LOCATION SUKOI                   AK

Established Series
Rev. CSC/JMD/JPM
02/2022

SUKOI SERIES

The Sukoi series consists of very shallow, poorly drained soils formed in volcanic ash overlying compact volcanic ash on mountain slopes and lava plains. Slopes range from 0 to 75 percent. Mean annual precipitation is in excess of 60 inches and the mean annual temperature is about 46 degrees F.

TAXONOMIC CLASS: Medial, amorphic, shallow Andic Cryaquods

TYPICAL PEDON: Sukoi silt loam - on a southwest facing slope of 20 percent at 120 feet elevation under forest vegetation. (All colors are for moist soil, all textures are apparent field textures)

Oe-- 4 to 0 inches; dark reddish brown (5YR 2.5/2) mucky peat; many very fine and fine and common medium roots; extremely acid (pH 4.0); abrupt smooth boundary. (4 to 7 inches thick)

E-- 0 to 1 inch; brown (7.5YR 5/2) silt loam; weak fine granular structure; friable; common very fine, fine and medium roots; extremely acid (pH 4.0); abrupt smooth boundary. (1 to 2 inches thick)

Bh-- 1 to 6 inches; reddish black (2.5YR 2.5/1) mucky silt loam; moderate medium subangular blocky structure; friable; nonsticky and nonplastic; strongly smeary; common fine roots; extremely acid (pH 4.0); abrupt smooth boundary. (4 to 6 inches thick)

Bhs-- 6 to 10 inches; black (5YR 2.5/2) loam; moderate medium subangular blocky structure; firm; nonsticky and nonplastic; strongly smeary; 5 percent gravel; moderately acid (pH 6.0); abrupt smooth boundary. (0 to 8 inches thick)

2Cd1-- 10 to 11 inches; dark reddish brown (2.5YR 3/4) silt loam; massive; very firm; strongly smeary; 5 percent gravel; slightly acid (pH 6.5); abrupt smooth boundary.

3Cd2-- 11 to 60 inches; very dark grayish brown (10YR 3/2) very gravelly sandy loam; massive; very firm; strongly smeary; 60 percent gravel size pumice; slightly acid (pH 6.5).

TYPE LOCATION: Mud Bay, Chatham Area, Alaska. SE1/4, SW1/4, Sec. 18, T.54S., R.62E., Copper River Meridian.

RANGE IN CHARACTERISTICS: MAST is 38 to 42 degrees F. Thickness of the solum and depth to the paralithic ash ranges from 5 to 10 inches. Phosphorous retention throughout is greater than 90 percent. Bulk density above the paralithic contact ranges from 0.30 to 0.60 grams/cc. Acid oxalate extractable aluminum plus 1/2 iron ranges from 4 to 11 throughout the profile. Moist 15 bar water ranges from 32 to 80 percent. Reaction increases with depth, ranging from extremely acid to slightly acid. Coarse fragment content in the control section ranges from 0 to 5 percent gravel.

An Oi horizon is present in some pedons. Combined thickness of the O horizons ranges from 4 to 8 inches. The E horizon has hue from 5YR to 10YR, value from 4 to 6 and chroma of 1 or 2. Texture is commonly silt loam but ranges to include fine sandy loam, very fine sandy loam or loam.

The Bh horizon has hue from 2.5YR to 10YR, value moist of 2 or 2.5 and chroma moist of 0 or 1. Texture is commonly silt loam but ranges to include fine sandy loam or very fine sandy loam. The coarse fragment content ranges from 0 to 5 percent gravel.

The Bhs or Bs horizon has hue from 5YR to 10YR, value moist from 2 to 3 and chroma moist from 2 to 4. Texture is commonly silt loam but ranges to include fine sandy loam, very fine sandy loam or loam. The coarse fragment content ranges from 0 to 5 percent gravel. Mottles are commonly present, but are often masked by the high accumulation of organic matter.

A buried Oa horizon commonly overlies the Cd horizon.

The Cd horizons are composed of strata of ash deposits which vary in texture. Hue ranges from 2.5YR to 10YR, value moist from 3 to 5, and chroma moist from 2 to 6. The coarse fragment content ranges from 0 to 60 percent gravel size pumice. Mottles are commonly present. Consistence is very firm or extremely firm with bulk density greater than 1.80 g/cm3.

COMPETING SERIES: There are no know competing series in this family.

GEOGRAPHIC SETTING: The Sukoi soils are on mountain slopes and lava plains and formed in volcanic ash overlying compact ash. The climate is humid maritime with a mean annual precipitation range of 60 to 220 inches. The mean annual temperature is about 46 degrees F. and the mean summer temperature is about 57 degrees F. Elevation ranges from 0 to 3000 feet.

GEOGRAPHICALLY ASSOCIATED SOILS: These include the Kina, Kushneahin, and Partofshikof soils on similar landforms. Kina and Kushneahin soils are very poorly drained organic soils. Partofshikof soils are somewhat poorly drained.
DRAINAGE AND PERMEABILITY: Poorly drained. Rapid permeability above the compact ash and very slow permeability within the compact ash layers. Runoff is very slow.

USE AND VEGETATION: Sukoi soils are used for timber production, watershed protection, wildlife habitat and recreation. The overstory is dominantly western and mountain hemlock and yellow cedar. The understory is dominantly blueberry with some rusty menziezia.

DISTRIBUTION AND EXTENT: Southeast Alaska. The series is of moderate extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: WASILLA, ALASKA

SERIES ESTABLISHED: Chatham Area, Alaska, 1992.

REMARKS: Diagnostic horizons and features recognized in this soil include: andic soil materials from 0 to 60 inches; an albic horizon from 0 to 1 inches and a spodic horizon from 1 to 10 inches; an assumed aquic moisture regime based on the presence of a high water table within 20 inches of the surface throughout most of the year, mottling is usually not observed in the saturated ash soils with high organic carbon content; 15 bar water content between 30 and 100 percent; a paralithic contact at 10 inches.

This soil has an albic horizon and underlying spodic horizon with pH's less than 5.0 (1:1,H20). Laboratory data as well as micromorphology show translocation and accumulation of iron.

ADDITIONAL DATA: Laboratory data is available for this soil: University of Idaho Number 83-AK-0352; NSSL number S87AK-220-010.

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National Cooperative Soil Survey
U.S.A.