LOCATION WALNUT GROVE MNTentative Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Aquic Hapludolls
TYPICAL PEDON: Walnut Grove clay loam with a plane slope of about 2 percent on a ground moraine in a cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 20 centimeters (0 to 8 inches); black (10YR 2/1) clay loam, very dark gray (10YR 3/1) dry; weak very fine and fine subangular blocky structure; friable; about 4 percent gravel; moderately acid; abrupt smooth boundary.
A--20 to 36 centimeters (8 to 14 inches); black (10YR 2/1) clay loam, very dark gray (10YR 3/1) dry; weak fine subangular blocky structure; friable; about 3 gravel; slightly acid; clear wavy boundary. [Combined thickness of the A horizon range from 15 to 61 centimeters (10 to 20 inches).]
Bw1--36 to 46 centimeters (14 to 18 inches); dark grayish brown (2.5Y 4/2) clay loam; very dark grayish brown crushed; moderate very fine subangular blocky structure; friable; very dark gray (10YR 3/1) worm casts; about 3 percent gravel; neutral; clear wavy boundary.
Bw2--46 to 71 centimeters (18 to 28 inches); olive brown (2.5Y 4/4) clay loam; very dark grayish brown crushed; moderate fine and medium subangular blocky structure; friable; few fine faint grayish brown (2.5Y 5/2) Fe depletions; about 3 percent gravel; neutral; clear smooth boundary. [Combined thickness of Bw horizons 15 to 56 centimeters (6 to 22 inches).]
Bk--71 to 99 centimeters (28 to 39 inches); light olive brown (2.5Y 5/4) clay loam; weak fine and very fine subangular blocky structure; firm; many fine faint grayish brown (2.5Y 5/2) Fe depletions; about 4 percent gravel; strongly effervescent; moderately alkaline; gradual smooth boundary. [8 to 41 centimeters (3 to 16 inches) thick.]
BC1--99 to 152 centimeters (39 to 60 inches); light yellowish brown (2.5Y 6/4) clay loam; moderate coarse prismatic structure parting to moderate medium angular blocky; firm; few concentrations of Fe & Mn; many coarse distinct grayish brown (2.5Y 5/2) Fe depletions; about 8 percent gravel; strongly effervescent; moderately alkaline. gradual wavy boundary.
BC2--152 to 203 centimeters (60 to 80 inches); light olive brown (2.5Y 5/4) clay loam; moderate coarse prismatic structure parting to moderate medium angular blocky; firm; few concentrations of Fe & Mn; many coarse distinct gray (2.5Y 6/1) Fe depletions; about 8 percent gravel; strongly effervescent; moderately alkaline.
TYPE LOCATION: Redwood County, Minnesota; about 1.4 miles south of Walnut Grove; about 561 meters(1,870 feet) south and 105 meters (350 feet) east of the northwest corner of sec. 31, T. 109 N., R. 38 W.; USGS Walnut Grove quadrangle, lat. 44 degrees 12 minutes 20 seconds N., Long. 95 degrees 28 minutes 20 seconds W., NAD 27.
RANGE IN CHARACTERISTICS: The depth to free carbonates ranges from 51 to 102 centimeters (20 to 40 inches). Rock fragments by volume range from 1 to 8 percent throughout. The mollic epipedon ranges from 36 to 61 centimeters (10 to 20 inches) in thickness.
The A horizon has hue of 10YR, value of 2 or 3 and chroma of 1 or 2. It typically is clay loam, silty clay loam or loam. Reaction is slightly acid to neutral.
An AB or BA horizon as thick as 20 centimeters (8 inches) is in some pedons. They have similar properties of the A and B horizons.
The Bw horizon has hue of 10YR or 2.5Y, value of 3 to 5, and chroma of 2 to 4. It is loam or clay loam, but sandy clay loam is within the range. It is friable. It has a few dark concretions or stains (oxides) in the lower part in some pedons. Reaction is slightly acid to neutral. Some pedons have Bt horizons that do not make the increase of 1.2 percent B/A clay ratio.
The Bk horizon has hue of 10YR or 2.5Y, value of 5 or 6, and chroma of 2 to 4. It is loam or clay loam. It is slightly alkaline or moderately alkaline with 15 to 25 percent calcium carbonate equivalent.
The BC or C horizon has a hue of 10YR or 2.5Y, value of 5 or 6, and chroma of 2 to 4. It is loam or clay loam. It is slightly alkaline or moderately alkaline with 10 to 20 percent calcium carbonate equivalent. The moist bulk density ranges from 1.65 to 1.75 g/cc.
COMPETING SERIES: These are the Arkton, Crippin, Floyd, Fostoria, Kensett, Merton, Nicollet, Ottosen, Readlyn, Snider, Stone and Wilmonton soils in the same family. Arkton soils have carbonates above 51 centimeters (20 inches). Crippin soils have carbonates beginning at depths of 25 centimeters (10 inches) or less. Floyd soils have thicker sola and coarser textured layers in the B horizons. Fostoria soils have loam sola and silt loam C horizons moderate permeability and friable consistence throughout. Kensett soils have hard limestone within depths of 102 centimeters (40 inches). Merton and Readlyn soils have thicker and acid sola. Ottosen soils have friable B and C horizons and moderate permeability in the C horizon within depths of 102 centimeters (40 inches) below the surface. Nicollet soils typically have friable C horizons. Snider soils formed in loamy alluvium on benches. Stone soils have a lithic contact between102 and 152 centimeters (40 and 60 inches) of the surface. Wilmonton soils have more than 45 percent silt in the A and Bw horizons.
GEOGRAPHIC SETTING: Walnut Grove soils have slightly concave through slightly convex slopes on ground moraines. The Walnut Grove formed in calcareous glacial till is firm with depth. Mean annual temperature is approximately 7 to 8 degrees C (45 to 47 degrees F.), and mean annual precipitation is about 56 to 69 centimeters (22 to 27 inches). Frost free days range from 124 to 172. The elevation above sea level is 270 to 480 meters (900 to 1,600 feet).
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Annton, North Twin, Pell Creek, and Storden soils which are members of a hydrosequence with Walnut Grove soils. The moderately well drained North Twin soils, and well drained Annton and Storden soils commonly are on more sloping terrain. The poorly drained Pell Creek soils are on nearby less sloping areas.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Somewhat poorly drained. Surface runoff is low. Saturated hydraulic conductivity, measured in cm per hour, is .5 to 1.5 (.2 to .6 in). The apparent seasonal high saturation is at a depth of 46 centimeters (1.5 feet) at some time from March through June and October through November in normal years. Perched conditions may exist as the wetting comes in contact with the firm till substratum.
USE AND VEGETATION: Largely cropped to corn, legume hay, small grains, and soybeans. Native vegetation is tall grass prairie.
DISTRIBUTION AND EXTENT: MLRA-103, Coteau des Prairies "bench". Southwestern Minnesota. Series is moderately extensive.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES PROPOSED: Redwood County, Minnesota, 2005.
REMARKS: Diagnostic horizons and properties recognized in this pedon are: mollic epipedon - the zone from the surface to a depth of 36 centimeters (14 inches) (Ap and A horizons); cambic horizon - the zone from 36 to 71 (14 to 28 inches) and 99 to 203 centimeters (39 to 80 inches) (Bw1, Bw2, BC1, and BC2 horizons); calcic horizon - the zone from 71 to 99 centimeters (28 to 39 inches) (Bk horizon); Aquic moisture regime.
This soil replaces Wilmonton soils that were correlated on the "bench"
The BC horizon is defined by having prismatic primary structure parting to angular or subangular blocky. This structure is evident in pits and cutbanks and rarely observed by boring tubes.