LOCATION MOBRIDGE SDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Pachic Argiustolls
TYPICAL PEDON: Mobridge silt loam - on a slope of less than 1 percent in a cultivated field. When described the soil was moist to 17 inches and dry below. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 7 inches; dark gray (10YR 4/1) silt loam, black (10YR 2/1) moist; weak fine granular structure; soft, very friable; slightly acid; clear smooth boundary.
A--7 to 11 inches; dark gray (10YR 4/1) silt loam, black (10YR 2/1) moist; weak coarse subangular blocky structure parting to weak fine granular; soft, very friable; neutral; clear smooth boundary. (Combined thickness of the A horizon is 7 to 14 inches.)
Bt1--11 to 17 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; weak medium prismatic structure parting to weak fine and medium subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; shiny surfaces on faces of peds; neutral; gradual smooth boundary.
Bt2--17 to 25 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium prismatic structure parting to moderate fine and medium blocky; hard, friable, slightly sticky and slightly plastic; shiny surfaces on faces of peds; few fine accumulations of carbonate in the lower 2 inches; slightly alkaline; clear smooth boundary. (Combined thickness of the Bt horizon is 10 to 36 inches.)
Bk1--25 to 30 inches; light brownish gray (2.5Y 6/2) silty clay loam, grayish brown (2.5Y 5/2) moist; weak coarse prismatic structure parting to weak medium and coarse subangular blocky; hard, friable, slightly sticky and slightly plastic; few fine accumulations of carbonate; strong effervescence; slightly alkaline; clear smooth boundary.
Bk2--30 to 42 inches; light brownish gray (2.5Y 6/2) silty clay loam, grayish brown (2.5Y 5/2) moist; few fine distinct mottles of yellowish brown (10YR 5/6) moist; weak coarse subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common medium and few coarse accumulations of carbonate; strong effervescence; slightly alkaline; gradual wavy boundary. (Combined Bk horizon is 8 to 36 inches thick.)
C--42 to 60 inches; light brownish gray (2.5Y 6/2) silty clay loam, containing very thin laminae of very fine sand and silt, dark grayish brown (2.5Y 4/2) moist; common fine distinct mottles of yellowish brown (10YR 5/6) and few fine distinct mottles of gray (10YR 5/1) moist; massive; hard, friable, slightly sticky and slightly plastic; few fine accumulations of carbonate; strong effervescence; slightly alkaline.
TYPE LOCATION: Walworth County, South Dakota; about 3 miles north and 4 miles west of Akaska; 1,192 feet west and 70 feet south of the NE corner of Sec. 24, T. 122 N., R. 78 W.
RANGE IN CHARACTERISTICS: The depth to carbonates ranges from 17 to 50 inches. The mollic epipedon ranges from 20 to 47 inches thick and includes part or all of the Bt horizon.
The A horizon has hue of 10YR, value of 3 or 4 and 2 or 3 moist, and chroma of 1, but has chroma of 2 in some pedons. It typically is silt loam but is silty clay loam in some pedons. It is moderately acid or neutral.
The Bt horizon has hue of 10YR, value of 3 to 5 and 2 to 4 moist, and chroma of 1 or 2. It typically is silty clay loam, but some pedons are clay loam averaging between 27 and 35 percent clay. It ranges from slightly acid to slightly alkaline. The Bt horizon typically contains few fine or very fine accumulations of carbonate in the lower part and the matrix typically is noncalcareous.
The Bk horizon has hue of 2.5Y or 10YR, value of 5 or 6 and 4 or 5 moist, and chroma of 1 to 4. It is silty clay loam or silt loam. It has few to many accumulations of carbonate and is slightly or moderately alkaline.
The C horizon has hue of 2.5Y or 10YR, value of 5 to 7 and 4 to 6 moist, and chroma of 2 to 4. It is silt loam, clay loam, or silty clay loam and is slightly or moderately alkaline. Thin strata of loam, clay loam, or silty clay are between depths of 40 and 60 inches in some pedons. Glacial till or sand and gravel are between depths of 40 and 60 inches in some pedons. Buried horizons are present in the C horizon in some pedons.
COMPETING SERIES: These are the Goshen, Hall, and Kuma series in the same family. Goshen soils typically have moist chroma of 2 or more in the A horizon, are leached of carbonates to greater depths, and are in a warmer climate. Hall soils typically are leached of carbonates to greater depths and are in a more moist climate. Kuma soils have polygenetic profiles. Simpatico soils have redder hue in the argillic horizon and have a more uniform distribution of rainfall throughout the year.
GEOGRAPHIC SETTING: Mobridge soils are in upland swales, slight depressions, drainageways, fans, and foot slopes. Surfaces are plain or concave. Slope gradients typically are less than 2 percent but range from 0 to 6 percent. Mobridge soils formed in local silty colluvial-alluvial sediments derived dominantly from silty glacial drift and loess. Mean annual temperature ranges from 45 to 50 degrees F, and the mean annual precipitation ranges from 15 to 24 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Agar, Akaska, Eakin, Highmore, Hoven, Lowry, Onita, and Tetonka soils. Agar, Akaska, Eakin, Highmore, and Lowry soils have mollic epipedons less than 20 inches thick and are on nearby higher parts of the landscapes. In addition, Lowry soils do not have an argillic horizon and have a coarse-silty control section. Hoven soils have a natric horizon and are in depressions. Onita soils are in similar positions and have a fine textured argillic horizon. Tetonka soils are poorly drained and are in depressions.
DRAINAGE AND PERMEABILTY: Well or moderately well drained. Runoff is slow. Permeability is moderate. These soils receive run-in water from adjacent higher areas.
USE AND VEGETATION: Most areas of Mobridge soils are cropped to spring and winter wheat, grain sorghum, corn, and alfalfa. Native vegetation includes green needlegrass, western wheatgrass, needleandthread, blue grama, big bluestem, little bluestem, sedges and forbs.
DISTRIBUTION AND EXTENT: Central South Dakota, mainly east of the Missouri River. It is of moderate extent.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to about 25 inches (Ap, A, Bt horizons) and an argillic horizon from 11 to 25 inches (Bt horizons).
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Walworth County, South Dakota, 1975.
ADDITIONAL DATA: Reference: Soil No. S72 SD-64-24, National Soil Survey Lab. No. 73L108-73L110.