LOCATION SAC IA+MNEstablished Series
The Sac series consists of very deep, moderately well drained, moderately to moderately slowly permeable soils formed in loess and the underlying glacial till on moraines. Slope ranges from 0 to 14 percent. Mean annual air temperature is about 47 degrees F. Mean annual precipitation is about 26 inches.
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Hapludolls
TYPICAL PEDON: Sac silty clay loam on a convex 3 percent slope in a cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 6 inches; black (10YR 2/1) silty clay loam, very dark gray (10YR 3/1) dry; weak fine granular structure; friable; common very fine and fine roots; common very fine and fine pores; slightly acid; clear smooth boundary.
A--6 to 12 inches; very dark brown (10YR 2/2) silty clay loam, very dark grayish brown (10YR 3/2) dry; weak medium granular structure; friable; common very fine and fine roots; common very fine and fine pores; slightly acid; gradual smooth boundary. (combined thickness of the A horizons is 10 to 20 inches)
AB--12 to 16 inches; dark brown (10YR 3/3) silty clay loam, brown (10YR 4/3) dry; weak fine subangular blocky structure parting to weak medium granular; friable; common very fine and fine roots; common very fine and fine pores; many distinct very dark grayish brown (10YR 3/2) organic coats on faces of peds; slightly acid; gradual smooth boundary. (0 to 8 inches thick)
Bw1--16 to 24 inches; brown (10YR 4/3) silty clay loam; weak fine subangular blocky structure; friable; common very fine roots; common very fine and fine pores; very few distinct very dark grayish brown (10YR 3/2) organic coats on faces of peds; neutral; gradual smooth boundary.
Bw2--24 to 32 inches; brown (10YR 4/3) silty clay loam; weak fine and medium subangular blocky structure; friable; common very fine and fine pores; common fine and medium distinct dark yellowish brown (10YR 4/6) redox concentrations; neutral; abrupt wavy boundary. (combined thickness of the Bw horizons is 10 to 24 inches)
2Bw3--32 to 38 inches; dark yellowish brown (10YR 4/4) loam; weak medium subangular blocky structure; friable; common very fine and fine pores; few faint patchy brown (10YR 4/3) coats; common fine prominent grayish brown (2.5Y 5/2) redox depletions; 3 percent rounded cobbles; strongly effervescent; slightly alkaline; abrupt wavy boundary. (3 to 15 inches thick)
2Bk1--38 to 46 inches; yellowish brown (10YR 5/4) clay loam; weak fine prismatic structure; firm; common very fine and fine pores; common fine and medium very pale brown (10YR 8/2) carbonate masses; common fine distinct grayish brown (10YR 5/2) redox depletions; 2 percent rounded mixed cobbles and 2 percent angular shale pebbles; strongly effervescent; moderately alkaline; clear wavy boundary.
2Bk2--46 to 55 inches; yellowish brown (10YR 5/6) clay loam; weak fine prismatic structure; firm; common very fine and fine pores; few prominent patchy yellowish red (5YR 4/6) iron stains; common fine and medium very pale brown (10YR 8/2) carbonate masses; common fine distinct yellowish brown (10YR 5/8) redox concentrations and common fine prominent grayish brown (2.5Y 5/2) redox depletions; 2 percent rounded mixed cobbles and 3 percent rounded mixed pebbles; strongly effervescent; moderately alkaline; clear wavy boundary. (combined thickness of the Bk horizons is 12 to 40 inches)
2C1--55 to 70 inches; yellowish brown (10YR 5/6) clay loam; massive; firm; common very fine and fine pores; few fine and medium very pale brown (10YR 8/2) carbonate masses; common fine prominent grayish brown (2.5Y 5/2) redox depletions; 2 percent well rounded mixed cobbles, 2 percent well rounded mixed gravel and 3 percent angular shale fragments; strongly effervescent; moderately alkaline; gradual smooth boundary.
2C2--70 to 80 inches; yellowish brown (10YR 5/4) clay loam; massive; firm; common very fine and fine pores; few fine and medium very pale brown (10YR 8/2) soft carbonate nodules; common fine and medium prominent yellowish brown (10YR 5/8) and many fine and medium prominent grayish brown (2.5Y 5/2) redox depletions; 2 percent rounded mixed cobbles and 2 percent rounded mixed pebbles; strongly effervescent; moderately alkaline
TYPE LOCATION: Clay County, Iowa; about 2 miles west and 2 miles south of Royal; 1,700 feet north and 400 feet west of the southeast corner of sec. 16, T.95 N., R. 38 W., USGS Royal, Iowa quadrangle; lat. 43 degrees 02 minutes 39 seconds N., long. 95 degrees 19 minutes 45 seconds W.; NAD27.
RANGE IN CHARACTERISTICS: The thickness of the mollic epipedon is 10 to 20 inches. Clay content typically is highest in the A horizon and decreases with depth. Carbonates are present within a few inches of the upper boundary of the glacial till. The loess typically is 24 to 36 inches thick but ranges from 20 to 40 inches in thickness. The part of the 10- to 40-inch control section formed in loess commonly averages less than 5 percent fine sand and coarser, but in some pedons contains up to 10 percent. The underlying glacial till averages between 20 and 35 percent fine sand and coarser, 25 to 32 percent clay, 1 to 10 percent rock fragments from pebble to cobble size and typical moist bulk density from 1.6 to 1.8 g/cc. The 10 to 40 inch control section averages between 8 and 15 percent fine sand and coarser. Some pedons have a coarse textured layer at the contact of the loess and glacial till that ranges from 3 to 8 inches in thickness.
The Ap and A horizons have hue of 10YR, value of 2 or 3 and chroma of 1 or 2. The texture is typically silty clay loam. The reaction is moderately acid or slightly acid.
Some pedons have an AB or BA horizon with hue of 10YR, value of 2 or 3, and chroma of 2 or 3. The texture and reaction are similar to the A horizon.
The Bw horizon has hue of 10YR or 2.5Y, value of 4 or 5, and chroma of 3 or 4. The texture is typically silty clay loam but may grade to silt loam in the lower part. The reaction is slightly acid or neutral. Darker colored coatings on faces of peds are common. Redox features are commonly present in this horizon.
The 2Bw horizon has hue of 10YR, value of 4 or 5, and chroma of 3 or 4. The texture is loam or clay loam. The reaction is slightly acid through slightly alkaline. Redox features are commonly present in this horizon.
The 2Bk horizon has hue of 10YR, value of 4 or 5, and chroma of 3 or 4. The texture is loam or clay loam. The reaction is slightly alkaline or moderately alkaline. Redox features are commonly present in this horizon. The calcium carbonate equivalent ranges from 15 to 30 percent.
The 2C or 2BC horizons have hue of 10YR, value of 4 or 5, and chroma of 3 through 6. The texture is loam or clay loam and typically has a firm, moist consistency. The reaction is slightly alkaline or moderately alkaline. Redox features are commonly present in this horizon. The calcium carbonate equivalent ranges from 10 to 25 percent.
COMPETING SERIES: This is the Crooksford series. This soil formed in a silty mantle overlying friable glacial till with typical moist bulk density of 1.4 to 1.6 g/cc.
GEOGRAPHIC SETTING: Sac soils typically are on convex slopes on the loess-mantled early Wisconsin (Tazewell) or Kansan till plain. Slope gradients range from 0 to 14 percent. The drainage pattern is usually fairly well established and slopes commonly are long. The soils developed from loess of low sand content and firm glacial till. Mean annual air temperature is approximately 45 to 48 degrees F. Mean annual precipitation is approximately 24 to 28 inches. The frost free days range from 150 to 860. The elevation above sea level ranges from 1100 to 1800 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Afton, Annieville (proposed), Galva, Marcus and Primghar soils which form a hydro sequence on the landscape. The poorly drained Afton and Marcus soils are in swales and toeslopes. The moderately well drained Annieville soils have similar positrons but have a thicker loess mantle. The well drained Galva soils are on similar positions and are better drained. The somewhat poorly drained Primghar soils are lower lying on the landscape.
DRAINAGE AND PERMEABILITY: Moderately well drained. Surface runoff is low to medium. Permeability is moderate to moderately slow. Seasonal high saturation occurs at depths as high as 30 to 40 inches from April to June in normal years. It appears that the discontinuity of materials (loess over firm till) perches water for transitory periods.
USE AND VEGETATION: Largely cropped to corn, soybeans, small grain, and legume hay. Native vegetation is tall grass prairie.
DISTRIBUTION AND EXTENT: Northwest Iowa and southwest Minnesota. Sac soils are of large extent.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Clay County, Iowa, 1970.
REMARKS: Diagnostic horizons and features recognized in this soil are: Mollic epipedon - the zone from 0 to 16 inches (Ap, A, AB); cambic horizon - the zone from 16 to 55 inches (Bw1, Bw2, 2Bw3, 2Bk1, 2Bk2); Oxyaquic subgroup based on having saturation above a depth of 40 inches and is supported by the presence of redox features.
This soil was previously considered as well drained. Field evidence of saturation and redox patterns support the current concept of moderately well drained.
ADDITIONAL DATA: Laboratory data are available for the typical pedon. See Soil Survey Investigations Report No. 3, Soil Survey Data and Descriptions for Some Soils of Iowa, Soil Conservation Service, U. S. Department of Agriculture in cooperation with Iowa Agriculture and Home Economics Experiment Station.