LOCATION FALFA COEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Aridic Haplustalfs
TYPICAL PEDON: Falfa clay loam, irrigated cropland. (Colors are for dry soil unless otherwise noted.)
Ap--0 to 9 inches; reddish brown (5YR 5/3) clay loam, reddish brown (5YR 4/3) moist; moderate medium granular structure; hard, firm, sticky, and slightly plastic; neutral (pH 7.0); clear smooth boundary. (7 to 11 inches thick)
BA--9 to 14 inches; reddish brown (5YR 5/3) clay loam, reddish brown (5YR 4/3) moist; moderate medium subangular blocky structure parting to moderate medium granular; hard, firm, sticky, and slightly plastic; common, distinct clay films on faces of peds; neutral (pH 7.0); clear smooth boundary. (3 to 8 inches thick)
Bt1--14 to 24 inches; reddish brown (5YR 5/3) clay, reddish brown (5YR 4/4) moist; moderate, medium prismatic structure parting to moderate medium angular and subangular blocks; very hard, very firm, very sticky and plastic; many prominent clay films on faces of peds and in pores; slightly alkaline (pH 7.4); clear smooth boundary. (7 to 13 inches thick)
Bt2--24 to 34 inches; reddish brown (5YR 5/4) clay, reddish brown (5YR 4/4) moist; moderate medium prismatic structure parting to moderate, medium angular blocks and subangular blocks; very hard, very firm, very sticky and plastic; many prominent clay films on faces of peds and in pores; slightly alkaline (pH 7.6); clear smooth boundary. (7 to 14 inches thick)
Btk--34 to 57 inches; light reddish brown (5YR 6/4) clay loam, reddish brown (5YR 5/4) moist; moderate, medium prismatic structure parting to moderate medium angular blocks; very hard, firm, very sticky and plastic; many prominent clay films on faces of peds and in pores; visible secondary carbonate as concretions, thin seams and streaks, and as coatings on peds; violently effervescent; moderately alkaline (pH 8.2); gradual smooth boundary. (19 to 27 inches thick)
BCk--57 to 60 inches; yellowish red (5YR 5/6) clay loam, yellowish red (5YR 5/6) moist; weak medium subangular blocky structure; hard, firm, and sticky; common distinct clay films on faces of peds; strongly effervescent in spots; moderately alkaline (pH 8.0).
TYPE LOCATION: La Plata County, Colorado; approximately 2,000 feet south, 370 feet east of the Northwest corner of Section 29, T. 34 N., R. 9 W. U.S.G.S. Loma Linda quad.; Lat. 37 degrees, 09 minutes, 50 seconds N.; and Long. 107 degrees, 51 minutes, 22 seconds W.
RANGE IN CHARACTERISTICS:
Soil moisture regime: Ustic bordering on aridic. The moisture control section is dry for 15 consecutive days from May 15 to July 15 when the soil temperature at 20 inches is greater than 41 degrees F. It is not dry in all parts of the moisture control section for at least 45 consecutive days following the summer solstice to October 20, and for at least 90 cumulative days during the period. Driest in May and June.
Mean annual soil temperature: 47 to 55 degrees F.
Mean summer soil temperature: 60 to 68 degrees F.
Depth to calcareous material: 20 to 40 inches
Thickness of the solum: exceeds 40 inches
Organic carbon content: .5 to 2 percent and decreases uniformly with increasing depth
Cracking: When dry, cracks develop that are typically less than .4 inches wide, less than 12 inches long, and that do not extend to the surface or the base of any Ap horizon
Total extensibility of the soil above 40 inches is normally less than 2.4 inches. A large portion of the sand fraction is very fine sand. Rock fragments range from 0 to 10 percent in the solum and C horizon but are normally less than 1 percent.
A horizon
Hue: 2.5YR through 7.5YR
Value: 4 through 6 dry, 3 or 4 moist
Chroma: 3 or 4 (when the value is as dark as 5 dry and 3 moist, the chroma is 4)
Structure: It usually has granular structure, but has subangular blocky structure in some pedons
Reaction: neutral or slightly alkaline.
Bt horizon
Hue: 5YR through 10R
Value: 5 through 7 dry, 4 through 6 moist
Chroma: 3 through 6
Texture: clay, silty clay, or clay loam
Clay content: 35 to 50 percent
Silt content: 20 to 55 percent
Sand content: 10 to 40 percent sand with less than 15 percent being fine or coarser sand
Structure: This horizon usually has prismatic structure and has subangular or angular blocky secondary structure
Reaction: neutral or slightly alkaline in the upper part and moderately alkaline in the lower part
BCk horizon
Hue: 5YR through 10R
Value: 5 through 7 dry, 4 through 6 moist
Chroma: 4 through 8
Texture: clay loam or loam
Clay content: less than 35 percent clay
COMPETING SERIES: These are the Baca, Hesper, Leiter, Manzanst, Norrest, and Ulmet series. These soils are all in the Western Great Plains Range and Irrigated Region (LRR-G) and are more moist in May and June.
GEOGRAPHIC SETTING: The Falfa soils are on upland mesas and benches. Slopes typically range from 0 to 12 percent. The soil formed in thick calcareous reddish brown eolian materials derived from redbed deposits. Elevation ranges from 6,000 to 7,200 feet. The mean annual precipitation ranges from 15 to 18 inches and is fairly evenly distributed throughout the year with about half the precipitation falling between April and September. May and June are the driest months. PE Index is about 45 at the type location and ranges from 30 to 50 for the series. Mean annual temperature ranges from 45 to 50 degrees F., and mean summer temperature ranges from 60 to 68 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arboles and Simpatico soils. Simpatico series are fine, silty. Arboles series has hue of 7.5 YR or yellower throughout.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; slow permeability.
USE AND VEGETATION: Used as native pastureland or for irrigated and dry cropland. Native vegetation is mainly pinon, juniper, sagebrush, blue grass, western wheatgrass, Indian ricegrass, gambel oak, bitterbrush, and serviceberry.
DISTRIBUTION AND EXTENT: Southwestern Colorado. MLRA is 36. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: La Plata County, Colorado, 1982.
REMARKS: Diagnostic horizons and features recognized are:
Ochric epipedon: 0 to 9 inches
Argillic horizon: 9 to 57 inches
Classified according to Soil Taxonomy Second Edition, 1999
The classification was changed from fine, smectitic, mesic Ustic Haplargids to fine, smectitic, mesic Aridic Haplustalfs in 2003
This revision updates the classification from an Ustic subgroup of Haplargids to an Aridic subgroup of Haplustalfs to be compatible with the soil moisture regime.