LOCATION ONITA SD+NE WYEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Pachic Argiustolls
TYPICAL PEDON: Onita silt loam - on a concave slope of less than 1 percent in native grass. When described the soil was moist throughout. (Colors are for dry soil unless otherwise stated.)
A1--0 to 6 inches; dark gray (10YR 4/1) silt loam, very dark gray (10YR 3/1) moist; moderate medium granular structure; soft, very friable; neutral; gradual smooth boundary.
A2--6 to 12 inches; dark gray (10YR 4/1) silt loam, very dark gray (10YR 3/1) moist; weak medium prismatic structure parting to weak medium and coarse subangular blocky; slightly hard, friable; neutral; clear smooth boundary. (Combined thickness of the A horizons is 8 to 20 inches.)
Bt1--12 to 18 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; weak medium prismatic structure parting to moderate medium subangular blocky; hard, friable, slightly sticky; shiny film on faces of peds; neutral; gradual smooth boundary.
Bt2--18 to 30 inches; dark grayish brown (2.5Y 4/2) silty clay, very dark grayish brown (2.5Y 3/2) moist; weak coarse prismatic structure parting to strong medium blocky; hard, firm, sticky, and plastic; shiny film on faces of peds; neutral; clear wavy boundary. (Combined thickness of the Bt horizons is 12 to 27 inches.)
Btk--30 to 38 inches; grayish brown (2.5Y 5/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; weak coarse prismatic structure parting to moderate medium blocky; hard, firm, slightly sticky, and slightly plastic; few fine threads of carbonate; strong effervescence; moderately alkaline; clear wavy boundary. (0 to 12 inches thick)
Bk--38 to 55 inches; light yellowish brown (2.5Y 6/4) silty clay loam, light olive brown (2.5Y 5/4) moist; weak medium subangular blocky structure; slightly hard, friable; disseminated carbonate and common fine threads of carbonate; strong effervescence; moderately alkaline; gradual smooth boundary. (7 to 20 inches thick)
C--55 to 60 inches; light yellowish brown (2.5Y 6/4) silty clay loam, light olive brown (2.5Y 5/4) moist; massive; slightly hard, friable, few fine accumulations of carbonates; strong effervescence; moderately alkaline.
TYPE LOCATION: Sully County, South Dakota; about 7 1/2 miles south of Onida; 112 feet east and 1,647 feet south of northwest corner, sec. 13, T. 113 N., R. 77 W.
RANGE IN CHARACTERISTICS: The thickness of the mollic epipedon typically ranges from 20 to 40 inches. The depth to carbonates ranges from 25 to 40 inches or more.
The A horizon has hue of 10YR, value of 3 to 5 and 2 or 3 moist, and chroma of 1 or 2. It typically is silt loam but is loam, clay loam, or silty clay loam in some pedons. It ranges from moderately acid to neutral.
The Bt horizon has hue of 10YR or 2.5Y, value of 3 to 5 and 2 to 4 moist, and chroma of 1 to 3. It is silty clay loam, clay loam, or silty clay averaging between 35 and 50 percent clay. It typically is slightly acid or neutral but is slightly or moderately alkaline in the Btk horizon. Some pedons do not have accumulations of carbonates in the lower Bt horizon.
The Bk horizon has hue of 10YR or 2.5Y, value of 4 to 6 and 3 to 5 moist, and chroma of 2 to 4. It is silty clay loam, clay loam, or silt loam. It is slightly or moderately alkaline.
The C horizon has hue of 10YR or 2.5Y, value of 5 to 7 and 4 to 6 moist, and chroma of 2 to 4. It is silty clay loam, clay loam, or silt loam. It is slightly or moderately alkaline. In some pedons, it is stratified loam, clay loam, or clay at depths between 40 and 60 inches.
COMPETING SERIES: These are the Crete, Detroit, Ladysmith, Lane, Rago, Smolan, and Sponiker series. Crete and Detroit soils have a more moist climate and a mean annual temperature of more than 50 degrees F. Ladysmith soils have 15 percent or more increase in clay content within a vertical distance of 3 inches from the surface layer to the argillic horizon. Lane soils have carbonates higher in the profile. Rago soils have buried paleosols in the lower part of the series control section. Spoiniker soils have a drier soil moisture control section in May and June. Smolan soils have redder hue.
GEOGRAPHIC SETTING: Onita soils are nearly level in slightly concave swales of the uplands and to a lesser extent on gently sloping alluvial fans and foot slopes. They are at elevations of 1,000 to 2,300 feet. Slope gradients range from 0 to 10 percent but typically are less than 2 percent. They formed in local clayey and loamy alluvium. Mean annual precipitation ranges from 15 to 26 inches, and mean annual temperature ranges from 45 to 52 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Lane soils and the Agar, Glenham, Highmore, Homme, Hoven, and Reliance soils. Lane soils are in higher positions in the landscape. Agar, Glenham, Highmore, Homme, and Reliance soils have mollic epipedons less than 20 inches thick and are in higher parts of the landscape. Hoven soils have natric horizons and are in depressions.
DRAINAGE AND PERMEABILITY: Well and moderately well drained. Runoff is low to high. Permeability is moderately slow or slow. A perched water table may rise to within 2 1/2 feet of the surface for short periods in the spring of most years. Onita soils receive run-in water from adjacent soils.
USE AND VEGETATION: Most areas of Onita soils are cultivated. Principal crops are winter wheat, grain sorghum, corn, and alfalfa. Native vegetation is mainly big bluestem, green needlegrass, little bluestem, switchgrass, needleandthread, western wheatgrass, sideoats grama, porcupine grass, sedges, and forbs.
DISTRIBUTION AND EXTENT: Mainly central and south-central South Dakota, adjoining part of north-central Nebraska and eastern Wyoming. The series is of large extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Hughes County, South Dakota, 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface to a depth of about 30 inches (A1, A2, Bt1, Bt2 horizon); argillic horizon - the zone from about 12 to 30 inches (Bt1, Bt2 horizon).
Other phases recognized: Moist, Dry, nonflooded, PE less than 31.