LOCATION LLANOS COSTA PREstablished Series
TAXONOMIC CLASS: Fine, mixed, semiactive, isohyperthermic Typic Haplargids
TYPICAL PEDON: Llanos Costa loam--pastureland (Colors are for moist soil).
Ap--0 to 9 inches; dark brown (7.5YR 3/4) loam; moderate fine granular structure; soft, friable; slightly sticky, slightly plastic; common very fine roots; about 3 percent, by volume, pebbles; moderately acid; clear wavy boundary. (5 to 11 inches thick)
Bt1--9 to 15 inches; dark reddish brown (5YR 3/4) gravelly clay loam; weak medium subangular blocky structure; slightly hard, friable; sticky, plastic; common very fine roots; common faint clay films on face of peds; about 30 percent, by volume, pebbles; slightly acid; clear smooth boundary.
Bt2--15 to 29 inches; yellowish red (5YR 4/6) gravelly clay; moderate fine and medium subangular blocky structure; slightly hard, firm; slightly sticky, slightly plastic; few very fine roots; many distinct clay films on face of peds; about 20 percent, by volume, pebbles and about 2 percent, by volume, cobbles; neutral; gradual smooth boundary.
Bt3--29 to 43 inches; yellowish red (5YR 4/6) very gravelly clay; moderate medium subangular blocky structure; slightly hard, firm; sticky, plastic; few very fine roots; many distinct clay films on face of peds; about 40 percent, by volume, pebbles and about 2 percent, by volume, cobbles; slightly acid; clear wavy boundary.
Bt4--43 to 56 inches; 75 percent strong brown (7.5YR 4/6) and 25 percent yellowish red (5YR 4/6) very gravelly sandy clay loam; weak medium subangular blocky structure; slightly hard, friable; sticky, plastic; few very fine roots; many distinct clay films on face of peds; about 40 percent, by volume, pebbles; moderately acid; gradual wavy boundary.
Bt5--56 to 68 inches; yellowish red (5YR 4/6) very gravelly sandy clay loam; weak medium subangular blocky structure; slightly hard, friable; sticky, plastic; common distinct clay films on face of peds; about 50 percent, by volume, pebbles; moderately acid; gradual wavy boundary.
Bt6--68 to 80 inches; yellowish red (5YR 4/6) very gravelly sandy clay loam; weak medium subangular blocky structure; slightly hard, friable; sticky, plastic; common distinct clay films on face of peds; about 40 percent, by volume, pebbles; moderately acid. (Combined thickness of Bt horizon range from 60 to more than 80 inches.)
TYPE LOCATION: Cabo Rojo, Puerto Rico. Approximately 3.3 miles west of P.R. Hwy. 303 from the intersection with P.R. Hwy. 305; about 1.4 miles west of Maguayo community on dirt road; about 80 feet south of the dirt road in native pasture; USGS San German topographic quadrangle (1966); lat. 18 degrees 07 minutes 46 seconds N.; long. 67 degrees 07 minutes 13 seconds W.
RANGE IN CHARACTERISTICS: Solum thickness is more than 60 inches. Reaction ranges from strongly acid to neutral in the A or Ap horizon and from moderately acid to neutral in the Bt horizons.
The A or Ap horizon has hue of 5YR to 10YR, value of 3 or 4, and chroma of 2 to 4. Content of pebbles and cobbles ranges from 2 to 15 percent, by volume. Texture is loam, clay loam or clay.
The upper part of the Bt horizon has hue of 2.5YR to 10YR, value of 3 or 4, and chroma of 4 to 8. Content of pebbles range from 15 to 50 percent, by volume, averaging less than 35 percent, by volume, in the control section. Texture is clay loam or clay in the fine-earth fraction.
The lower part of the horizon has hue of 2.5YR to 10YR, value of 3 or 4, and chroma of 4 to 8. Content of pebbles and cobbles range from 20 to 75 percent, by volume. Texture is sandy clay loam or clay loam in the fine-earth fraction.
COMPETING SERIES: There are no known series in the same family.
GEOGRAPHIC SETTING: Llanos Costa soils are on mountain foot slopes and alluvial fans of the Semiarid Mountains and Valleys MLRA. Slopes range from 2 to 12 percent. They formed in gravelly sediments that weathered from basalt, chert and rhyolite. The climate is semiarid tropical. The average annual precipitation ranges from 28 to 36 inches and the average annual temperature ranges from 78 to 82 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bermeja (T), Cerro Mariquita (T) and Maguayo series. Bermeja (T) and Cerro Mariquita (T) soils are on higher positions and are shallow to chert bedrock. Maguayo soils are on similar positions and do not have gravelly subsoils.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Most areas of Llanos Costa soils are on pastureland. A few small areas are in cropland, primarily corn and sorghum. Vegetation consists of Guinea grass, Kleberg bluestem grass and other native and introduced grasses and shrubs.
DISTRIBUTION AND EXTENT: Mountain foot slopes and alluvial fans of the Semiarid Mountains and Valleys MLRA. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Raleigh, North Carolina.
SERIES ESTABLISHED: Cabo Rojo Municipality, Puerto Rico; 2007. The name is from the Llanos Costa ward where it was originally recognized.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Ochric epipedon - the zone from 0 to 9 inches (Ap horizon).
Argillic horizon - the zone from 9 to 80 inches (Bt1, Bt2, Bt3, Bt4, Bt5 and Bt6 horizons).
These soils were formerly included in the Amelia series. A soil moisture study performed in the San German Area Soil Survey Update recognizes the Aridic Soil Moisture Regime in southern Puerto Rico.
Llanos Costa soils formed in the Alluvium Formation (Qal) (Holocene and Pleistocene).
Llanos Costa soils are in MLRA 271.