LOCATION FORTBENTON MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Aridic Haplustolls
TYPICAL PEDON: Fortbenton fine sandy loam, cropland (colors are for dry soil unless otherwise noted).
Ap--0 to 6 inches; grayish brown (10YR 5/2) fine sandy loam, very dark grayish brown (10YR 3/2) moist; strong, very fine and fine granular structure; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; neutral (pH 7.2); abrupt smooth boundary. (6 to 8 inches thick)
Bw1--6 to 13 inches; grayish brown (10YR 5/2) fine sandy loam, very dark grayish brown (10YR 3/2) moist; weak medium prismatic structure parting to moderate medium subangular blocky; slightly hard, very friable, nonsticky and nonplastic; common very fine and fine roots; many very fine and few fine tubular pores; neutral (pH 7.2); clear wavy boundary. (0 to 7 inches thick)
Bw2--13 to 23 inches; brown (10YR 5/3) fine sandy loam, dark brown (10YR 4/3) moist; moderate medium prismatic structure parting to moderate fine and medium subangular blocky; hard, very friable, nonsticky and nonplastic; common very fine and fine roots; many very fine and few fine tubular pores; few faint clay films on faces of peds; slightly alkaline (pH 7.4); abrupt wavy boundary. (9 to 17 inches thick)
2Bk1--23 to 32 inches; light brownish gray (2.5Y 6/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; weak medium prismatic structure parting to moderate fine and medium subangular blocky; hard, friable, sticky and plastic; few very fine roots; many very fine and few fine tubular pores; many fine and medium masses of lime; violently effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (0 to 20 inches thick)
2Bk2--32 to 60 inches; light brownish gray (2.5Y 6/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; massive; hard, friable, sticky and plastic; few very fine roots; common very fine and few fine tubular pores; many fine and medium masses of lime; violently effervescent; moderately alkaline (pH 8.2).
TYPE LOCATION: Chouteau County, Montana; 600 feet south and 10 feet east of the NW corner of sec. 2, T. 28 N., R. 10 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 47 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 15 inches.
Depth to Bk horizon - 11 to 30 inches.
Depth to 2Bk horizon - 15 to 30 inches.
Ap horizon - Hue: 10YR or 2.5Y
Value: 4 or 5 dry
Chroma: 2 or 3
Texture: fine sandy loam, sandy loam, or loam
Clay content: 5 to 18 percent
Reaction: pH 6.6 to 7.8
Bw1 horizon - Hue: 10YR or 2.5Y
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 2 or 3
Texture: fine sandy loam or sandy loam
Clay content: 5 to 18 percent
Reaction: pH 6.6 to 7.8
Bw2 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry
Chroma: 2, 3, or 4
Texture: fine sandy loam or sandy loam
Clay content: 5 to 18 percent
Reaction: pH 6.6 to 7.8
2Bk horizons - Hue: 10YR or 2.5Y
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 2, 3, or 4
Texture: clay loam, silty clay loam, or silt loam
Clay content: 20 to 35 percent
Calcium carbonate equivalent: 5 to 15 percent
EC: 0 to 4 mmhos/cm
SAR: 0 to 4
Reaction: pH 7.9 to 9.0
A Bk horizon is allowed and is less than 10 inches thick and a loam, sandy loam, fine sandy loam, or sandy clay loam.
A 2Bky horizon is allowed and has 2 to 5 percent gypsum.
COMPETING SERIES:
Anaconda (MT) - does not have a lithological discontinuity above a depth of 40 inches.
Boxwell (MT) - has a paralithic contact at depths of 20 to 40 inches.
Diagulch (UT) - does not have a lithologic discontinuity above a depth of 40 inches and has hues redder than 10YR.
Kremlin (MT) - does not have a lithological discontinuity above a depth of 40 inches.
Littlemo (ND) - has a discontinuity of loamy-skeletal material at depths between 20 and 40 inches.
GEOGRAPHIC SETTING:
Landform - stream terraces and till plains.
Elevation - 2,300 to 4,000 feet.
Slope- 0 to 25 percent.
Parent material - alluvium or eolian deposits over till or over glaciofluvial or glaciolacustrine deposits.
Climate - long, cold winters; moist springs; and hot, dry summers.
Mean annual precipitation - 10 to 14 inches.
Mean annual air temperature - 40 to 45 degrees F.
Frost-free period - 100 to 135 days.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability to 23 inches and slow below 23 inches.
USE AND VEGETATION: Fortbenton soils are used mainly for nonirrigated crops and for range. Potential native vegetation is mainly prairie sandreed, needleandthread, Indian ricegrass, bluebunch wheatgrass, western wheatgrass, and sand dropseed.
DISTRIBUTION AND EXTENT: Fortbenton soils are moderately extensive in the plains area of north-central Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Liberty County, Montana, 1991. Series proposed in Chouteau County Area, Montana 1987.
REMARKS: Soil interpretation record: MT1152.
Diagnostic horizons and features recognized in this pedon are: mollic epipedon - from the soil surface to 13 inches (Ap and Bw1 horizons); cambic horizon - from 13 to 23 inches (Bw2 horizon); horizon of lime accumulation - from 23 to 60 inches (2Bk1 and 2Bk2 horizons). Fortbenton soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.