LOCATION ELCO ILEstablished Series
The Elco series consists of very deep, moderately well drained soils on till plains. They formed in 20 to 40 inches of loess and in the underlying till or glacial drift that contains a strongly developed paleosol. Most pedons have a layer of silty or loamy pedisediment between the loess and the underlying till. These soils are moderately permeable in the upper part and moderately slowly permeable in the lower part. Slopes range from 2 to 25 percent. Mean annual air temperature is about 52 degrees F., and mean annual precipitation is about 36 inches.
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Hapludalfs
TYPICAL PEDON: Elco silt loam - on a west-facing convex slope of 10 percent in idle land at an elevation of about 575 feet above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 4 inches; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; strong very fine granular structure; friable; many roots throughout; slightly acid; clear smooth boundary. (3 to 7 inches thick)
E--4 to 12 inches; brown (10YR 4/3) silt loam; weak thin platy structure parting to moderate very fine granular; friable; many distinct light gray (10YR 7/1) dry, clay depletions on faces of peds; few faint very dark grayish brown (10YR 3/2) organic coatings on faces of peds and linings in pores; few distinct yellowish brown (10YR 5/4) flecks and fragments of subsoil; slightly acid; clear smooth boundary. (0 to 10 inches thick)
BE--12 to 15 inches; yellowish brown (10YR 5/4) silt loam; moderate very fine and fine subangular blocky structure; friable; few faint dark brown (10YR 3/3) organo-clay films and very few faint dark grayish brown (10YR 4/2) clay films on faces of peds; few distinct light gray (10YR 7/1) dry, clay depletions on faces of peds; few fine black (5YR 2.5/1) iron-manganese oxide concretions throughout; slightly acid; clear smooth boundary. (0 to 7 inches thick)
Bt--15 to 26 inches; yellowish brown (10YR 5/4) silty clay loam; moderate fine and medium subangular blocky structure; firm; many distinct brown (10YR 4/3) clay films on faces of peds; few distinct light gray (10YR 7/1) dry, silt coatings on faces of peds; few fine distinct yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine distinct grayish brown (10YR 5/2) iron depletions along micropores; few fine black (5YR 2.5/1) iron-manganese oxide concretions throughout; slightly acid; clear smooth boundary. (10 to 30 inches thick)
2Btg1--26 to 39 inches; grayish brown (2.5Y 5/2) and yellowish brown (10YR 5/6) silty clay loam; moderate medium and coarse subangular and angular blocky structure; firm; common distinct olive brown (2.5Y 4/4) and brown (10YR 4/3) clay films on faces of peds; few fine prominent strong brown (7.5YR 5/8) masses of iron accumulation in the matrix; common very fine black (5YR 2.5/1) iron-manganese oxide concretions throughout; slightly acid; gradual smooth boundary. (Combined thickness of the 2Btg and/or 2Bt horizons in pedisediment is 0 to 30 inches.)
3Btg2--39 to 55 inches; grayish brown (2.5Y 5/2) and yellowish brown (10YR 5/6) silty clay; weak medium prismatic structure parting to moderate coarse subangular and angular blocky; firm; many distinct gray (5Y 5/1) clay films on faces of peds; few fine prominent strong brown (7.5YR 5/8) masses of iron accumulation in the matrix; few fine black (5YR 2.5/1) iron-manganese concretions throughout; slightly acid; clear smooth boundary.
3Btg3--55 to 70 inches; grayish brown (2.5Y 5/2) silty clay; moderate fine and medium subangular and angular blocky structure; friable; common distinct gray (5Y 5/1) clay films on faces of peds and in pores; common fine prominent strong brown (7.5YR 5/6) masses of iron accumulation in the matrix; few fine black (5YR 2.5/1) iron-manganese concretions throughout; slightly acid; clear smooth boundary.
3Btg4--70 to 80 inches; gray (5Y 5/1) silty clay; moderate coarse subangular blocky structure; firm; common distinct greenish gray (5GY 5/1) clay films on faces of peds; few distinct black (10YR 2/1) organic coatings in root channels and pores; many fine strong brown (7.5YR 4/6) masses of iron accumulation in the matrix; few fine black (5YR 2.5/1) iron-manganese concretions throughout; slightly alkaline.
TYPE LOCATION: Sangamon County, Illinois; about 3 miles southeast of Rochester, Illinois; 2520 feet east and 2200 feet south of the northwest corner of section 35, T. 15 N., R. 4 W. U.S.G.S. New City, IL topographic quadrangle; latitude 39 degrees, 42 minutes; 30 seconds North and, longitude 89 degrees, 30 minutes, 28 seconds West., NAD 27.
RANGE IN CHARACTERISTICS: The solum thickness is greater than 48 inches. Loess thickness ranges from 20 to 40 inches. The till that contains a strongly developed paleosol is within a depth of 60 inches. The particle size control section averages between 25 and 35 percent clay. Average sand content is less than 10 percent in the loess and ranges from 10 to 35 percent in the pedisediment and from 15 to 35 percent in the till. The sand fraction is poorly sorted, well graded. These soils do not have carbonates within a depth of 60 inches. Base saturation is greater than 60 percent at a depth of 50 inches below the top of the argillic horizon.
The A horizon has hue of 10YR, value of 3 or 4 (4 to 6 dry), and chroma of 1 or 2 and is less than 6 inches thick. The Ap horizon has value of 4 or 5, and chroma of 2 to 4. The Ap or A horizon typically is silt loam, but severely eroded pedons include silty clay loam. Reaction ranges from moderately acid to neutral.
The E horizon has hue of 10YR, value of 4 or 5, and chroma of 3 or 4. It is silt loam. Reaction ranges from moderately acid to neutral.
The BE horizon has hue of 10YR, value of 4 or 5, and chroma of 3 to 6. It is silt loam or silty clay loam. Reaction ranges from strongly acid to neutral.
The Bt horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 3 to 6 in the upper part and 2 to 6 in the lower part. It typically is silty clay loam, but some pedons contain one or more subhorizons that are silt loam. Reaction ranges from strongly acid to slightly alkaline.
The 2Btg or, where present, the 2Bt horizon has hue of 5Y, 2.5Y, 10YR, or 7.5YR; value of 3 to 6; and chroma of 1 to 6 and has redoximorphic features. It is loam, clay loam, silty clay loam, or silt loam. Reaction strongly acid to slightly alkaline.
The 3Bt or 3Btg horizon has hue of 5Y, 2.5Y, 10YR, or 7.5YR; value of 3 to 6; and chroma of 1 to 6 and commonly has redoximorphic features in some part. In some pedons the redox accumulations have redder hue or chroma as high as 8, or both redder hue and higher chroma. The 3Bt or 3Btg horizon is loam, clay loam, silty clay loam, silty clay, or clay. Reaction is strongly acid to slightly alkaline.
COMPETING SERIES: These are the
Barony,
Birkbeck,
Campton,
Downsouth,
Eleroy,
Grays,
Hedrick,
Homen,
Inton,
Iona,
Kaneville,
Libre,
Mayville,
Middletown,
Minnith,
Newvienna,
Redbud,
Richview,
Rocheport,
Rockfield, Somanauk,
Throckmorton,
Windere,
Winfield,
Wingate,
Zurich. The Barony, Downsouth, Kaneville, Newvienna, Richview, and Wingate soils have a surface layer more than 6 inches thick with value and chroma both less than 3.5. Birkbeck, Campton, Hedrick, Homen, Inton, Iona,
Jeneva, and Winfield soils have less than 10 percent sand in all horizons within a depth of 40 inches. Eleroy and
Rocheport soils have a paralithic contact within a depth of 60 inches. Grays, Mayville, Rockfield, Throckmorton, Windere, and Zurich soils have carbonates within a depth of 60 inches and the underlying material is stratified sediments. Libre soils have a base saturation of less than 60 percent at a depth of 50 inches below the top of the argillic horizon. Middletown soils average more than 35 percent sand in the lower part of the series control section. Minnith soils have a mean annual soil temperature greater than 55 degrees and the sand fraction in the lower part is well sorted, poorly graded. Redbud soils average less than 15 percent sand in the lower part of the series control section. Zurich soils have carbonates above 40 inches and formed in loess and the underlying outwash. The Richview series has not been updated for the addition of cation exchange activity class to its classification and may or may not compete when its taxonomy is updated.
GEOGRAPHIC SETTING: Elco soils are on side slopes and some ridge tops on loess covered till plains and moraines. Slope gradients are 1 to 25 percent. These soils formed in 20 to 40 inches of loess and in the underlying till that contains a strongly developed paleosol. Most pedons have a layer of silty or loamy
pedisediment between the loess and till. Mean annual temperature ranges from 46 to 54 degrees F, and mean annual precipitation varies from 32 to 40 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Atlas, Fayette, Hickory, Ursa, and Winfield soils. The somewhat poorly drained Atlas soils are in similar positions where the loess cap is less than 20 inches thick. Fayette and Winfield soils are upslope or at higher elevations and formed entirely in loess. Hickory and Ursa soils are downslope and have less than 20 inches of loess.
DRAINAGE AND PERMEABILITY: Moderately well drained. The potential for surface runoff is low to very high. Permeability is moderate in the loess, moderately slow in the pedisediment, and moderately slow or slow in the till that contains a strongly developed paleosol. Seepy spots on side slopes are common as
the result of perched water above the paleosol.
USE AND VEGETATION: Most areas are cropped. Corn, soybeans, small grain, and meadow are the principal crops. Other areas are in pastureland, woodland, or idle land. Native vegetation is upland hardwood forest.
DISTRIBUTION AND EXTENT: Illinois. Extent is moderate.
MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Shelby County, Illinois, 1932.
REMARKS: This pedon was relocated approximately 300 feet east of the previous type location by RAT- Springfield MLRA. Pedon number 97IL-167-026.
Elco soils have been correlated only as moderately well drained and have been used only in Illinois. At one time, the definition allowed for well-drained pedons also, but we now believe that they do not occur because of the influence of the paleosol on water movement in the solum. The 3Btg or 3Bt horizon of Elco soils is the lower part of the solum superimposed upon a Sangamon paleosol in the Illinoian till. Many of the properties of those horizons are believed to be inherited from the paleosol. The variability of the properties is related to the geologic truncation of the paleosol before it was buried by loess, and to the extent of modern soil development into the old materials. Some pedons have a dark-colored layer at the top of the paleosol that was the surface layer of the paleosol, and is now part of the 2Bt or 3Bt horizon of the modern soil. In pedons that do not have the pedisediment layer the Peoria loess lies directly on the paleosol. The paleosolic Bt horizon typically is gray, but ranges to brown in some pedons. Calcium and other bases have been replenished in the paleosol in some pedons after burial by loess by seepage from the mantling material up slope. It is difficult to differentiate the properties of the lower part of the modern solum from those of the paleosol in many pedons.
Diagnostic horizons and features recognized in this pedon are:
ochric epipedon - the zone from the surface to a depth of about 15 inches (Ap, E, and BE) horizons;
argillic horizon - the zone from about 15 to 80 inches (Bt1, 2Btg1, 3Btg3, and 3Btg4 horizons;
two lithologic discontinuities - one between the Peoria loess and the Roxana silts (pedisediment) at a depth of 26 inches, and the other between the Roxana silts and the glacial till (paleosol) at a depth of 39 inches.
ADDITIONAL DATA: Data on pedon S70IL-167-001 is from a pedon within the same delineation as this typical pedon. Data from other pedons are on file at the Illinois NRCS State Office.