LOCATION SONAHNPIL FM

Established Series
Rev: WEL/RTG/JVP/MK
03/2017

SONAHNPIL SERIES

The Sonahnpil series consists of very deep, well drained soils on flood plains and alluvial fans. These soils formed in alluvium derived from basic volcanic lava. Slope is 0 to 5 percent. The mean annual rainfall is about 4,699 millimeters (185 inches), and the mean annual air temperature is about 27 degrees C. (81 degrees F.).

TAXONOMIC CLASS: Clayey-skeletal, mixed, semiactive, isohyperthermic Fluventic Humic Dystrudepts

TYPICAL PEDON: Sonahnpil very stony silty clay loam - on a 1 percent slope in agricultural forest. When described (7/30/79) the soil was moist throughout. (Colors are for moist soil. All textures are apparent field textures.)

Oi--0 to 3 centimeters (0 to 1 inches); freshly fallen and partially decomposed organic litter; very strongly acid (pH 5.3, 1:1 in water) (1.0 to 5 centimeter (0.4 to 2 inches) thick)

A--3 to 18 centimeters (1 to 7 inches); very dark brown (10YR 2/2) very stony silty clay loam; moderate fine and medium granular structure; very friable, slightly sticky and slightly plastic; many fine and medium roots and a few coarse roots; common fine and medium tubular and interstitial pores; about 20 percent rounded hard basalt stones; 10 percent cobbles and 10 percent gravel; very strongly acid (pH 4.6, 1:1 water); abrupt smooth boundary. (10 to 25 centimeter (4 to 10 inches) thick)

Bw1--18 to 25 centimeters (7 to 10 inches); dark brown (10YR 3/3) cobbly silty clay loam; moderate fine and medium subangular blocky structure; friable, slightly sticky and slightly plastic; common fine and medium roots and few coarse roots; common fine tubular pores; about 15 percent rounded hard basalt cobbles and 10 percent gravel; very strongly acid (pH 5.0, 1:1 water); abrupt wavy boundary.

2Bw2--25 to 51 centimeters (10 to 20 inches); dark brown (10YR 3/3) extremely stony sandy clay loam; weak medium subangular blocky structure; friable, slightly sticky and nonplastic; few medium roots; common fine and very fine interstitial and tubular pores; about 40 percent rounded hard basalt stones, 20 percent cobbles, and 20 percent rounded gravel; very strongly acid (pH 4.8, 1:1 water); clear wavy boundary.)

2Bw3--51 to 76 centimeters (20 to 30 inches); dark yellowish brown (10YR 3/4) extremely stony sandy clay loam; weak fine and medium subangular blocky structure; friable, slightly sticky and nonplastic; few fine and coarse roots; common very fine interstitial pores; about 30 percent rounded hard basalt stones, 20 percent cobbles, and 20 percent gravel; very strongly acid (pH 4.8, 1:1 water); gradual wavy boundary.

2Bw4--76 to 150 centimeters (30 to 59 inches); dark yellowish brown (10YR 4/4) extremely cobbly sandy clay loam; weak fine and medium subangular blocky structure; friable, slightly sticky and nonplastic; about 50 percent stones and cobbles and 20 percent gravel; very strongly acid (pH 4.6, 1:1 water). Combined thickness of the B horizons ranges from 51 to 150 cm (20 to 59 inches).

TYPE LOCATION: Island of Pohnpei, Federated States of Micronesia; 52 feet south of the hanging Mwelilap bridge over the Nanpil River; lat. 6 degrees 55 minutes 55 seconds N. and long. 158 degrees 13 minutes 22 seconds E. (WGS84 datum)

RANGE IN CHARACTERISTICS:
All horizons are very strongly acid or strongly acid.

The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, and chroma of 2 or 3 moist. It is silty clay loam, silt loam, or clay loam and is 10 to 40 percent stones and cobbles and 5 to 20 percent gravel.

The Bw horizon has hue of 10YR, value of 3 or 4 moist, and chroma of 3, 4 or 6 moist. 3/3, 3/4, 4/4, or 4/6. It is silty clay loam, clay loam, or sandy clay loam and is 15 to 60 percent stones and cobbles and 10 to 25 percent gravel.

C horizon - May be present in some pedons.

COMPETING SERIES: There are no competing series.

GEOGRAPHIC SETTING: Sonahnpil soils are on alluvial fans and flood plains. They formed in alluvium derived from basic volcanic lava. Slopes are 0 to 5 percent. The elevation is sea level to 255 meters (0 to 837 feet). The mean annual precipitation is 4064 to 6934 millimeters (160 to 273 inches). The mean annual air temperature is about 27 degrees C. (81 degrees F.) and ranges from 24 to 30 degrees C. (75 to 86 degrees F.).

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Dolen, Nansepsep, and Tolonier soils. Dolen and Tolonier soils are on steeper slopes and formed in residuum and colluvium. Nansepsep soils are somewhat poorly drained and nonskeletal.

DRAINAGE AND PERMEABILITY: Well drained; low runoff; moderately rapid permeability.

USE AND VEGETATION: Sonahnpil soils are used for subsistence agriculture, woodland, and wildlife habitat. The main crops are banana, breadfruit, and coconut.

DISTRIBUTION AND EXTENT: Islands of Kosrae and Pohnpei, Federated States of Micronesia. The series is of small extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Davis, California

SERIES ESTABLISHED: Island of Pohnpei, Federated States of Micronesia, 1981.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Perudic soil moisture regime
Umbric epipedon - the zone from a depth of 3 to 18 centimeters (1 to 7 inches) (A horizon)
Cambic horizon- the zone from a depth of 18 to 150 centimeters (7 to 59 inches) (Bw, 2Bw1, 2Bw2, 2Bw3 and 2Bw4 horizons)
Lithological discontinuity - the zone from a depth of 25 to 150 centimeters (10 to 59 inches) (2Bw1, 2Bw2, 2Bw3 and 2Bw4 horizons)

National Cooperative Soil Survey
U.S.A.