LOCATION THATUNA ID+OR WAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Argixerolls
TYPICAL PEDON: Thatuna silt loam, cultivated. (Colors are for dry soil unless otherwise noted.)
Ap--0 to 5 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; very weak thin platy structure parting to moderate fine and very fine granular; slightly hard, friable, slightly sticky and slightly plastic; many fine roots; many very fine irregular pores; neutral (pH 6.8) clear smooth boundary. (5 to 10 inches thick)
A1--5 to 12 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine and very fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many fine roots; many very fine irregular and tubular pores; neutral (pH 6.6); clear smooth boundary. (6 to 8 inches thick)
A2--12 to 19 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many fine roots; many very fine tubular pores; neutral (pH 6.6); clear smooth boundary. (8 to 15 inches thick)
Bw--19 to 27 inches; brown (10YR 5/3) silt loam, dark brown (10YR 3/3) moist; moderate medium and fine subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common fine roots; many very fine tubular pores; slightly acid (pH 6.5); abrupt smooth boundary. (7 to 13 inches.)
E--27 to 37 inches; very pale brown (10YR 7/3) and pale brown (10YR 6/3, rubbed) silt loam, brown (10YR 4/3, rubbed) moist; some streaks of brown B like material; massive; slightly hard, friable, slightly sticky and slightly plastic; few fine roots; common very fine tubular pores; many small (less than 1 mm) black concretions; slightly acid (pH 6.5); abrupt smooth boundary. (6 to 13 inches thick)
Btb1--37 to 45 inches; light yellowish brown (10YR 6/4) heavy silt loam, dark brown (7.5YR 4/4) moist; weak medium and fine prismatic structure parting to weak medium subangular blocky; very hard, very firm, moderately sticky and moderately plastic; white speckling in interior or peds, upper inch has most speckling; few fine roots; many very fine tubular pores; many fine black concretions; continuous prominent dark yellowish brown (10YR 4/4) clay films on faces of peds; some uncoated light brownish gray (10YR 6/2) silt grains on faces of peds; slightly acid (pH 6.4); clear smooth boundary. (7 to 9 inches thick)
Btb2--45 to 56 inches; light yellowish brown (10YR 6/4) silty clay loam, dark brown (7.5YR 4/3) moist; weak medium or prismatic structure; very hard, very firm, moderately sticky and moderately plastic; few fine roots; many very fine tubular pores; many fine iron-manganese concretions; continuous distinct clay films on faces of peds; some light speckling in interior of peds; slightly acid (pH 6.5); clear smooth boundary. (9 to 13 inches thick)
Btb3--56 to 64 inches; yellowish brown (10YR 5/4) silt loam, dark brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few fine roots; many very fine tubular pores; many fine iron-manganese concretions; many distinct clay films on faces of peds; neutral (pH 6.7).
TYPE LOCATION: Benewah County, Idaho; along state line road 1,220 feet north of section corner in NW1/4 SW1/4 section 24, T.44N., R.6W. Slope is 10 percent, northwest facing and on the east side of the road.
RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon - 18 to 36 inches
Depth to Btb horizon - 29 to 40 inches
Depth to seasonally perched water table - 24 to 48 feet
Days continually moist - 60 to 90 in late winter and spring
Consecutive days dry - 60 to 80 in late summer and early fall
Depth to calcareous material - 43 to greater than 60 inches
Average summer soil temperature - 62 to 65 degrees F.
Average annual soil temperature - 47 to 50 degrees F.
Present in some pedons: 0 to 5 percent volcanic ash in horizons above the Btb
A horizon
Value - 3 to 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry, 1 or 2 moist
Organic matter content, upper 7 inches - 3 to 6 percent
C:N ratio, upper 7 inches - 11.5 to 13
Reaction - moderately acid to neutral
Bw horizon
Value - 3 to 5 dry
Chroma - 2 or 3 moist
Reaction - moderately acid to neutral
Clay content - 18 to 25 percent
E horizon
Hue - 10YR or 7.5YR
Value - 6 or 7 dry, 3 to 5 moist
Content of iron-manganese concretions - few or common, fine
Reaction - moderately acid to neutral
Btb horizon
Hue - 10YR or 7.5YR
Value- 5 or 6 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - silt loam or silty clay loam
Content of particles coarser than very fine sand - 0 to 10 percent
Content of iron-manganese concretions - few or common, fine
Reaction - slightly acid or neutral Clay content - 24 to 35 percent
COMPETING SERIES: This is the Southwick series. Southwick soils are dry 45 to 60 days in late summer and early fall.
GEOGRAPHIC SETTING: Thatuna soils are on loess hills at elevations of 1,800 to 3,200 feet. In most places they have northerly slopes and other slopes that receive runoff from higher positions or additional moisture from snow drifts that accumulate on the northerly slopes. Slopes are 0 to 55 percent. The soils formed in deep loess, probably mostly of recent Pinedale, Bull Lake, and Pre-Bull Lake stages. The upper 1 to 2 feet of the loess deposit contains a small percentage of volcanic ash in some areas. The climate is subhumid. The average annual precipitation is 18 to 23 inches. The average annual temperature is 45 to 50 degrees F. The frost-free season is 110 to 160 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Caldwell, Garfield, Naff, Palouse, Schumacher and Staley soils and the competing Latah, Latahco, and Tilma soils. Caldwell soils aquic conditions with chroma of 2 or less with redox concentrations at 30 to 40 inches, have a mollic epipedon 20 to 38 inches thick and are in drainageways and flood plans. Garfield, Naff, Palouse, and Staley soils do not have an E horizon and are on loess hills. Schumacher soils have a fine-loamy particle-size control section and are on hills.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow permeability. There is a perched water table at a depth of 24 to 48 inches from February to April.
USE AND VEGETATION: Most areas are cultivated. Wheat, barley, hay, pasture, lentils, and peas are the major crops. Principal plants in uncultivated areas are Idaho fescue, wild rose, snowberry, small forbs, and other shrubs.
DISTRIBUTION AND EXTENT: Loess region in the prairies in northern Idaho, eastern Washington, and northeastern Oregon; MLRA 9. The series is moderately extensive.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: South Palouse River Project, WASH-1, SCS (Whitman County, Washington and Latah County, Idaho), 1940.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 27 inches (Ap, A1, A2, and Bw horizons).
Albic horizon - the zone from 27 to 37 inches (E horizon)
Argillic horizon - the zone from 37 to 64 inches (Btb1, Btb2, and Btb3 horizons).
Oxyaquic feature - the zone beginning at 27 inches having saturation with water for 30 or more cumulative days.
Particle-size control section - the zone from 37 to 57 inches (Btb1, Btb2, and part of the Btb3 horizon).
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.
ADDITIONAL DATA: Chemical and physical data on 2 profiles (65IDA 0502-Modal and 6IDA 0513).