LOCATION IRWIN KSEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Pachic Argiustolls
TYPICAL PEDON: Irwin silty clay loam-rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 6 inches; very dark gray (10YR 3/1) silty clay loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; hard, friable, slightly plastic and slightly sticky; many fine and medium roots throughout; few distinct gray (10YR 5/1) discontinous skeltans (sand or silt) on faces of peds; strongly acid; clear smooth boundary.
BA--6 to 13 inches; very dark grayish brown (10YR 3/2) silty clay loam, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; hard, firm, plastic and sticky; many fine roots throughout; few distinct gray (10YR 5/1) discontinuous skeleton (sand or silt) on faces of peds; strongly acid; abrupt smooth boundary. (Combined thickness of the A and BA horizons is 5 to 13 inches.)
Bt1--13 to 23 inches; dark grayish brown (10YR 4/2) clay, very dark brown (10YR 2/2) and very dark grayish brown (10YR 3/2) crushed moist; strong medium subangular blocky structure; very hard, very firm, very plastic and very sticky; common very fine and fine roots throughout; few faint very dark brown (10YR 2/2) continuous clay films (cutans) on faces of peds; slightly acid; gradual smooth boundary.
Bt2--23 to 30 inches; brown (10YR 4/3) clay, dark brown (10YR 3/3) moist; moderate medium blocky structure; extremely hard, extremely firm, very plastic and very sticky; common very fine roots between peds; few faint very dark grayish brown (10YR 3/2) discontinuous clay films (cutans) on faces of peds; neutral; gradual smooth boundary.
Btk--30 to 41 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; weak medium blocky structure; very hard, very firm, very plastic and very sticky; few very fine roots throughout; very few faint discontinuous clay films (cutans) on faces of peds; common fine and medium rounded lime concretions; slightly alkaline; gradual smooth boundary. (Combined thickness of the Bt horizons is 15 to 30 inches.)
2Bt1--41 to 54 inches; brown (7.5YR 5/4) silty clay loam, brown to brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; hard, firm, plastic and sticky; very few discontinuous clay films (cutan) on faces of peds; moderately alkaline; clear smooth boundary.
2Bt2--54 to 72 inches; 70 percent brown (7.5YR 4/4), with 30 percent brown (10YR 5/3) silty clay loam; 70 percent dark brown (7.5YR 3/4), with 20 percent brown to brown (10YR 4/3), and 10 percent dark grayish brown (10YR 4/2) moist; weak fine subangular blocky structure; hard, firm, plastic and sticky; very few faint discontinuous clay films (cutans) and faces of peds; 1 percent limestone pebbles; slightly alkaline; gradual smooth boundary. (Combined thickness of the 2Bt2 horizons is 0 to 35 inches)
TYPE LOCATION: Geary County, Kansas; about 10 miles south of Junction City; 2,340 feet east and 320 feet north of the southwest corner of section 25, T. 13 S., R. 5 E. Wreford, Kansas USGS topographic quadrangle, latitude 38 degrees, 53 minutes, 6 seconds north; longitude 96 degrees, 49 minutes, 32 seconds west.
RANGE IN CHARACTERISTICS:
Thickness of the mollic epipedon: 20 to 40 inches.
Depth to limestone or shale: 40 to more than 60 inches.
Depth to a subhorizon containing more than 40 percent clay is less than 14 inches.
Lime concretions occur below 24 inches in some pedons. A bedrock substratum phase is recognized.
A horizon:
Hue: 10YR
Value: 4 or 5 dry, 2 or 3 moist
Chroma: of 1 to 3
Texture: silty clay loam, but the range includes silty clay.
Reaction: moderately acid to neutral.
Bt horizon:
Hue: 10YR or 7.5YR
Value: 4 to 6 and 3 or 4 moist
Chroma: 2 or 3
Texture: silty clay or clay
Reaction: medium acid to neutral in the upper part and slightly acid to slightly alkaline in the lower part
C horizon:
Hue: 2.5Y to 5YR
Value: 4 to 6 and 3 to 5 moist
Chroma: of 2 to 5
Texture: silty clay, clay, or silty clay loam. Unconforming strata are common; however, strata with less than 40 percent clay are at depths below 40 inches. Reaction: neutral to moderately alkaline.
COMPETING SERIES: These are the Conchovar, Knifehill, Lubbock, Millpaw, Nutreeah, Ruidoso, and Tully series. Lubbock soils are drier in the soil moisture control section during June and July and have free carbonates at shallower depths. Conchovar soils are somewhat poorly drained and have a water table within 60 inches. Knifehill, Millpaw and Ruidoso soils are drier in the soil moisture control section during May and June. In addition these soils have more than 20 percent sand in the Bt horizon. Nutreeah soils have an intermittent water table below 40 inches. The well drained Tully soils do not have horizons within 14 inches of the surface that contains more than 40 percent clay. In addition, Tully soils formed in colluvium.
GEOGRAPHIC SETTING: The Irwin soils are on erosional uplands. The slope gradient commonly is 1 to 3 percent, but the range is 0 to 8 percent. The Irwin soils formed in clayey sediments believed to be old alluvium or residuum derived largely from clay shales. The upper part of some pedons is probably formed in loess. Mean annual precipitation ranges from 27 to 35 inches; Thornthwaite Annual P-E Index ranges from 48 to 62; and mean annual temperature ranges from 54 to 59 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Tully soils and the Clime, Dwight, Florence, Labette, Ladysmith, and Sogn soils. The moderately deep Clime and Labette soils occur lower on the slopes. Dwight and Ladysmith soils occur higher on the slopes and on ridge tops. Dwight soils have a natric horizon. Ladysmith soils have montmorillonitic mineralogy. The skeletal Florence and shallow Sogn soils occur lower on the slopes. Tully soils are usually on foot slopes below Clime, Florence, and Sogn soils in the same landscape but are rarely directly adjacent to Irwin soils.
DRAINAGE AND PERMEABILITY: Moderately well drained. Runoff is high or very high. Permeability is very slow.
USE AND VEGETATION: About half is cultivated; wheat and sorghum are the principal crops. The remainder is used as rangeland. Native vegetation is mid or tall grass prairie.
DISTRIBUTION AND EXTENT: Mostly in or just west of the Bluestem Hills of east central Kansas. The series is extensive. Estimated acreage is more than one million acres.
MLRA OFFICE RESPONSIBLE: Salina, Kansas
SERIES ESTABLISHED: Geary County, Kansas, 1958.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon the zone from the surface of the soils to a depth of approximately 30 inches (A, BA, Bt1 and Bt2 horizon)
Argillic horizon: the zone from approximately 13 to 72 inches.
07/2003 WAW CEC activity class added, change to semi-tabular format. Added additional competing series
ADDITIONAL DATA:
NSSL Laboratory samples 87P0011, (86KS015001); 90P0510, (90KS061002); Kansas State University Soil Characterization Laboratory samples 2423-2429, pedon 01KS197003, 2480-2487, pedon 88KS061004