LOCATION MARIANA PREstablished Series
TAXONOMIC CLASS: Fine, mixed, active, isohyperthermic Typic Haplohumults
TYPICAL PEDON: Mariana gravelly clay loam--naturalized pastureland (Colors are for moist soil).
Ap--0 to 8 inches; brown (7.5YR 4/2) gravelly clay loam; moderate fine subangular blocky structure; slightly hard; friable; slightly sticky, moderately plastic; many fine roots; about 27 percent, by volume, pebbles; extremely acid; clear smooth boundary. (4 to 8 inches thick)
AB--8 to 15 inches; 50 percent dark brown (7.5YR 3/2) and 50 percent dark brown (7.5YR 3/4) gravelly clay loam; moderate fine subangular blocky structure; slightly hard, friable; slightly sticky, moderately plastic; common very fine roots; about 23 percent, by volume, pebbles; extremely acid; clear wavy boundary. (0 to 18 inches thick)
Bt1--15 to 26 inches; 50 percent yellowish red (5YR 5/6) and 50 percent reddish brown (5YR 4/4) clay; moderate fine and medium subangular blocky structure; hard, friable; slightly sticky, moderately plastic; few faint clay films on faces of peds; common very fine roots; about 11 percent, by volume, pebbles; extremely acid; clear wavy boundary.
Bt2--26 to 33 inches; 60 percent strong brown (7.5YR 5/6), 30 percent pinkish gray (7.5YR 7/2) and 10 percent dark yellowish brown (10YR 3/6) clay; weak fine and medium subangular blocky structure; hard, firm; moderately sticky, moderately plastic; few faint clay films on faces of peds; few very fine roots; about 9 percent, by volume, pebbles; extremely acid; gradual wavy boundary. (Combined thickness of the Bt horizons ranges from 12 to 20 inches.)
BC--33 to 50 inches; 60 percent light gray (10YR 7/2), 30 percent strong brown (7.5YR 5/8), and 10 percent dark red (2.5YR 3/6) silty clay; weak medium subangular blocky structure; hard, firm; slightly sticky, moderately plastic; few fine roots; about 6 percent, by volume, pebbles; extremely acid; gradual wavy boundary. (0 to 20 inches thick)
C--50 to 60 inches; 80 percent white (10YR 8/1) and 20 percent strong brown (7.5YR 5/8) saprolite having a silty clay texture; massive; extremely hard, firm; slightly sticky, moderately plastic; extremely acid.
TYPE LOCATION: San German, Puerto Rico. Approximately 1.8 miles southwest of Sabana Eneas community from the intersection of P.R. Hwy. 102 and P.R. Hwy. 317; about 0.45 mile northwest from the intersection of P.R. Hwy. 314 and P.R. Hwy. 312; about 0.40 mile northeast from the end of paved road P.R. Hwy. 312 on dirt road. USGS San German topographic quadrangle (1966); lat. 18 degrees 02 minutes 40 seconds N. and long. 67 degrees 04 minutes 48 seconds W.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 16 to 33 inches. The reaction ranges from extremely acid to very strongly acid throughout.
The A or Ap horizon has hue of 5YR or 7.5YR, value of 3 to 5, and chroma of 2 or 4. Content of pebbles ranges from 15 to 32 percent, by volume. Texture is clay loam or clay in the fine-earth fraction.
The AB horizon, where present, has hue of 7.5YR, value of 3, and chroma of 2 or 4 or there is a mix of colors in shades of brown. Content of pebbles ranges from 10 to 25 percent, by volume. Texture is clay in the fine-earth fraction.
The Bt horizon has hue of 10R to 10YR, value of 3 to 7, and chroma of 2 to 8; or there is no dominant color is and multicolored in shades of yellow, red, brown and gray. Content of pebbles ranges from 2 to less than 15 percent, by volume. Texture is clay loam or clay.
The BC horizon, where present, has hue of 2.5YR to 10YR, value of 3 to 8, and chroma of 2 to 8; or there is no dominant color is and multicolored in shades of yellow, red, brown and gray. Texture is silty clay loam, clay loam or silty clay loam or silty clay.
The C horizon has no dominant color and is multicolored saprolite in shades of yellow, red, brown, gray and white. The original rock structure is visible and weathered rock fragments can be easily broken between fingers. Low chroma colors appear to have been inherited from the parent material and are not thought to be due to wetness. Texture is silty clay loam, clay loam or silty clay.
COMPETING SERIES: These are no known series in the same family.
GEOGRAPHIC SETTING: Mariana soils are on summits and side slopes of hills of the Humid Mountains and Valley MLRA. They formed in residuum that weathered from basalt lava flow and tuff. This soil is located in a transition zone between the Semiarid Coastal Plains and the Humid Mountains and Valleys MLRA. Slopes range from 12 to 40 percent. The average annual temperature ranges from 75 to 79 degrees F., and the average annual precipitation ranges from 43 to 73 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the Descalabrado, Jacana and Palmarejo series. Descalabrado and Jacana soils have mollic epipedons and have Ustic soil moisture regimes. In addition, Descalabrado soils are shallow to bedrock and Jacana soils have Vertic properties. The Palmarejo soils are moderately well drained and have an Ustic soil moisture regime.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Most areas of Mariana soils are on naturalized pastureland or pineapple plantations. Vegetation consists of native and introduced grasses, shrubs and trees.
DISTRIBUTION AND EXTENT: Side slopes and summits of hills of the Humid Mountains and Valleys MLRA. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Raleigh, North Carolina.
SERIES ESTABLISHED: Soil Survey of Puerto Rico; 1942. The name is coined.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Ochric epipedon - the zone from 0 to 8 inches (Ap horizon).
Argillic horizon - the zone from 15 to 33 inches (Bt1 and Bt2 horizons).
The Mariana series was formerly classified in the Gray Brown Podzolic Great Soil Group. The classification was updated with the 12/2004 draft from Fine, mixed, active, isohyperthermic Typic Dystrudepts to Fine, mixed active, isohyperthermic Typic Haplohumults due to recognition of Bt horizons and high level of organic carbon between mineral soil surface and a depth of about 40 inches.
Mariana soils are in MLRA 270.
ADDITIONAL DATA: Characterization pedon - Lajas Municipality, Puerto Rico; S85PR-079-001. Sample by NSSL, Lincoln, NE., 07/1985.