LOCATION KOBASE MTEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Torrertic Haplustepts
TYPICAL PEDON: Kobase silty clay loam, in cropland (colors are for dry soil unless otherwise noted).
Ap--0 to 7 inches; grayish brown (2.5Y 5/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; moderate very fine granular structure in upper 3 inches grading to weak medium and fine subangular blocky in the lower part; hard, very friable, sticky and plastic; many fine and very fine roots; many fine and very fine pores; slightly effervescent; neutral (pH 7.3); abrupt wavy boundary. (5 to 8 inches thick)
Bw--7 to 15 inches; light brownish gray (2.5Y 6/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; moderate medium prismatic structure parting to moderate medium and fine angular blocky; very hard, friable, sticky and plastic; many fine and very fine roots; many fine and very fine pores; disseminated lime; strongly effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (6 to 15 inches thick)
Bk1--15 to 20 inches; light brownish gray (2.5Y 6/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; moderate medium prismatic structure parting to weak medium and coarse subangular blocky; extremely hard, firm, sticky and plastic; common fine and very fine roots; many fine and very fine pores; few fine masses of lime; strongly effervescent; strongly alkaline (pH 8.8); gradual wavy boundary.
Bk2--20 to 31 inches; light brownish gray (2.5Y 6/2) clay loam, dark grayish brown (2.5Y 4/2) moist; weak medium and coarse angular blocky structure; extremely hard, friable, sticky and plastic; common fine and very fine roots; many fine and very fine pores; few fine masses of lime; strongly effervescent; strongly alkaline (pH 8.8); gradual wavy boundary. (Combined Bk horizons 8 to 38 inches thick)
Bky--31 to 60 inches; light brownish gray (2.5Y 6/2) clay loam, dark grayish brown (2.5Y 4/2) moist; weak coarse angular blocky structure; hard, friable, sticky and plastic; few fine and very fine roots; many very fine pores; common fine masses of lime; common fine threads of gypsum and other salts; strongly effervescent; strongly alkaline (pH 8.8). (0 to 30 inches thick.)
TYPE LOCATION: Fergus County, Montana; 800 feet east and 1,350 feet north of the southwest corner of sec. 9, T. 18 N., R. 26 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 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 20 inches is 41 degrees F or higher.
Depth to Bk horizon - 12 to 17 inches.
The one chromas are lithochromic in the B horizons, a C horizon is allowed.
Soil phases - moist, saline.
Ap horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3
Texture: silty clay loam, silty clay, clay, or clay loam
Clay content: 27 to 45 percent
Rock fragments: 0 to 5 percent pebbles
EC: 0 to 4 mmhos/cm (saline phase 2 to 4 mmhos/cm)
SAR: 0 to 4
Calcium carbonate equivalent: 0 to 5 percent
Reaction: pH 6.6 to 8.4
Bw horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 1, 2, 3, or 4
Texture: clay loam, silty clay loam, silty clay, or clay
Clay content: 35 to 45 percent
Rock fragments: 0 to 5 percent pebbles
Calcium carbonate equivalent: 0 to 10 percent
EC: 0 to 2 mmhos/cm
SAR: 0 to 4
Reaction: pH 7.4 to 8.4
Bk1 horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 1, 2, 3, or 4
Texture: clay loam, silty clay loam, silty clay, or clay
Clay content: 35 to 45 percent
Rock fragments: 0 to 5 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
SAR: 0 to 10
EC: 0 to 2 mmhos/cm
Reaction: pH 7.4 to 9.0
Bk2 horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: clay loam, silty clay loam, silty clay, or clay
Clay content: 35 to 45 percent
Rock fragments: 0 to 5 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
SAR: 0 to 10
EC: 0 to 4 mmhos/cm
Reaction: 7.9 to 9.0
Bky horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 1, 2, 3, or 4
Texture: clay loam, silty clay loam, silty clay, or clay
Clay content: 35 to 45 percent
Rock fragments: 0 to 5 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
SAR: 1 to 20
EC: 0 to 8 mmhos/cm
Gypsum: 1 to 5 percent
Reaction: pH 7.9 to 9.0
Some pedons have thin strata of silt loam or loam below depths of 40 inches and a BCy or Byz horizon.
COMPETING SERIES:
Alzada (MT) - has a lithological discontinuity within depths of 40 inches.
Brunelda (MT) - has a gypsic horizon; does not have a cambic horizon.
Megonot (MT) - has a paralithic contact above a depth of 40 inches.
Nunemaker (MT) - has a discontinuity of till that has a bulk density of 1.65 g/cc and greater.
Teigen (MT) - is noncalcareous throughout the profile; has very strongly acid to medium acid reaction in the surface and cambic horizons.
Zatoville (MT) - has a gypsic horizon; has a paralithic contact at depths between 40 and 60 inches.
GEOGRAPHIC SETTING:
Landform - till plains; stream terraces; alluvial fans; sedimentary plains; drainageways; lake plains; hills.
Elevation - 2,200 to 5,200 feet.
Slope- 0 to 40 percent.
Parent material - alluvium derived from semiconsolidated shale and sandstone, glacial meltwater deposits, and glaciofluvial or glaciolacustrine deposits.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 10 to 14 inches, most of which fall during the spring and the early part of summer.
Mean annual temperature - 39 to 45 degrees F.
Frost-free period - 90 to 135 days.
DRAINAGE AND PERMEABILITY: Well drained, slow permeability.
USE AND VEGETATION: Kobase soils are used for irrigated and nonirrigated cropland and for rangeland. The potential native vegetation is green needlegrass, bluebunch wheatgrass, western wheatgrass, forbs, and shrubs.
DISTRIBUTION AND EXTENT: The Kobase series is extensive in the plains area of Montana, in adjacent states, and in Colorado.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Hill County, Montana, 1994. Kobase is a coined name.
REMARKS: Soil interpretations records: MT0106, MT0892.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - from the soil surface to 7 inches (Ap horizon); cambic horizon - from 7 to 15 inches (Bw horizon); accumulations of lime - from 15 to 60 inches (Bk1, Bk2, Bky horizons); particle-size control section - from 10 to 40 inches (Bw, Bk1, Bk2, Bky horizons). Kobase soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.