LOCATION BROCKO MT
Established Series
Rev. JB-KTS-RJS
03/2011
BROCKO SERIES
The Brocko series consists of very deep, well drained soils that formed in eolian materials, alluvium and lake sediments. These soils are on hills, stream terraces, alluvial fans and lake plains. Slopes are 0 to 45 percent. Mean annual precipitation is about 12 inches, and mean annual temperature is about 41 degrees F.
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, frigid Aridic Calciustepts
TYPICAL PEDON: Brocko silt loam, cultivated (colors are for dry soil unless otherwise noted).
Ap--0 to 7 inches; light gray (10YR 7/2) silt loam, grayish brown (10YR 5/2) moist; weak fine granular structure; slightly hard, very friable, slightly sticky and nonplastic; disseminated calcium carbonate; strongly effervescent; slightly alkaline (pH 7.6); abrupt smooth boundary. (5 to 8 inches thick)
Bk1--7 to 28 inches; light gray (10YR 7/2) silt loam, brown (10YR 5/3) moist; weak coarse prismatic structure; slightly hard, very friable, slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine tubular pores; common fine seams and masses of calcium carbonate; disseminated calcium carbonate; violently effervescent; moderately alkaline (pH 8.0); gradual smooth boundary. (7 to 30 inches thick)
Bk2--28 to 44 inches; very pale brown (10YR 7/3) silt loam, brown (10YR 5/3) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine tubular pores; common fine seams and masses of calcium carbonate; disseminated calcium carbonate; violently effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (5 to 25 inches thick)
Bky--44 to 60 inches; very pale brown (10YR 7/3) silt loam, brown (10YR 5/3) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; few fine masses of calcium carbonate; disseminated calcium carbonate; few masses and filaments of gypsum crystals; violently effervescent; moderately alkaline (pH 7.9).
TYPE LOCATION: Broadwater County, Montana; 1,600 feet east and 300 feet north of the SW corner of sec. 6, T. 3 N., R. 1 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 40 to 47 degrees
Depth to calcic horizon - 5 to 8 inches
Note: Some pedons may have a C horizon.
A horizon
Hue: 10YR, 2.5Y or 5Y; dry or moist
Value: 5 to 7 dry; 4 to 6 moist
Chroma: 2 or 3; dry or moist
Texture: loam or silt loam
Clay content: 10 to 18 percent
Calcium carbonate equivalent: 1 to 10 percent
Reaction: pH 7.4 to 8.4
Bk1 and Bk2 horizons
Hue: 10YR, 2.5Y or 5Y; dry or moist
Value: 6 to 8 dry; 4 to 6 moist
Chroma: 2 or 3; dry or moist
Texture: silt loam, very fine sandy loam or loam
Clay content: 10 to 18 percent
Sand content: less than 15 percent fine sand and coarser
Calcium carbonate equivalent: 15 to 35 percent
SAR: 0 to 13
EC: 2 to 8 mmhos/cm
Reaction: pH 7.9 to 8.5
Bky horizon
Hue: 10YR, 2.5Y 5Y; dry or moist
Value: 6 to 8 dry; 4 to 6 moist
Chroma: 2 or 3; dry or moist
Texture: silt loam, loam or very fine sandy loam
Clay content: 10 to 18 percent
Sand content: less than 15 percent fine and coarser sand
Calcium carbonate equivalent: 5 to 25 percent
SAR: 0 to 25
EC: 2 to 16 mmhos/cm
Gypsum: 1 to 3 percent
Reaction: pH 7.9 to 9.0
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - hills, stream terraces, alluvial fans and lake plains
Elevation - 3,800 to 6,500 feet
Slope - 0 to 45 percent
Parent material - eolian materials, alluvium and lake sediments
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 10 to 14 inches
Mean annual air temperature - 38 to 45 degrees F.
Frost-free period - 90 to 120 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Brocko soils are mainly dry farmed to wheat and barley. Potential native vegetation is mainly blue grama, needleandthread, prairie junegrass, Sandberg bluegrass, fringed sagewort, and broom snakeweed.
DISTRIBUTION AND EXTENT: Brocko soils are of moderate extent in valleys in western and central Montana. MLRA - 43B, 44B and 52.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Broadwater County Area, Montana, 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 7 inches (Ap horizon)
Calcic horizon - from 7 to 60 inches (Bk1, Bk2 and Bky horizons)
Accumulation of gypsum - from 44 to 60 inches (Bky horizon)
Particle-size control section from 10 to 40 inches (part of Bk1 and part of Bk2 horizons).
Brocko soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.
ADDITIONAL DATA: Laboratory sample - S70MT-007-02; Soil interpretations records - MT0530 and MT0915.
COMMENTS: Classification changed from Borollic Calciorthids to Haplocalcidic Ustochrepts in 1994.
National Cooperative Soil Survey
U.S.A.