LOCATION COBURG OREstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Oxyaquic Argixerolls
TYPICAL PEDON: Coburg silty clay loam, cultivated. (Colors are for moist soil unless otherwise noted.)
Ap--0 to 7 inches; very dark grayish brown (10YR 3/2) silty clay loam, dark grayish brown (10YR 4/2) dry; weak medium subangular blocky and moderate medium granular structure; hard, friable, moderately sticky and moderately plastic; many very fine roots; common very fine and few fine and medium tubular pores; moderately acid (pH 5.6); abrupt smooth boundary. (6 to 11 inches thick)
AB--7 to 18 inches; very dark grayish brown (10YR 3/2) heavy silty clay loam, dark grayish brown (10YR 4/2) dry; weak medium subangular blocky and moderate medium granular structure; hard, friable, moderately sticky and moderately plastic; many very fine roots; common very fine and few fine and medium tubular pores; moderately acid (pH 5.6); abrupt smooth boundary. (5 to 15 inches thick)
Bt1--18 to 28 inches; dark brown (10YR 3/3) silty clay, dark grayish brown (10YR 4/2) dry; weak medium subangular blocky and moderate fine subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few very fine roots; many very fine and fine tubular pores; common distinct very dark grayish brown (10YR 3/2) clay films on faces peds and in pores; few 1 to 3 mm black concretions; slightly acid (pH 6.2); clear wavy boundary. (4 to 12 inches thick)
Bt2--28 to 41 inches; dark brown (10YR 3/3) silty clay loam, brown (10YR 4/3) dry; moderate medium and fine subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few very fine roots; many very fine and fine tubular pores; many prominent very dark grayish brown (10YR 3/2) clay films in pores and few distinct clay films on faces of peds; common fine prominent strong brown (7.5YR 5/6) masses of iron accumulation; few small black manganese films on peds; slightly acid (pH 6.3); clear wavy boundary. (6 to 15 inches thick)
Bt3--41 to 53 inches; dark brown (10YR 3/3) silty clay, brown (10YR 4/3) dry; weak medium subangular blocky structure; very hard, friable, moderately sticky and moderately plastic; few very fine roots; many very fine and fine tubular pores; many prominent very dark grayish brown (10YR 3/2) clay films in pores; common fine prominent strong brown (7.5YR 5/6) masses of iron accumulation; few small black manganese films on peds; neutral (pH 6.6); clear wavy boundary. (0 to 19 inches thick)
2C--53 to 65 inches; brown (10YR 4/3) fine sandy loam, pale brown (10YR 6/3) dry; massive; slightly hard, very friable, slightly sticky and slightly plastic; few fine roots; many very fine and common fine pores; common medium prominent strong brown (7.5YR 5/6) masses of iron accumulation; neutral (pH 6.8).
TYPE LOCATION: Lane County, Oregon; about 1,200 feet west and 100 feet south of the NE corner of section 19, T. 16 S., R. 4 W. Willamette Meridian, Junction City, Oregon. USGS 7.5 minute quad. Latitude 44 degrees, 10 minutes, 16 seconds N.; Longitude 123 degrees, 12 minutes, 46 seconds W. NAD 27.
RANGE IN CHARACTERISTICS: Soils are usually moist but are dry during the summer in all parts between depths of 4 and 12 inches for about 45 to 70 consecutive days. The mean annual soil temperature ranges from 52 to 55 degrees F. The pscs has 35 to 45 percent clay and 0 to 5 percent gravel. The soils are more than 60 inches deep. Hue is 10YR or 7.5YR. The mollic epipedon is 20 to 30 inches thick. Depth to saturation (Oxyaquic) conditions with redox concentrations and with or without chroma of 2 or less is 30 to 40 inches.
The A horizon has value of 2 or 3 moist, 3 to 5 dry, and chroma of 2 or 3 moist and dry. It has weak to moderate granular or subangular blocky structure. It has 0 to 5 percent gravel. Reaction is moderately acid or slightly acid.
The AB or BA horizon has value of 2 or 3 moist, 4 or 5 dry, and chroma of 2 or 3 moist and dry. It is silty clay loam or silty clay with 35 to 45 percent clay and 0 to 5 percent gravel. It is weak to moderate subangular blocky structure and moderate to strong granular structure. Reaction is moderately acid or slightly acid.
The Bt horizon has value of 3 to 5 moist, 4 to 6 dry, and chroma of 2 to 4 moist and dry. Moist value of 4 or 5, moist chroma of 4 and dry value of 6 occur below 20 inches. It is silty clay loam or silty clay with 35 to 45 percent clay. Reaction is moderately acid to slightly acid.
In some pedons, the BC horizon is clay loam below a depth of 40 inches. It commonly has weak prismatic and moderate medium and fine subangular blocky structure. Reaction is moderately acid to neutral.
The 2C horizon is fine sandy loam, loam, sandy clay loam, or clay loam. It has value of 3 or 4 moist, 4 to 6 dry, and chroma of 3 or 4 moist and dry. It has 0 to 10 percent gravel. Reaction is slightly acid or neutral.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Coburg soils are on stream terraces at elevations of 100 to 1,100 feet. Slope gradients are dominantly 0 to 7 percent. The soils formed in clayey alluvium from mixed materials. The summers are warm and dry and the winters are cool and moist. The mean annual precipitation is 30 to 60 inches. Mean annual temperature is 50 to 55 degrees F., average January temperature is 39 to 40 degrees F., and average July temperature is 65 to 67 degrees F. The frost-free season is 160 to 235 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Awbrig, Clackamas, Conser, Courtney, Darby, Malabon, Oxley, Redbell, and Salem soils. Awbrig and Conser soils have conditions with chroma of 2 or less within 10 inches of the surface and occur in depressions and on low terraces. Courtney soils have aquic conditions with chroma of 2 or less within 10 inches of the surface and occur in depressions. Clackamas and Oxley soils have aquic conditions with chroma of 2 or less at a depth of 10 to 20 inches. In addition, Clackamas soils have a very gravelly or extremely gravelly C horizon. Oxley soils are loamy-skeletal. Clackamas and Oxley soils occur on terraces. Darby soils do not have oxyaquic conditions within 40 inches of the soil surface and occur on footslopes. Malabon soils do not have oxyaquic conditions within 40 inches of the soil surface and occur on high terraces. Redbell soils have aquic conditions and redox depletions with chroma of 2 or less within 30 inches of the soil surface and occur on low terraces.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow runoff; moderately slow permeability. Some areas of Coburg soils are subject to rare or occasional flooding for brief periods from December to March. An apparent water table is at its uppermost limit from December to March.
USE AND VEGETATION: These soils are used for production of small grain, hay, pasture, and grass seed crops. Natural vegetation is Douglas fir, Oregon white oak, blackberries, Pacific poison oak, other shrubs and grasses.
DISTRIBUTION AND EXTENT: Valley stream terraces of the Willamette and Umpqua Valleys, Oregon; MLRA 2, 5. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Benton County (Benton Area), Oregon, 1970.
REMARKS: Diagnostic horizons and features include:
Mollic epipedon - (pachic) the zone from 0 to 28 inches (Ap, AB, and Bt1 horizons) Argillic horizon - the zone from 18 to 53 inches (Bt1, Bt2, and Bt3 horizons)
Oxyaquic feature - the zone from 28 to 65 inches having redox concentrations and saturation for more than 30 cumulative days in a normal year.
Particle-size control section - the zone form 18 to 38 inches
The Coburg soils are found on both high and low Winkle geomorphic surfaces as recognized in the Willamette Valley, Oregon. Those soils associated with the low Winkle surface have a flooding hazard.
Classification revised 2/2000 from Pachic Ultic Argixerolls to Oxyaquic Argixerolls based on revision of Soil Taxonomy and Oxyaquic subgroup.