LOCATION NUNN CO+MT NE SD WYEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Aridic Argiustolls
TYPICAL PEDON: Nunn clay loam - grassland. (Colors are for dry soil unless otherwise noted)
A--0 to 6 inches; grayish brown (10YR 5/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; soft, very friable; neutral (pH 7.2); clear smooth boundary. (4 to 8 inches thick)
BA--6 to 10 inches; grayish brown (10YR 5/2) clay loam, very dark grayish brown (10YR 3/2) moist; weak medium prismatic structure parting to moderate medium subangular blocky; hard, very friable, sticky and plastic; few faint clay films on faces of peds; neutral (pH 7.2); clear smooth boundary. (0 to 6 inches thick)
Bt--10 to 24 inches; pale brown (10YR 6/3) clay loam, brown (10YR 4/3) moist; moderate medium and coarse prismatic structure parting to moderate medium subangular blocky; very hard, firm, very sticky and very plastic; many distinct clay films on faces of peds; slightly alkaline (pH 7.6); clear smooth boundary. (6 to 24 inches thick)
Btk--24 to 29 inches; pale brown (10YR 6/3) clay loam, brown (10YR 5/3) moist; weak medium subangular blocky structure; very hard, firm, very plastic; few faint clay films on faces of peds; visible calcium carbonate occurring as small concretions; strongly effervescent; moderately alkaline (pH 8.0); gradual smooth boundary. (0 to 10 inches thick)
Bk1--29 to 47 inches; light yellowish brown (10YR 6/4) clay loam, dark yellowish brown (10YR 4/4) moist; massive; very hard, firm, sticky and plastic; visible calcium carbonate occurring as concretions, thin seams and streaks; strongly effervescent; moderately alkaline (pH 8.2); gradual smooth boundary. (6 to 20 inches thick)
Bk2--47 to 60 inches; light yellowish brown (2.5Y 6/3) clay loam, light olive brown (2.5Y 5/3) moist; massive; very hard, firm, sticky and plastic; some visible calcium carbonate but less than in the horizon above; slightly effervescent; moderately alkaline (pH 8.2).
TYPE LOCATION: Larimer County, Colorado; 1 mile east and 1/2 mile south of the Harmony School near the east 1/4 corner of Sec. 5, T. 6 N., R. 68 W.
RANGE IN CHARACTERISTICS: Mean annual soil temperature at depth of 20 inches is 47 to 54 degrees F, and mean summer temperature is 59 to 79 degrees F. The mollic epipedon is 7 to 19 inches thick, depth to lime is 10 to 30 inches, and the solum is 16 to 46 inches thick. Organic carbon in the mollic epipedon ranges from .8 to 3 percent. The soil is typically 90 to 100 percent base-saturated. Rock fragments are typically less than 5 percent and range from 0 to 15 percent. The soil temperature at depth of 20 inches is 41 degrees F or warmer for about 200 to 240 days. The soils are moist in some part of the moisture control section for about 56 to 152 days while the soil temperature is 41 degrees F or above.
The A horizon has hue of 5Y to 7.5YR, value of 4 or 5, 2 or 3 moist, and chroma of 1 to 3. Usually it has granular or crumb structure but the structure is subangular blocky in some pedons. This horizon is soft or slightly hard. It is slightly acid to slightly alkaline.
The Bt horizon has hue of 5Y to 7.5YR, value of 3 to 7, 2 to 6 moist, and chroma of 2 to 5. It is typically clay, silty clay loam or clay loam and has 35 to 50 percent clay, 15 to 45 percent silt, and 15 to 45 percent sand with more than 15 percent, being fine sand or coarser. Some pedons have sandy clay loam textures in the lower parts of the argillic layer, however, the weighted clay average is greater than 35 percent in the control section. It is slightly acid to moderately alkaline. CEC of the Bt horizon ranges from 60 to 90 millequivalents per 100 grams of clay.
The Bk or C horizon has hue of 5Y to 7.5YR, value of 5 to 7, 4 to 6 moist, and chroma of 2 to 4. They are typically clay loam with more than 28 percent clay, however, where the C horizon has less than 28 percent clay it contains more than 15 percent fine or coarser sand and has a texture of sandy clay loam, loam or sandy loam. These horizons are slightly alkaline to strongly alkaline and have 4 to 15 percent calcium carbonate equivalent.
COMPETING SERIES: These are Ashfork, Bethune, Blackpipe, Boneek, Boquillas, Chapin, Collbran, Collide, Emigrant, Huggins, Kube, Leyden, Loma, Nuncho, Querc, Rednun, Richfield, Ryus, Savo, Showlow, Standley, Thunderbird, Weld and Wormser series. Ashfork, Bethune, Chapin, Thunderbird and Wormser soils have lithic contact at depths of 20 to 40 inches. Blackpipe, Boquillas, Emigrant, Huggins, Leyden and Querc soils have paralithic contact at depths of 20 to 40 inches. Boneek, Kube, Richfield, Savo and Weld soils have less than 15 percent fine sand or coarser in the Bt horizon. Collbran, Collide, Loma and Rednun soils have hues redder than 7.5YR in the Bt. Ryus soils are calcareous throughout. Showlow soils have a calcic horizon. Standley soils have greater than 15 percent coarse fragments in the Bt horizon. The Nuncho soils have soil temperatures at 20 inches that are greater than 41 degrees F. for less than 200 days.
GEOGRAPHIC SETTING: The Nunn soils are on terraces or alluvial fans, or in drainageways. Slope gradients range from 0 to 25 percent. The soils formed in mixed alluvium. At the type location the average annual precipitation is 13 inches, 9 inches of which falls during the months of April through September. Mean annual air temperature is 47 to 53 degrees F, and an average summer temperature is 67 degrees F. The frost-free period is 120 to 210 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Weld soils and the Fort Collins, Platner and Satanta soils. Fort Collins and Satanta soils have less than 35 percent clay in the Bt horizon. Platner soils have an abrupt textural boundary between the A and B horizons.
DRAINAGE AND PERMEABILITY: Well drained; negligible to very high runoff depending on slope; moderately slow or slow permeability. Some small areas are seasonally wet due to seepage from irrigation.
USE AND VEGETATION: A large percentage of the Nunn soils are now under irrigation where they are used for alfalfa, sugar beets, potatoes, small grains, corn and truck crops. Some dryland areas are cropped principally to winter wheat. Native vegetation is blue grama, buffalograss, needlegrass and wheatgrass.
DISTRIBUTION AND EXTENT: Eastern Colorado, southeastern Montana and southeastern Wyoming. The series is of large extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: The Greeley Area, Colorado, 1929.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to a depth of 10 inches (A and BA horizons); argillic horizon - the zone from 10 to 29 inches (Bt and Btk horizons).