LOCATION BRONEC MT

Established Series
Rev. TJK-KTS-RJS
03/2011

BRONEC SERIES

The Bronec series consists of very deep, well drained soils that formed in alluvium, colluvium, slide deposits and tertiary fill material. These soils are on stream terraces, alluvial fans, fan remnants, hills, mountain slopes, escarpments, landslides and debris flows. Slopes are 0 to 60 percent. Mean annual precipitation is about 12 inches and mean annual air temperature is about 42 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Aridic Calciustepts

TYPICAL PEDON: Bronec gravelly loam, in rangeland (colors are for dry soil unless otherwise noted).

A--0 to 2 inches; grayish brown (10YR 5/2) gravelly loam, dark brown (10YR 3/3) moist; weak medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine pores; 15 percent gravel; slightly effervescent; slightly alkaline (pH 7.6); clear wavy boundary. (2 to 6 inches thick)

Bk1--2 to 9 inches; pale brown (10YR 6/3) gravelly loam, brown (10YR 5/3) moist; moderate medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine pores; 25 percent gravel; disseminated calcium carbonate, few fine masses and threads of calcium carbonate, common faint calcium carbonate coatings on undersides of gravel; strongly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (5 to 13 inches thick)

Bk2--9 to 21 inches; very pale brown (10YR 7/3) gravelly loam, pale brown (10YR 6/3) moist; weak coarse prismatic structure parting to moderate medium subangular blocky; hard, friable, moderately sticky and slightly plastic; few fine and very fine roots; common fine and very fine pores; 30 percent gravel; disseminated calcium carbonate, common fine masses and threads of calcium carbonate, common distinct calcium carbonate coatings on gravel; violently effervescent; strongly alkaline (pH 8.6); clear wavy boundary. (7 to 22 inches thick)

Bk3--21 to 35 inches; pale brown (10YR 6/3) very gravelly sandy loam, brown (10YR 5/3) moist; weak coarse prismatic structure; slightly hard, very friable, slightly sticky and nonplastic; few very fine roots; common very fine pores; 45 percent gravel; disseminated calcium carbonate, common fine masses and threads of calcium carbonate, common distinct calcium carbonate coatings on undersides of gravel; violently effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (10 to 15 inches thick)

Bk4--35 to 48 inches; pale brown (10YR 6/3) very gravelly sandy loam, yellowish brown (10YR 5/4) moist; weak coarse prismatic structure; slightly hard, very friable, nonsticky and nonplastic; 45 percent gravel; disseminated calcium carbonate, few faint calcium carbonate coatings on undersides of gravel; violently effervescent; moderately alkaline (pH 8.0); gradual wavy boundary. (0 to 15 inches thick)

BCk--48 to 60 inches; brown (10YR 5/3) very gravelly loamy sand, dark brown (10YR 3/3) moist; single grain; loose, nonsticky and nonplastic; 40 percent gravel; few faint calcium carbonate coatings on undersides of gravel; strongly effervescent; moderately alkaline (pH 8.0). (0 to 25 inches thick)

TYPE LOCATION: Jefferson County, Montana; 2,390 feet east and 2,160 feet north of the SW corner of sec. 4, T. 2 N., R. 4 W.

RANGE IN CHARACTERISTICS:
Soil temperature - 40 to 46 degrees F.
Depth to secondary calcium carbonate accumulation - 2 to 6 inches

Note: When mixed to 7 inches, the surface does not meet the color requirements for a mollic epipedon. Some pedons may have a BC horizon.

A horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 or 6 dry; 3 or 4 moist
Chroma: 2 to 4; dry or moist
Texture: loam, sandy loam or fine sandy loam
Clay content: 5 to 25 percent
Rock fragments: 10 to 60 percent--10 to 50 percent gravel, 0 to 25 percent cobbles and stones
Calcium carbonate equivalent: 0 to 5 percent
Reaction: pH 6.6 to 8.4

Saline phase -
Electrical conductivity: 8 to 16 mmhos/cm
Sodium absorption ratio: 13 to 30
Reaction: 8.5 to 9.6

Bk1 horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: loam or sandy loam
Clay content: 15 to 27 percent
Rock fragments: 15 to 60 percent--15 to 50 percent gravel, 0 to 15 percent cobbles and stones
Calcium carbonate equivalent: 5 to 30 percent
Electrical conductivity: 0 to 4 mmhos/cm
Reaction: pH 7.8 to 8.4

Saline phase -
Electrical conductivity: 16 to 30 mmhos/cm
Sodium absorption ratio: 13 to 30
Reaction: 8.5 to 9.6

Bk2 horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 8 dry; 4 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: loam or sandy loam
Clay content: 15 to 27 percent
Rock fragments: 20 to 60 percent--20 to 50 percent gravel, 0 to 20 percent cobbles and stones
Calcium carbonate equivalent: 5 to 40 percent
Electrical conductivity: 0 to 4 mmhos/cm
Reaction: pH 7.9 to 8.6

Saline phase -
Electrical conductivity: 4 to 25 mmhos/cm
Sodium absorption ratio: 4 to 20
Reaction: 8.5 to 9.6

Bk3, Bk4 horizons
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: loam or sandy loam
Clay content: 12 to 25 percent
Rock fragments: 35 to 65 percent--25 to 50 percent gravel, 0 to 25 percent cobbles and stones
Calcium carbonate equivalent: 5 to 25 percent
Electrical conductivity: 0 to 4 mmhos
Reaction: pH 7.9 to 8.4

Saline phase -
Electrical conductivity: 4 to 25 mmhos/cm
Sodium absorption ratio: 4 to 20
Reaction: 8.5 to 9.6

BCk horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 3 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: sandy loam, coarse sandy loam or loamy sand
Clay content: 10 to 20 percent
Rock fragments: 35 to 70 percent--25 to 60 percent gravel, 0 to 25 percent cobbles and stones
Calcium carbonate equivalent: 3 to 25 percent
Reaction: pH 7.4 to 8.4

Saline phase -
Electrical conductivity: 4 to 25 mmhos/cm
Sodium absorption ratio: 4 to 20
Reaction: 8.5 to 9.6

COMPETING SERIES:
Barkelew (CO) - have a cambic horizon
Devilsthumb (NV) - is moderately deep to a lithic contact
Foy (UT) - have a cambic horizon
Tabyago (UT) - is moderately deep to a lithic contact
Wildmount (UT) - have a cambic horizon
Yampa (CO) - have hues of 7.5YR or 5YR throughout

GEOGRAPHIC SETTING:
Landform - stream terraces, alluvial fans, fan remnants, hills, mountain slopes, escarpments, landslides and debris flows
Elevation - 3,800 to 6,500 feet
Slope - 0 to 70 percent
Parent material - alluvium, colluvium, slide deposits and tertiary fill material
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 10 to 14 inches
Mean annual air temperature - 38 to 44 degrees F.
Frost-free period - 70 to 115 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Amesha and Riverrun soils. The Amesha soils are coarse-loamy and the Riverrun soils are sandy-skeletal. These soils occur on similar landforms as the Bronec soils.

DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.

USE AND VEGETATION: Bronec soils are used for irrigated and nonirrigated cropland and for rangeland. The potential native vegetation is mainly bluebunch wheatgrass, blue grama, needleandthread, fringed sagewort, big sagebrush, and rubber rabbitbrush. Some areas have a thin overstory of Douglas-fir and limber pine and an understory of bluebunch wheatgrass, blue grama, big sagebrush, and Rocky Mountain juniper.

DISTRIBUTION AND EXTENT: The Bronec soils are of moderate extent in the intermountain valleys of southwestern Montana. MLRAs - 43B and 44B.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.

SERIES ESTABLISHED: Jefferson County, Montana, 1998.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 7 inches, mixed (A, Bk1 horizons)
Calcic horizon from 9 to 35 inches (Bk2, Bk3, Bk4 horizons)
Particle-size control section from 10 to 40 inches (part of Bk2, Bk3, part of Bk4 horizons)

Bronec soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.

ADDITIONAL DATA: Soil interpretations records - MT1543, MT1544.

National Cooperative Soil Survey
U.S.A.