LOCATION LA PALMA AZEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, hyperthermic Argic Petrocalcids
TYPICAL PEDON: La Palma fine sandy loam-rangeland. (Colors are for dry soil unless otherwise noted)
A--0 to 3 inches; pale brown (10YR 6/3) fine sandy loam, dark yellowish brown (10YR 4/4) moist; weak thin platy structure; soft, very friable, nonsticky and nonplastic; common very fine roots; common very fine pores; strongly effervescent; moderately alkaline; abrupt wavy boundary.
Btn1--3 to 5 inches; pink (7.5YR 7/4) loam, brown (7.5YR 5/4) moist; strong coarse subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine pores; few thick clay films on faces of peds; violently effervescent; very strongly alkaline; abrupt wavy boundary.
2Btn2--5 to 13 inches; pink (7.5YR 7/4) clay loam, brown (7.5YR 5/4) moist; moderate coarse prismatic structure parting to moderate medium subangular blocky; hard, friable, sticky and plastic; common very fine roots; common very fine pores; common thick clay films on faces of peds; violently effervescent; very strongly alkaline; clear wavy boundary.
2Btkn--13 to 18 inches; pinkish gray (7.5YR 7/2) clay loam, light brown (7.5YR 6/4) moist; weak medium subangular blocky structure; slightly hard, friable, sticky and plastic; few very fine roots; few very fine pores; few medium clay films on faces of peds; few lime masses; violently effervescent; very strongly alkaline; abrupt smooth boundary.
2Bkn--18 to 28 inches; pinkish white (7.5YR 8/2) loam, pinkish gray (7.5YR 7/2) moist; massive; very hard, friable, sticky and plastic; common fine lime masses; violently effervescent; very strongly alkaline; clear wavy boundary.
3Bkm--28 inches; petrocalcic horizon, thin laminar cap about 2 inches thick; indurated.
TYPE LOCATION: Pinal County, Arizona; 700 feet east and 200 feet south of the northwest corner of sec. 24, T. 7 S., R. 8 E.
RANGE IN CHARACTERISTICS:
Soil moisture - Intermittently moist in some part of the soil moisture control section during July-September and December-February. May and June are the driest months. Typic aridic moisture regime.
Rock fragments - Averages less than 35 percent in the particle-size control section.
Depth to petrocalcic - Dominantly 24 to 34 inches but ranges from 20 to 40 inches.
SAR- 13 to 100 or more throughout.
Salinity- Slightly saline to moderately saline; EC - 4 to 16 dS/m or more.
Relict water table - In some pedons there is evidence of a relict perched water table in the B horizon. Therefore, high and low chroma mottles are allowed in this horizon.
A horizon
Hue: 10YR or 7.5YR
Value: 5, 6 or 7 dry, 3, 4 or 5 moist
Chroma: 3 or 4 dry, 3, 4 or 6 moist
Texture: Very fine sandy loam, fine sandy loam, loam
Organic matter: Less than 1 percent
Carbonates: Disseminated.
Bt horizon
Hue: 5YR, 7.5YR or 10YR
Value: 5, 6 or 7 dry, 4, 5 or 6 moist
Chroma: 3 or 4 dry, 3, 4 or 6 moist
Texture: Very fine sandy loam, loam, sandy clay loam, clay loam
Structure: Usually blocky but is columnar or prismatic in some pedons.
Bk horizon
Hue: 7.5YR or 10YR
Value: 5, 6, 7 or 8 dry, 5, 6 or 7 moist
Chroma: 2 or 3 dry, 3 or 4 moist
Texture: Clay loam, loam
Carbonates: Occur as soft lime masses and as nodules; calcium carbonate equivalent is 5 to 25 percent. The horizon immediately above the petrocalcic horizon is calcic where it is thick enough.
Bm horizon
This lime-cemented pan occurs in two ways. As a single horizon 4 to 10 inches thick or as many thin horizons (1 to 2 inches) separated by thin layers of soil material. Most areas have a thin laminar cap.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: La Palma soils are on nearly level to gently sloping relict basin floors and fan terraces. These soils formed in a thin layer of eolian loams and mixed alluvium from acid igneous rocks. Elevations are 400 to 2000 feet. Slopes range from 0 to 3 percent, but are usually less than 2 percent. The mean annual precipitation is 4 to 10 inches. The average annual temperature is 67 to 75 degrees F. The frost-free period is about 240 to 325 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Casa Grande, Cavelt, Gilman, Laveen, Mohall, Perryville, Pinal and Toltec soils. Casa Grande, Gilman, Laveen, Mohall and Perryville soils lack indurated pans. Cavelt, Gilman, Laveen, Perryville, Pinal and Toltec soils lack argillic horizons.
DRAINAGE AND PERMEABILITY: Well drained; slow runoff; slow permeability.
USE AND VEGETATION: Used for irrigated crops and rangeland. Irrigated areas are cropped to barley, grain, sorghum, cotton and alfalfa. Desert areas are used as rangeland and are sparsely vegetated with desert saltbush, yucca, creosotebush, bursage and some mesquite.
DISTRIBUTION AND EXTENT: south central Arizona, mainly in the central valley areas. MLRA is 40. La Palma soils are inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pinal County (Casa Grande Area), Arizona, 1936.
REMARKS: Type location is being moved back to where series was first established. Diagnostic horizons and features recognized are:
Petrocalcic horizon - The hard, nonporous lime cemented pan at about 28 inches.
Argillic horizon - The zone of clay enrichment from about 3 to 18 inches.
Calcic horizon - Some pedons have sufficient accumulations of secondary carbonates, others do not. Because of the presence of a petrocalcic horizon the calcic horizon is not used as series differentia.
Classified according to Soil Taxonomy Second Edition, 1999