LOCATION MCKNIGHT OKEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, active, thermic Typic Haplustalfs
TYPICAL PEDON: McKnight loamy sand, on a 1 percent slope in cropland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 14 inches; reddish brown (5YR 5/4) loamy sand, reddish brown (5YR 4/4), moist; single grain; loose, loose; common fine and very fine roots; 1 percent rounded quartz gravels; noneffervescent; moderately acid; abrupt smooth boundary. (6 to 15 inches thick)
Bt1--14 to 21 inches; reddish brown (2.5YR 5/4) sandy clay loam, reddish brown (2.5YR 4/4), moist; moderate coarse prismatic structure parting to moderate medium subangular blocky; firm, hard; common fine and very fine roots; common fine and common medium pores; common distinct clay films on faces of peds; 2 percent rounded quartz gravels; noneffervescent; neutral; clear smooth boundary.
Bt2--21 to 29 inches; red (2.5YR 5/6) fine sandy loam, red (2.5YR 4/6), moist; moderate coarse prismatic structure parting to moderate medium subangular blocky; firm, hard; common fine and very fine roots; common fine and common medium pores; common distinct clay films on faces of peds; 3 percent rounded quartz gravels; a gravel line exists at the contact with the 2Bt horizon; noneffervescent; neutral; abrupt smooth boundary. (Combined thickness of the Bt horizons is 8 to 30 inches thick)
2Bt--29 to 36 inches; red (2.5YR 4/6) clay, dark red (2.5YR 3/6), moist; few medium prominent light greenish gray (10Y 7/1) mottles; strong coarse prismatic structure parting to strong medium angular blocky; very firm, extremely hard; common fine and very fine roots; common fine pores; many distinct clay films on faces of peds; noneffervescent; moderately alkaline; clear smooth boundary. (5 to 18 inches thick)
2CBk--36 to 43 inches; 80 percent greenish gray (5GY 6/1) and 20 percent red (2.5YR 4/6) silty clay loam, 80 percent greenish gray (5GY 5/1) and 20 percent dark red (2.5YR 3/6), moist; 60 percent massive and 40 percent weak medium prismatic structure; firm, hard; few fine and very fine roots; common fine pores; common carbonate coats on ped faces; 2 percent angular moderately cemented 5 to 76 millimeter claystone fragments and about 35% by volume noncemented claystone fragments; slight effervescence; moderately alkaline; clear smooth boundary. (0 to 10 inches thick)
2Ck--43 to 52 inches; 50 percent red (2.5YR 4/6) and 50 percent greenish gray (5GY 6/1) highly fractured claystone, 50 percent dark red (2.5YR 3/6) and 50 percent greenish gray (5GY 5/1), moist; moderate excavation difficulty; few fine and very fine roots around fragments; few fine pores; common carbonate coats along fractures; 6 percent angular moderately cemented 5 to 76 millimeter claystone fragments; slight effervescence; moderately alkaline; gradual smooth boundary. (0 to 10 inches thick)
2Cd--52 to 95 inches; 80 percent red (2.5YR 4/6) and 20 percent greenish gray (5GY 6/1) noncemented calcareous claystone bedrock, fractured at intervals of 4 to less than 18 inches, 80 percent dark red (2.5YR 3/6) and 20 percent greenish gray (5GY 5/1), moist; high excavation difficulty; 2 percent angular moderately cemented 5 to 76 millimeter claystone fragments; slight effervescence; moderately alkaline.
TYPE LOCATION: Harmon County, Oklahoma; from the intersection of U.S. Highway 62 and OK State Highway 30 in Hollis, about 5.66 miles north and 0.25 miles west in cropland; about 1,800 feet south and 1,350 feet west of the northeast corner of Sec. 3, T. 3 N., R. 26 W. Latitude: 34 degrees, 45 minutes, 48.8 seconds N; Longitude: 99 degrees, 55 minutes, 00.65 seconds W. McKnight, OK - topographic quadrangle; NAD - 1983.
RANGE IN CHARACTERISTICS:
Particle-size control section (weighted average)
Clay content: 20 to 35 percent
Sand content: 45 to 80 percent
Coarse Fragments: 0 to 5 percent
CEC/clay ratio: 0.4 to 0.6
Thickness of the solum, 30 to 50 inches
Depth to densic bedrock: 40 to 60 inches
Depth to discontinuity: 20 to 40 inches
Depth to secondary calcium carbonate: 20 to 40 inches
A Horizon
Hue: 5YR or 7.5YR
Value: 4 or 5 (3 or 4 moist)
Chroma: 3 to 6
Texture: loamy sand, loamy fine sand, or fine sandy loam
Coarse Fragments: 0 to 3 percent rounded quartz, by volume
Effervescence: noneffervescent
Reaction: moderately acid to moderately alkaline
Bt Horizon
Hue: 2.5YR or 5YR
Value: 4 or 5 (3 or 4 moist)
Chroma: 3 to 6
Texture: sandy clay loam or fine sandy loam
Clay content: 18 to 30 percent
Coarse Fragments: 0 to 5 percent rounded quartz, by volume
Calcium carbonate equivalent: 0 to 5 percent
Effervescence: noneffervescent to slightly effervescent
Reaction: neutral to moderately alkaline
2Bt or 2BC Horizon
Hue: 2.5YR or 5YR
Value: 4 or 5 (3 or 4 moist)
Chroma: 2 to 6
Texture: silty clay loam, clay loam, silty clay, or clay
Clay content: 35 to 60 percent
Pararock fragments: 0 to 10 percent by volume
Calcium carbonate equivalent: 0 to 15 percent
Identifiable secondary carbonate: none to common - masses, films, or threads
EC (dS/m): 0 to 2
Gypsum: 0 to 2 percent
SAR: 0 to 4
Effervescence: noneffervescent to violently effervescent
Reaction: moderately alkaline
2CB or 2C Horizon (where present)
Color: reddish brown, red, and/or greenish gray
Texture: clay loam, silty clay loam, silty clay, clay, or highly fractured noncemented claystone that is massive or has rock structure in 50 percent or more by volume and has weathered from Permian age redbeds.
Clay content: 35 to 60 percent
Excavation difficulty: moderate to high
Pararock fragments: 0 to 10 percent by volume
Calcium carbonate equivalent: 2 to 15 percent
Identifiable secondary carbonate: none to common masses, films, or threads
EC (dS/m): 0 to 2
Gypsum: 0 to 2 percent
SAR: 0 to 4
Effervescence: slightly effervescent to violently effervescent
Reaction: moderately alkaline
2Cd Horizon
Color: reddish brown, red, and/or greenish gray
Texture: noncemented shale or sandstone bedrock that may contain thin strata which are extremely weakly to moderately cemented. This horizon is root restrictive densic material and has a contact that qualifies as a densic contact.
Excavation difficulty: moderate to very high
Effervescence: noneffervescent to strongly effervescent
Reaction: slightly alkaline or moderately alkaline
COMPETING SERIES: These are the
Arnett,
Cobb,
Decobb, and
Grandmore series. Similar soils are the
Grandfield,
Honeycreek,
Hye,
Lou,
Menard,
Rochelle, and
Seagraves series.
Arnett and Rochelle series: These soils are very deep to bedrock and contain more than 5 percent siliceous gravel within the solum.
Cobb, Hye, and Lou series: These soils are less than 40 inches deep to paralithic or lithic bedrock and do not contain a discontinuity within the solum.
Decobb, Grandfield, and Menard series: These soils are very deep to bedrock and do not contain a discontinuity within the solum.
Grandmore and Seagraves series: These soils are very deep to bedrock.
Honeycreek series: These soils are 40 to 60 inches deep to paralithic schist or gneiss bedrock and may contain up to 35 percent siliceous gravel in the subsoil.
GEOGRAPHIC SETTING:
Parent material: The upper part of the soil formed in loamy alluvial or eolian sediments of Pleistocene age over material derived from claystone or sandstone bedrock of Permian age.
Landform: Dissected stream terraces on alluvial plains. These soils formed in stream terrace sediments that were deposited over a pediment and have since been dissected leaving a thin mantle of alluvial/eolian sediments over bedrock.
Slope: 0 to 5 percent
Mean annual air temperature range: 57 to 64 degrees F.
Mean annual precipitation range: 20 to 28 inches
Frost-free period: 185 to 230 days
Elevation: 1000 to 2200 feet
Thornthwaite annual P-E indices: 32 to 44
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Burford,
Devol,
Grandfield,
Grandmore, and
Tilvern series.
Burford and Tilvern series: These soils occur on similar positions, but are fine-silty and fine respectively in the particle-size control section.
Devol series: These soils occur on higher dunes, are coarse-loamy in the particle-size control section, and do not contain a discontinuity within 40 inches.
Grandfield series: These soils occur on slightly higher positions and do not contain a discontinuity within 40 inches or bedrock within 60 inches.
Grandmore series: These soils occur on lower positions, are moderately well drained, and do not contain bedrock within 60 inches.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate in the upper part and slow or moderately slow in the lower part. Runoff is low on 0 to 1 percent slopes and medium on 1 to 5 percent slopes.
USE AND VEGETATION: Soils are mainly cultivated. Cotton, wheat, sorghum, alfalfa, improved bermudagrass, and weeping lovegrass are the main crops. Native vegetation is mid and tall grasses.
DISTRIBUTION AND EXTENT: Central Rolling Red Plains of southwestern Oklahoma and possibly northwest Texas; LRR H; MLRA 78B & 78C; Moderate extent
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Harmon County, OK, 1982. The name comes from an old town site near the type location.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Particle size control section: 14 to 34 inches. (Bt1, Bt2, and 2Bt horizons)
ochric epipedon: 0 to 14 inches. (Ap horizon)
Argillic horizon: 14 to 36 inches. (Bt1, Bt2, and 2Bt horizons)
Densic contact: The contact with claystone bedrock at 52 inches. (2Cd horizon)
Lithologic discontinuity: At the upper boundary of the 2Bt horizon. (29 inches)
Additional Comments:
NSSL Data S03-OK-057-005 from this site shows that the clay content of the Bt2 and the 2Bt horizons has an absolute difference of 25.4 percent which meets the criteria for a contrasting particle-size class (fine-loamy over clayey) by 0.4 percent. This is within normal lab error and the particle-size class was left fine-loamy until lab analysis is performed to justify changing the classification.
The depth to bedrock was originally described as 30 to 50 inches and was changed to 40 to 60 inches to fit present depth classes.
The assignment of the cation-exchange activity class is supported by laboratory data number S03-OK-057-005 from Harmon county, OK
Ecological Site:
MLRA 78C, Loamy sand surface - Loamy Sand Prairie PE 31-44 (R078CY105TX),
Sandy loam surface - Sandy Loam Prairie PE 31-44 (R078CY110TX)
Soil Interpretation Record Number: OK0271
Taxonomic version: Keys to Soil Taxonomy, Ninth Edition, 2003
ADDITIONAL DATA: NSSL Data S03-OK-057-005