LOCATION SUSITNA AK

Established Series
Rev. MHC/JPM/DM
10/2001

SUSITNA SERIES

The Susitna series consists of very deep, well drained soils that formed in stratified alluvium. Susitna soils are on floodplains and low alluvial terraces. Slopes range from 0 to 7 percent. The mean annual temperature is about 34 degrees F., and the average annual precipitation is about 25 inches.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, nonacid Typic Cryofluvents

TYPICAL PEDON: Susitna silt loam -- on a 1 percent slope under native vegetation of mixed paper birch and white spruce forest at 300 feet elevation. (All colors are for moist soil)

Oe--0 to 1 inch; very dark brown (10YR 2/2) moderately decomposed plant material; many roots; strongly acid (pH 5.2); clear smooth boundary. (1 to 4 inches thick)

A--1 to 4 inches; dark brown (10YR 3/3) silt loam with common medium prominent reddish brown (5YR 4/4) mottles; weak medium granular structure; very friable, nonsticky and nonplastic; many roots; strongly acid (pH 5.4); clear smooth boundary. (1 to 4 inches thick)

C1--4 to 12 inches; dark grayish brown (10YR 4/2) fine sand stratified with silt and very fine sand with common large reddish brown (5YR 4/4) mottles; weak medium subangular blocky structure; very friable, nonsticky and nonplastic; strongly acid (pH 5.4); clear smooth boundary. (6 to 20 inches thick)

C2--12 to 34 inches; very dark grayish brown (10YR 3/2) fine sand stratified with silt and very fine sand with few fine prominent brown (7.5YR 4/4) mottles; massive; very friable, nonsticky and nonplastic; moderately acid (pH 5.6); gradual smooth boundary. (15 to 35 inches thick)

C3--34 to 52 inches; very dark grayish brown (2.5Y 3/2) and dark grayish brown (2.5Y 4/2) fine sand stratified with silt and very fine sand; few fine prominent yellowish red (5YR 4/6) mottles; massive; very friable, nonsticky and nonplastic; moderately acid (pH 5.6); gradual smooth boundary. (0 to 20 inches thick)

2C--52 to 60 inches; variegated extremely gravelly coarse sand; single grain; loose; nonsticky and nonplastic; 60 percent rounded gravel; moderately acid (pH 5.8).

TYPE LOCATION: Matanuska-Susitna Valley Area, Alaska; in the SE 1/4 of the NW 1/4 of section 34, T.26N., R.5W., Seward Meridian.

RANGE IN CHARACTERISTICS: Typically, the upper mineral soil material is stratified, composed of lenses including silt loam, loam, fine sandy loam, and loamy fine sand. These upper sediments range from 40 to 60 inches in thickness over very gravelly and extremely gravelly sand. The weighted average particle size of the control section has greater than 15 percent fine sand or coarser, less than 18 percent clay, and less than 35 percent coarse fragments. Organic carbon content varies irregularly with increasing depth. Reaction throughout the profile ranges from very strongly acid to moderately acid.

The A horizon has hue of 10YR to 5Y; value of 2 to 4; and chroma of 1 to 3. Texture is silt loam, fine sandy loam, loamy fine sand.

The C horizons have hue of 10YR to 5Y; value of 3 to 6; and chroma of 1 to 4. These horizons have reddish, brownish, or olive relic mottles. The individual strata range from less than 1 inch up to 18 inches in thickness.

The 2C horizon (where present) is variegated sand and gravel. Coarse fragment content ranges from 35 to 70 percent; 0 to 20 percent cobbles, and 35 to 60 percent gravel.

COMPETING SERIES: These are the Kluna, Petrof, Salchaket and Takotna(T) series. Kluna soils have slightly acid reaction in the 2C horizon. Petrof soils are moderately well drained. Salchaket soils contain large quantities of micaceous material. Takotna soils are calcareous within the control section.

GEOGRAPHIC SETTING: The Susitna soils are on floodplains and alluvial terraces. Slopes range from 0 to 7 percent. In a few places the soils are undulating. Susitna soils formed in stratified loamy alluvium more than 40 inches thick, underlain by very gravelly sand. The mean annual temperature ranges from 30 to 40 degrees F. Average annual precipitation ranges from 15 to 30 inches. Elevation ranges from 50 to 800 feet.

GEOGRAPHICALLY ASSOCIATED SOILS:

DRAINAGE AND PERMEABILITY: Well drained. Low to medium runoff. Moderate permeability in the upper horizons and rapid in the gravelly underlying material. Susitna soils are subject to flooding.

USE AND VEGETATION: Mostly forested. Dominant trees are cottonwood (balsam poplar), paper birch, and white spruce. Cleared areas are used for bromegrass, timothy, oats, barley, potatoes, and hardy vegetables.

DISTRIBUTION AND EXTENT: Cook Inlet-Susitna Lowlands, South Central, Alaska. The soil is extensive.

MLRA OFFICE RESPONSIBLE: Anchorage, Alaska

SERIES ESTABLISHED: Soil Reconnaissance of Alaska. 1914.

REMARKS: Diagnostic features recognized in this profile include: no diagnostic horizons; assumed irregular decrease in organic carbon based on colors, stratification, and occasional flooding; cryic temperature regime; coarse loamy particle size (weighted average) from 10 to 40 inches.

National Cooperative Soil Survey
U.S.A.

Contact: Mike Gracz Kenai Watershed Forum  PO Box 15301 Fritz Creek, AK  99603 907-235-2218

04 May 2007 10:26