LOCATION SOAPCREEK MT
Established Series
Rev. LCB-JB-JCK
04/2021
SOAPCREEK SERIES
The Soapcreek series consists of very deep, somewhat poorly drained soils that formed in alluvium. These soils are on flood plains, flood-plain steps, and stream terraces. Slopes are 0 to 2 percent. Mean annual precipitation is about 330 mm, and mean annual temperature is about 6 degrees C.
TAXONOMIC CLASS: Fine, mixed, superactive, frigid Fluvaquentic Haplustolls
TYPICAL PEDON: Soapcreek silty clay, in irrigated hayland (colors are for dry soil unless otherwise noted).
Ap--0 to 13 cm; dark gray (10YR 4/1) silty clay, very dark gray (10YR 3/1) moist; strong very fine granular structure; hard, firm, moderately sticky and moderately plastic; many very fine roots; many fine tubular and interstitial pores; common worm casts; moderately alkaline (pH 8.1); clear smooth boundary. (10 to 15 cm thick)
A--13 to 30 cm; gray (10YR 5/1) silty clay, very dark gray (10YR 3/1) moist; strong fine and very fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many very fine roots; many very fine tubular and interstitial pores; common worm casts; slightly effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (15 to 30 cm thick)
Bk1--30 to 51 cm; gray (10YR 5/1) silty clay, dark gray (10YR 4/1) moist; moderate fine and very fine granular structure; hard, firm, moderately sticky and moderately plastic; common very fine roots; many very fine tubular and interstitial pores; few fine calcium carbonate masses; strongly effervescent; moderately alkaline (pH 8.2); gradual smooth boundary. (0 to 38 cm thick)
Bk2--51 to 76 cm; gray (10YR 5/1) silty clay, dark gray (10YR 4/1) moist; common medium prominent light brown (7.5YR 6/4) redox concentrations, brown (7.5YR 4/4) moist; weak fine and very fine granular structure; hard, firm, moderately sticky and moderately plastic; common very fine roots; many very fine tubular and interstitial pores; finely disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.2); gradual smooth boundary. (13 to 38 cm thick)
Bg1--76 to 102 cm; gray (5Y 6/1) silty clay, dark gray (5Y 4/1) moist; common medium prominent light yellowish brown (2.5Y 6/4) redox depletions, light olive brown (2.5Y 5/4) and dark grayish brown (2.5Y 4/2) moist; massive; hard, firm, moderately sticky and moderately plastic; few very fine roots; common very fine tubular and interstitial pores; slightly alkaline (pH 7.8); gradual smooth boundary. (13 to 38 cm thick)
Bg2--102 to 152 cm; gray (5Y 6/1) silty clay, gray (5Y 5/1) moist; many distinct light brownish gray (2.5Y 6/2) redox depletions, light olive brown (2.5Y 5/4) moist; massive; hard, firm, moderately sticky and moderately plastic; few very fine roots; 5 percent gravel and charcoal fragments; slightly alkaline (pH 7.8).
TYPE LOCATION: Lewis and Clark County, Montana; 152 meters south and 213 meters west of the NE corner of sec. 18, T. 11 N., R. 4 W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 5 to 8 degrees C
Mollic epipedon thickness - 25 to 38 cm
Depth to seasonal high water table - 60 to 100 cm
Some pedons have redox concentrations above 60 cm where irrigated.
Ap, A horizons
Hue: 10YR or 2.5Y
Value: 3, 4 or 5 dry, 2 or 3 moist
Chroma: 1 or 2
Texture: silty clay, clay loam, or silty clay loam
Clay content: 27 to 50 percent
Rock fragments: 0 to 5 percent gravel
Reaction: pH 7.4 to 8.4
Bk horizons
Hue: 10YR, 5Y, or 2.5Y
Value: 4, 5 or 6 dry, 3, 4 or 5 moist
Chroma: 1 or 2
Texture: silty clay or silty clay loam
Clay content: 35 to 50 percent
Rock fragments: 0 to 5 percent gravel
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.9 to 8.4
Bg1 horizon
Hue: 2.5Y or 5Y
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 1 or 2
Texture: clay, silty clay or silty clay loam
Clay content: 35 to 50 percent
Rock fragments: 0 to 15 percent gravel
Calcium carbonate equivalent: 0 to 15 percent
Reaction: pH 7.4 to 8.4
Bg2 horizon
Hue: 2.5Y or 5Y
Value: 4 or 5 moist
Chroma: 1 or 2
Texture: silty clay loam or silty clay with thin strata of fine sandy loam, loam, and silt loam
Clay content: 27 to 45 percent
Rock fragments: 0 to 15 percent gravel
Calcium carbonate equivalent: 0 to 15 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - flood plains, flood-plain steps, and stream terraces
Elevation - 1,127 to 1,890 meters
Slope - 0 to 2 percent
Parent material - alluvium
Mean annual precipitation - 304 to 483 mm, most of which falls during spring and early summer
Mean annual air temperature - 3.8 to 7.2 degrees C
Frost-free season - 70 to 130 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow permeability.
USE AND VEGETATION: Soapcreek soils are used mainly for irrigated cropland. Some areas are used for rangeland. Potential native vegetation is mainly western wheatgrass, basin wildrye, prairie cordgrass, tall reedgrasses, tufted hairgrass, forbs, and shrubs.
DISTRIBUTION AND EXTENT: Soapcreek soils are moderately extensive in west-central and southwestern Montana. MLRAs - 44B, 46, 58A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Lewis and Clark County Area, Montana, 1991.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 0 to 30 cm (Ap and A horizons)
Secondary calcium carbonate accumulation - from 30 to 76 cm (Bk1 and Bk2 horizons)
Redox concentrations - from 51 to 76 cm (Bk2 horizon)
Redox depletions - from 76 to 152 cm (Bg1 and Bg2 horizons)
Particle-size control section - from 25 to 100 cm (part of the A, Bk1, Bk2, and Bg1 horizons)
Soapcreek soils have a frigid temperature regime and an ustic moisture regime.
ADDITIONAL DATA: Soil interpretations record - MT0195.
National Cooperative Soil Survey
U.S.A.