LOCATION PREGO MTEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, frigid Aridic Argiustolls
TYPICAL PEDON: Prego sandy loam, in rangeland (colors are for dry soil unless otherwise stated).
A--0 to 5 inches; brown (10YR 5/2) sandy loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine and few fine roots; slightly acid (pH 6.2); clear smooth boundary. (3 to 7 inches thick)
Bt1--5 to 10 inches; brown (10YR 5/3) sandy loam, dark brown (10YR 3/3) moist; weak coarse subangular blocky structure parting to moderate medium and fine subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; clay bridging between mineral grains; neutral (pH 6.6); clear smooth boundary.
Bt2--10 to 16 inches; yellowish brown (10YR 5/4) sandy loam, dark yellowish brown (10YR 4/4) moist; moderate medium subangular blocky structure parting to moderate fine subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; few faint clay films on faces of peds; clay bridging between mineral grains; neutral (pH 6.8); abrupt smooth boundary. (Combined thickness of the Bt horizons is 9 to 17 inches.)
2C--16 to 60 inches; light olive brown (2.5Y 5/4) sand; olive brown (2.5Y 4/4) moist; single grain; loose, nonsticky and nonplastic; 10 percent pebbles; neutral (pH 7.0).
TYPE LOCATION: Carter County, Montana; 1,300 feet south and 1,400 feet west of the NE corner of sec. 7, T.1 N., R.57 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 47 degrees F.
Moisture control section - between 12 and 35 inches. Dry in some part for six tenths or more of the cumulative days per year when the soil temperature, at 20 inches, exceeds 5 degrees C.
Mollic epipedon thickness - 7 to 10 inches (includes part of the Bt horizon).
Depth to 2C horizon - 10 to 20 inches.
These soils are noncalcareous throughout.
A horizon - Hue: 7.5YR, 10YR, or 2.5Y
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Clay content: 8 to 14 percent
Rock fragments: 0 to 15 percent pebbles
Reaction: pH 6.1 to 7.3
Bt horizons - Hue: 7.5YR, 10YR, or 2.5Y
Value: 4, 5, or 6 dry; 3, 4, or 5 moist
Chroma: 2, 3, or 4
Texture: sandy loam or fine sandy loam
Clay content: 14 to 18
Rock fragments: 0 to 15 percent pebbles
Reaction: pH 6.1 to 7.3
2C horizon - Hue: 10YR or 2.5Y
Value: 4, 5, or 6 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: sand or loamy sand
Clay content: 1 to 8 percent
Rock fragments: 5 to 35 percent
Reaction: pH 6.1 to 7.3
COMPETING SERIES:
Cruckton (CO) - have more than 35 percent fine and coarser sand in the particle-size control section.
Ironsprings (CO) - are dry 45 or more consecutive days in all parts of the moisture control section after July 1.
Sappington (MT) - have secondary carbonates above a depth of 60 inches.
GEOGRAPHIC SETTING:
Landform - relict stream terraces and alluvial fans.
Elevation - 3,000 to 3,800 feet.
Slope- 0 to 15 percent.
Parent material - noncalcareous alluvium that is 12 to 24 inches deep over sand or loamy sand.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 10 to 14 inches.
Mean annual temperature - 40 to 45 degrees F.
Frost-free period - 110 to 135 days.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability in the A and B horizons and rapid permeability in the 2C horizon.
USE AND VEGETATION: Prego soils are used mainly for range. The native vegetation consists of needleandthread, prairie sandreed, bluebunch wheatgrass, blue grama, little bluestem, forbs, and shrubs.
DISTRIBUTION AND EXTENT: Southeastern Montana. Prego soils are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Fallon County, Montana, 1991; proposed Carter County, Montana, 1990.
REMARKS: Soil interpretations record: MT1268. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from 0 to 10 inches (A, Bt1 horizons); an argillic horizon from 5 to 16 inches which is the particle-size control section (Bt1 and Bt2 horizons); and a discontinuity from 16 to 60 inches (2C horizon). Prego soils have a frigid temperature regime and ustic moisture regime bordering on aridic.