LOCATION KNOCO                   TX+KS OK

Established Series
Rev. WMR:CLN:DDR:RFG
10/2014

KNOCO SERIES

The Knoco series consists of very shallow and shallow, well drained, very slowly permeable soils that formed in residuum weathered from claystone over dense noncemented claystone bedrock of Permian age. These very gently sloping to very steep soils occur on interfluves, side slopes and erosional footslopes on dissected plains. Slopes range from 1 to 60 percent. Mean annual precipitation is about 686 mm (27 in) and the mean annual air temperature is about 17.2 degrees C (63 degrees F).

TAXONOMIC CLASS: Clayey, mixed, active, calcareous, thermic, shallow Aridic Ustorthents

TYPICAL PEDON: Knoco clay--rangeland.
(Colors are for dry soil unless otherwise stated.)

A1--0 to 13 cm (0 to 5 in); red (2.5YR 4/6) clay, dark red (2.5YR 3/6) moist; moderate fine subangular blocky structure; very hard, firm, slightly sticky, plastic; many fine and common medium roots; few medium and coarse concretions of calcium carbonate; many caliche and few sandstone pebbles on the surface; slightly effervescent; moderately alkaline; clear smooth boundary. Thickness is 8 to 36 cm (3 to 14 in)

A2--13 to 23 cm (5 to 9 in); reddish brown (2.5YR 5/4) clay, reddish brown (2.5YR 4/4) moist, weak fine and medium subangular blocky structure; very hard, firm, slightly sticky, plastic; many fine and common medium roots; few medium and coarse concretions of calcium carbonate; slightly effervescent; moderately alkaline; gradual smooth boundary. Thickness is 0 to 28 cm (0 to 11 in)

C--23 to 48 cm (9 to 19 in); reddish brown (2.5YR 5/4) dense clay and noncemented claystone fragments; reddish brown (2.5YR 4/4) moist; massive with moderate medium angular rock structure; extremely hard, very firm, sticky, plastic; common fine and medium roots; few masses of light greenish gray (5GY 7/1) and gray (5Y 6/1) claystone; very slightly effervescent; moderately alkaline; clear smooth boundary. Thickness is 3 to 41 cm (1 to 16 in)

Cd1--48 to 71 cm (19 to 28 in); reddish brown (2.5YR 4/4) noncemented claystone bedrock, reddish brown (2.5YR 4/4) moist; massive with moderate coarse angular rock structure parting to fine angular blocks; extremely hard, extremely firm, very sticky, plastic; very few medium roots about 10 to 14 inches apart along fracture planes; few reduction masses of light greenish gray (5GY 7/1) and gray (5Y 6/1) claystone; very slightly effervescent; moderately alkaline; clear smooth boundary. Thickness is 0 to 30 cm (0 to 12 inches thick)

Cd2--71 to 152 cm (28 to 60 in); reddish brown (2.5YR 4/4) noncemented claystone bedrock, reddish brown (2.5YR 4/4) moist; massive with moderate very coarse angular rock structure; extremely hard, extremely firm, very sticky, plastic; common masses and thin strata of light greenish gray (5GY 7/1) and gray (5Y 6/1) claystone; very slightly effervescent; moderately alkaline.

TYPE LOCATION: Wilbarger County, Texas; from the intersection of U.S. Highway 183-283 and Texas Farm to Market Road 1763 about 12.5 miles south-southeast of Vernon, 2.62 miles south-southeast on U.S. Highway 183-283 (0.96 mile south-southeast of Beaver Creek), 175 feet east-northeast in rangeland.
USGS topographic quad: Grayback, Texas;
Latitude - 35 degrees, 57 minutes, 00 seconds N;
Longitude - 99 degrees, 12 minutes, 22.1 seconds W;
Datum: WGS84.

RANGE IN CHARACTERISTICS:

Soil Moisture: Typic ustic soil moisture regime.
Depth to bedrock, densic: 8 to 51 cm (3 to 20 in)
Thickness of the ochric epipedon: 0 to 36 cm (0 to 14 in)
Depth to secondary carbonates: 0 to 41 cm (0 to 16 in)
Surface fragments: Calcareous nodules and sandstone pebbles range from a few to a pavement. There are a few siliceous pebbles on the surface of some pedons. Some pedons have sandstone or limestone stones or boulders on the surface. Fragments range from 1 to 20 feet across the long axis, and are about 1 to 5 feet thick. These fragments cover about 2 to 25 percent of the surface layer in some soil areas.

Particle-size control section (weighted average):
Clay Content: 35 to 60 percent

A horizon
Hue: 10R to 5YR
Value: 3 to 5
Chroma: 3 to 6; where value and chroma are 3 or less, thickness is less than 10 cm (4 in)
Texture: Clay loam, silty clay, clay
Clay content: 35 to 60 percent
Electrical Conductivity (ds/m): 0.1 to 4
Calcium carbonate equivalent: 1 to 8 percent
Effervescence: very slight to strong
Reaction (pH): Slightly to moderately alkaline (7.4 - 8.4)

C horizon(s)
Hue: 5YR, 2.5YR
Value: 4 or 5
Chroma: 4 to 8
Texture: silty clay, clay
Coarse fragments: Few to common fragments of noncemented claystone that crush or slake to clay texture
Densic materials: The material slakes rapidly in water and is densic material in less than 50 percent of the layer
Bulk density: 1.25 to 1.7 g/cm3
Roots: Penetrate this material mainly along cracks
Visible calcium carbonate: occurs in cracks of some pedons
Gypsum: 0 to 2 percent
Electrical Conductivity (EC): 0.1 to 8 ds/m
Calcium carbonate equivalent: 1 to 8 percent
Effervescence: very slight to violent
Reaction (pH): slightly to moderately alkaline (7.4 - 8.4)

Cd horizon(s)
Color: mainly in shades of red or gray
Texture: noncemented claystone or siltstone that has texture of silty clay or clay
Densic materials: The material slakes rapidly in water and is densic material that may or may not qualify as a densic contact.
Roots: 25 to 36 cm (10 to 14 in) apart and along cleavage planes or fractures in the upper part in some pedons
Bulk density: 1.5 to 2.25 g/cm3
Electrical Conductivity (EC): 0.1 to 8 ds/m
Gypsum: 0 to 2 percent
Effervescence: none to strong
Reaction (pH): slightly to moderately alkaline (7.4 - 8.4)
Other features: some pedons contain thin discontinuous strata of limestone or sandstone.

COMPETING SERIES: seriesThe Harpersville series in the same family. Similar soils are the Burson, Cottonwood, Latom, Masham, Owens, and Vernon series.
Harpersville: These soils have hue of 7.5YR or yellower.
Burson, Cottonwood, and Latom: These soils have less than 35 percent clay in the particle-size control section. Also, Cottonwood soils are over gypsum and Burson and Latom soils are over sandstone.
Masham, Owens and Vernon: These soils have cambic horizons. In addition, Owens soils have hue of 7.5YR or yellower, and Vernon soils are more than 51 cm (20 in) deep to bedrock.

GEOGRAPHIC SETTING:

Parent material: clayey residuum derived from claystone of Permian age
Landscape: dissected plains
Landform: Erosional positions on hills, pediments, and ridges
Slope: 1 to 60 percent
Mean annual precipitation: 559 to 762 mm (22 to 30 in)
Thornthwaite P-E Index: 32 to 44
Mean annual air temperature: 13.9 to 18.9 degrees C (22 to 30 degrees F)
Frost Free Days: 190 to 230 days
Elevation: 304.8 to 685.8 m (1,000 to 2,250 ft)

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Aspermont, Beckman, Cottonwood, Heman, Talpa, Tillman, Tilvern, Vinson, Vernon, and Westill series.
Aspermont: These soils have less than 35 percent clay in the particle-size control section and occur on higher landscape positions.
Beckman: These soils are very deep to bedrock and occur on lower floodplains.
Cottonwood and Vinson: These soils are over gypsum and occur on similar positions.
Heman: These soils have a strongly contrasting particle-size control section and occur on floodplains.
Talpa: These soils are over dolomitic limestone and occur on higher positions.
Tillman and Westill: These soils have a mollic epipedon and occur on higher broad plains.
Tilvern: These soils are deep to bedrock and occur on higher positions.
Vernon: These soils are moderately deep to bedrock and occur on similar positions.

DRAINAGE AND PERMEABILITY: Well drained. Permeability is very slow. Runoff is high on 0 to 1 percent slopes, and very high on slopes greater than 1 percent.

USE AND VEGETATION: Used mainly for rangeland. The native vegetation consists of a sparse cover of tobosagrass, buffalograss, blue grama and sideoats grama, with a few scrubby mesquite, juniper, and pricklypear cactus; about 10 to 50 percent ground cover in most areas.

DISTRIBUTION AND EXTENT: North central Texas, western Oklahoma, and a small part of south central Kansas; Land Resource Region - H; MLRA-78A (Rolling Limestone Prairie), MLRAs - 78B and 78C (Central Rolling Red Plains); The series is extensive.

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

SERIES ESTABLISHED: Wichita County, Texas; 1973.

REMARKS:
Edited 10/2014 (RFG-CJV): Changed to tabular format. Changed Cd1 to C horizon and bedrock-densic restriction from 23cm to 48cm. 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: 0 to 23 cm (0 to 9 in). (A1 and A2 horizons)
Ochric epipedon: 0 to 23 cm (0 to 9 in). (A1 and A2 horizons)
Secondary carbonates: 0 to 23 cm (0 to 9in). (A1 and A2 horizons)
Densic material: 48 to 152 cm (19 to 60 in). (Cd horizons)
Densic contact: 48 cm (19 in). (Top of Cd1 horizon)

ADDITIONAL DATA: None

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

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National Cooperative Soil Survey
U.S.A.