LOCATION BACKBONE                IA+IL MN

Established Series
Rev. RJK-SRS-TWN
10/2012

BACKBONE SERIES

The Backbone series consists of moderately deep, well drained soils formed in moderately coarse or coarse textured eolian material, with or without a thin layer of residuum overlying limestone bedrock at a depth of 50 to 100 centimeters. Backbone soils are on convex ridges and back slopes on uplands. Slope ranges from 2 to 18 percent. Mean annual air temperature is about 8 degrees C. Mean annual precipitation is about 850 millimeters.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, mesic Mollic Hapludalfs

TYPICAL PEDON: Backbone sandy loam, on a west-facing, convex slope of 4 percent, in a cultivated field. (Colors are for moist soil unless otherwise stated.)

Ap--0 to 20 centimeters; very dark gray (10YR 3/1) sandy loam, gray (10YR 5/1) dry; weak fine granular structure; very friable; neutral; abrupt smooth boundary. (15 to 23 centimeters thick)

BE--20 to 43 centimeters; brown (10YR 4/3) and dark grayish brown (10YR 4/2) sandy loam; few streaks of very dark gray (10YR 3/1) from the Ap horizon; weak fine subangular blocky structure; very friable; neutral; clear smooth boundary. (15 to 25 centimeters thick)

Bt1--43 to 61 centimeters; brown (10YR 4/3) and dark yellowish brown (10YR 4/4) sandy loam; weak fine prismatic structure parting to weak fine and very fine subangular blocky; very friable; few distinct dark brown (10YR 3/3) clay films on faces of peds; neutral; clear wavy boundary. (15 to 40 centimeters thick)

2Bt2--61 to 76 centimeters; brown (10YR 4/3) and dark yellowish brown (10YR 3/4) clay loam; moderate fine subangular blocky structure; very firm; common distinct dark brown (7.5YR 3/2) clay films on faces of peds; about 5 percent small chert fragments; neutral; abrupt wavy boundary. (0 to 25 centimeters thick)

2R--76 centimeters; hard, fractured, limestone bedrock.

TYPE LOCATION: Major Land Resource Area (MLRA) 105-Northern Mississippi Valley Loess Hills, Winneshiek County, Iowa subset; about 1/2 mile north of Spillville; located about 1,700 feet west and 1,140 feet north of the southeast corner of section 18, T. 97 N., R. 9 W.; USGS Fort Atkinson topographic quadrangle; lat. 43 degrees 12 minutes 55.2 seconds N. and long. 91 degrees 56 minutes 56.8 seconds W., NAD 83.

RANGE IN CHARACTERISTICS:
Depth to bedrock--50 to 100 centimeters
Clay content in the particle-size control section (weighted average)--12 to 18 percent
Sand content in the particle-size control section (weighted average)--55 to 80 percent

A or Ap horizon:
Hue--10YR
Value--3
Chroma--1 or 2
Texture--sandy loam, fine sandy loam, or loamy sand
Clay content--5 to 18 percent
Reaction--moderately acid to neutral

BE or E horizon:
Hue--10YR
Value--4 or 5
Chroma--2 or 3
Texture--sandy loam, fine sandy loam, or loamy sand
Clay content--5 to 18 percent
Reaction--strongly acid to neutral

Bt horizon:
Hue--10YR
Value--3 to 5
Chroma--3 to 5
Texture--sandy loam
Clay content--12 to 18 percent
Reaction--strongly acid to neutral

2Bt horizon:
Hue--5YR, 7.5YR, or 10YR
Value--3 to 5
Chroma--3 to 6
Texture--clay loam, sandy clay loam, or clay
Clay content--32 to 42 percent
Rock fragment content--0 to 10 percent, mostly chert or limestone fragments
Reaction--moderately acid to neutral

Some pedons have a 2BC horizon that is very channery, very flaggy, extremely channery, or extremely flaggy. It is loam, clay loam, or sandy clay loam in the fine-earth fraction. This horizon is 0 to 25 centimeters thick.

COMPETING SERIES: These are the Billet, Brownchurch, Desker, Kingsley, Oronoco, and Ulster series.
Billett--do not have bedrock within 100 centimeters
Brownchurch--do not have bedrock within 100 centimeters
Desker--do not have bedrock within 100 centimeters
Kingsley--do not have bedrock within 100 centimeters
Oronoco--do not have bedrock within 100 centimeters
Ulster--do not have bedrock within 100 centimeters

GEOGRAPHIC SETTING:
Parent material--moderately coarse or coarse textured eolian material, with or without a thin layer of residuum overlying limestone bedrock at a depth of 50 to 100 centimeters
Landform--convex ridges and back slopes on uplands
Slope--2 to 18 percent
Elevation--200 to 400 meters above sea level
Mean annual air temperature--6 to 10 degrees C
Mean annual precipitation--735 to 965 millimeters
Frost-free period--145 to 205 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Marlean, Nordness, Rockton, and Winneshiek soils.
Marlean--are in landscape positions similar to those of the Backbone soils and have a rock fragment content of more than 35 percent in the particle-size control section
Nordness--are on shoulder slopes and have limestone bedrock within 50 centimeters
Rockton--are in landscape positions similar to those of the Backbone soils and have a clay content that averages more than 18 percent in the particle-size control section
Winneshiek--are in landscape positions similar to those of the Backbone soils and have a clay content that averages more than 18 percent in the particle-size control section

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class--well drained--a frequently saturated zone does not occur within a depth of 1.8 meters during the wettest periods of years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Saturated hydraulic conductivity--10 to 100 micro meters per second in the eolian material and 1.0 to 10 micrometers per second in the residuum

USE AND VEGETATION:
More gently sloping areas are cultivated. Corn, small grains, and legume hay are the principal crops. Land use of more strongly sloping areas consists of permanent pasture or woodland. The native vegetation is oak savanna, deciduous trees (oak and hickory) and big bluestem, little bluestem, switchgrass, and other grasses of the tall grass prairie.

DISTRIBUTION AND EXTENT:
Physiographic Division--Interior Plains
Physiographic Province--Central Lowland
Physiographic sections--Dissected till plains, Till plains, and Wisconsin driftless section
MLRAs--Southern Wisconsin and Northern Illinois Drift Plain (95B), Eastern Iowa and Minnesota Till Prairies (104), and Northern Mississippi Valley Loess Hills (105)
LRRs M and K; northeastern Iowa, northern Illinois, and southern Minnesota
Extent--small

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana

SERIES ESTABLISHED: Bremer County, Iowa, 1965

REMARKS:
Particle-size control section--the zone from a depth of 43 to 76 centimeters;
series control section--the zone from the surface to a depth of 76 centimeters.

Diagnostic horizons and features recognized in this pedon include:
ochric epipedon--the zone from the surface to a depth of 43 centimeters (Ap and BE horizons);
argillic horizon--the zone from a depth of 43 to 76 centimeters (Bt1 and 2Bt2 horizons);
udic moisture regime.

Cation-exchange class is inferred from lab data from similar soils in the surrounding area.

Taxonomy version--Keys to Taxonomy, tenth edition, 2006.

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National Cooperative Soil Survey
U.S.A.