LOCATION NGARDMAU PW+PBEstablished Series
TAXONOMIC CLASS: Very-fine, parasesquic, isohyperthermic Oxic Dystrudepts
TYPICAL PEDON: Ngardmau very gravelly silty clay loam - on an 18 percent convex, east-facing slope in a degraded anthropic savannah. When described (10/5/79), the soil was moist throughout. (Colors are for moist soil unless otherwise noted. All textures are apparent field textures.)
(Approximately 80 percent of the surface is covered with pebble-size irregular platy ironstone and ferritic gibbsitic concretions.)
A1--0 to 5 inches; strong brown (7.5YR 4/6) very gravelly silty clay loam; brown (7.5YR 5/4) dry; moderate very fine and fine subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common very fine and fine roots and few medium roots; common very fine and fine tubular pores within interstices; approximately 50 percent by volume pebble-sized vesicular irregular gibbsite pendants and irregular blocky solid ironstone fragments; extremely acid (pH 4.3, 1:1 water); clear wavy boundary. (4 to 8 inches thick)
B2--5 to 10 inches; 60 percent yellowish red (5YR 4/6) and 40 percent red (2.5YR 4/6) silty clay; moderate medium subangular blocky structure parting to strong very fine and fine angular blocky; firm, sticky and plastic; few very fine and fine roots; common very fine and fine tubular pores within interstices and common medium tubular pores; continuous thin coatings on faces of peds and lining pores; approximately 2 percent ironstone pebbles; extremely acid (pH 4.5, 1:1 water); gradual wavy boundary. (4 to 10 inches thick)
B3--10 to 16 inches; 40 percent red (2.5YR 4/6) and 30 percent yellowish red (5YR 4/6) silty clay; with 30 percent variegated dark red (10R 3/6) and red (10R 4/8) saprolite that contains common fine greenish gray (5GY 6/1) and light greenish gray (5GY 7/1) specks of pseudomorphs of feldspar; moderate medium and coarse subangular blocky structure parting to moderate very fine and fine angular blocky; saprolite shows rock structure; firm, sticky and plastic; few very fine and fine roots; common very fine and fine tubular and interstitial pores; many thin coatings on the faces of peds and lining pores; approximately 2 percent ironstone pebbles; extremely acid (pH 4.5, 1:1 water); gradual irregular boundary. (0 to 8 inches thick)
C--16 to 59 inches; 50 percent weak red (10R 4/4) and 50 percent yellowish red (5YR 4/6) silty clay loam; with many fine greenish gray (5GY 6/1, 5BG 6/1) specks of pseudomorphs of feldspar; moderate medium and coarse subangular blocky structure; friable, slightly sticky and slightly plastic; few very fine and fine roots within interior of peds; common very fine tubular pores in interstices between peds; common thin coatings on the faces of peds and lining pores; approximately 4 percent ironstone pebbles and a few vesicular irregular gibbsite fragments; extremely acid (pH 4.5, 1:1 water).
TYPE LOCATION: Airai Municipality, Babelthuap Island, Palau, Western Caroline Islands; about 4,707 feet N. and 3,198 E. of SE. corner of Ngerimel Reservoir dam; proceed N. on the road to Nekken, approximately 1.3 miles N. past the road to Ngerimel Reservoir, then 147 feet E. of the road; lat. 7 degrees 22 minutes 45 seconds N. and long. 134 degrees 32 minutes 36 seconds E.
RANGE IN CHARACTERISTICS: Coarse fragments on the surface range from 25 to 90 percent pebble-size and 0 to 15 percent irregular vesicular ferritic and gibbsitic concretions 3 to 6 inches in size. Thickness of the solum ranges from 10 to 20 inches.
The A horizon has moist color of 10YR 3/2, of 7.5YR 4/6, of 5YR 3/4 or 3/3, or of 2.5YR 3/4, 4/4, or 4/6. It has an apparent field texture of loam, silt loam, or silty clay loam and is gravelly, very gravelly, or extremely gravelly. It is 30 to 75 percent pebble-size iron and gibbsite concretions. It is as much as 10 percent cobble-size concretions in some pedons. Reaction in 1:1 water ranges from extremely acid to strongly acid.
A B1 horizon in some pedons has moist color of 7.5YR 4/4 or 4/6.
The B2 horizon has moist color of 10R 4/6, of 2.5YR 3/6 or 4/6, of 5YR 4/6, or of 7.5YR 4/6 or 5/6. The apparent field texture is silty clay loam or silty clay. The amount of clay, as measured by the product of 2.5 times the 15-bar water percentage, is more than 75 percent. The horizon is 2 to 15 percent pebble-sized ferritic and gibbsitic concretions. Reaction in 1:1 water ranges from extremely acid to strongly acid. CEC is less than 12 meq/100 grams of clay. Aluminum extractable in 1N NH4C1 is less than 1.5 meq/100 grams of clay in some subhorizons. Aluminum saturation (NH4OAc/CK1) ranges from 50 to 90 percent.
The C horizon has moist color of 10R 3/3, 3/6, 4/4, 4/6, or 4/8, of 2.5YR 4/6, of 5YR 4/6, of 7.5YR 4/6, 5/6, or 6/0, or of 10YR 3/6, 4/4, or 4/6. The apparent field texture is silt loam or silty clay loam. Pebble-size ferritic and gibbsitic concretions range from 2 to 15 percent by volume. Reaction in 1:1 water ranges from very strongly acid to strongly acid.
COMPETING SERIES: This is the Oatuu series. Oatuu soils are very shallow to a paralithic contact and have greater than 35 percent by volume, firm to hard, saprolitic volcanic pebbles and cobbles.
GEOGRAPHIC SETTING: Ngardmau soils are primarily on convex ridges and other erosional surfaces of hills and low mountains. Slopes are 2 to 75 percent. The soils formed in highly weathered saprolitic volcanic breccia and, less commonly, tuff. They support a degraded anthropic savannah vegetation. Elevation ranges from 0 to 689 feet. The mean annual temperature is 81 degrees F. and does not vary by more than 34 degrees F from month to month. Mean annual maximum temperature is 88 degrees F. and mean annual minimum temperature is 75 degrees F. Mean annual rainfall is 145 inches and varies from 130 to 183 inches from year to year, with the driest months of February, March, and April averaging 7 to 9 inches per month.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Aimeliik, Babelthuap, and Palau soils. Aimeliik and Palau soils also have a higher organic-matter content, CEC, fertility, and lack the high content of concretions. They are under forest and anthropic savannah that exhibits good stands of grasses and forbs. Babelthuap soils are on similar topographic positions to Ngardmau soils but are 20 to 39 inches deep to a saprolitic C horizon.
DRAINAGE AND PERMEABILITY: Well drained; slow through very rapid runoff; moderately rapid permeability. In general, areas where a high value, low chroma color dominates the saprolite, a slower permeability is noted.
USE AND VEGETATION: Most areas are idle land and used only for watershed. The vegetation is a degraded anthropic savannah consisting of poor stands of Gleichenia linearis, Nepenthes mirabilis, Extrosia lepornia, Paspalum orbiculare and scattered shrubs and pandanus.
DISTRIBUTION AND EXTENT: Ngardmau soils are of small extent in Palau on the island of Babelthuap.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Airai Municipality, Babelthuap Island, Palau, Western Caroline Islands, 1981.
REMARKS: Ngardmau soils have a perudic moisture regime. The surface layer becomes dry for short periods, particularly during the months of February, March, and April, due to the high coarse fragment content. The mean annual soil temperature is 82 degrees F. In local pronunciation of the word Ngardmau, the "g" is silent. This soil meets all the requirements at an oxic horizon except thickness.