LOCATION WITHAM OREstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Vertic Haploxerolls
TYPICAL PEDON: Witham silty clay loam - pasture. (Colors are for moist soil unless otherwise noted.)
A--0 to 4 inches; very dark grayish brown (10YR 3/2) silty clay loam, dark grayish brown (10YR 4/2) dry; moderate medium and fine granular structure; slightly hard, friable, moderately sticky and moderately plastic; many very fine roots; many very fine irregular pores; strongly acid (pH 5.4); clear smooth boundary. (3 to 6 inches thick)
BA--4 to 12 inches; very dark grayish brown (10YR 3/2) silty clay, dark grayish brown (10YR 4/2) dry; moderate coarse and medium subangular blocky structure; very hard, firm, very sticky and very plastic; common very fine roots; many very fine irregular pores; very dark brown (10YR 2/2) coatings on peds; strongly acid (pH 5.4); gradual smooth boundary. (0 to 12 inches thick)
Bw1--12 to 21 inches; dark brown (10YR 3/3) clay, dark grayish brown (10YR 4/2) dry; weak coarse prismatic structure parting to moderate coarse subangular blocky; extremely hard, very firm, very sticky and very plastic; few very fine roots; many very fine tubular pores; few fine black concretions; 2 percent gravel; common fine (1-2 millimeter) yellowish brown (10YR 5/6) pararock fragments; few slickensides, not intersecting; moderately acid (pH 5.6); gradual smooth boundary. (6 to 12 inches thick)
Bw2--21 to 29 inches; dark brown (10YR 3/3) and brown (10YR 4/3) clay, brown (10YR 5/3) dryweak coarse prismatic and weak coarse subangular blocky structure; extremely hard, very firm, very sticky and very plastic; few very fine roots; many very fine and fine tubular pores; few fine black concretions; 2 percent gravel; many fine 1-2 millimeter) yellowish brown (10YR 5/6) pararock fragments; few fine distinct yellowish brown (10YR 5/4 and 5/6) and brown (7.5YR 4/4) masses of iron accumulation; few slickensides, not intersecting; moderately acid (pH 5.8); gradual wavy boundary. (6 to 12 inches thick)
C--29 to 60 inches; very dark grayish brown (10YR 3/2) clay,; massive; extremely hard, very firm, very sticky and very plastic; few very fine roots; few very fine pores; 2 percent fine gravel; common medium black stains, many medium distinct strong brown (7.5YR 5/6) and brown (10YR 4/3) masses of iron accumulation and brown (7.5YR 4/2) iron depletions; common fine and medium slickensides; not intersecting; moderately acid (pH 5.8).
TYPE LOCATION: Benton County, Oregon; in a native pasture located about 200 feet north of creek; about 1,700 feet south and 100 feet east of the NW corner of section 15, T. 11 S., R. 5 W. Willamette Meridian. Corvallis, Oregon USGS 7.5 minute topographic quadrangle; Latitude 44 degrees, 36 minutes, 52 seconds N. and Longitude 123 degrees, 17 minutes, 24 seconds W. NAD 27.
RANGE IN CHARACTERISTICS: The soils are usually moist but are dry between depths of 4 and 12 inches for 45 to 60 consecutive days during the summer in 7 out of 10 years. The mean annual soil temperature ranges from 52 to 56 degrees F. Depth to bedrock is greater than 60 inches. Redoximorphic features including depletions occur at a depth of 10 to 30 inches. The soil cracks to the surface during the summer and early fall. The mollic epipedon is 10 to 25 inches thick. The pscs has 50 to 60 percent clay and 0 to 5 percent gravel.
The A horizon has value of 2 or 3 moist, 3 or 4 dry and chroma of 1 or 2 moist, 2 or 3 dry. Texture is silty clay loam or silty clay with 27 to 60 percent clay and 0 to 5 percent gravel. Reaction is strongly acid to slightly acid.
The BA or A2 horizon, when present, has value of 2 or 3 moist, 3 or 4 dry and chroma of 2 or 3 moist and dry. Texture is silty clay or clay with 40 to 60 percent clay and 0 to 5 percent gravel. Reaction is strongly acid to slightly acid.
The Bw horizon has hue of 2.5Y or 10YR, value of 3 or 4 moist, 4 or 5 dry and chroma of 1 to 3 moist, 2 or 3 dry. Texture is silty clay or clay with 50 to 60 percent clay and 0 to 5 percent gravel. Reaction is moderately acid or slightly acid.
The C horizon has hue of 10YR or 2.5Y, value of 3 or 4 moist, 4 or 5 dry and chroma of 1 to 3 moist, 2 or 3 dry. Texture is silty clay or clay with 50 to 60 percent clay. It has 0 to 15 percent paragravel. Reaction is moderately acid or slightly acid.
COMPETING SERIES: This is the Heppsie series. Heppsie soils are 20 to 40 inches deep to a paralithic contact.
GEOGRAPHIC SETTING: The Witham soils are on fans, foot slopes and toe slopes of hills at elevations of 250 to 1,200 feet. The soils formed in clayey slope alluvium and/or colluvium derived primarily from basalt. Slopes are 2 to 20 percent. The climate is characterized by warm, wet winters and hot, dry summers. The mean annual precipitation is 40 to 60 inches. The mean annual temperature is 50 to 54 degrees F. The mean January temperature is 38 to 40 degrees F. and the mean July temperature is 64 to 68 degrees F. The frost-free period is 165 to 210 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bashaw, Dixonville, Gellatly, Philomath and Ritner soils. Bashaw soils have chroma of 1 or less to a depth of 40 inches, have intersecting slickenslides and are on flood plains and lower elevation fans. Dixonville soils are 20 to 40 inches to a paralithic contact and occur on linear to convex hillslopes. Gellatly soils do not have redoximorphic features and occur on linear to concave hillslopes. Philomath soils are 12 to 20 inches to a paralithic contact and are on convex hillslopes. Ritner soils are clayey-skeletal and are on convex hillslopes at higher elevations.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; very slow permeability. An apparent high water table is at its uppermost limit from December to April.
USE AND VEGETATION: The Witham soils are used for pasture, hay, woodland, grain and wildlife habitat. The native vegetation is Oregon white oak, Douglas fir, baldhip rose, Pacific poison oak, common snowberry, blackberries, sedges, rushes and bentgrass.
DISTRIBUTION AND EXTENT: Fans and foot slopes or toe slopes of hills along the margins of the Willamette Valley in western Oregon; MLRA 2. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Benton County (Benton Area), Oregon, 1970.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 21 inches (A, BA and Bw1 horizons)
Cambic horizon - the zone from 21 to 29 inches (Bw2 horizon)
Vertic feature - the zone from 12 to 60 inches having slickensides and an estimated linear extensibility of 6.0 cm or more between the mineral soil surface and and depth of 40 inches.
Aquultic feature - the zone from 29 to 60 inches having redox depletions and in some horizon between 10 and 30 inches, having an assumed base saturation (sum) of 75 percent of less.