LOCATION DUNCAN AZ+NMEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, thermic Typic Natridurids
TYPICAL PEDON: Duncan loam - grassland. (Colors are for dry soil unless otherwise noted.)
En1--0 to 2 inches; light gray (10YR 7/2) loam, dark grayish brown (10YR 4/2) moist; weak thick platy structure; slightly hard, friable, slightly sticky, slightly plastic; many fine and medium roots; common fine, medium and coarse vesicular and tubular pores; slightly effervescent; strongly alkaline (pH 8.8); abrupt smooth boundary. (0 to 2 inches thick)
En2--2 to 5 inches; light gray (10YR 7/2) loam, dark grayish brown (10YR 4/2) moist; massive; slightly hard, very friable, slightly sticky, slightly plastic; many fine and medium roots; common very fine, fine and medium vesicular and few tubular pores; slightly effervescent; strongly alkaline (pH 8.8); abrupt smooth boundary. (2 to 4 inches thick)
Btkn1--5 to 11 inches; brown (10YR 5/3) clay, dark brown (10YR 3/3) moist; moderate medium prismatic parting to strong medium and coarse angular and subangular blocky structure; hard, friable, sticky, plastic; many fine and medium and few coarse roots; common moderately thick clay films on faces of peds; slightly effervescent; few fine very pale brown (10YR 8/2) soft lime masses; light brownish gray (10YR 6/2) moist; very strongly alkaline (pH 9.6); clear wavy boundary. (5 to 8 inches thick)
Btkn2--11 to 19 inches; light brown (7.5YR 6/4) clay, brown (7.5YR 4/4) moist; moderate medium prismatic structure; hard, friable, sticky, plastic; many fine and medium and few coarse roots; few fine tubular pores; common thin clay films on faces of peds; strongly effervescent; few fine very pale brown (10YR 8/2) soft lime masses, light brownish gray (10YR 6/2) moist; very strongly alkaline (pH 9.6); clear wavy boundary. (7 to 10 inches thick)
Btkn3--19 to 31 inches; pinkish gray (7.5YR 7/2) clay, brown (7.5YR 5/4) moist; moderate fine subangular blocky structure; very hard, friable, sticky, very plastic; common fine and medium and few coarse roots; few very fine tubular pores; common thin clay films on faces of peds; strongly effervescent; few fine very pale brown (10YR 8/2) soft lime masses, light brownish gray (10YR 6/2) moist; very strongly alkaline (pH 9.6); clear wavy boundary. (4 to 12 inches thick)
Btkn4--31 to 35 inches; pinkish gray (7.5YR 7/2) clay, brown (7.5YR 5/4) moist; moderate fine and medium subangular blocky structure; very hard, friable, sticky, plastic; few medium roots; common very fine tubular pores; few thin clay films on faces of peds; violently effervescent; many medium and large very pale brown (10YR 8/2) soft lime masses, pale brown (10YR 6/3) moist; very strongly alkaline (pH 9.6); abrupt smooth boundary. (2 to 4 inches thick)
Bkqnm--35 to 40 inches; very pale brown (10YR 7/3) and light yellowish brown (10YR 6/4) indurated duripan, yellowish brown (10YR 5/4) and brown (7.5YR 5/4) moist; massive; extremely hard; few fine and coarse roots in fractures; few very fine vesicular pores; violently effervescent; very strongly alkaline (pH 9.6); clear smooth boundary. (4 to 14 inches thick)
2Btkqnb--40 to 46 inches; mottled reddish brown (5YR 5/4) and pinkish white (7.5YR 8/2) gravelly clay loam, reddish brown (5YR 4/4) and light brown (7.5YR 6/4) moist; moderate medium subangular blocky structure; very hard, friable, sticky, plastic; few fine tubular pores; common thin clay films on faces of peds; strongly effervescent; many medium and large pinkish white (7.5YR 8/2) soft lime masses and mottles, common durinodes; very strongly alkaline (pH 9.6); clear wavy boundary. (6 to 15 inches thick)
2Btkzb--46 to 60 inches; reddish brown (5YR 5/4) clay loam, reddish brown (5YR 4/4) moist; moderate medium subangular blocky structure; hard, friable, sticky, plastic; common very fine and fine tubular pores; common thin clay films on faces of peds and in pores; slightly effervescent; few fine pinkish white (7.5YR 8/2) lime masses and salt crystals; moderately alkaline (pH 8.4).
TYPE LOCATION: Cochise County, Arizona; 100 feet north and 2,200 feet west of SW corner sec. 23, T.13S., R.24E.
RANGE IN CHARACTERISTICS:
Depth to the Bkqnm horizon: about 35 inches but range from 20 to 40 inches.
The average annual soil temperature ranges from 60 degrees to 65 degrees F.
Soil moisture: Typic aridic moisture regime
E1 horizon
Hue: dominantly of 10YR but ranging to 7.5YR
Value: 5 through 7 dry, 3 or 4 moist
Chroma: less than 4
texture: sandy loam through loam to silt loam with clay loam in plowed areas.
E2 horizon
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 1 through 3
Effervescence: noneffervescent or effervescent
Reaction: neutral (pH 7.0) to strongly alkaline (pH 9.0).
B horizon
Hue: 10YR or 7.5YR
Value: 4 through 7 dry, 3 through 5 moist
Chroma: 2 through 4
Texture: clay loam or clay with more than 35 percent clay
Effervescence: noneffervescent in its upper portion in some pedons but ranges to effervescent throughout
Calcium carbonate: filaments and segregations of calcium carbonate
Reaction: strongly alkaline (pH 8.8) to very strongly alkaline (pH 10.0)
Gypsum: Small amounts of amorphous or crystalline gypsum are present in the lower portion of the B or upper portion of the C horizon in some pedons.
The horizons below the Bkqnm are variable ranging from buried argillic horizons to weakly cemented calcareous materials or gleyed lacustrine materials.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Duncan soils are on level to nearly level alkali flats bordering playas. Slopes range from 0 to .5 percent, but may have uneven microrelief due to wind shifting of the surface soil. The soils formed in old lake and fan deposited alluvium from mixed sources including rhyolite, andesite, quartzite, granite, and limestone. Duncan soils are at elevations of 3,800 to 4,300 feet in a warm, semiarid continental climate. The mean annual temperature ranges from 58 degrees to 66 degrees F. The frost-free period ranges from 155 to 220 days. The annual precipitation ranges from 10 to 12 inches and occurs as thundershowers from July through September and as gentle fall and winter rains. The months of May and June are usually warm and dry.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Cogswell, Crot, Frye, Gothard, and McAllister soils and the Comoro, Elfrida, Karro, and Stewart soils. Comoro, Elfrida, Karro, and Stewart soils all lack argillic horizons.
DRAINAGE AND PERMEABILITY: Well-drained; very slow runoff; very slow permeability.
USE AND VEGETATION: Used mainly for rangeland. Native vegetation is alkali sacaton, saltgrass, tobosa, scattered mesquite, annual weeds and grasses with many barren areas.
DISTRIBUTION AND EXTENT: Southeastern Arizona and southwestern New Mexico adjacent to playas and intermittent streams. The series is moderately extensive. MLRA 41.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Sulphur Spring Valley Area, Arizona, 1942.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Albic horizon - The zone from 0 to 5 inches (E horizons)
Argillic horizon The zone from 5 to 35 inches (Btkn horizons)
Natric horizon - The zone from 5 to 19 inches (Btkn1 & Btkn2 horizons)
Duripan The zone from 35 to 40 inches (Bkqnm horizon)
Classified according to Keys to Soil Taxonomy Tenth Edition, 2006
The Duncan soils were formerly classified as Solonetz soils.