LOCATION NIU HIEstablished Series
TAXONOMIC CLASS: Very-fine, kaolinitic, isohyperthermic Rhodic Eutrustox
TYPICAL PEDON: Niu silty clay loam - sugarcane. (Colors are for moist soil unless otherwise noted. All textures are "apparent field textures".)
A--0 to 10 inches; dark reddish brown (2.5YR 3/4) silty clay loam, same color rubbed,, dark reddish brown (2.5YR 3/4) dry; weak fine subangular blocky structure; hard, friable, sticky and plastic; common medium, fine and very fine roots; strong to violent effervescence with hydrogen peroxide; moderately acid (pH 5.9); abrupt wavy boundary. (8 to 14 inches thick)
Bo1--10 to 22 inches; dark red (2.5YR 3/6) silty clay loam, red (2.5YR 4/6) dry; weak coarse prismatic structure; hard, friable, sticky and plastic; common medium, fine and very fine roots; common medium and many fine and very fine pores; thin patchy coatings on peds, coatings look like clay films; upper 2 inches compacted by tillage; slight to moderate effervescence with hydrogen peroxide; neutral (pH 6.8); gradual smooth boundary. (8 to 14 inches thick)
Bo2--22 to 36 inches; dark red (10R 3/6) silty clay, dark red (10R 3/6) dry; moderate fine and very fine subangular blocky structure; hard, friable, sticky and plastic; few medium and common fine and very fine roots; few medium, common fine, and many very fine pores; nearly continuous moderately thick coatings on some peds, coatings look like clay films; compact in places; slight to moderate effervescence with hydrogen peroxide; neutral (pH 6.8); gradual smooth boundary. (12 to 16 inches thick)
Bo3--36 to 60 inches; dark red (10R 3/6) silty clay, same color rubbed, dark red (10R 3/6) dry; moderate fine and very fine subangular blocky structure; hard, friable, sticky and plastic; few medium, fine and very fine roots; few medium, common fine and very fine pores; continuous moderately thick coatings on some peds, coatings look like clay films; compact in place; no effervescence with hydrogen peroxide; neutral (pH 6.8).
TYPE LOCATION: Island of Kauai, Kauai County, Hawaii; on Niu Ridge, Kekaha Quadrangle - 22 degrees 02 minutes 07 seconds north latitude and 159 degrees 44 minutes 37 seconds west longitude.
RANGE IN CHARACTERISTICS: Mean annual soil temperature is about 72 degrees F. Few to common small black concretions occur throughout the solum.
The A horizon has hue of 2.5YR or 10R, value of 2 or 3, and chroma of 3 or 4. It has weak or moderate structure.
The B horizon has hue of 2.5YR or 10R, value of 2 or 3 and chroma of 5 through 7. It has weak to moderate structure in the upper part and moderate to strong structure in the lower part. Effervescence with hydrogen peroxide ranges from slight to violent.
COMPETING SERIES: There are no competing series in this family.
The Kahana, Lahaina, Lihue, Molokai, and Wahiawa series are similar. Kahana soils have silty clay texture throughout the solum and strong structure and continuous pressure faces in the B horizon. Lahaina soils have nearly continuous pressure faces in the B horizon and do not have clay film-like coatings in the upper part of the B horizon. Lihue soils have silty clay texture throughout the solum, strong structure in the lower part of the B horizon, and ferruginous mineralogy. Molokai soils do not have continuous moderately thick coatings in the lower part of the B horizon. Wahiawa soils have a mollic epipedon and effervesce with hydrogen peroxide throughout the profile.
GEOGRAPHIC SETTING: Niu soils are on gently sloping to steep uplands. Elevation ranges from 750 to 1,800 feet. Mean annual rainfall is 22 to 35 inches, over 70 percent of which falls from November to April. Mean annual temperature is about 72 degrees F.; average January temperature is 68 degrees F.; and average July temperature is 73 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Mahana and Makaweli soils. Mahana soils are isothermic and have very friable silt loam Bo horizons. Makaweli soils have silt loam or silty clay loam texture in the B horizon and do not have an oxic horizon.
DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff depending on slope; moderate permeability.
USE AND VEGETATION: Most of these soils are used for irrigated sugarcane. Noncultivated areas are used for pasture. Vegetation in the noncultivated areas is kiawe (Prosopis pallida), lantana (Lantana camara), klu (Acacia farnesiana), koa haole (Leucaena glauca), aalii (Dodonea viscosa), fingergrass (Chloris spp.), piligrass (Heteropogon contortus), guineagrass (Panicum maximum), and indigo (Indigofera suffruiticosa).
DISTRIBUTION AND EXTENT: West side of the Island of Kauai, Hawaii. The series is of small extent comprising 3,300 acres.
MLRA OFFICE RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Island of Kauai, Kauai County, Hawaii, 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon- the zone from the surface to 10 inches (A)
Oxic horizon- the zone from 10 to 60 inches (Bo1, Bo2, Bo3)