LOCATION KILLDUFF IAEstablished Series
The Killduff series consists of deep, well and moderately well drained, moderately permeable soils formed in loess on uplands. Slope ranges from 2 to 18 percent. Mean annual temperature is about 50 degrees F, and mean annual precipitation is about 33 inches.
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Dystric Eutrudepts
TYPICAL PEDON: Killduff silty clay loam on a convex 6 percent east-facing slope - cultivated. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 7 inches; black (10YR 2/1) silty clay loam, very dark grayish brown (10YR 3/2) dry; weak medium subangular blocky and weak fine granular structure; friable; neutral; abrupt smooth boundary. (6 to 9 inches thick)
A--7 to 9 inches; very dark brown (10YR 2/2) silty clay loam, dark grayish brown (10YR 4/2) dry; moderate very fine subangular blocky and moderate fine granular structure; friable; slightly acid; gradual smooth boundary. (0 to 3 inches thick)
BA--9 to 14 inches; brown (10YR 4/3) silty clay loam, coatings on faces of peds are dark brown (10YR 3/3) and very dark grayish brown (10YR 3/2), brown (10YR 4/3) crushed; moderate very fine subangular blocky and moderate fine granular structure; friable; slightly acid; gradual smooth boundary. (0 to 6 inches thick)
Bw1--14 to 20 inches; brown (10YR 4/3) silty clay loam, coatings on faces of a few peds are dark brown (10YR 3/3); moderate very fine subangular blocky structure; friable; few thin discontinuous very dark grayish brown (10YR 3/2) clay films on faces of peds; slightly acid; gradual smooth boundary.
Bw2--20 to 25 inches; brown (10YR 4/3) silty clay loam; few fine distinct grayish brown (2.5Y 5/2) mottles and few fine faint yellowish brown (10YR 5/6) mottles; weak very fine subangular blocky structure; friable; few thin discontinuous dark brown (10YR 3/3) clay films on faces of peds; few dark accumulations (iron maganese); slightly acid; gradual smooth boundary.
Bw3--25 to 35 inches; dark yellowish brown (10YR 4/4) silty clay loam; many fine distinct grayish brown (2.5Y 5/2) and common fine distinct strong brown (7.5YR 5/6) mottles; weak fine and very fine subangular blocky structure; friable; few fine dark accumulations (iron maganese); slightly acid; gradual smooth boundary. (Combined thickness of the BW horizon is 17 to 25 inches.)
BC--35 to 46 inches; mottled grayish brown (2.5Y 5/2) and yellowish brown (10YR 5/4) silt loam; many fine distinct strong brown (7.5YR 5/6) mottles; weak medium prismatic structure parting to weak medium subangular blocky; friable; few fine dark accumulations (iron maganese); slightly acid; gradual smooth boundary. (7 to 12 inches thick)
C--46 to 60 inches; mottled grayish brown (2.5Y 5/2) and yellowish brown (10YR 5/4) silt loam; many fine distinct strong brown (7.5YR 5/6) mottles; massive with some vertical cleavage; friable; few fine dark accumulations (iron maganese); neutral.
TYPE LOCATION: Poweshiek County, Iowa; about 4 miles east and 4 miles north of Grinnell; 2,015 feet east and 160 feet south of the northwest corner, sec. 30, T. 81 N., R. 15 W.
RANGE IN CHARACTERISTICS: The solum typically is 36 to 48 inches thick but ranges from 30 to 55 inches. Free carbonates are absent to depths of 40 inches or more. Sand content is less than 5 percent throughout the solum. The solum is slightly or medium acid in the most acid part. The depth to clay maximum, maximum percent clay, depth to free carbonates, and depth to relict gray colors decrease with increasing percent gradient on convex slopes. The 10- to 40-inch - control section averages between 27 and 33 percent clay. Maximum clay content ranges from about 30 to 35 percent and is within a depth ranging from about 6 to 18 inches below the surface.
In uneroded or only slightly eroded pedons, the Ap horizon typically is black (10YR 2/1), very dark brown (10YR 2/2), or very dark gray (10YR 3/1). The A horizon is very dark brown (10YR 2/2) or very dark grayish brown (10YR 3/2). Some pedons have an AB horizon that is very dark grayish brown (10YR 3/2) or dark brown (10YR 3/3). The total thickness of the A horizons is less than 10 inches. In moderately eroded pedons, the Ap horizon is very dark grayish brown (10YR 3/2), or dark brown (10YR 3/3) with evident mixing of brown (10YR 4/3 or 5/3) material from the B horizon. The A horizon is silty clay loam with a clay content ranging from about 28 to 33 percent.
The Bw horizons typically are brown (10YR 4/3 or 5/3), dark yellowish brown (10YR 4/4), or yellowish brown (10YR 5/4). Mottles with hue of 10YR, 2.5Y, or 5Y; value of 5 or 6; and chroma of 2 increase with depth in the B horizons. The percentage of mottles with chroma of 2 ranges from 20 to 40 percent of the matrix within depths ranging from 24 to 30 inches.
The BC horizon is grayish brown (2.5Y or 10YR 5/2), light brownish gray (2.5Y 6/2), or yellowish brown (10YR 5/4 and 5/6). In many pedons, the matrix is about equal parts of brown and grayish colors. The BC horizon is silt loam or silty clay loam.
The C horizon has hue of 10YR, 2.5Y, or 5Y; value of 5 or 6; and chroma of 1 to 4. The gray colors are relict features that are related stratigraphically to a deoxidized weathering zone. It is silt loam or, less commonly, silty clay loam.
COMPETING SERIES: These are the Contrary, Drury, and Exette series of the same family and the Downs, Exira, Hedrick, Ladoga, Mt. Carroll, Nira, Port Byron, Seaton, and Tama series. Contrary soils have a lower maximum clay content and a lower average clay content in the control section. Drury soils have lighter colored A horizons, have less clay in the A and B horizons, and lack 20 percent grayish mottles in any part of the B horizon. Exette soils have less clay in the B horizons. Downs, Hedrick, Ladoga, Mt. Carroll, Seaton, and Tama soils all have argillic horizons. In addition, Downs, Ladoga, Mt. Carroll, Seaton, and Tama soils lack grayish mottles above 30 inches, and Hedrick soils have dominantly gray matrix colors at shallower depths. Exira, Nira, and Port Byron soils have mollic epipedons. In addition, Nira soils have gray deoxidized matrix colors at a shallower depth; and Port Byron soils have somewhat less clay in the B horizon and are deeper to grayish mottles.
GEOGRAPHIC SETTING: Killduff soils are on short, convex to straight side slopes, coves at the head of drainageways, and in a few places, the tops of lowered interfluves in uplands. Slope gradients range from 2 to 18 percent. These soils formed in a deoxidized and leached or a thin, mottled, oxidized and leached over a deoxidized and leached weathering zone in Wisconsinan Age loess. The loess is 4 to 15 feet thick and is underlain by pre-Wisconsin glacial till. The mean annual temperature ranges from about 49 to 52 degrees F, and mean annual precipitation ranges from about 30 to 34 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Tama soils, which are upslope.
DRAINAGE AND PERMEABILITY: These soils are well and moderately well drained. The grayish colors are inherited from a geological weathering zone and are not a reflection of the present drainage. Permeability is moderate. Surface runoff is medium on the gently or moderately sloping areas and rapid on the steeper slopes.
USE AND VEGETATION: Used mainly for cultivated crops with some hay or pasture in rotation. Native vegetation was tall prairie grasses.
DISTRIBUTION AND EXTENT: Central and east-central Iowa. These soils are of moderate extent.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Jasper County, Iowa, 1975.
REMARKS: Clay films are noticeable, but the increase in clay from the A to the B horizons fails to meet the 1.2 required for an argillic horizon. The gray colors were not used in the classification of this soil, as they are considered to be inherited from a relict deoxidized and leached weathering zone.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - the zone from the surface to a depth of 9 inches (Ap and A horizons); cambic horizon - the zone from 9 inches to 46 inches (BA, Bw1, Bw2, Bw3, and BC horizons).