LOCATION COAMO PREstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, isohyperthermic Typic Argiustolls
TYPICAL PEDON: Coamo clay loam. (Colors are for moist soil unless otherwise stated.)
A1--0 to 5 inches; very dark brown (10YR 2/2) very dark grayish brown (10YR 3/2) dry, clay loam; weak medium subangular blocky structure; slightly hard, friable; slightly sticky and slightly plastic; few fine roots; few fine pebbles; slightly acid; diffuse wavy boundary.
A2--5 to 15 inches; very dark brown (10YR 2/2) very dark grayish brown (10YR 3/2) dry, clay loam; weak coarse subangular blocky structure; slightly hard, friable; slightly sticky, slightly plastic; few fine roots; few fine pebbles; slightly acid; clear smooth boundary. (Combined thickness of the A horizons ranges from 8 to 12 inches)
Bt--15 to 25 inches; brown (7.5YR 4/2) dark brown (7.5YR 3/2) dry, clay; weak medium subangular blocky structure; very hard, firm; slightly sticky, slightly plastic; common fine pebbles; few distinct clay films along root channels and vertical cleavage planes; few faint masses of secondary calcium carbonate; slightly alkaline; gradual wavy boundary. (8 to 15 inches thick)
Bk--25 to 38 inches; dark brown (10YR 3/3) brown (7.5YR 4/2) dry, gravelly clay; weak medium subangular blocky structure; very hard, firm; slightly sticky, slightly plastic; peds coated with secondary calcium carbonate; moderately alkaline; clear smooth boundary. (10 to 20 inches thick)
2C--38 to 48 inches; stratified layers of pebbles and gravelly clay loam; pebbles ranging in size from 0.5 to 2.0 inches in diameter; common fine dark minerals; common fine coatings of secondary calcium carbonate; moderately alkaline.
TYPE LOCATION: Salinas, Puerto Rico. Approximately 1.7 miles south of Km. 85.1 on Highway No. 1, Salinas to Cayey.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 24 to 50 inches. Soil reaction ranges from slightly acid to slightly alkaline in the A or Ap horizon, slightly alkaline to moderately alkaline in the Bt horizons, and moderately alkaline in the Bk, C, and 2C horizons. Depth to the calcic horizon ranges from 20 to 36 inches.
The A or Ap horizon has hue of 10YR, value of 2 or 3, and chroma of 1 to 3. Texture is loam or clay loam.
The Bt horizon has hue of 7.5YR or 10YR, value of 3 to 5, and chroma of 2 to 6. Texture is clay loam or clay.
The Btk, Bk, or BCk horizon has hue of 7.5YR or 10YR, value of 3 to 5, and chroma of 2 to 6. Texture is clay loam, clay, or their gravelly analogs.
The C or 2C horizon has hue of 10YR, value of 4 or 5, and chroma of 3 or 4. It consists of stratified layers. Texture is gravelly to extremely gravelly sandy loam to clay loam.
COMPETING SERIES: There are no other known series in the same family.
GEOGRAPHIC SETTING: Coamo soils are on alluvial fans and terraces. They formed in sediments derived from volcanic and limestone rocks that are underlain by materials from moderately coarse to coarse. The climate is tropical semiarid. Slopes range from 0 to 5 percent. The average annual temperature ranges from 78 to 80 degrees F., and the average annual rainfall ranges from 30 to 40 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the Amelia, Descalabrado, Jancana, and San Anton series. Amelia soils are on similar to slightly higher positions, are clayey-skeletal, and do not have mollic epipedons. Descalabrado soils are on higher positions and are shallow to hard volcanic rock. Jacana soils are on similar to slightly higher positions and are moderately deep. San Anton soils are on adjacent lower flood plains and have weakly developed cambic horizons.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Most areas of Coamo soils are used as pasture. Vegetation consists of introduced native grasses and shrubs.
DISTRIBUTION AND EXTENT: Semiarid sections of southern Puerto Rico. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Raleigh, North Carolina.
SERIES ESTABLISHED: Puerto Rico; 1936.
REMARKS: The classification was updated with the 4/91 draft from Fine, mixed, isothermic Typic Argiustolls to Fine, mixed, isohyperthermic Typic Argiustolls. The previous OSED was dated 7/65.
Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - the zone from 0 to 15 inches (A1 and A2 horizons).
Argillic horizon - the zone from 15 to 25 inches (Bt horizon).
Calcic horizon - the zone from 25 to 38 inches (Bk horizon).