LOCATION SOUTHWICK IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Argixerolls
TYPICAL PEDON: Southwick silt loam-forested. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 1 inch; needles, leaves and twigs.
Oe--1 to 1.5 inches; decomposed needles, leaves and twigs.
A1--1.5 to 10 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine and medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many fine irregular pores; moderately acid (pH 6.0); clear smooth boundary. (6 to 12 inches thick)
A2--10 to 18 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and medium roots; common very fine and fine tubular pores; moderately acid (pH 6.0); diffuse smooth boundary. (6 to 14 inches thick)
Bw--18 to 24 inches; brown (10YR 5/3) silt loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and few medium roots; many very fine, common fine, and few medium tubular pores; moderately acid (pH 6.0); clear smooth boundary. (4 to 17 inches thick)
Ec--24 to 32 inches; light gray (10YR 7/2) silt loam, brown (10YR 5/3) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; many very fine tubular pores; common fine concretions; moderately acid (pH 6.0); clear wavy boundary. (4 to 10 inches thick)
Btb1--32 to 47 inches; brown (10YR 5/3) silty clay loam, brown (10YR 4/3) moist; strong medium and coarse prismatic structure; very hard, very firm, moderately sticky and moderately plastic; common very fine and fine roots that follow surfaces of peds; many very fine and fine tubular pores; common fine concretions; common prominent clay films on faces of peds; peds and pores have uncoated mineral grains on faces; slightly acid (pH 6.2); diffuse smooth boundary. (10 to 16 inches thick)
Btb2--47 to 61 inches; yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 4/4) moist; moderate medium and coarse prismatic structure; very hard, very firm, moderately sticky and moderately plastic; few very fine and fine roots that follow surfaces of peds; many very fine and fine tubular pores; common fine concretions; common prominent clay films on faces of peds; slightly acid (pH 6.4); gradual smooth boundary. (6 to 14 inches thick)
Btb3--61 to 70 inches; pale brown (10YR 6/3) silty clay loam, dark yellowish brown (10YR 4/4) moist; weak medium and coarse prismatic structure; hard, firm, slightly sticky and slightly plastic; few fine roots that follow surfaces of peds; many very fine, fine, and few medium tubular pores; common fine concretions; peds and pores have uncoated mineral grains on faces; few distinct clay films on faces of peds; slightly acid (pH 6.3).
TYPE LOCATION: Benewah County, Idaho; 1,080 feet south and 380 feet east of the northwest corner of section 30, T.44, N., R.4 W.
RANGE IN CHARACTERISTICS:
Depths to diagnostic horizons and features are measured from the top of the first mineral layer.
Thickness of mollic epipedon - 16 to 30 inches
Depth to argillic horizon - 28 to 38 inches
Days dry, moisture control section - 45 to 60 in late summer and early fall. Average annual soil temperature - 47 to 54 degrees F.
The layer from 33 to 62 inches has some characteristics of a fragipan but does not qualify as a fragipan
Particle-size control section (weighted average)
Clay content - 28 to 35 percent
A horizon
Value - 3 to 5 dry, 2 or 3 moist
Chroma - 2 or 3, dry or moist
Clay content - 15 to 26 percent
Reaction - moderately acid to neutral
Bw horizon (a Bt in some pedons)
Hue - 10YR or 7.5YR
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3, dry or moist
Clay content - 15 to 26 percent
Reaction - moderately acid to neutral
E horizon
Hue - 7.5YR to 2.5Y
Value - 6 to 8 dry, 4 to 6 moist
Chroma - 2 or 3 dry
Texture - SIL, SI
Clay content - 10 to 23 percent
Reaction - moderately acid to neutral
Btxb/E horizon - present in some pedons
Btb1 and Btb2 horizons (Btxb horizon, when present)
Hue - 10YR or 7.5YR
Value - 4 to 7 dry, 3 to 5 moist
Chroma - 3 to 6 dry, 3 or 4 moist
Texture - SIL, SICL
Clay content - 23 to 35 percent
Bulk density - 1.60 to 1.70 g/cc
Reaction - moderately acid to neutral
Btb3 horizon (when present)
Hue - 10YR or 7.5YR
Value - 4 to 7 dry, 3 to 5 moist
Chroma - 3 or 4 dry or moist
Clay content - 27 to 38 percent
Reaction - moderately acid to neutral
COMPETING SERIES: This is the Thatuna series. Thatuna soils are dry for 60 to 80 days in late summer and early fall.
GEOGRAPHIC SETTING: The soils are on dissected loess hills on plains and plateaus. Slopes range from 3 to 40 percent, but 3 to 15 percent slopes are predominant. Elevation is 1,700 to 3,500 feet. The soils formed in loess, possibly of two ages (Pinedale, Bull Lake). The average annual precipitation is 22 to 30 inches. The average annual temperature is 45 to 52 degrees F. The frost-free period is 90 to 180 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cald, Larkin, Latahco, and Worley soils. Cald soils lack an argillic horizon and are somewhat poorly drained. Larkin soils lack an A2 horizon. Worley soils have a silty clay B2t horizon. Latahco soils have frigid temperatures and are somewhat poorly drained.
DRAINAGE AND PERMEABILITY: Moderately well drained; moderate permeability in the upper part and slow or very slow permeability in the lower part. There is a perched water table is at its uppermost limit from December to June.
USE AND VEGETATION: This soil is used mainly for wheat, barley, peas, hay, pasture and timber production. The natural vegetation is mainly an overstory of ponderosa pine. Understory is common snowberry, white spirea, and rose.
DISTRIBUTION AND EXTENT: Northern Idaho; MLRA 9. The series is moderately extensive.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Nez Perce and Lewis Counties, Idaho, 1917.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - the zone from 1.5 to 25 inches (A1, A2, and Bw horizons).
Albic horizon - the zone from 25 to 33 inches (E horizon) with chroma never less than 3 moist.
Argillic horizon - the zone from 33 to 71 inches (Btb1, Btb2, Btb3 horizons).
Oxyaquic feature - the zone beginning at 25 inches having saturation with water for 30 or more cumulative days.
Particle-size control section - the zone from 33 to 53 inches (Btb1 and part of Btb2 horizons).
This pedon does not meet Albolls suborder criteria based on presence of moist chroma of 3 within the E horizon (albic).
This pedon does not meet the aquic subgroup criteria based on the absence of redox depletions (zones of chroma less than those in the matrix) within 30 inches of the mineral soil.
The classification of this series has been revised as of 5/00 from fine-silty, mixed, mesic Boralfic Argixerolls to fine-silty, mixed, superactive, mesic Oxyaquic Argixerolls based on revision to Soil Taxonomy.
ADDITIONAL DATA: This soil has been sampled in Nez Perce County by NSSL. Laboratory sample number 86P 880, soil survey sample number S86ID 069 001.