LOCATION COBB TX+OK

Established Series
Rev. RFG-CRC-CLN
01/2017

COBB SERIES

The Cobb series consists of moderately deep, well drained, moderately permeable soils that formed in residuum derived from sandstone. These nearly level to moderately sloping soils occur on ridges. Slope ranges from 0 to 8 percent. Mean annual precipitation is about 635 mm (25 in) and the mean annual air temperature is about 17.2 degrees C (63 degrees F).

TAXONOMIC CLASS: Fine-loamy, mixed, active, thermic Typic Haplustalfs

TYPICAL PEDON: Cobb fine sandy loam, in a cultivated field.
(Colors are for dry soil unless otherwise stated.)

Ap--0 to 20 cm (0 to 8 in); reddish brown (5YR 4/3) fine sandy loam, dark reddish brown (5YR 3/3) moist; weak fine subangular blocky structure; hard, very friable; few fine roots; slightly acid; gradual smooth boundary. Thickness is 8 to 30 cm (3 to 12 in)

Bt1--20 to 56 cm (8 to 22 in); reddish brown (5YR 4/4) sandy clay loam, dark reddish brown (5YR 3/4) moist; weak coarse prismatic structure parting to weak medium subangular blocky; very hard, friable; few fine roots; few fine pores; slightly acid; clear wavy boundary. Thickness is 20 to 46 cm (8 to 18 in)

Bt2--56 to 76 cm (22 to 30 in); reddish brown (5YR 5/4) sandy clay loam, reddish brown (5YR 4/4) moist; weak coarse prismatic structure parting to weak medium subangular blocky; very hard, friable; neutral; abrupt irregular boundary. Thickness is 15 to 46 cm (6 to 18 in), Combined thickness of the Bt horizon is 38 to 91 cm (15 to 36 in)

Cr--76 to 152 cm (30 to 60 in); weakly cemented reddish sandstone with common distinct coatings of calcium carbonate in the fissures or crevices; neutral.

TYPE LOCATION: Foard County, Texas; from the intersection of Texas Highway 6 and U.S. Highway 70 in Crowell; 1.5 miles west on U.S. Highway 70; 0.3 mile north on county road; 0.2 mile west in cropland.
USGS topographic quadrangle: Foard City, Texas;
Latitude, 33 degrees, 59 minutes, 28seconds N;
Longitude, 99 degrees, 45 minutes, 15 seconds W.
Datum: WGS84

RANGE IN CHARACTERISTICS:
Soil Moisture: A typic-ustic soil moisture regime.
Depth to paralithic bedrock: 51 to 102 cm (20 to 40 in)

Particle-size control section (weighted average):
Clay content: 18 to 35 percent
CEC/clay ratio: 0.4 to 0.6
Base saturation: 75 to 100 percent throughout the argillic horizon.

A Horizon
Hue: 5YR or 7.5YR
Value: 4 to 6 (3 to 5 moist)
Chroma: 4 to 6 (3 to 5 moist)
Texture: Fine sandy loam or loamy fine sand
Clay content: 6 to 18 percent
Electrical conductivity (dS/m): 0 to 2
Effervescence: None
Reaction (pH): Slightly acid to neutral (6.1-7.3)

Bt Horizon
Hue: 2.5YR or 5YR
Value: 4 to 6 (3 to 5 moist)
Chroma: 4 or 6
Texture: Typically sandy clay loam or clay loam, but includes fine sandy loam in the lower part.
Clay content: 18 to 35 percent
Coarse fragments: 0 to 10 percent; 2 to 75 mm (< 3 in) sandstone fragments
Base saturation: 75 to 100 percent
Calcium carbonate equivalent: 0 to 5 percent
Electrical conductivity (dS/m): 0 to 2
Effervescence: None to slight
Reaction (pH): Slightly acid to moderately alkaline (6.1-8.4)

BC Horizon (where present)
Hue: 2.5YR or 5YR
Value: 4 to 6 (3 to 5 moist)
Chroma: 4 or 6
Texture: Fine sandy loam, sandy clay loam, or clay loam
Clay content: 10 to 35 percent
Coarse fragments: 0 to 10 percent; 2 to 75 mm (< 3 in) sandstone fragments
Calcium carbonate equivalent: 0 to 5 percent
Electrical conductivity (dS/m): 0 to 2
Effervescence: None to slight
Reaction (pH): Slightly acid to moderately alkaline (6.1-8.4)

Cr Horizon
Hue: 2.5YR to 10YR
Value: 4 or 5 (3 or 4 moist)
Chroma: 2 to 6
Texture: Extremely weakly to moderately cemented sandstone bedrock
Moist bulk density (g/cc): 1.85 to 2.35
Excavation difficulty: Moderate to high
Identifiable secondary carbonate: Thin coatings of calcium carbonate are in fissures or crevices of most pedons.
Effervescence: None to slight
Reaction (pH): Slightly acid to moderately alkaline (6.1-8.4)

COMPETING SERIES: These are the Arnett, Decobb, Grandfield, Grandmore, Honeycreek, Hye, Lou, McKnight, Menard, and Rochelle series.
Arnett, Decobb, Grandfield, Grandmore, Menard and Rochelle series: These soils are more than 152 cm (60 in) deep to bedrock. In addition, Rochelle soils have a very gravelly substratum.
Honeycreek series: These soils are 102 to 152 cm (40 to 60 in) deep to schist bedrock.
Hye series: These soils have base saturation between 40 and 75 percent in the argillic horizon.
Lou series: These soils have a paralithic contact with granite bedrock.
McKnight series: These soils have a lithologic discontinuity between 51 to 102 cm (20 to 40 in) and depth to bedrock is 102 to 152 cm (40 to 60 in).

GEOGRAPHIC SETTING:
Parent material: Residuum derived from sandstone, mainly of the San Angelo Formation of Permian age.
Landscape: Dissected plains
Landform: Convex interfluves and side slopes of ridges.
Slope: 0 to 8 percent
Mean annual precipitation: 559 to 762 mm (22 to 30 in)
Thornthwaite annual P-E indices: 32 to 44
Mean annual air temperature: 15.6 to 18.3 degrees C (60 to 65 degrees F)
Frost-free period: 200 to 230 days
Elevation: 304.8 to 716.3 m (1000 to 2350 ft)

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Abilene, Bluegrove, Cosh, Decobb, Grandfield, Miles, Spade, Spikebox, Tillman, Tilvern, Vernon, and Westill series.
Abilene series: These soils have a mollic epipedon and occur on lower alluvial or footslope positions.
Cosh and Spikebox series: These soils are shallow to sandstone bedrock and occur on slightly convex positions higher in the landscape.
Decobb series: These soils are very deep to sandstone and occur slightly lower in the landscape.
Grandfield and Miles series: These soils occur on slightly lower positions and have developed in loamy, Pleistocene age alluvial sediments.
Spade series: These soils occur on similar positions, have a cambic horizon, and are calcareous to the surface.
Tillman and Westill series: These soils have a mollic epipedon, a fine textured particle-size control section, and occur on slightly lower positions.
Bluegrove, Tilvern and Vernon series: These soils occupy similar to slightly lower landscape positions and have a fine textured particle-size control section.

DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Runoff is negligible on slopes less than 1 percent, low on 1 to 5 percent slopes and medium on 5 to 8 percent slopes.

USE AND VEGETATION: Used mainly for rangeland. Native vegetation is mainly grasses such as sideoats grama, blue grama, little bluestem, dropseed, threeawn, Arizona cottontop, and buffalograss. Mesquite trees are the dominant woody plants. A small acreage is farmed. Grain sorghum, cotton, and wheat are the major crops.

DISTRIBUTION AND EXTENT: north and northwestern Texas and southwestern Oklahoma. Land Resource Region H - Central Great plains Winter Wheat and Range Region. The Central Rolling Red Plains (MLRA 78); the series is of large extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Washita County, Oklahoma; 1935.

REMARKS:
Edited 01/2017 (RFG-ROG): Added metric measurements. Updated competing series, geographic setting, and associated soils sections.

Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: 20 to 70 cm (8 to 27 in). (Top 50 cm of argillic horizon)
Ochric epipedon:0 to 20 cm (0 to 8 in). (Ap horizon)
Argillic horizon:20 to 76 cm (8 to 30 in). (Bt1 and Bt2 horizons)
Paralithic contact: The contact at 76 cm (30 in). (Top of Cr horizon)

ADDITIONAL DATA: None

Taxonomic version: Keys to Soil Taxonomy, Twelfth Edition, 2014

National Cooperative Soil Survey
U.S.A.