LOCATION MCILWAINE MT
Established Series
Rev. NRS-PJH-JCK
07/2013
MCILWAINE SERIES
The McIlwaine series consists of very deep, well drained soils that formed in alluvium. These soils are on flood plains and flood-plain steps. Slopes are 0 to 2 percent. Mean annual precipitation is about 457 mm, and mean annual temperature is about 5.5 degrees C.
TAXONOMIC CLASS: Coarse-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Cumulic Haplustolls
TYPICAL PEDON: McIlwaine fine sandy loam in cropland (colors are for dry soil unless otherwise noted).
Ap--0 to 15 cm; very dark grayish brown (10YR 3/2) fine sandy loam, very dark brown (10YR 2/2) moist; strong fine and medium granular structure; soft, very friable, slightly sticky and nonplastic; many fine and very fine roots; 5 percent gravel; neutral (pH 6.8); abrupt smooth boundary. (0 to 20 cm thick)
A1--15 to 38 cm; very dark grayish brown (10YR 3/2) fine sandy loam, very dark brown (10YR 2/2) moist; strong medium granular structure; slightly hard, very friable, slightly sticky and nonplastic; many fine and very fine roots; 5 percent gravel; neutral (pH 6.8); clear wavy boundary. (20 to 40 cm thick)
A2--38 to 66 cm; dark grayish brown (10YR 4/2) fine sandy loam with thin strata of silt loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common fine and very fine roots; many very fine tubular pores; 5 percent gravel; neutral (pH 7.0); clear wavy boundary. (20 to 46 cm thick)
2C1--66 to 109 cm; dark gray (10YR 4/1) very gravelly loamy sand, very dark gray (10YR 3/1) moist; single grain; loose, nonsticky and nonplastic; few fine and very fine roots; many very fine irregular pores; 40 percent gravel, 10 percent cobbles; neutral (pH 6.8); gradual wavy boundary. (0 to 50 cm thick)
2C2--109 to 152 cm; dark gray (10YR 4/1) extremely gravelly sand, very dark gray (10YR 3/1) moist; single grain; loose, nonsticky and nonplastic; many fine and very fine pores; 50 percent gravel, 20 percent cobbles; neutral (pH 7.0).
TYPE LOCATION: Chouteau County, Montana; 488 meters west and 30 meters north of the SE corner of sec. 8, T. 20 N., R. 8 E.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 4.4 to 6 degrees C
Mollic epipedon thickness - 40 to 86 cm
Depth to the lithologic discontinuity - 50 to 100 cm
The coarse-loamy material in the A1 and A2 horizons contains less than 50 percent, by weight, fine sand or coarser sand.
Ap horizon (where present)
Hue: 7.5YR, 10YR or 2.5Y
Value: 3, 4, or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: fine sandy loam or loam
Clay content: 5 to 18 percent
Rock fragments: 0 to 15 percent gravel
Reaction: pH 6.6 to 7.8
A1 and A2 horizons
Hue: 7.5YR, 10YR or 2.5Y
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2 or 3
Texture: fine sandy loam, very fine sandy loam, or loam consisting of mostly very fine and fine sand, with thin strata of silt loam and/or sandy loam
Clay content: 5 to 18 percent
Rock fragments: 0 to 15 percent gravel
Reaction: pH 6.6 to 8.2
2C1 and 2C2 horizons
Hue: 2.5Y, 10YR or 7.5YR
Value: 4, 5, 6, 7 or 8 dry; 3, 4, 5 or 6 moist
Chroma: 1, 2 or 3
Texture: loamy sand, sand, loamy coarse sand, or coarse sand
Clay content: 0 to 5 percent
Rock fragments: 35 to 80 percent--25 to 50 percent gravel, 10 to 30 percent cobbles
Reaction: pH 6.6 to 8.2
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - flood plains and flood-plain steps
Elevation - 823 to 1,829 meters
Slope - 0 to 2 percent
Parent material - alluvium
Climate - long, cold winters; moist springs; and warm summers
Mean annual precipitation - 380 to 483 mm
Mean annual air temperature - 4 to 7.2 degrees C
Frost-free period - 70 to 120 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability through the A horizons, rapid and very rapid below.
USE AND VEGETATION: McIlwaine soils are used mainly for rangeland. Some areas are used for cropland. The potential native vegetation is prairie sandreed, bluebunch wheatgrass, rough fescue, Idaho fescue, Indian ricegrass, and needleandthread. Some areas have cottonwood trees with an understory of common snowberry, common chokecherry, redosier dogwood, basin wildrye, and slender wheatgrass.
DISTRIBUTION AND EXTENT: McIlwaine soils are of small extent in west-central Montana. MLRA 46.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Granite County, Montana, 1972.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 0 to 66 cm (Ap, A1, and A2 horizons)
Lithogogic discontinuity - at 66 cm (2C1 horizon)
Particle-size control section - from 25 to 100 cm (part of the A1, A2, and 2C1 horizons)
McIlwaine soils have a frigid temperature regime and an ustic moisture regime.
ADDITIONAL DATA: Soil interpretations record - MT0579.
National Cooperative Soil Survey
U.S.A.