LOCATION RIO ARRIBA PREstablished Series
TAXONOMIC CLASS: Fine, mixed, subactive, isohyperthermic Vertic Paleudults
TYPICAL PEDON: Rio Arriba clay - sugarcane.
(Colors are for moist soil unless otherwise stated.)
Ap--0-8 inches; Brown (10YR 4/3) clay; weak coarse granular structure; hard, firm slightly sticky, plastic; many fine roots; neutral; clear smooth boundary. (4 to 10 inches thick)
B21t--8-16 inches; Yellowish brown (10YR 5/8) clay; moderate coarse prismatic breaking to weak medium subangular blocky structure with yellowish brown (10YR 5/4) thin continuous coatings on vertical surfaces of peds and patchy coatings on horizontal ped surfaces; hard, firm, slightly sticky, plastic; common fine roots; common fine black nodules; medium acid; clear smooth boundary. (6 to 12 inches thick)
B22t--16-28 inches; Yellowish brown (10YR 5/6) clay with common medium distinct yellowish red (5YR 4/6) mottles; weak coarse angular blocky with few slickensides and pressure faces; firm, slightly sticky, plastic, many fine black nodules; few fine roots; neutral; clear wavy boundary. (10 to 20 inches thick)
B23t--28-60 inches; Reddish yellow (7.5YR 6/6) clay with many medium distinct red (2.5YR 5/6) mottles; massive with few slickensides and pressure faces; firm, slightly sticky, plastic, many fine black nodules; mildly alkaline.
TYPE LOCATION: Turabo SCS, Puerto Rico; 0.4 kilometers west of the town of Gurabo on the Gurabo Experiment substation; 800 feet east of the western boundary of the farm and 600 feet north of the railroad tracks.
RANGE IN CHARACTERISTICS: Thickness of the solum is more than 60 inches. Base saturation at 50 inches below the top of the argillic horizon is 60 percent or more. The A horizon has colors in hues of 10YR or 7.5YR, values of more than 3 and chromas of 3 or 4. The B horizon has colors in hues of 10YR or 7.5YR, values of 4 through 6 and chromas of 4 through 8. Cracks occur at 20 inches and COLE values of 0.09 or more for more than 20 inches of B horizon. Fine clay content is higher in the B horizon than the A. The structure of the B horizon ranges from weak to moderate. Depth to the horizon with red mottles ranges from 20 to 42 inches. The soil ranges from medium acid through mildly alkaline.
COMPETING SERIES: These are the Fajardo, Juncal, Machete, San Sebastian, and Tanama series, all of which lack the .09 COLE value common to the VERTIC subgroups. The Fajardo soils are more acid, have gray mottles in the lower part. The Juncal soils have free carbonates in the lower profile. The San Sebastian soils have more than 50 percent limestone rock fragments in the profile. The Tanama soils have hard limestone rock within 20 inches of the surface.
GEOGRAPHIC SETTING: The Rio Arriba soils occur on gently to strongly sloping alluvial fans and terraces above the river flood plains. Slope gradients range from 2 to 12 percent. The soil formed in fine textured sediments of mixed origin. The climate is humid tropical. The average annual precipitation is 65 inches and the mean temperature is 77 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Caguabo, Gurabo, Juncos, Mabi, and Mucara series. The Caguabo, Gurabo, Juncos, Mabi, and Mucara soils lack argillic horizons and occur above the Rio Arriba soils in the landscape, with the exception of Guarabo and Mabi which occur at lower positions.
DRAINAGE AND PERMEABILITY: Moderately well drained, medium to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Most of the acreage is in sugar cane and pasture.
DISTRIBUTION AND EXTENT: Humid inner valleys of Puerto Rico. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Raleigh, North Carolina
SERIES ESTABLISHED: Soil Survey of Puerto Rico; 1942.
REMARKS: These soils were formerly classified in the yellowish-brown Lateritic intergrading to the Grumusols great soil group.