제주도 토양인 용흥통의 분류 및 생성

This study was conducted to reclassify Yongheung series based on the second edition of Soil Taxonomy and to discuss the formation of Yongheung series in Jeju Island. Morphological properties of typifying pedon of Yongheung series were investigated and physico-chemical properties were analyzed according to Soil Survey Laboratory Methods Manual. The typifying pedon contains 3.2~3.4% oxalate extractable (Al + 1/2 Fe), less than 85% phosphate retention, and higher bulk density than $0.90Mg\;m^{-3}$. That can not be classified as Andisol. But it has an argillic horizon from a depth of 15 to 150 cm and a base saturation (sum of cations) of less than 35% at 125 cm below the upper boundary of the argillic horizon. That can be classified as Ultisol, not as Andisol or Alfisol. The typifying pedon has 0.9 % or more organic carbon in the upper 15 cm of the argillic horizon and accordingly, can be classified as Humult. It has a clay distribution in which the percentage of clay does not decrese from its maximum amount by 20% or more within a depth of 150 cm from the mineral soil surface, and keys out as Palehumult. Also that meets the requirements of Typic Palehumult. That has 35 % or more clay at the particle-size control section and has mesic soil temperature regime. Yongheung series can be classified as fine, mixed, thermic family of Typic Palehumults, not as fine, mixed, thermic family of Typic Hapludalfs. Most soils distributed in the southern coastal areas in Jeju island which have a humid climate are developed as Andisols. But Yongheung series distributed in this areas and derived from mainly trachyte, trachytic andesite, and volcanic ash are developed as Ultisols. 제주도 남부 해안지대의 용암류대지에 Andisols로 분류되는 토양들과 인접하여 주로 분포하며, Alfisols로 분류되고 있는 용흥통을 재분류하고, 그 생성에 대하여 고찰하고자 용흥통 대표단면의 형태적 특성을 조사하고, Soil Taxonomy의 표준 분석방법인 Soil Survey Laboratory Methods Manual에 따라서 토양을 분석하여 Laboratory data sheets를 작성하였다. oxalate 침출성 (Al + 1/2 Fe) 함량은 3.2$\sim$3.4%로 andic 토양 특성의 분류기준을 충족시키고 있으나, 인산보유능이 72.7$\sim$84.5%로 85% 미만이며, 용적밀도가 $1.21{\sim}1.42Mg\;m^{-3}$으로 $0.90Mg\;m^{-3}$ 이상이다. 따라서 용흥통은 Andic 토양 특성을 보유하고 있지 않으므로 Andisols로 분류할 수 없다. 반면에 BAt층에서 Bt4층 (15~150 cm)까지 점토집적층인 argillic층을 보유하고 있으며, 기준깊이에서의 염기포화도 (양이온합)가 35% 미만이므로 Andisols, 또는 Alfisols이 아니라 Ultisols로 분류되어야 한다. Argillic 층위의 상부 15 cm 깊이에서 유기탄소 함량이 $9g\;kg^{-1}$ 이상이므로 아목은 Humults로 분류된다. 무기질 토양표면에서 150 cm 이내 깊이에 암석질이나 준암석질 접촉면 등이 없으며, 무기질 토양표면에서 150 cm까지 깊이의 argillic 층위에서 점토함량이 최대치와 비교하여 20% 이상 감소되는 층위가 없으므로 대군은 Palehumults로 분류된다. An