses of oxidized iron in the matrix; few fine prominent yellowish red (5YR 5/8) masses of oxidized iron lining tubular pores; 40 percent light gray (10YR 7/2) silt loam (Eg); weak medium subangular blocky structure; friable; few fine roots throughout; few fine prominent yellowish red (5YR 5/8) masses of oxidized iron lining tubular pores; few fine prominent spherical very dark brown (10YR 2/2) strongly cemented iron-manganese concretions throughout; krotovinas; very strongly acid; gradual wavy boundary. [25 to 102 cm (10 to 14 inches) thick]

2Eg/Btgx--97 to 127 cm (38 to 50 inches); 60 percent light gray (10YR 7/2) silt loam (Eg); weak fine subangular blocky structure; friable; common fine roots throughout; common medium prominent yellowish brown (10YR 5/8) masses of oxidized iron in the matrix; few medium spherical strongly cemented black (10YR 2/1) iron-manganese concretions; 40 percent light brownish gray (10YR 6/2) silt loam (Btgx); moderate coarse prismatic structure parting to moderate medium angular blocky; firm; brittle; few fine roots between peds; common prominent gray (10YR 6/1) clay films on vertical faces of peds; common fine distinct yellowish brown (10YR 5/4) and prominent strong brown (7.5YR 5/6) masses of oxidized iron in the matrix; few fine prominent yellowish red (5YR 4/6) masses of oxidized iron lining tubular pores; common fine prominent black (10YR 2/1) mangans lining pores; few fine spherical very dark brown (10YR 2/2) strongly cemented iron-manganese concretions throughout; krotovinas; 1 percent gravel (3 to 10 mm or 1/8-3/8 inch); very strongly acid; gradual wavy boundary. [25 to 46 cm (10 to 18 inches) thick]

2Btx--127 to 216 cm (50 to 85 inches); yellowish brown (10YR 5/4) silt loam; weak medium and coarse prismatic structure parting to weak medium subangular blocky; firm; common faint gray (10YR 6/1) clay films on vertical faces of peds; few fine faint light yellowish brown (10YR 6/4) masses of oxidized iron in the matrix; common medium spherical black (10YR 2/1) strongly cemented iron-manganese concretions; many faint gray (10YR 6/1) clay depletions on vertical faces of peds; 2 percent gravel (3 to 10 mm or 1/8-3/8 inch); 70 percent brittle; very strongly acid; diffuse wavy boundary. [66 to 97 cm (26 to 38 inches) thick]

3Btb--216 to 229 cm (85 to 90 inches); strong brown (7.5YR 5/8) clay loam; weak coarse subangular blocky structure; firm; few prominent light brownish gray (2.5Y 6/2) clay films on faces of peds; common medium spherical very dark gray (10YR 3/1) strongly cemented iron-manganese concretions; common fine and medium prominent gray (10YR 6/1) iron depletions in the matrix; 4 percent gravel; slightly acid.

TYPE LOCATION: Jefferson County, Indiana; about 10 miles north of Madison; 150 feet west and 1,300 feet north of the southeast corner, sec. 2, T. 5 N., R. 10 E.; USGS Rexville topographic quadrangle; lat. 38 degrees 54 minutes 06.267 seconds N. and long. 85 degrees 22 minutes 12.885 seconds W.; UTM Zone 16, 641322 easting and 4307133 northing, NAD 83.

RANGE IN CHARACTERISTICS:
Depth to the base of the argillic horizon: greater than 203 cm (80 inches)
Depth to the top of the glossic horizon: 61 to 91 cm (24 to 36 inches)
Depth to the top of the horizon with fragic soil properties: 91 to 114 cm (36 to 45 inches)
Particle-size control section: averages 20 to 28 percent clay and 10 to 15 percent fine sand and coarser

Ap horizon:
Hue: 10YR
Value: 4 to 6
Chroma: 2 or 3
Texture: silt loam
Clay content: 10 to 15 percent
Sand content: 12 to 24 percent
Reaction: very strongly acid to neutral

A horizon (where present):
Hue: 10YR
Value: 3 to 5; where value is 3, thickness is 2 to 10 cm (1 to 4 inches)
Chroma: 1 or 2
Texture: silt loam
Clay content: 10 to 15 percent
Sand content: 12 to 24 percent
Reaction: very strongly acid or strongly acid

EBg or BEg horizon:
Hue: 10YR or 2.5Y
Value: 5 to 7
Chroma: 1 or 2
Texture: silt loam
Clay content: 10 to 20 percent
Sand content: 12 to 24 percent
Reaction: very strongly acid or strongly acid, and ranges to slightly acid in limed areas

Btg horizon:
Hue: 10YR
Value: 6 or 7
Chroma: 1 or 2
Texture: silt loam or silty clay loam
Clay content: 20 to 30 percent
Sand content: 10 to 20 percent
Reaction: extremely acid or very strongly acid

Btg/Eg horizon
Btg part:
Hue: of 10YR
Value: 5 to 7
Chroma: 1 or 2
Texture: silt loam or silty clay loam
Clay content: 20 to 30 percent
Eg part:
Hue: 10YR or 2.5Y
Value: 6 or 7
Chroma: 1 or 2
Texture: silt loam
Clay content: 20 to 26 percent
Both parts:
Sand content: 10 to 15 percent
Reaction: extremely acid or very strongly acid

2Eg/Btgx horizon:
Eg part:
Hue: of 10YR or 2.5Y
Value: 6 or 7
Chroma: 1 or 2
Texture: is silt loam
Clay content: 20 to 26 percent
Btgx part:
Hue: 7.5YR or 10YR
Value: 4 to 6
Chroma: 1 or 2
Texture: silt loam or silty clay loam
Clay content: 20 to 28 percent
Both parts:
Sand content: 18 to 28 percent sand
Rock fragment content: 1 to 2 percent gravel (3 to 10 mm or 1/8 to 3/8 inch)
Reaction: extremely acid or very strongly acid
Brittle material content: 30 to 55 percent

2Btx or 2Btgx horizon:
Hue: 7.5YR or 10YR
Value: 4 to 6
Chroma: 1 to 6
Texture: silt loam
Clay content: 20 to 26 percent
Sand content: 18 to 28 percent
Rock fragment content: 1 to 2 percent gravel (3 to 10 mm or 1/8 to 3/8 inch)
Reaction: extremely acid to strongly acid
Brittle material content: 60 to 70 percent

3Btb or 3Btgb horizon:
Hue: 7.5YR or 10YR
Value: 5 or 6
Chroma: 1 to 8
Texture: clay loam
Clay content: 27 to 38 percent
Sand content: 25 to 35 percent
Rock fragment content: 2 to 10 percent gravel
Reaction: commonly strongly acid or moderately acid in the upper part and ranges to neutral in the lower part

COMPETING SERIES: There are no other series in the same family.

GEOGRAPHIC SETTING: Cobbsfork soils are on broad level summits of loess covered till plains. Typically, undisturbed areas have a surface morphometry of micro highs and micro lows. Slope ranges from 0 to 1 percent. They formed in 191 to 244 cm (75 to 96 inches) of loess and the underlying paleosol in Illinois age glacial till, (Sangamon age paleosol). The upper 51 to 102 cm (20 to 40 inches) of loess averages about 15 percent sand, and the lower loess averages about 24 percent. This lower loess has been called "gritty loess". Mean annual precipitation ranges from 1016 to 1168 mm (40 to 46 inches). Mean annual temperature ranges from 11 to 14 degrees C (51 to 57 degrees F). Frost-free period is 170 to 200 days. Elevation is 107 to 305 meters (350 to 1000 feet).

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Avonburg, Blocher, Bonnell, Cincinnati, Hickory, and Nabb soils. The somewhat poorly drained Avonburg soils, and the moderately well drained Nabb soils are on summits and shoulders between the broad areas of Cobbsfork soils. The well drained Bonnell and Hickory soils, and the moderately well drained Blocher and Cincinnati soils are on backslopes.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Poorly drained. In undrained areas, this soil has a surface morphometry of micro-highs and micro-lows. The potential for surface water runoff on the micro-highs is low and negligible in the micro-lows. In undrained areas, the depth to the top of a perched seasonal high water table ranges from 15 cm (0.5 feet) above the surface to 15 cm (0.5 feet) below the surface in normal years. Saturated hydraulic conductivity is moderately high or high in the upper part of the solum and low to moderately high in the lower part. Permeability is moderate or moderately slow above the horizon with fragic soil properties and is slow or very slow in and below the horizon with fragic soil properties.

USE AND VEGETATION: Most areas are used to grow corn and soybeans. Some areas are woodland. A few areas are used for wheat, pasture and hay. Native vegetation is mixed hardwood forest.

DISTRIBUTION AND EXTENT: MLRA 114A in southeastern Indiana. This series is of large extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: AMHERST, MASSACHUSETTS

SERIES ESTABLISHED: Jefferson County, Indiana, 1982.

REMARKS: An undrained phase is recognized. The type location was investigated in 1995. A glossic horizon is recognized, and the classification was changed to a Glossaqualf. Also adjustments and additions were made to the typical pedon description. In future updates, the Cobbsfork series will be correlated for the Clermont series in Indiana. Soil Survey Investigations Report No. 41 gives more information on the parent materials of the Cobbsfork and geographically associated soils. The 2Btx horizon meets the brittleness criteria for a fragipan but not the structure criteria.

The representative component and horizon data is in DMU# 124491.

Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: from 0 to 46 cm (18 inches) (Ap and EBg horizons).
Argillic horizon: from 46 to 229 cm (18 to 90 inches) (Btg, Btg/Eg, 2Eg/Btgx, 2Btx, 3Btb horizons).
Fragic soil properties: from 97 to 216 cm (38 to 85 inches) (2Eg/Btgx, 2Btx horizons).
Glossic horizon: from 69 to 127 cm (27 to 50 inches) (Btg/Eg, 2Eg/Btgx horizons).
Redoximorphic features: present from 0 to 229 cm (90 inches).

ADDITIONAL DATA: Lab data: Agricultural Experiment Station, Purdue University, Station Bulletin No. 174, file no. JE7005; Station Bulletin No. 222, file no. DC7621; Station Bulletin No. 274, file no. DC7901, DC9012; Station Bulletin No. 323, file no's JF7605 (Typical pedon) and RI7907; Station Bulletin No. 451, file no. SW8106. National Soil Survey Lab, Lincoln, NE data available: S82IN-071-001, S90IN-143-008, S92IN-079-004.

National Cooperative Soil Survey
U.S.A.