Taxonomical Classification and Genesis of Donggui Series in Jeju Island

Jeju Island is a volanic island which is located about 96 km south of Korean Peninsula. Volcanic ejecta, and volcaniclastic materials are widespread as soil parent materials throughout the island. Soils on the island have the characteristics of typical volcanic ashsoils. This study was conductedto reclassify Jejuseries basedonthe second edition of Soil Taxonomy and to discuss the formation of Jeju series in Jeju Island. Morphological properties of typifying pedonof Jejuseries were investigated, andphysico-chemical properties were analyzed according to Soil survey laboratory methods manual. The typifying pedonhas darkbrown(10YR3/3) siltclay loamA horizon(0~22 cm), strong brown(7.5YR4/6) silty clay BAthorizon(22~43 cm), brown(7.5YR4/4) silty clay Bt1 horizon (43~80 cm), brown (7.5YR 4/6) silty clay loam Bt2 horizon (80~105 cm), and brown (10YR5/4) silty clay loamBt3 horizon(105~150 cm). Itis developedinelevatedlavaplain, andare derived from basalt, and pyroclastic materials. The typifying pedon contains 1.3~2.1%oxalate extractable (Al + 1/2 Fe), less than 85%phosphate retention, and higherbulk density than 0.90 Mg m -3 . That can not be classified as Andisol. But it has an argillic horizon from a depth of 22 to 150 cm, and a base saturation (sum of cations) of less than 35%at 125 cm below the upperboundary of the argillic horizon. That can be classified as Ultisol, not as Andisol. Its has 0.9%ormore organic carbon in the upper15 cm of the argillic horizon, and can be classified as Humult. It dose not have fragipan, kandic horizon, sombric horizon, plinthite, etc. in the given depths, and key out as Haplohumult. A hoizon (0~22 cm) has a fine-earth fraction with both a bulk density of 1.0 Mg cm -3 orless, and Al plus 1/2 Fe percentages (by ammonium oxalate) totaling more than 1.0. Thus, it keys out as Andic Haplohumult. It has 35%ormore clay at the particle-size control section, and has thermic soil temperature regime. Jejuseries canbe classifiedas fine, mixed, themic family of Andic Haplohumults, not as ashy, thermic family of Typic Hapludands. Inthe western, andnortherncoastal areas whichhave arelatively dry climate in Jeju Island, non Andisols are widely distributed. Mean annual precipitation increase 110 mm, andmeanannual temperaturedecrease 0.8 withincreasingelevationof100m . Inthewestern, andnorthern ℃ mid-mountaineous areas Andisols, and non Andisols are distributed simultaneously. Jeju series distributed mainly in the western and northern mid-mountaineous areas are developed as Ultisols with Andic subgroup.