LOCATION WATKINS IAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Mollic Hapludalfs
TYPICAL PEDON: Watkins silt loam, on a west-facing, convex slope of 3 percent, in a cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 18 centimeters (0 to 7 inches); very dark gray (10YR 3/1) silt loam, gray (10YR 5/1) dry; weak fine granular structure; friable; moderately acid; clear smooth boundary. [13 to 23 centimeters (5 to 9 inches) thick]
E--18 to 30 centimeters (7 to 12 inches); about 90 percent very dark grayish brown (10YR 3/2) and dark grayish brown (10YR 4/2) silt loam, gray (10YR 6/1) dry; weak thick platy structure parting to weak fine subangular blocky; friable; about 10 percent brown (10YR 4/3) peds from BE horizon; common distinct light gray (10YR 7/1) dry, silt and very fine sand coats on faces of peds; moderately acid; gradual smooth boundary. [8 to 15 centimeters (3 to 6 inches) thick]
BE--30 to 46 centimeters (12 to 18 inches); about 85 percent brown (10YR 4/3) and about 15 percent dark yellowish brown (10YR 4/4) silt loam; moderate fine subangular blocky structure; friable; few distinct light gray (10YR 7/1) dry, silt and very fine sand coatings on faces of peds; few distinct very dark grayish brown (10YR 3/2) organic coats on faces of peds; moderately acid; clear smooth boundary. [0 to 20 centimeters (0 to 8 inches) thick]
Bt1--46 to 74 centimeters (18 to 29 inches); brown (10YR 4/3) silty clay loam; weak fine prismatic structure parting to moderate medium subangular and angular blocky; firm; common distinct dark grayish brown (10YR 4/2) clay films on faces of peds; few distinct light gray (10YR 7/1) dry, silt and very fine sand coats on faces of peds; slightly acid; gradual smooth boundary.
Bt2--74 to 89 centimeters (29 to 35 inches); brown (10YR 4/3) silty clay loam; weak coarse prismatic structure parting to moderate coarse subangular and angular blocky; firm; common distinct dark grayish brown (10YR 4/2) clay films on faces of peds; few distinct light gray (10YR 7/1) dry, silt and very fine sand coats on faces of peds; few fine distinct yellowish brown (10YR 5/6) redoximorphic concentrations; few fine very dark brown (10YR 2/2) concretions (oxides); slightly acid; gradual smooth boundary.
Bt3--89 to 132 centimeters (35 to 52 inches); brown (10YR 4/3) silty clay loam; weak coarse prismatic structure parting to weak coarse subangular blocky; firm; few distinct dark grayish brown (10YR 4/2) clay films on faces of peds; few distinct light gray (10YR 7/1) dry, silt and very fine sand coats on faces of peds; few fine black (N 2/0) concretions (oxides); moderately acid; gradual smooth boundary. [Combined thickness of the Bt horizon is 40 to 107 centimeters (16 to 42 inches).]
C--132 to 203 centimeters (52 to 80 inches); brown (10YR 5/3) silty clay loam; massive; friable; few fine prominent strong brown (7.5YR 5/6) redoximorphic concentrations and few fine prominent gray (5Y 6/1) redoximorphic depletions; few fine black (N 2/0) concretions (oxides); moderately acid.
TYPE LOCATION: Major Land Resource Area (MLRA) 108C-Illinois and Iowa Deep Loess and Drift, West Central Part; Iowa County, Iowa subset; about 2 miles east of Marengo; about 710 meters (2,330 feet) east and 61 meters (200 feet) south of the northwest corner of section 33, T. 81 N., R. 10 W.; USGS Marengo quadrangle; lat. 41 degrees 47 minutes 17.6 seconds N. and long. 92 degrees 1 minute 2.9 seconds W., NAD 83.
RANGE IN CHARACTERISTICS:
Depth to carbonates--greater than 152 centimeters (greater than 60 inches)
Clay content of the particle-size control section (weighted average)--30 to 35 percent
Sand content of the particle-size control section (weighted average)--less than 15 percent
Rock fragment content--0 to 2 percent in the series control section
A or Ap horizon:
Hue--10YR
Value--3
Chroma--1 or 2
Texture--silt loam
Clay content--18 to 24 percent
Sand content--less than 15 percent
Reaction--moderately acid to neutral
E horizon:
Hue--10YR
Value--3 or 4
Chroma--2
Texture--silt loam
Clay content--18 to 24 percent
Sand content--less than 15 percent
Reaction--moderately acid to neutral
BE horizon (when present):
Hue--10YR
Value--4
Chroma--3 or 4
Texture--silt loam or silty clay loam
Clay content--25 to 35 percent
Sand content--less than 15 percent
Reaction--strongly acid to slightly acid
Bt horizon (upper part):
Hue--10YR
Value--4
Chroma--3 or 4
Texture--silty clay loam
Clay content--30 to 35 percent
Sand content--less than 15 percent
Reaction--strongly acid to slightly acid
Bt horizon (lower part) and BC horizon (when present):
Hue--10YR or 2.5Y
Value--4 to 6
Chroma--2 to 6
Texture--silty clay loam
Clay content--30 to 35 percent
Sand content--less than 15 percent
Reaction--strongly acid to slightly acid
C horizon:
Hue--10YR or 2.5Y
Value--4 to 6
Chroma--2 to 6
Texture--silty clay loam - some pedons have thin strata of loam, sandy loam, or loamy sand at depths greater than 102 centimeters (40 inches)
Clay content--27 to 32 percent
Sand content--less than 15 percent
Reaction--moderately acid or slightly acid
2C horizon (when present below a depth 60 inches):
Hue--10YR or 2.5Y
Value--4 to 6
Chroma--2 to 6
Texture--sand, loamy sand, or gravelly sand
Clay content--0 to 15 percent
Sand content--75 to 95 percent
Rock fragment content--0 to 15 percent
Reaction--moderately acid or slightly acid
COMPETING SERIES: These are the
Batavia,
Bowes,
Churchtown,
Deroin,
Downs,
Ella,
Festina,
Frankville,
Gladek,
Greenbush,
Harvard,
Hersey,
Knox,
Luana,
Mannon,
Massbach,
Mellott,
Mt. Carroll,
Myrtle,
Nasset,
Newhouse,
Waubeek, and
Yutan series.
Batavia--have a sand content of more than 15 percent in the lower third of the series control section
Bowes--have a rock fragment content of 15 to 75 percent in the lower third of the series control section
Churchtown--have a clay content of 22 to 27 percent in the particle-size control section
Deroin--do not have albic horizons, have a clay content of 27 to 35 percent in the surface horizons, and have matrix hues of 5YR or 7.5YR in the middle part of the series control section
Downs--have a clay content of 24 to 32 percent in the particle-size control section and have a clay content of 20 to 30 percent in the lower third of the series control section
Ella--have a clay content of 18 to 30 percent in the particle-size control section
Festina--have a clay content of 24 to 29 percent in the particle-size control section
Frankville--have a lithic contact with limestone bedrock within depths of 51 to 102 centimeters (20 to 40 inches)
Gladek--have carbonates within depths of 76 to 152 centimeters (30 to 60 inches)
Greenbush--have a frequently saturated zone within depths of 1.2 to 1.8 meters (4 to 6 feet) in normal years
Harvard--have a sand content of 30 to 75 percent in the lower third of the series control section
Hersey--have a clay content of 18 to 27 percent in the particle-size control section
Knox--are in areas that have a mean annual air temperature range of 12 to 14 degrees C (54 to 57 degrees F)
Luana--have a rock fragment content of 10 to 35 percent in the lower third of the series control section
Mannon--have a clay content of 18 to 27 percent in the particle-size control section
Massbach--have a paralithic with calcareous silty clay or clay shale within depths of 102 to 152 centimeters (40 to 60 inches)
Mellott--have carbonates within depths of 102 to 152 centimeters (40 to 60 inches) and have a sand content of 35 to 65 percent in the lower third of the series control section
Mt. Carroll--have a clay content of 18 to 24 percent in the particle-size control section
Myrtle--have a matrix hue of 2.5YR, 5YR or 7.5YR in the lower third of the series control section
Nasset--have a lithic contact with limestone within depths of 102 to 152 centimeters (40 to 60 inches)
Newhouse--have a clay content of 18 to 27 percent in the particle-size control section, have 5 to 35 percent chert and sandstone fragments in the lower third of the series control section
Waubeek--have a sand content of 35 to 55 percent in the lower third of the series control section
Yutan--have a clay content of 20 to 27 percent in the lower third of the series control section
GEOGRAPHIC SETTING:
Parent material--alluvium
Landform--treads and risers on stream terraces
Slopes--0 to 5 percent
Elevation--183 to 411 meters (600 to 1,350 feet) above sea level
Mean annual air temperature--7 to 11 degrees C (45 to 52 degrees F)
Mean annual precipitation--76 to 91 centimeters (30 to 36 inches)
Frost-free period--155 to 180 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Amana,
Colo,
Koszta, and
Wiota soils.
Amana--are at lower elevations, have mollic epipedons 25 to 50 centimeters (10 to 20 inches) thick, do not have albic horizons or argillic horizons, and have a frequently saturated zone within depths of 0.3 to 1.1 meters (1 to 3.5 feet) in normal years
Colo--are at lower elevations on flood plains, have mollic epipedons more than 91 centimeters (36 inches) thick, do not have albic horizons or argillic horizons, and have a frequently saturated zone within a depth of 0.3 meter (0 to 1 foot) in normal years
Koszta--are in landscape positions similar to those of the Watkins soils and have a frequently saturated zone within depths of 0.3 to 1.1 meters (1 to 3.5 feet) in normal years
Wiota--are in landscape positions similar to those of the Watkins soils and mollic epipedons 50 to 81 centimeters (20 to 32 inches) thick
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class--well drained--a frequently saturated zone does not occur within a depth of 1.8 meters (6 feet) during the wettest periods of normal years
Saturated hydraulic conductivity--moderately high or high
Surface runoff potential--negligible to low
Flooding--rarely flooded for brief or very brief periods during the months of February to November from precipitation events and snowmelt
USE AND VEGETATION:
Most areas are cultivated. The principal crops are corn, soybeans, small grains, and legume hays. Some areas are pastured. The native vegetation is mixed big bluestem, indiangrass, switchgrass, other grasses of the tall grass prairie and deciduous trees.
DISTRIBUTION AND EXTENT:
Physiographic Division--Interior Plains
Physiographic Province--Central Lowland
Physiographic section--Dissected till plains
MLRAs--Illinois and Iowa Deep Loess and Drift (108) and Iowa and Missouri Heavy Till Plain (109)
LRR M; eastern and southern Iowa
Extent--small
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Iowa County, Iowa, 1961
REMARKS:
Particle-size control section--the zone from a depth of 46 to 96 (18 to 38 inches) (Bt1, Bt2 and Bt3 horizons);
series control section--the zone from the surface to a depth of 150 centimeters (0 to 59 inches) (Ap, E, BE, Bt1, Bt2, Bt3, and C horizons).
Diagnostic horizons and features recognized in this pedon:
ochric epipedon--the zone from the surface to a depth of 18 centimeters (0 to 7 inches) (Ap horizon);
albic horizon--the zone from a depth of 18 to 30 centimeters (7 to 12 inches) (E horizon);
argillic horizon--the zone from a depth of 46 to 132 centimeters (18 to 52 inches) (Bt1, Bt2, and Bt3 horizons);
udic moisture regime.
Cation-exchange activity class is inferred from lab data from similar soils in the surrounding area.
Taxonomy version--Keys to Soil Taxonomy, ninth edition, 2003.