LOCATION DECHEL PW+ FM PBEstablished Series
TAXONOMIC CLASS: Very-fine, mixed, semiactive, acid, isohyperthermic Fluvaquentic Endoaquepts
TYPICAL PEDON: Dechel silt loam in a level area under hydrophytic grasses and sedges at an elevation of 9 meters (30 feet.) (Colors are for moist soil unless otherwise noted. All textures are apparent field textures. When described on November 29, 1979, water table was at the soil surface.)
A-- 0 to 10 centimeters (0 to 4 inches); dark gray (5Y 4/1) mucky silt loam; structureless massive; slightly sticky and nonplastic; many very fine and fine roots; common very fine and fine tubular pores; strongly acid (pH 5.1, 1:1 water); abrupt smooth boundary. (10 to 30 centimeters thick)
Bg1--10 to 28 centimeters (4 to 11 inches); olive gray (5Y 4/2) silty clay loam; areas of yellowish red (5YR 5/6) and bluish gray (5B 5/1) oxidized material along surfaces of pores; weak fine and medium subangular blocky structure; slightly sticky and slightly plastic; common very fine and fine roots and few medium roots; many very fine and fine tubular and interstitial pores and few medium tubular pores; strongly acid (pH 5.5; 1:1 water); abrupt smooth boundary. (5 to 25 centimeters thick)
Bg2--28 to 61 centimeters (11 to 24 inches); greenish gray (5GY 5/1) silty clay loam; common olive (5Y 4/3) organic stains on ped faces and along surfaces of pores; yellowish red (5YR 5/6) oxidized material along surfaces of pores; weak medium subangular blocky structure; sticky and slightly plastic; many very fine and fine tubular and interstitial pores and common medium tubular pores; rock fragments are petroferric fragments, 12 gravel; moderately acid (pH 5.9; 1:1 water); clear wavy boundary. (30 to 99 centimeters thick)
BCg1--61 to 102 centimeters (24 to 40 inches); dark greenish gray (5GY 4/1) silty clay loam; few small specks of dark bluish gray (5B 4/1); massive; sticky and slightly plastic; many very fine and fine roots and common medium roots; many very fine and fine pores and few medium tubular pores; rock fragments are petroferric fragments, 12 gravel; moderately acid (pH 5.9 in water); abrupt smooth boundary. (41 to 79 centimeters thick)
2BCg2-- 102 to 109 centimeters (40 to 43 inches); dark greenish gray (5GY 4/1) very gravelly silty clay loam; massive; sticky and slightly plastic; few very fine roots; few very fine and fine tubular pores; rock fragments ironstone concretions and basalt; 45 gravel, 5 cobbles; moderately acid (pH 5.6 in water); clear smooth boundary. (0 to 15 centimeters thick)
3Cg--109 to 203 centimeters (43 to 80 inches); dark grayish brown (2.5Y 4/2) silty clay loam; massive; sticky and slightly plastic; few very fine roots; few very fine and fine tubular pores; 2 percent gravel, subrounded petroferric fragments; strongly acid (pH 5.1 in water).
TYPE LOCATION: Airai Municipality, Babeldaob Island, Republic of Palau: about 6.4 kilometers (4 miles) along main road SE of T intersection of main road and road leading to Nekken. Turn NE and head 32 meters (105 feet) along trail and up small escarpment to first small, nearly level area of ancient anthropogenic terrace then head NW 73 meters (240); WGS 84 UTM 447290 meters E, 814179 meters N, zone 53; Lat 7 21' 55.67" N and Long 134 31' 20.63" E.
RANGE IN CHARACTERISTICS:
Soil moisture:
Soil moisture regime subclass: oxyaquic
Soil moisture regime class: aquic
Seasonal pattern: Precipitation falls mostly even during the year with the exception of February to April being the driest months averaging 179 to 229 millimeters (7 to 9 inches) per month.
Mean annual soil temperature: 27 C (81 F)
Control section: 25 to 100 centimeters (10 to 39 inches)
Depth to diagnostic feature: redox concentrations: 3 to 30 centimeters (1 to 12 inches)
redox depletions with chroma 2 or less: 0 to 15 centimeters (0 to 6 inches)
aquic conditions: 0 to 15 centimeters (0 to 6 inches)
reduced matrix: 0 to 15 centimeters (0 to 6 inches)
endosaturation: 0 to 10 centimeters (0 to 4 inches)
cambic horizon: 3 to 15 centimeters (1 to 6 inches)
Thickness of diagnostic feature:
redox concentrations: 7 to 40 centimeters (3 to 16 inches)
hemic soil materials: 0 to 10 centimeters (0 to 4 inches)
ochric epipedon: 3 to 15 centimeters (1 to 6 inches)
redox depletions with chroma 2 or less: 3 to 30 centimeters (1 to 12 inches)
aquic conditions: 180 to 200 centimeters (71 to 79 inches)
reduced matrix: 3 to 30 centimeters (1 to 12 inches)
endosaturation: 180 to 200 centimeters (71 to 79 inches)
cambic horizon: 12 to 57 centimeters (5 to 22 inches)
Linear extensibility: 1 to 3 percent, weighted average RV is 1.7 percent
Seasonal high water table: All months of the year
Depth to top: 0 to 25 centimeters (0 to 4 inches)
A horizon(s):
Hue: 10YR, 2.5Y, 5Y, 5G, 5GY
Value: 3 or 5 moist
Chroma: 1 or 2 moist
Texture: of silt loam, silty clay loam, or mucky silty loam
Sand content: 5 to 35 percent
Clay content: 10 to 60 percent
Silt content: 40 to 80 percent
Reaction: pH 4.5 to 5.6
Aluminum Saturation: 25 to 55 percent
New Zealand P Retention: 60 to 80 percent
Cation exchange capacity: 35 to 50 meq/100grams
Effective cation exchange capacity: 10 to 20 meq/100grams
Organic matter content: 3 to 9 percent
Ag and Bg horizon(s):
Hue: 10YR, 2.5Y, 5Y, 5G, or 5GY
Value: 3 to 5 moist
Chroma: 1 to 2 moist
Texture: silty loam or silty clay loam and may have a gravelly or very gravelly modifier
Fragment size and content: Some pedons contain strata of rock fragments containing petroferric fragments, gibbsitic concretions, schist; 0 to 45 percent total rock fragments; 0 to 45 percent gravel; 0 to 5 percent cobbles
Sand content: 0 to 30 percent
Silt content: 15 to 70 percent
Clay content: 30 to 80 percent
Reaction: pH 4.5 to 5.5
Aluminum Saturation: 25 to 55 percent
New Zealand P Retention: 60 to 80 percent
Cation exchange capacity: 20 to 30 meq/100grams
Effective cation exchange capacity: 10 to 15 meq/100grams
Organic matter content: 3.5 to 7.5 percent
CBg, Cg or BCg horizon(s):
Hue:10YR, 5BG, 5GY, 2.5Y, 5Y
Value: 2.5 to 5
Chroma: 1 to 3
Texture: clay, silty clay loam
Fragment size and content: Some pedons contain strata of rock fragments containing petroferric fragments, gibbsitic concretions, schist; 0 to 15 percent total rock fragments; 0 to 15 percent gravel
Sand content: 0 to 30 percent
Silt content: 15 to 70 percent
Clay content: 30 to 80 percent
Reaction: pH 4.5 to 5.5
Aluminum Saturation: 25 to 55 percent
New Zealand P Retention: 60 to 80 percent
Cation exchange capacity: 25 to 35
Effective cation exchange capacity: 10 to 20
Organic matter content: 2 to 6 percent
COMPETING SERIES: There are no competing series at this time.
GEOGRAPHIC SETTING: Dechel soils are very poorly drained soils on swamps, marshes, backswamps, and flood plains of valley floors located on volcanic islands.. Slope is 0 to 2 percent. These soils formed in formed in organic deposits and alluvial sediments derived from basalt, andesite, dacite, marine deposits, volcanic breccias, tuff, bedded tuff, or schist Elevation is 0 to 67 meters (0 to 220 feet.) Depth to the water table ranges from 10 centimeters (4 inches) above mineral soil surface to about 25 centimeters (10 inches) below. The soils are flooded frequently for extremely brief periods and ponded frequently for very long periods all months of the year. The climate is tropical and moist. Because of the strong marine influence, the diurnal and annual range of temperature is limited. Rainfall averages about 3685 millimeters (145 inches) per year and ranges from approximately 2900 to 4400 mm (114 to 173 in.) The seasonal wet (May to November) and dry seasons (December to April) with the driest months (February, March, and April) averaging 178 to 229 milliliters (7 to 9 inches) per month. Rainfall is derived from convective uplift, which results in short duration rainstorms of high intensity. Rainfall is irregularly distributed geographically. These soils lie within the latitudinal zone that receives more solar radiation than it re-radiates back to space. This imbalance maintains the atmospheric temperatures in a quasi-steady state. The mean daily temperature throughout the year averages 27 C (81 F) with a mean diurnal range of about 4 C (7 F.) Relative humidity averages about 90 percent at night and 75 to 80 percent during the day.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ilachetomel, Mesei, Naniak, and Ngersuul soils. The Ilachetomel soils are organic and Naniak soils are mineral with sulfidic materials, are flooded daily with seawater, and support mangrove vegetation. The Mesei soils are organic soils overlying clayey alluvium. Ngersuul is a better-drained version of the Dechel series and lacks stratification.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Very poorly drained. Low runoff, moderately high saturated hydraulic conductivity. Depth to the water table ranges from 10 centimeters (4 inches) above mineral soil surface to about 25 centimeters (10 inches) below. The soils are flooded frequently for extremely brief periods and ponded frequently for very long periods all months of the year.
USE AND VEGETATION: These soils are in wetland taro (Crytosperma and Colocasia) patches or swamp forest plant communities and are used for production of taro, watershed, and wildlife. Native vegetation includes; Campnosperma brevipetiolata, Horsfieldia amklaal, Stemmonorus ammui, Samadera indica, Callophyllum pelewense, Inocarpus fagifer, Hibiscus tiliaceous, Pandanus kanehirae, Crudia cynometroides, Dolichandrone, Barringtonia racemosa, Donax canneformis, Hanguana malayana
DISTRIBUTION AND EXTENT: MLRA 193 Volcanic Islands of Western Micronesia; Republic of Palau; Yap State, Federated States of Micronesia. These soils of this series are of small extent; about 1,100 acres in the Republic of Palau; about 1,100 acres in Yap State, Federated States of Micronesia. They are mapped on the islands of Babeldaob, Republic of Palau and Yap, Federated States of Micronesia.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Airai Municipality, Babeldaob Island, Republic of Palau, 1981. Local pronunciation of the word Dechel is "Dey-ell."
REMARKS: The Dechel series had an O horizon when originally mapped in 1980 but due to changes in management practices such as; drainage ditches, fluctuating water table, lack of organic inputs, and turning over the soil. Over time, the organic matter has been oxidized and removed from the system. Now much of the Dechel series with O horizons can only be found in native vegetation. Dechel soils that formed in alluvium derived from soils that formed from schist typically have a higher pH value and base status than Dechel soils derived from soils on volcanic parent material. Dechel soils in Yap are classified as Fluvaquents and derived from schist. These soils have a high water table, are susceptible to subsidence, and have poor engineering properties.
The traditional system of agriculture included intensive taro cultivation. The soil is first dug out down to the fresh water lens, tall grasses and sedges, weeds, and young trees are removed or pushed into the mud as fertilizer. The soil is turned over and work, which requires the Palauans to dig down deep as far as they can with their hands and lift the mud and organic matter to turn it over. Wood ashes, twigs, grasses, and leaves are added below the mud to keep insects, fungus, and bacteria away and for fertilizer.
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - From the surface to a depth of 10 centimeters (A horizon).
Cambic horizon - from 10 to 109 centimeters (Bg and BCg horizons)
Aquic Conditions - 10 to 200 centimeters
Reduced Matrix - 10 to 200 centimeters
Endosaturation - 10 to 200 centimeters
Redox depletions with chroma 2 or less -10 to 200 centimeters
Particle-size control section - 25 to 100 centimeters
N value: greater than 0.7
Lithologic discontinuity - 28 and 61 centimeters (61 and 103 inches) (2BCg and 3Cg horizons)
ADDITIONAL DATA: National Soil Survey Laboratory Data No. S79TQ63910 used to define mineralogy, and Military Geology of Palau Islands, 1956, and Yap Islands, 1960, are used to define the series. Additional data are National Soil Survey Laboratory # 03PW004001 and 07FM060001.
Taxonomic Version: Keys to Soil Taxonomy, 10th edition 2006.