LOCATION ROLFE IA+MNEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Typic Argialbolls
TYPICAL PEDON: Rolfe silt loam, in a depression, in a hayfield. (Colors are for moist soil unless otherwise stated.)
A--0 to 25 centimeters; black (10YR 2/1) silt loam, dark gray (10YR 4/1) dry; weak fine granular structure; friable; common prominent strong brown (7.5YR 5/6) iron oxide coats in root channels; slightly acid; clear smooth boundary. (18 to 25 centimeters thick)
Eg1--25 to 33 centimeters; dark gray (10YR 4/1) silt loam, gray (10YR 6/1) dry; moderate thin platy structure; friable; common medium prominent yellowish brown (10YR 5/6) iron concentrations; moderately acid; clear smooth boundary.
Eg2--33 to 53 centimeters; gray (10YR 5/1) silt loam, light gray (10YR 7/1) dry; moderate thick platy structure; friable; few prominent very dark gray (5Y 3/1) organic coats on faces of peds; few fine distinct yellowish brown (10YR 5/4) iron concentrations; moderately acid; abrupt smooth boundary. (Combined thickness of the E horizon is 10 to 40 centimeters.)
Btg1--53 to 69 centimeters; very dark gray (5Y 3/1) silty clay, dark gray (5Y 4/1) dry; strong fine and medium angular blocky structure; firm; common distinct silt coats on faces of peds; few fine prominent brown (7.5YR 5/4) iron concentrations; moderately acid; gradual smooth boundary.
Btg2--69 to 81 centimeters; dark gray (5Y 4/1) silty clay; strong fine prismatic structure parting to strong fine angular blocky; firm; many distinct very dark gray (5Y 3/1) clay films on faces of peds; common fine prominent dark yellowish brown (10YR 4/6) iron concentrations; slightly acid; gradual smooth boundary.
Btg3--81 to 102 centimeters; olive gray (5Y 4/2) silty clay; strong fine prismatic structure; friable; common distinct very dark gray (5Y 3/1) clay films on faces of peds; few fine dark nodules (oxides); common medium distinct light olive brown (2.5Y 5/4) iron concentrations; neutral; gradual smooth boundary.
Btg4--102 to 140 centimeters; olive gray (5Y 5/2) silty clay; moderate medium prismatic structure; firm; few distinct very dark gray (5Y 3/1) clay films on faces of peds; few fine dark nodules (oxides); common medium prominent yellowish brown (10YR 5/6) iron concentrations; neutral; clear smooth boundary. (Combined thickness of the Btg horizon is 60 to 100 centimeters.)
2BCg--140 to 180 centimeters; light olive gray (5Y 6/2) clay loam; weak medium prismatic structure; friable; few distinct black (10YR 2/1) clay films in root channels; few fine dark nodules (oxides); many fine and medium prominent yellowish brown (10YR 5/4) iron concentrations; about 2 percent gravel; neutral; clear smooth boundary. (0 to 50 centimeters thick)
2Cg--180 to 200 centimeters; light brownish gray (2.5Y 6/2) loam; massive: friable; few fine dark nodules (oxides); common fine and medium prominent yellowish brown (10YR 5/6) iron concentrations; about 2 percent gravel; slightly effervescent; slightly alkaline.
TYPE LOCATION: Major Land Resource Area (MLRA) 103-Central Iowa and Minnesota Till Prairies; Humboldt County, Iowa subset; about 5 miles west of Humboldt; located about 500 feet south and 620 feet east of the northwest corner of section 6, T. 91 N., R. 29 W., USGS Unique topographic quadrangle; lat. 42 degrees 43 minutes 52 seconds N. and long. 94 degrees 19 minutes 26 seconds W., NAD 83.
RANGE IN CHARACTERISTICS:
Mollic epipedon thickness--25 to 60 centimeters, and commonly is interrupted by an albic horizon
Depth to the top of the argillic horizon--less than 60 centimeters
Depth to the underlying glacial drift--60 to 150 centimeters
Depth to carbonates--107 to 200 centimeters
Clay content in the particle-size control section (weighted average)--35 to 45 percent
Sand content in the particle-size control section (weighted average)--15 to 25 percent
A or Ap horizon:
Hue--10YR
Value--2 or3
Chroma--1 or 2
Texture--silt loam or silty clay loam
Clay content--18 to 35 percent
Sand content--7 to 20 percent
Reaction--strongly acid to neutral
E horizon:
Hue--10YR or 2.5Y
Value--3 to 6
Chroma--1 or 2
Texture--silt loam
Clay content--15 to 25 percent
Sand content--5 to 18 percent
Reaction--strongly acid to slightly acid
Btg horizon:
Hue--10YR, 2.5Y, or 5Y
Value--3 to 6 (3 being mostly in the upper part)
Chroma--1 or 2
Texture--clay, silty clay, or clay loam
Clay content--35 to 45
Sand content--3 to 35 percent
Reaction--moderately acid to neutral
Clay content of the Btg horizon increases by 20 percent or more as compared to the clay content of the E horizon
2Btg horizon (when present):
Hue--2.5Y or 5Y
Value--4 or 5
Chroma--1 or 2
Texture--loam or clay loam
Clay content--25 to 35 percent
Sand content--30 to 45 percent
Rock fragment content--1 to 5 percent
Reaction--slightly acid or neutral
2BCg and 2Cg horizon:
Hue--2.5Y or 5Y
Value--4 to 6
Chroma--1 to 3
Texture--loam or clay loam
Clay content--18 to 35 percent
Sand content--30 to 45 percent
Rock fragment content--1 to 5 percent
Reaction--slightly alkaline or moderately alkaline
COMPETING SERIES: These are the
Chauncey,
Holcomb
Plankinton,
Sperry, and
Willowfork series.
Chauncey and Willowfork--have argillic horizons that start at depths of more than 60 centimeters
Concord and Sperry--have a sand content of less than 10 percent in the lower third of the series control section
Plankinton--have a mollic epipedon greater than 60 centimeters thick
GEOGRAPHIC SETTING:
Parent material--60 to 150 centimeters of local loamy alluvium and in the underlying glacial drift
Landform--shallow potholes on relatively undissected, gently undulating till plains
Slope--0 to 1 percent
Elevation--300 to 400 meters above mean sea level
Mean annual air temperature--6 to 10 degrees C
Mean annual precipitation--585 to 890 millimeters
Frost-free period--155 to 200 days
GEOGRAPHICALLY ASSOCIATED SOILS: Near the type location, these are the
Clarion,
Garmore,
Nicollet, and
Webster soils.
Clarion--are on higher landscape positions on convex side slopes and have a frequently saturated zone between depths of 1.2 and 1.8 meters during the wettest periods in years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Garmore--are on slightly higher landscape positions on convex slopes and have a frequently saturated zone between depths of 1.2 and 1.8 meters during the wettest periods in years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Nicollet--are on slightly higher landscape positions on convex or plane slopes and have a frequently saturated zone between depths of .46 to 1.0 meter during the wettest periods in years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Webster--are on slightly higher landscape positions on plane to slightly concave slopes and do not have an albic horizon
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class--very poorly drained--these soils are frequently saturated at the soil surface during the wettest periods in years when precipitation is within one standard deviation of the 30 year mean of annual precipitation and both perched and apparent saturation can occur
Saturated hydraulic conductivity--0.10 to 1.0 micrometers per second
Ponding--frequently or occasionally ponded for long duration
USE AND VEGETATION:
Most areas are cultivated. The principal crops are corn, meadows, small grains, and soybeans. The native vegetation is big bluestem, western wheatgrass, sedges, blue grama, and other species of the tall grass prairie that are tolerant of excessive wetness.
DISTRIBUTION AND EXTENT:
Physiographic Division--Interior Plains
Physiographic Province--Central Lowland
Physiographic Sections--Western lake section
MLRAs--Central Iowa and Minnesota Till Prairies (103)
LRR M; north-central Iowa and southern Minnesota
Extent--moderate
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota; MLRA SSO 10-5 (Albert Lea, Minnesota)
SERIES ESTABLISHED: Polk County, Iowa, 1958.
REMARKS:
Particle size-control section--the zone from a depth of 53 to 103 centimeters;
series control section--the zone from the surface to a depth of 150 centimeters.
Diagnostic horizons and features recognized in this pedon include:
mollic epipedon--the zone from the surface to a depth of 25 centimeters and the zone from a depth of 53 to 69 centimeters (A and Btg1 horizons);
albic horizon--the zone from a depth of 25 to 53 centimeters (Eg1 and Eg2 horizons);
argillic horizon--the zone from a depth of 53 to 140 centimeters (Btg1, Btg2, Btg3, and Btg4 horizons);
abrupt textural change--53 centimeters;
aquic moisture regime.
Taxonomy version--Keys to Soil Taxonomy, tenth edition, 2006.
There is some question as to whether Rolfe soils in some areas do not have an abrupt clay increase in the argillic horizon, but at the present time it is believed best to classify them as Typic Argialbolls.
The type location was moved to this site from a site in Clay County to better portray the series concept and its geographic location.