LOCATION POLSON MTEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, frigid Typic Natrixerolls
TYPICAL PEDON: Polson silt loam, cultivated (colors are for dry soil unless otherwise noted.)
Ap--0 to 7 inches; grayish brown (10YR 5/2) silt loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structures; slightly hard, very friable, nonsticky and nonplastic; many very fine roots; many fine pores; slightly alkaline (pH 7.4); abrupt wavy boundary. (7 to 9 inches thick)
E/Btn--7 to 10 inches; E part (60 percent) very pale brown (10YR 8/2) silt loam, light brownish gray (10YR 6/2) moist that surrounds the B part; B part (40 percent) very pale brown (10YR 7/3) silt loam, brown (10YR 5/3) moist; weak coarse subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; common very fine roots; many very fine pores; few faint clay films on faces of peds; slightly alkaline (pH 7.4); clear wavy boundary. (4 to 8 inches thick)
Btn--10 to 15 inches; pale brown (10YR 6/3) silt loam, brown (10YR 4/3) moist; weak medium and coarse prismatic structure; hard, very friable, slightly sticky and slightly plastic; few very fine roots; many very fine discontinuous tubular pores; few faint clay films on faces of peds; moderately alkaline (pH 8.4); clear wavy boundary. (4 to 10 inches)
Bkn1--15 to 18 inches; very pale brown (10YR 7/3) silt loam, brown (10YR 4/3) moist; weak medium and coarse prismatic structure; hard, very friable, slightly sticky and slightly plastic; common threads and seams of lime; violently effervescent; strongly alkaline (pH 8.8); clear wavy boundary. (0 to 10 inches thick)
Bkn2--18 to 24 inches; very pale brown (10YR 8/2) silt loam, light brownish gray (10YR 6/2) moist; massive 1/8- to 1-inch varved material that breaks to weak very coarse blocks; slightly hard, very friable, slightly sticky and nonplastic; few very fine roots; common very fine pores; disseminated lime and few small masses of lime; violently effervescent; strongly alkaline (pH 9.0); gradual irregular boundary. (4 to 15 inches thick)
BC--24 to 60 inches; very pale brown (10YR 8/2) silt loam with thin (about 1/4- to 1/2-inch thick) brown (10YR 5/3) clay varves, light brownish gray (10YR 6/2) and dark yellowish brown (10YR 4/4) moist; massive; slightly hard, very friable, slightly sticky and nonplastic; few very fine pores; disseminated lime; violently effervescent; strongly alkaline (pH 9.0).
TYPE LOCATION: Lake County, Montana; 1,840 feet west and 660 feet south of the NE corner of sec. 10, T. 21 N., R. 20 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 47 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 19 inches.
Control section - 18 to 35 percent clay.
Depth to Bk horizon - 15 to 26 inches.
Varves are at a depth of 15 to 36 inches.
Ap horizon - Hue: 10YR or 2.5Y
Value: 4 or 5 dry, 2 or 3 moist
Chroma: 2 or 3
Clay content: 15 to 25 percent
Reaction: pH 7.4 to 7.8
E/Btn horizon - Hue: E part 10YR or 2.5Y; B part 10YR or 2.5Y
Value: E part 7 or 8, B part 6 or 7 dry; E part 5 or 6, B part 4 or 5 moist.
Chroma: E part 2 or 3; B part 2 or 3
Clay content: 15 to 25 percent
EC: less than 2 mmhos/cm
Reaction: pH 7.4 to 7.8
Btn horizon - Hue: 10YR or 2.5Y
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 2 or 3
Texture: silt loam or silty clay loam
Clay content: 18 to 35 percent
EC: 2 to 4 mmhos/cm
SAR: 13 to 15
Reaction: pH 7.4 to 8.4
Bkn1 horizon - Hue: 10YR or 2.5Y
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 2 or 3
Texture: silt loam or silty clay loam
Clay content: 18 to 35 percent
EC: 2 to 4 mmhos/cm
Calcium carbonate equivalent: 10 to 15 percent
SAR: 13 to 18
Reaction: pH 8.5 to 9.0
Bkn2 horizon - Hue: 10YR or 2.5Y
Value: 7 or 8 dry, 5 or 6 moist
Chroma: 2 or 3
Texture: silt loam or silty clay loam
Clay content: 15 to 30 percent
Calcium carbonate equivalent: 10 to 15 percent
EC: 4 to 8 mmhos/cm
SAR: 15 to 20
Reaction: pH 8.5 to 9.0
BC horizon - Hue: 10YR or 2.5Y
Value: 7 or 8 dry, 5 or 6 moist
Chroma: 2 or 3
Texture: silt loam or silty clay loam
Clay content: 15 to 30 percent
EC: 4 to 8 mmhos/cm
SAR: 15 to 30
Reaction: pH 8.5 to 9.0
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Polson soils are on dissected alluvial fans, stream terraces on glaciated uplands and dissected lake plains. Elevations are 2,900 to 3,300. Slopes are 0 to 8 percent. These soils formed in silty glacial and lacustrine deposits. The climate is characterized by long, cold winters; moist springs and falls; and warm, dry summers. Mean annual precipitation is 14 to 18 inches. Mean annual temperature is 40 to 45 degrees F. The frost-free period is 105 to 135 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Gird and Kerl series. These soils do not have natric horizons.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderately slow permeability.
USE AND VEGETATION: Used as irrigated and dry cropland.
DISTRIBUTION AND EXTENT: Intermountain valleys of western Montana. It is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Lake County, Montana, 1991; proposed Lake County (Lower Flathead Valley Area), Montana, 1929.
REMARKS: Soil interpretation records: MT0663. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 7 inches (Ap horizon); a transitional thin albic horizon from 7 to 10 inches (E/Btn horizon); natric horizons from 10 to 26 inches (Btn, Bkn1, Bkn2, and part of BCn horizons); and a fine-silty particle-size control section from 10 to 15 inches (Btn horizon). Polson soils have a frigid temperature regime and a xeric moisture regime.
ADDITIONAL DATA: Laboratory samples S84MT-047-000.