LOCATION SONNETT MTEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Aridic Haplustalfs
TYPICAL PEDON: Sonnett loam, 2 to 8 percent slopes, in rangeland (Colors are for dry soil unless otherwise noted).
E--0 to 6 inches; light brownish gray (10YR 6/2) loam; dark grayish brown (10YR 4/2) moist; moderate medium subangular blocky structure parting to weak fine granular; soft, very friable, slightly sticky and slightly plastic; common fine and medium roots throughout; common very fine and fine vesicular pores; neutral (pH 7.2); clear smooth boundary. (1 to 7 inches thick)
Bt--6 to 14 inches; grayish brown (10YR 5/2) silty clay; very dark grayish brown (2.5Y 3/2) moist; strong fine and medium columnar structure parting to strong medium and coarse subangular blocky; very hard, very firm, moderately sticky and very plastic; common fine and medium roots between peds; few medium discontinuous tubular pores, common very fine vesicular pores; very few distinct black (10YR 2/1) patchy organic coats on vertical faces of peds, few continuous distinct clay films on faces of peds and in pores; slightly alkaline (pH 7.4); gradual wavy boundary. (6 to 14 inches thick)
Btk--14 to 20 inches; grayish brown (10YR 5/2) silty clay loam; dark brown (10YR 3/3) moist; strong coarse prismatic structure parting to strong coarse subangular blocky; very hard, firm, moderately sticky and moderately plastic; common very fine and fine roots between peds; common fine discontinuous tubular pores; very few faint black (10YR 2/1) patchy organic coats on vertical faces of peds, very few discontinuous clay films (cutans) on faces of peds and in pores; common medium irregular masses of lime; strongly effervescent; slightly alkaline (pH 7.7); gradual wavy boundary. (0 to 8 inches thick)
Bk--20 to 25 inches; light brownish gray (10YR 6/2) clay loam; dark grayish brown (10YR 4/2) moist; moderate coarse prismatic structure; hard, friable, slightly sticky and slightly plastic; common very fine and fine roots between peds; common fine discontinuous tubular pores; common medium irregular masses of lime; violently effervescent; slightly alkaline (pH 7.7); gradual irregular boundary. (4 to 8 inches thick)
Bky1--25 to 31 inches; grayish brown (10YR 5/2) clay loam; very dark grayish brown (10YR 3/2) moist; moderate coarse prismatic structure parting to moderate medium and coarse angular blocky; hard, firm, moderately sticky and moderately plastic; few very fine and fine roots throughout; few fine discontinuous tubular pores; very few faint black (10YR 2/1) patchy organic coats on vertical faces of peds; few medium irregular gypsum threads, common medium irregular masses of lime; violently effervescent; moderately alkaline (pH 8.2); gradual wavy boundary.
Bky2--31 to 47 inches; light brownish gray (10YR 6/2) clay loam; very dark grayish brown (10YR 3/2) moist; weak coarse prismatic structure; slightly hard, friable, moderately sticky and moderately plastic; few fine roots throughout; common fine continuous tubular pores, common very fine discontinuous tubular pores; common medium irregular gypsum threads, common medium irregular threads of lime; strongly effervescent; strongly alkaline (pH 8.6); gradual smooth boundary. (Combined thickness of Bky1 and Bky2 horizons is 8 to 24 inches)
Bky3--47 to 60 inches; light brownish gray (10YR 6/2) clay loam; dark brown (10YR 3/3) moist; weak coarse prismatic structure; hard, friable, moderately sticky and moderately plastic; common fine discontinuous tubular pores; common fine and medium irregular gypsum threads, common fine irregular threads of lime; strongly effervescent; strongly alkaline (pH 8.8).
TYPE LOCATION: Custer County, Montana; 2,000 feet west and 1,800 feet south of the NE corner of sec. 24, T. 5 N., R. 51 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 44 to 47 degrees F.
Moisture control section - between 4 and 12 inches; dry in all parts between four-tenths and five-tenths of the cumulative days per year when the soil temperature at a depth of 20 inches is 41 degrees F or higher.
Soil phases - thin surface (1 to 3 inches thick E horizon)
E horizon - Value: 6 or 7 dry; 3 or 4 moist
Texture: loam (mixed to 7 inches it is a clay loam or silty clay loam)
Clay content: 15 to 35 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 6.6 to 7.8
Bt horizon - Hue: 10YR or 2.5Y
Value: 5 dry, 3 or 4 moist
Chroma: 2 or 3
Texture: silty clay or clay
Clay content: 40 to 45 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 7.4 to 8.4
Btk horizon - Hue: 10YR or 2.5Y
Value: 5 dry, 3 or 4 moist
Chroma: 2 or 3
Texture: clay loam or silty clay loam
Clay content: 30 to 40 percent
Electrical conductivity: 0 to 2 mmhos/cm
Calcium carbonate equivalent: 1 to 5 percent
Reaction: pH 7.4 to 8.4
Bk horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 4 moist
Chroma: 2 or 3
Texture: clay loam or loam
Clay content: 20 to 30 percent
Electrical conductivity: 0 to 2 mmhos/cm
Calcium carbonate equivalent: 5 to 10 percent
Reaction: pH 7.4 to 8.4
Bky1 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 3 or 4 moist
Chroma: 2 or 3
Texture: clay loam or loam
Clay content: 20 to 30 percent
Electrical conductivity: 0 to 4 mmhos/cm
Calcium carbonate equivalent: 5 to 10 percent
Gypsum content: 1 to 3 percent
Reaction: pH 7.9 to 9.0
Bky2 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 3 or 4 moist
Texture: clay loam or loam
Clay content: 20 to 30 percent
Electrical conductivity: 0 to 4 mmhos/cm
Sodium absorption ratio: 5 to 10
Calcium carbonate equivalent: 5 to 10 percent
Gypsum content: 1 to 3 percent
Reaction: pH 8.5 to 9.0
Bky3 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 3 or 4 moist
Chroma: 2 or 3
Texture: clay loam or loam
Clay content: 20 to 30 percent
Content of rock fragments: 0 to 5 percent pebbles
Electrical conductivity: 0 to 4 mmhos/cm
Sodium absorption ratio: 5 to 10
Calcium carbonate equivalent: 1 to 5 percent
Gypsum content: 1 to 3 percent
Reaction: pH 8.5 to 9.0
COMPETING SERIES:
Campspass (MT) - has a lithic contact above a depth of 60 inches; has a mixed B/E horizon.
Citadel (SD) - does not have a horizon of secondary calcium carbonate accumulation; is mainly strongly acid above a depth of 23 inches; has a mixed B/A horizon.
Fortwingate (NM) - does not have a horizon of secondary calcium carbonate accumulation; has a lithic contact of sandstone at a depth of 20 to 40 inches.
Goldvale (CO) - does not have a horizon of secondary calcium carbonate accumulation; has stone size rock fragments throughout; has mixed E/B horizons.
Larkson (CO) - does not have a horizon of secondary calcium carbonate accumulation; has mixed E/B horizons; has a 2-inch O horizon of forest litter.
McVickers (AZ) - does not have a horizon of secondary calcium carbonate accumulation; has a lithic contact at depths of 40 to 60 inches; has the base of the argillic horizon at a depth of 40 inches or deeper.
Osoridge (NM) - does not have a horizon of secondary calcium carbonate accumulations; has a lithic contact of sandstone at depths of 20 to 40 inches.
Phillips (MT) - has a moist bulk density of 1.55 to 1.75 g/cc in the till; formed in till; has EC of 4 to 8 mmhos/cm below a depth of 30 inches.
Pinehill (MT) - does not have horizons with accumulation of gypsum with secondary calcium carbonate.
Pylon (MT) - has a very hard or hard and massive surface and an extremely hard argillic horizon; has a paralithic contact of shale at depths of 20 to 40 inches.
Zuni (NM) - does not have a horizon of secondary calcium carbonate accumulation; formed in coarse-grained granite; has a lithic contact of granite bedrock at depths of 40 to 60 inches.
GEOGRAPHIC SETTING:
Landform - alluvial fans; stream terraces; sedimentary plains.
Elevation - 2,200 to 3,500 feet.
Slope- 0 to 8 percent.
Parent material - alluvium derived mainly from weakly consolidated sedimentary beds of Tertiary age.
Climate - long, cold winters; cool, moist springs; warm, dry summers.
Mean annual precipitation - 11 to 14 inches.
Mean annual air temperature - 42 to 45 degrees F.
Frost-free season - 110 to 135 days.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Sonnett soils are used mainly for rangeland and nonirrigated cropland. Potential native vegetation is mainly western wheatgrass, green needlegrass, blue grama, needleandthread, silver sagebrush, and Wyoming big sagebrush.
DISTRIBUTION AND EXTENT: Sonnett soils are of small extent in southeastern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Custer County, Montana, 1995.
REMARKS: Soil interpretation record: MT1394. Diagnostic horizons and features recognized in this pedon are: an ochric epipedon from the soil surface to 6 inches (E horizon); an argillic horizon that is the particle-size control section from 6 to 20 inches (Bt, Btk horizons); accumulations of calcium carbonates and gypsum from 25 to 60 inches (Bky1, Bky2, Bky3 horizons). Sonnett soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.
A preferred classification is Aridic Eutroboralfs. A proposal adding this subgroup has been submitted.