LOCATION KNAPPA OR+WA

Established Series
Rev. GEO/JAS/RWL
06/2011

KNAPPA SERIES

The Knappa series consists of very deep, well drained soils that formed in alluvium derived dominantly from sedimentary rock. Knappa soils are on coastal marine and valley terraces and have slopes of 0 to 30 percent. The mean annual precipitation is about 80 inches and the mean annual air temperature is about 51 degrees F.

TAXONOMIC CLASS: Fine-silty, isotic, isomesic Andic Humudepts

TYPICAL PEDON: Knappa medial silt loam, cultivated, on a 4 percent slope at an elevation of 70 feet. (Colors are for moist soil unless otherwise noted.)

Ap--0 to 9 inches; very dark brown (10YR 2/2) medial silt loam; brown (10YR 4/3) dry; moderate very fine and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; weakly smeary; many very fine and few fine roots throughout; many very fine irregular pores; contains common peds affected by heat from fire; very strongly acid (pH 4.6); clear smooth boundary.

A--9 to 20 inches; very dark brown (10YR 2/2) silt loam; brown (10YR 4/3) dry; moderate very fine and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; weakly smeary; common very fine and few fine roots throughout; many very fine irregular pores; contains few peds affected by heat from fire; very strongly acid (pH 4.6); clear smooth boundary. (Combined thickness of the A horizon is 10 to 25 inches)

Bw1--20 to 25 inches; dark yellowish brown (10YR 3/4) silty clay loam; yellowish brown (10YR 5/4) dry; moderate very fine and fine subangular blocky structure; slightly hard, friable, moderately sticky and slightly plastic; few very fine roots throughout; common very fine and fine tubular pores; many dark brown (10YR 3/3) organic coatings on faces of peds; very strongly acid (pH 4.8); gradual smooth boundary.

Bw2--25 to 45 inches; dark yellowish brown (10YR 4/6) silty clay loam; yellow (10YR 7/6) dry; moderate fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and slightly plastic; few very fine roots throughout; common very fine and fine tubular pores; common worm casts; 1 percent gravel and 2 percent paragravel; very strongly acid (pH 4.8); gradual smooth boundary. (Combined Bw1 and Bw2 horizon is 20 to 25 inches thick)

Bw3--45 to 60 inches; dark yellowish brown (10YR 4/6) silty clay loam; yellow (10YR 7/6) dry; fine coarse subangular blocky parting to moderate fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and slightly plastic; few very fine roots throughout; common very fine and fine tubular pores; few worm casts; 2 percent gravel and 5 percent paragravel; very strongly acid (pH 4.8).

TYPE LOCATION: Tillamook County, Oregon; about 1.4 miles southwest of Cloverdale Oregon, about 400 feet north and 800 feet east of the southwest corner of section 27, T. 4S., R. 10W., Willamette Meridian; Nestucca Bay USGS 7.5 minute topographic quadrangle; Latitude 45 degrees 11 minutes 22 seconds N and Longitude 123 degrees 53 minutes 34 seconds W. NAD 27.

RANGE IN CHARACTERISTICS: The mean annual soil temperature is 49 to 53 degrees F. The soils are usually moist and they are dry for less than 45 consecutive days in all parts between depths of 4 and 12 inches following the summer solstice. The difference between mean summer and mean winter soil temperature varies from 5 to 9 degrees F under canopy cover. Depth to bedrock is more than 60 inches. The solum ranges from 40 to 70 inches thick. Soil reaction ranges from strongly through extremely acid. Coarse fragments are generally lacking above depth of 40 inches but the lower part of the control section contains as much as 15 percent by volume. The umbric epipedon is 20 to 30 inches thick and may include part of the upper Bw horizon. The upper 5 to 13 inches has an estimated Alox + Feox of 2.0 to 3.0 percent and a moist bulk density of 0.80 to 0.90 g/cc. The lower 10 to 25 inches has an estimated Alox + Feox of 1.0 to 3.0 percent and a moist bulk density of 0.90 to 1.0 g/cc. Andic soil properties, when present, do not extend beyond a depth of 14 inches.

The Ap and A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 3 through 5 dry, and chroma of 2 or 3. Texture is medial silt loam in the upper part and medial silt loam or silt loam in the lower part with 18 to 25 percent clay by field estimates. It has 8 to 12 percent organic matter.

The Bw1 and Bw2 horizons have hue of 10YR or 7.5YR, value of 3 through 5 moist, 4 through 7 dry and chroma of 3 through 6 moist and dry. Texture is silty clay loam or silt loam with 22 to 35 percent clay and less than 15 percent coarser than very fine sand. It has 0 to 10 percent rounded gravel and 0 to 10 percent rounded paragravel.

The Bw3 horizon and the BC or C horizons, when present, have hue of 10YR or 7.5YR, value of 3 through 5 moist, 4 through 7 dry and chroma of 4 through 6 moist and dry. Texture is silty clay loam, silt loam, paragravelly silty clay loam, or paragravelly silty loam. It has 0 to 10 percent rounded gravel and 0 to 35 percent rounded paragravel. Paragravelly textures occur below a depth of 40 inches. In some areas sandy and gravelly substrata are below a depth of 40 inches.

COMPETING SERIES: This is the Ecola, Templeton, and Walluski series. Ecola soils have an umbric epipedon dominantly 14 to 20 inches thick although it ranges to 25 inches, and is 20 to 40 inches deep to a paralithic contact. Templeton soils have an umbric epipedon 10 to 20 inches thick and when present, has subangular shaped rock and pararock fragments of colluvial origin. Walluski soils have an umbric epipedon 10 to 20 inches thick and have redox depletions with chroma of 2 or less within 24 to 40 inches.

GEOGRAPHIC SETTING: The Knappa soils are on smooth, nearly level to strongly sloping coastal marine and valley terraces at elevations of 20 to 550 feet. Slopes are 0 to 30 percent. The soil formed in moderately fine-textured alluvium underlain by stratified alluvium at depths of more than 40 inches. The climate is characterized by cool wet winters and cool moist summers. The mean annual temperature is about 49 to 53 degrees F. The mean January temperature is 42 degrees F. and the mean July temperature is about 62 degrees F. The mean frost-free period is 145 to 300 days. The mean annual precipitation is 60 to 100 inches.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chitwood, Hebo and competing Walluski series. These soils occur on coastal marine and valley terraces. Chitwood soils are somewhat poorly drained, fine textured and occur in slightly concave areas. Hebo soils are poorly drained, fine textured and occur in swales and concave areas. Walluski soils are moderately well drained and occur in nearly level to slightly concave areas.

DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; moderate permeability.

USE AND VEGETATION: Most of the soils have been cleared, and are used for growing improved pasture and hay. Native vegetation is Sitka spruce, western hemlock, Douglas-fir, red alder, salal, western swordfern, red elderberry and grasses.

DISTRIBUTION AND EXTENT: Terraces of the Coast Range in Oregon and Washington; MLRA 4A. The series is moderately extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Astoria Area, Oregon, 1945.

REMARKS: Diagnostic horizons and features in this pedon include:
Umbric epipedon - from the surface to 20 inches (Ap and A horizons).
Cambic horizon - from 20 to 60 inches (Bw1, Bw2 and Bw3 horizons).
Andic subgroup feature - from 0 to 20 inches (Ap and A horizons) of which the zone from 0 to 9 inches has andic soil properties.

A proposal was submitted to NSSC (2000) to revise the definition of medial to also include those soil properties qualifying for the Andic subgroup under criteria #1 for andic soil properties. If accepted, medial modifiers would be used for those horizons meeting the andic subgroup criteria although not always meeting andic soil properties.

National Cooperative Soil Survey
U.S.A.