LOCATION SOFIA MTEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Torrertic Argiustolls
TYPICAL PEDON: Sofia silty clay - cultivated. (Colors are for dry soil unless otherwise noted)
Ap--0 to 7 inches; brown (10YR 5/3) silty clay, dark brown (10YR 3/3) moist; clods that separate to moderate fine granular structure; very hard, firm, very sticky, very plastic; neutral; abrupt smooth boundary.
Bt--7 to 12 inches; dark brown (10YR 4/3) silty clay, dark yellowish brown (10YR 3/4) moist; weak medium prismatic structure parting to strong medium and fine blocky; very hard, very firm, very sticky and very plastic; few very fine and fine roots; common very fine and fine and few medium tubular pores; continuous organically stained films on faces of all peds; slightly alkaline; clear boundary. (4 to 10 inches thick)
Btk--12 to 16 inches; brown (10YR 5/3) silty clay, dark brown (10YR 4/3) moist; weak medium prismatic structure parting to moderate medium and fine blocky; very hard, firm, very sticky and plastic; few very fine roots; common very fine and fine and few medium tubular pores; strong effervescence; moderately alkaline; clear wavy boundary. (4 to 8 inches thick)
Bk1--16 to 22 inches; pale brown (10YR 6/3) silty clay, brown (10YR 5/3) moist; moderate medium blocky structure; very hard, firm, very sticky and plastic; few very fine and fine roots; common very fine and fine and few medium tubular pores; violent effervescence; moderately alkaline; gradual boundary. (0 to 10 inches thick)
Bk2--22 to 40 inches; pale brown (10YR 6/3) silty clay, brown (10YR 5/3) moist; weak coarse blocky structure; very hard, firm, very sticky and plastic; few very fine and fine roots; common very fine and fine and few medium tubular pores; violent effervescence; common fine and medium masses of lime increasing with depth; moderately alkaline; clear wavy boundary. (20 to 30 inches thick)
2C--40 to 50 inches; very gravelly sand.
TYPE LOCATION: Big Horn County, Montana; 200 feet east and 250 feet south of center of sec. 32, T.4S., R.30E.
RANGE IN CHARACTERISTICS:
Soil Temperature: 48 to 50 degrees F
Mollic Epipedon Thickness: 7 to 16 inches
Depth to lime: 10 to 16 inches
Solum thickness: 14 to 22 inches
Depth to 2C horizon: 40 to 80 inches
Notes: Uncultivated pedons have a 2 to 4 inch thick, silt loam A horizon. The soil is usually dry but their surface horizons are moistened by occasional summer rains of one or more inch intensity.
A horizon:
Hue: 10YR or 2.5Y
Chroma: 2 or 3
Bt horizon:
Hue: 10YR or 2.5Y
Value: 4 or 5, 3 or 4 moist
Chroma: 2 to 4
Texture: silty clay
Clay Content: 50 to 60 (5 to 15 percent more clay than the Ap, 15 to 25 percent more clay than A, and 10 to 20 percent more clay than the Bk horizons)
Bk horizon:
CaCO3 equivalent: 6 to 12 percent
Notes: few to many masses of lime
Rock Fragments: 0 to 5 percent
COMPETING SERIES: These are the Ethridge and Linnet series. The Ethridge soils have 35 to 45 percent clay in the Bt horizon. The Linnet soils have a BCy horizon and do not have a 2C horizon.
GEOGRAPHIC SETTING: Sofia soils are on undulating to rolling residual uplands and on nearly level to sloping old river terraces. The soils formed in calcareous silty clay loam or silty clay alluvium or deep residuum from calcareous clayey shales. The climate is semiarid with from 14 to 16 inches mean annual precipitation, from 45 to 48 degrees F. mean annual temperature, with average July temperature of 70 to 73 degrees F., and average January temperature of 15 to 18 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Beauvais, Lavina, Nunn, Richfield, Ryegate and Wages soils. Beauvais soils formed in loess and have fine-silty particle-size class. Lavina soils are shallow. Nunn and Richfield soils have 35 to 50 percent clay in the Bt horizon. In addition, Richfield soils formed in silty loess. Ryegate soils are moderately deep over hard sandstone. Wages soils have fine-loamy Bt horizons.
DRAINAGE AND PERMEABILITY: Well-drained; slow permeability.
USE AND VEGETATION: Dryland crop production and range. Native vegetation is needle-and-thread grass, prairie junegrass, western wheatgrass, green needlegrass, green sagewort and blue grama.
DISTRIBUTION AND EXTENT: Southeastern Montana. The soils are moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Big Horn County (Big Horn Area), Montana, 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 7 inches (Ap horizon); argillic horizon - the zone from 7 to 16 inches (Bt and Btk horizons); vertic subgroup criteria - silty clay texture throughout and smectitic mineralogy.
The type location for Sofia series has been transferred to Montana by agreement with New Mexico.