LOCATION MILLBORO SDEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Typic Haplusterts
TYPICAL PEDON: Millboro silty clay - on plane, north-facing slope of 3 percent in a cultivated field. When described the soil was moist throughout. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 5 inches; dark grayish brown (10YR 4/2) silty clay, very dark brown (10YR 2/2) moist; weak coarse and medium subangular blocky structure; hard, firm, sticky and plastic; neutral; abrupt smooth boundary.
A--5 to 7 inches; dark grayish brown (10YR 4/2) silty clay, very dark grayish brown (10YR 3/2) moist; weak coarse and medium subangular blocky structure; very hard, firm, sticky and plastic; slightly alkaline; clear smooth boundary. (Combined A horizons is 4 to 10 inches thick.)
Bt1--7 to 13 inches; dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; moderate medium and coarse prismatic structure parting to moderate fine and very fine subangular blocky; very hard, firm, sticky and plastic; neutral; clear smooth boundary.
Bt2--13 to 19 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; moderate medium prismatic structure parting to moderate fine and very fine subangular blocky; very hard, firm, sticky and plastic; many tongues (1/4 to 1 inch wide) of dark grayish brown (10YR 4/2); strong effervescence; slightly alkaline; clear smooth boundary. (Combined Bt horizons 8 to 24 inches thick)
Bkss1--19 to 28 inches; grayish brown (2.5Y 5/2) silty clay, dark grayish brown (2.5Y 4/2) moist; weak coarse prismatic structure parting to moderate medium blocky; extremely hard, very firm, very sticky and very plastic; many tongues (1/4 to 1 inch wide) of dark grayish brown (10YR 4/2); many pressure faces and common slickensides; common medium accumulations of carbonate; strong effervescence; moderately alkaline; clear smooth boundary.
Bkss2--28 to 36 inches; grayish brown (2.5Y 5/2) silty clay, dark grayish brown (2.5Y 4/2) moist; moderate medium and coarse blocky structure; extremely hard, very firm, very sticky and very plastic; many tongues (1/4 to 1 inch wide) of dark grayish brown (10YR 4/2); many pressure faces and common slickensides; many fine and medium accumulations of carbonate; strong effervescence; moderately alkaline; clear wavy boundary. (Combined Bkss horizons 0 to 20 inches thick.)
C--36 to 43 inches; grayish brown (2.5Y 5/2) silty clay, dark grayish brown (2.5Y 4/2) moist; massive; very hard, very firm, very sticky and very plastic; few 1/4 inch tongues of dark grayish brown (10YR 4/2); few fine accumulations of carbonate; strong effervescence; moderately alkaline; gradual wavy boundary.
Ckz--43 to 56 inches; light yellowish brown (2.5Y 6/4) silty clay, olive brown (2.5Y 4/4) moist; massive; hard, firm, sticky and plastic; few 1/4 inch tongues of dark grayish brown (10YR 4/2); many fine accumulations of carbonate and salts; strong effervescence; moderately alkaline; gradual wavy boundary.
C'--56 to 60 inches; light yellowish brown (2.5Y 6/4) silty clay, olive brown (2.5Y 4/4) moist; massive; hard, firm, sticky and plastic; strong effervescence; moderately alkaline.
TYPE LOCATION: Tripp County, South Dakota; about 3 miles east of Witten; 2555 feet west and 240 feet north of southeast corner, sec. 25, T. 100 N., R. 78 W.
RANGE IN CHARACTERISTICS: The depth to free carbonate ranges from 7 to 20 inches in native grass, but some cultivated areas contain carbonate to the surface. The thickness of mollic epipedon ranges from 7 to 19 inches. Common or many tongues of A horizon extend through the solum and into the C horizon of most pedons.
The A horizon has hue of 10YR or 2.5Y, value of 3 to 5 and 2 or 3 moist, and chroma of 1 or 2. It is silty clay, silty clay loam, or clay. It is neutral or slightly alkaline. Some pedons have a thin mantle of silt loam on the surface.
The Bt horizon has hue of 10YR or 2.5Y, value of 4 or 5 and 3 or 4 moist, and chroma of 1 through 3. It is clay or silty clay averaging between 45 and 60 percent clay. It is neutral to moderately alkaline.
The Bkss horizon has hue of 2.5Y or 5Y, value of 5 or 6 and 4 or 5 moist, and chroma of 2 to 4. It is clay or silty clay. It has common or many pressure faces and slickensides and common or many accumulations of carbonate. It is slightly alkaline or moderately alkaline. Some pedons have BC horizons.
The C horizon has hue of 2.5Y or 5Y, value of 5 to 7 and 4 or 5 moist, and chroma of 2 to 4. It is clay or silty clay in the lower part of some pedons. It has few to many fragments of shale and accumulations of salts in the lower part of some pedons. It is slightly alkaline or moderately alkaline. Some pedons have bedded shale between depths of 40 and 60 inches.
COMPETING SERIES: These are the Oko, Okreek, and Witten series in the same family. Oko soils contain more sand and formed in glacial till. Okreek soils typically contain less clay and have shale between depths of 20 and 40 inches. Witten soils have a mollic epipedon greater than 20 inches thick.
GEOGRAPHIC SETTING: Millboro soils are on nearly level to rolling uplands. Slopes range from 0 to 15 percent and surface are plane to convex. These soils formed in clayey materials weathered from shale. Mean annual air temperature ranges from 45 to 50 degrees F, and mean annual precipitation ranges from 15 to 24 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Witten soils and the Boro, Lakoma, Reliance, and McClure soils. Witten soils are in swales. Boro and Lakoma soils have convex slopes and are above the Millboro soils. Boro soils do not have a mollic epipedon. Lakoma soils have shale between depths of 20 and 40 inches. Reliance and McClure have plane slopes on tablelands above the Millboro soils. They contain less clay.
DRAINAGE AND PERMEABILITY: Well drained. Surface runoff is low to high depending on slope. Permeability is slow.
USE AND VEGETATION: Mostly cropped to winter wheat, corn grain sorghum and alfalfa. Native vegetation mainly is western wheatgrass, green needlegrass, blue grama, and sideoats grama.
DISTRIBUTION AND EXTENT: South-central South Dakota. It is extensive.
MLRA OFFICE RESPONSIBLE: Bismarck, North Dakota
SERIES ESTABLISHED: Hughes County, South Dakota, 1970.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to a depth of 13 inches (Ap, A and Bt1 horizons); argillic horizons - the zone from 7 to 19 inches (Bt1 and Bt2 horizons).
ADDITIONAL DATA: NSSL Sample Nos. 71L409-417.