LOCATION SOUTHWICK ID
Established Series
Rev. RJB/TWH/CLM/SHB
06/2016
SOUTHWICK SERIES
Landscape--Columbia basalt plateau
Landform--loess hills
Slope--3 to 40 percent; dominantly north-facing slopes
Parent material--recent loess over older loess
Mean annual precipitation--about 585 mm
Mean annual air temperature--about 8 degrees C
Depth class--very deep
Drainage class--moderately well drained
Soil moisture regime--xeric
Soil temperature regime--mesic
Soil moisture subclass--oxyaquic
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Argixerolls
TYPICAL PEDON: Southwick silt loam, cultivated, on a 4-percent, east-southeast-facing slope at an elevation of 945 m (When described on July 8, 1987, the soil was moist throughout. Textures are apparent as determined in the field.)
Ap1--0 to 15 cm; silt loam, dark grayish brown (10YR 4/2) dry, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure parting to moderate fine and medium granular; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine and few fine tubular pores; many worm casts; slightly acid (pH 6.2); gradual wavy boundary
Ap2--15 to 38 cm; silt loam, dark grayish brown (10YR 4/2) dry, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine and few fine tubular pores; slightly acid (pH 6.2); gradual wavy boundary
A--38 to 56 cm; silt loam, dark grayish brown (10YR 4/2) dry, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common very fine roots; common very fine tubular pores; neutral (pH 6.7); clear wavy boundary
Bw1--56 to 66 cm; silt loam, brown (10YR 5/3) dry, dark brown (10YR 3/3) moist; weak medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine and few fine tubular pores; slightly acid (pH 6.5); clear wavy boundary
Bw2--66 to 86 cm; silt loam, pale brown (10YR 6/3) dry, brown (10YR 4/3) moist; moderate medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine tubular pores; slightly acid (pH 6.3); clear wavy boundary
E--86 to 97 cm; silt loam, light gray (10YR 7/2) dry, grayish brown (10YR 5/2) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine and fine tubular pores; slightly acid (pH 6.3); abrupt wavy boundary
Btxb--97 to 150 cm; silty clay loam, brown (10YR 5/3) and yellowish brown (10YR 5/4) dry, brown (10YR 4/3) and dark yellowish brown (10YR 4/4) moist; moderate coarse prismatic structure; very hard, brittle, very firm, moderately sticky and moderately plastic; few very fine roots between prisms; common very fine tubular pores; many prominent clay films on faces of peds and lining pores; common prominent silt coatings on faces of prisms; common fine iron-manganese stains and accumulations; slightly acid (pH 6.5)
TYPE LOCATION: Nez Perce County, Idaho, about 5.5 km northeast of Lenore, Idaho; about 395 m north and 700 m east of the southwest corner of section 18, T. 37 N., R. 1 W.; Lenore, Idaho, U.S. Geological Survey topographic quadrangle; latitude 46.5474380, longitude -116.5049129, datum WGS 84 (coordinates estimated from PLSS details)
RANGE IN CHARACTERISTICS:
Depth to diagnostic horizons and other features are measured from the top of the first mineral layer.
Thickness of mollic epipedon--40 to 75 cm
Depth to argillic horizon--70 to 100 cm
Moisture control section--dry 45 to 60 consecutive days late in summer and early in fall
Mean annual soil temperature--8 to 12 degrees C
Content of clay in particle-size control section (weighted average)--24 to 35 percent
The zone from 97 to 150 cm has characteristics of a fragipan. More review is needed as many pedons appear to meet the criteria for a fragipan.
An Oi horizon is in some pedons.
Ap and A horizons
Value--3 to 5 dry, 2 or 3 moist
Chroma--2 or 3 dry or moist
Content of clay--12 to 27 percent
Reaction--5.6 to 7.3
Combined thickness of Ap horizon--0 to 50 cm
Thickness of A horizon--13 to 40 cm
Bw horizon, and Bt horizon (where present)
Hue--10YR, 7.5YR
Value--4 to 6 dry, 2 to 4 moist
Chroma--2 or 3 dry or moist
Content of clay--15 to 27 percent
Reaction--5.6 to 7.3
Combined thickness of Bw horizon--15 to 40 cm
E horizon
Hue--7.5YR to 2.5Y
Value--6 to 8 dry, 4 to 6 moist
Chroma--2 or 3 dry
Texture--silt loam, silt
Content of clay-- 8 to 23 percent
Reaction--5.6 to 7.3
Thickness--3 to 13 cm
A Btxb/E horizon is in some pedons.
Btxb horizon
Hue--10YR, 7.5YR
Value--4 to 7 dry, 3 to 5 moist
Chroma--3 to 6 dry, 3 or 4 moist
Texture--silt loam, silty clay loam
Content of clay--24 to 35 percent
Bulk density--1.60 to 1.70 g/cm3
Reaction--5.6 to 7.3
Btb horizon (where present)
Hue--10YR, 7.5YR
Value--4 to 7 dry, 3 to 5 moist
Chroma--3 or 4 dry or moist
Texture--silt loam, silty clay loam
Content of clay--24 to 38 percent
Reaction--5.6 to 7.3
COMPETING SERIES:
Thatuna--dry 60 to 80 days late in summer and early in fall
GEOGRAPHIC SETTING:
Elevation--520 to 1075 m
Mean annual precipitation--485 to 760 mm
Mean annual air temperature--7 to 11 degrees C
Frost-free period--90 to 180 days
GEOGRAPHICALLY ASSOCIATED SOILS:
Agatha--on backslopes of north-facing canyons; frigid soil temperature regime; deep to hard basalt
Driscoll--on summits of loess hills on basalt plateaus; silty clay subsoil
Gwin--shallow to hard basalt; on summits and shoulders of basalt plateaus
Kettenbach--loamy-skeletal; moderately deep to hard basalt; on summits and shoulders of basalt plateaus
Keuterville--loamy-skeletal; very deep; on basalt plateaus
Larkin--on south-facing slopes of loess hills on basalt plateaus; no E horizon; no perched water table
DRAINAGE AND PERMEABILITY:
Drainage class--moderately well drained
Saturated hydraulic conductivity (Ksat)--moderately high in upper part; moderately low or very low in lower part
Perched water table--uppermost limit in December through June
USE AND VEGETATION:
Use--dominantly wheat, barley, peas, hay, pasture, and timber production
Natural vegetation--ponderosa pine, common snowberry, white spirea, rose
DISTRIBUTION AND EXTENT: Northern Idaho; MLRA 9; moderate extent
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Nez Perce and Lewis Counties, Idaho; 1917
REMARKS:
Diagnostic horizons and other features in this pedon
*Mollic epipedon--zone from 0 to 56 cm
*Albic horizon--zone from 86 to 97 cm; not an alboll because albic horizon does not directly underly mollic epipedon and no redoximorphic concentrations in or below albic horizon
*Argillic horizon--zone from 97 to 150 cm
*Cambic horizon--zone from 56 to 86 cm
*Oxyaquic feature--zone beginning at a depth of 86 cm that is saturated with water 30 cumulative days or more
*Particle-size control section--zone from 97 to 147 cm
This pedon does not meet the criteria for the aquic subgroup based on the absence of redoximorphic depletions (zones with chroma less than that of matrix) within a depth of 75 cm of the mineral soil surface. The Btxb horizon is not considered to meet the criteria for a fragipan, but further review is needed.
5/2000--The classification of this series was changed from fine-silty, mixed, mesic Boralfic Argixerolls to fine-silty, mixed, superactive, mesic Oxyaquic Argixerolls based on a revision to Soil Taxonomy.
12/2010--The type location was moved from Benewah County, Idaho, to the current location to reflect a non-vitrandic subgroup.
Further investigation of MLRA 9 is needed to determine several classification issues (vitrandic/non-vitrandic; fragipan/non-fragipan; alboll/non-alboll) and to evaluate the slope and landform of the existing mapped Southwick components and their relationship to these classification issues.
6/2016--This official series description (OSD) was updated as part of the final correlation of the Spokane County, Washington, soil survey. These soils may have volcanic ash above the Btb horizon; further investigation required. The formatting was updated according to SSR1 Technical Note 11--Content and Format of Official Series Descriptions (revised 12/2015).
ADDITIONAL DATA:
Laboratory data--Nez Perce County; Kellogg Soil Survey Laboratory sample number 86P 880, soil survey sample number S86ID 069 001
National Cooperative Soil Survey
U.S.A.