LOCATION ISKNAT ID

Established Series
Rev. DL/DA/GHL/JVC
01/2019

ISKNAT SERIES

The Isknat series consists of very deep, well drained soils that formed in alluvium and colluvium derived from mixed sources. Isknat soils are on fan remnants and stream terraces. Slopes are 0 to 15 percent. The mean annual precipitation is about 330 mm and the mean annual temperature is about 6.7 degrees C.

TAXONOMIC CLASS: Clayey-skeletal, smectitic, frigid Pachic Ultic Argixerolls

TYPICAL PEDON: Isknat gravelly loam--on a 3 percent slope at 1,630 meter elevation--rangeland. (When described on June 30, 1981, the soil was slightly moist throughout. Colors are for dry soil unless otherwise noted.)

A--0 to 20 cm; gray (10YR 5/1) gravelly loam, very dark gray (10YR 3/1) moist; moderate medium platy structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine to fine tubular pores; 25 percent gravel; slightly acid (pH 6.4); clear smooth boundary. (8 to 25 cm thick)

Bt1--20 to 36 cm; dark grayish brown (10YR 4/2) very gravelly clay loam, black (10YR 2/1) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common very fine and fine roots; common very fine tubular pores; common distinct clay films on faces of peds and lining pores; 40 percent gravel; neutral (pH 6.8); gradual wavy boundary. (13 to 33 cm thick)

Bt2--36 to 58 cm; dark grayish brown (10YR 4/2) very gravelly clay, black (10YR 2/1) moist; strong fine angular blocky structure; very hard, very firm, very sticky and very plastic; few very fine roots; few very fine tubular pores; many prominent clay films on faces of peds and lining pores; 50 percent gravel; slightly acid (pH 6.4); abrupt smooth boundary. (20 to 56 cm thick)

Bt3--58 to 97 cm; pale brown (10YR 6/3) extremely gravelly clay, brown (10YR 4/3) moist; moderate fine angular blocky structure; very hard, very firm, very sticky and very plastic; few very fine tubular pores; many prominent clay films on faces of peds and lining pores; 70 percent gravel; slightly acid (pH 6.4); abrupt smooth boundary. (36 to 66 cm thick)

2C--97 to 152 cm; pale brown (10YR 6/3) extremely gravelly sandy loam, brown (10YR 4/3) moist; massive; extremely hard, very firm, nonsticky and nonplastic; few very fine tubular pores; 75 percent gravel; neutral (pH 6.8).

TYPE LOCATION: Twin Falls County, Idaho; about 13 miles southwest of Rogerson; about 180 feet south and 630 feet east of the northwest corner of section 26, T. 15 S., R. 14 E.; USGS Browns Bench South 7.5 minute topographic quadrangle; latitude 42 degrees 05 minutes 57 seconds N and longitude 114 degrees 47 minutes 22 seconds W; WGS84 Decimal Degrees 42.0991667 latitude, -114.7894444 longitude.

RANGE IN CHARACTERISTICS:

Depth to bedrock - 152 cm or more.
Mollic epipedon - 50 to 86 cm.
Base saturation in upper 76 cm - 65 to 75 percent.
Average clay percent in control section - 35 to 50
Coarse fragments in control section - 35 to 70 percent
Average annual soil temperature - 5.6 to 7.8 degrees F.
Soil Moisture: This soil is usually moist, but is dry for 45 to 70 consecutive days during the late summer and autumn. Typic xeric moisture regime.
2Bq and 2Bkq horizons are present in some pedons.
2Bt horizons are present in some pedons and have clayey textures (below 100 cm).

A horizon
Value - 3 through 5 dry, 2 or 3 moist
Chroma - 1 through 3 dry or moist

Bt1 horizon
Value - 3 through 5 dry, 2 or 3 moist
Chroma - 1 or 2 dry or moist
Texture - GRV-CL, GR-CL, or GRV-C
Gravel - 30 to 50 percent

Bt2 and Bt3 horizons
Hue - 10YR or 7.5YR
Value - 4 through 6 dry, 2 through 4 moist
Chroma - 1 through 4 dry or moist
Texture - GRV-SCL, GRV-C, GRV-SC, GRV-CL, GRX-CL, GRX-C
Gravel - 40 to 70 percent
Cobbles - 0 to 20 percent
Reaction - moderately acid through neutral

2C horizon (when present)
Value - 5 through 8 dry, 4 through 6 moist
Chroma - 3 through 6 dry or moist
Texture - GRX-SL, GRX-LS, GRX-LCOS, CBX-LCOS, CBX-COS, and GRX-COS (sandy-skeletal textures do not occur above 100 cm)
Gravel - 40 to 70 percent
Cobbles - 10 to 30 percent
Stones - 0 to 5 percent

COMPETING SERIES: This is the Mound series. Mound soils are 100 to 150 cm to a paralithic contact.

GEOGRAPHIC SETTING: Isknat soils are on fan remnants and stream terraces. The soils formed in colluvium and alluvium derived from mixed sources. Slopes are 0 to 15 percent. Elevations range from 1,510 1,865 meters. The mean annual precipitation is 300 to 460 mm, the mean annual temperature is 5.0 to 7.2 degrees C., and the frost-free period is 60 to 90 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ackett, Chuska, Elhina, and Player soils. Ackett and Chuska soils are shallow to a duripan, and occur on terraces. Elhina soils are moderately deep to a duripan, and occur on terraces. Player soils are not Pachic, and occur on breaks.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained, slow and medium runoff; slow saturated hydraulic conductivity in the upper part and moderately rapid to very rapid in the substratum.

USE AND VEGETATION: Isknat soils are used for rangeland. Native vegetation is mountain big sagebrush, bluebunch wheatgrass, and Idaho fescue.

DISTRIBUTION AND EXTENT: Southwestern and south-central Idaho. These soils are not extensive. The series concept and main acreage is in MLRA 25, while other acreage occurs in MLRA 10.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.

SERIES ESTABLISHED: Blaine County, Idaho, 1985.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 58 cm (A, Bt1, and Bt2 horizons).
Argillic horizon - The zone from 20 to 97 cm (Bt1, Bt2, and Bt3 horizons).

Particle-size control section - The zone from 20 to 70 cm (Bt1 and Bt2 horizons and part of the Bt3 horizon).

ADDITIONAL DATA: Base saturation: 0 - 20 cm - 73 percent; 20 -36 cm - 66 percent; 36 - 58 cm - 66 percent; 58 - 97 cm 68 percent.

National Cooperative Soil Survey
U.S.A.