LOCATION KIRBY MT+SDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal over fragmental, mixed, superactive, calcareous, frigid Aridic Ustorthents
TYPICAL PEDON: Kirby very channery loam in rangeland. (Colors are for dry soil unless otherwise noted)
A--0 to 4 inches; reddish brown (5YR 5/4) very channery loam, reddish brown (5YR 4/4) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many fine and very fine roots; 40 percent porcelanite channers; slightly effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (4 to 7 inches thick)
Bk--4 to 12 inches; reddish brown (5YR 5/4) extremely channery loam, reddish brown (5YR 4/4) moist; weak fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and very fine roots between and matted on top of channers; 70 percent porcelanite channers, 5 percent flagstones; common distinct lime coats on coarse fragments; disseminated lime; strongly effervescent; moderately alkaline (pH 8.2); gradual wavy boundary. (7 to 16 inches thick)
2C--12 to 60 inches; light red (2.5YR 6/6) hard, shattered and fractured porcelanite, red (2.5YR 5/6) moist; few fine roots in cracks; common faint lime coats on lower surfaces of fragments in the upper few inches of the horizon.
TYPE LOCATION: Rosebud County, Montana; 700 feet north and 700 feet east of the SW corner of sec. 35, T. 7 S., R. 42 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 47 degrees F.
Moisture control section - between 8 and 24 inches, dry in all parts between four-tenths and five-tenths of the cumulative days per year when the soil temperature at a depth of 20 inches is 41 degrees F or higher.
Control section - 8 to 22 percent clay and 40 to 90 percent rock fragments. The rock fragments are porcelanite.
Depth to fragmental material - 11 to 20 inches.
Soil phases - nonstony.
A horizon - Hue: 5YR or 7.5YR
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3, 4, or 6
Texture: loam or sandy loam
Clay content: 10 to 25 percent
Rock fragments: 15 to 70 percent--0 to 10 percent flagstones and stones, 15 to 70 percent channers
Reaction: pH 6.6 to 8.4
*The rock fragments in the Kirby soil are porcelanite but more locally called scorio which is defined as the product resulting from baking of shale and sandstone bedrock that was adjacent to burning coal beds.
Bk horizon - Hue: 2.5YR, 5YR, or 7.5YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 3, 4, or 6
Texture: loam or sandy loam
Clay content: 8 to 25 percent
Rock fragments: 40 to 90 percent--5 to 20 percent flagstones and cobbles, 35 to 70 percent channers
Calcium carbonate equivalent: 2 to 15 percent
Reaction: pH 7.4 to 8.4
2C horizon: This horizon consists of highly fractured and displaced porcelanite. The coloring of this material ranges from reddish gray (10R 6/1) through yellowish red (5YR 4/6). Rock fragments of flagstones, stones, and channers make up 90 to 95 percent of this horizon.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - sedimentary plains; hills; alluvial fans; ridges.
Elevations - 1,900 to 5,500 feet.
Slope- 2 to 70 percent.
Parent material - alluvium, colluvium, or residuum derived from porcelanite.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 10 to 16 inches.
Mean annual temperature - 39 to 45 days.
Frost-free season - 100 to 135 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Excessively drained; rapid permeability.
USE AND VEGETATION: Kirby soils are used mainly for range. The potential native vegetation is mainly bluebunch wheatgrass, little bluestem, sideoats grama, needleandthread, forbs, and shrubs. In some places there are low density stands of ponderosa pine.
DISTRIBUTION AND EXTENT: Kirby soils are moderately extensive in southeastern Montana and possibly in adjacent states.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: McCone County, Montana, 1981.
REMARKS: Soil interpretations records: MT0264, MT0805. Diagnostic horizons and features recognized in this pedon are: an ochric epipedon from the soil surface to 7 inches (A, Bk horizons); an accumulation of lime from 4 to 12 inches (Bk horizon); fragmental material from 12 to 60 inches (2C horizon). A particle-size control section from 10 to 40 inches (Bk, 2C horizons). Kirby soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.