LOCATION KNOCO TX+OKEstablished Series
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 5 inches; 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. (3 to 14 inches thick)
A2--5 to 9 inches; 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. (0 to 11 inches thick)
Cd1--9 to 19 inches; 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. (1 to 16 inches thick)
Cd2--19 to 28 inches; 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. (0 to 12 inches thick)
Cd3--28 to 60 inches; 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. Latitude - 35 degrees, 57 minutes, 00 seconds N; Longitude - 99 degrees, 12 minutes, 21 seconds W.
RANGE IN CHARACTERISTICS: Thickness of soil or depth to weakly consolidated claystone ranges from 3 to 20 inches. Calcareous nodules and sandstone pebbles range from a few on the surface 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.
The A horizon has hue of 10R to 5YR, value of 3 to 5, and chroma of 3 to 6. A few pedons have hue of 7.5YR and chroma of 3, but are less than 4 inches thick. Texture is clay loam, silty clay or clay with clay content ranging from 35 to 60 percent. Reaction is slightly to moderately alkaline and effervescence is very slight to strong. Electrical conductivity is 0.1 to 4 ds/m.
The Cd1 layer has colors in shades of red or reddish brown. Texture is clay or silty clay which contains few to common fragments of claystone that crush or slake to clay texture. Some pedons contain a few gypsum crystals. Roots penetrate this material in cracks and in C material along cracks. Reaction is typically slightly to moderately alkaline and effervescence is very slight to violent. In some pedons carbonates are along cleavage planes or fractures. The moist bulk density ranges from 1.55 to more than 1.9. The material slakes rapidly in water and is densic material in more than 50 percent of the layer. Electrical conductivity is 0.1 to 8 ds/m.
The Cd2 and Cd3 layers have colors mainly in shades of red or gray. It is dense claystone of clay or silty clay texture. Some pedons contain thin discontinuous strata of limestone or sandstone. There are a few roots in the upper part in some pedons. The roots are 10 to 14 inches apart and along cleavage planes or fractures. The material is massive or has coarse or very coarse angular rock-like fragments. Reaction is slightly to moderately alkaline and effervescence ranges from noneffervescent to strongly effervescent. The moist bulk density ranges from 1.70 to more than 2.0. The material slakes rapidly in water and is densic material that may or may not qualify as a densic contact. Electrical conductivity is 0.1 to 8 ds/m.
COMPETING SERIES: There are no other series in this family. Similar soils are Burson, Cottonwood, Harpersville, Latom, Masham, Owens, and Vernon series. Burson, Cottonwood, and Latom soils have less than 35 percent clay in the control section. Also, Cottonwood soils are over gypsum and Burson and Latom soils are over sandstone. Harpersville soils have hue of 7.5YR or yellower. Masham, Owens and Vernon soils have cambic horizons. In addition, Owens soils have hue of 7.5YR or yellower, and Vernon soils have solum development more than 20 inches thick.
GEOGRAPHIC SETTING: Knoco soils are on narrow ridges, divides, and sideslopes, and on erosional footslopes. Slopes range from less than 1 to 60 percent. The soil formed in claystone redbeds of Permian age. Mean annual precipitation ranges from 22 to 30 inches, and mean annual temperature ranges from 57 to 66 degrees F. Frost free days range from 190 to 230 days, and elevation ranges from 1,000 to 2,250 feet. Thornthwaite annual P-E indices range from 32 to 44.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Aspermont, Beckman, Burson, Cottonwood, Heman, Vinson, Vernon, Talpa, Tillman, Tilvern, and Westill series. Aspermont soils have 18 to 35 percent clay in the control section and are on higher landscape positions. Beckman soils are very deep, and are on lower floodplains. Burson soils are underlain by sandstone and are on higher landscape positions. Cottonwood soils are over gypsum and are on similar landscapes. Heman soils have strongly contrasting particle-size classes and are on floodplains. Vinson soils have mollic epipedons and have gypsum parent materials, and are on higher landscape positions. Vernon soils are similar landscapes and are 20 to 40 inches deep. Talpa soils are on higher landscape positions and are over dolomitic limestone. Tillman and Westill soils are above on broad plains and have a mollic surface horizon. Tilvern soils are on higher landscape positions and are 40 to 60 inches deep.
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 is 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: The Central Rolling Red Plains (MLRA-78B, 78C), Rolling Limestone Prairie (MLRA-78D), and North Central Prairie (MLRA 80B) of Texas, Kansas and Oklahoma; The series is extensive.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Wichita County, Texas; 1973.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 9 inches. (A1 and A2 horizon)
No diagnostic subsurface horizon
Densic material - the zone from 9 to 60 inches
Densic contact - at 19 inches. (Top of Cd2 horizon)
Soil Interpretation Record: TX0338 Knoco series
TX1095 Bouldery
OK0422 Cool