Taxonomical Classification of Namweon Series, Black Volcanic Ash Soils

흑색 화산회토인 남원통의 분류

  • Received : 2009.08.14
  • Accepted : 2009.09.20
  • Published : 2009.10.30

Abstract

This study was conducted to reclassify Namweon series, black volcanic ash soils, in Jeju Island based on the second edition of Soil Taxonomy : A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Morphological properties of typifying pedon of Namweon series were investigated and physicochemical properties were analyzed according to Soil Survey Laboratory Methods Manual. The typifying pedon of Namweon series has black (10YR 2/1) silt loam Ap horizon (0~11 cm) and black (10YR 2/1) silt loam BA horizon (11~72 cm). Bw horizon (72~100 cm) is very dark brown (10YR 2/2) silt loam. That occurs on lava plain derived from volcanic ash materials. The typifying pedon contains 5.2~6.4% oxalate extractable (Al + 1/2 Fe), over 85% phosphate retention, and lower bulk density than $0.90Mg\;m^{-3}$. Ap, BA, and Bw horizons of the pedon have andic soil properties. That can be classified as Andisol. The typifying pedon has an udic soil moisture regime and has a 1,500 kPa water retention of 15% or more on air-dried samples throughout all horizons, and can be classified as Udand. Ap and BA horizons (0~72 cm) have a color value, moist, and chroma of 2 or less, melanic index of 1.70 or less, and 6% or more organic carbon. That meets the requirements of melanic epipedon. That keys out as Melanudand. That has more than 6.0% organic carbon and the colors of mollic epipedon throughout a layer 50 cm or more thick within 60 cm of the mineral soil surface.. Thus, that keys out as Pachic Melanudand. The pedon has a fine-earth fraction that has a water content at 1,500 kPa tension of 12% or more on air-dried samples and has less than 35% (by volume) rock fragments. Thus, the substitute for particle-size class is medial. That has a sum of 8 times the Si (percnt by weight extracted by acid oxalate) plus 2 times the Fe (percnt by weight extracted by acid oxalate) of 5 or more, and 2 times the Fe is more than 8 times the Si. Thus, the mineralogy class is ferrihydritic. Namweon series can be classified as medial, ferrihydritic, thermic family of Pachic Melanudands, not as ashy, thermic family of Typic Melanudands.

대표적인 흑색 화산회토인 남원통은 Ap, BA 및 Bw층에서 Oxalate 침출성 (Al + 1/2 Fe) 함량이 각각 5.2%, 7.4%, 9.8%로 높고 인산보유능이 각각 85.4%, 98.4% 98.3%로 매우 높다. 용적밀도가 각각 $0.72,\;0.62,\;0.76Mg\;m^{-3}$으로 매우 낮다. 전 토층이 Andic 토양 특성을 보유하고 있어서 Andisols로 분류 된다. Udic 토양수분상을 보유하고 있으며, 토양수분 장력 1,500 kPa에서의 토양수분함량이 전토층에서 15% 이상이므로 아목은 Udands로 분류된다. Ap층과 BA층에서는 Allophane과 Al-유기복합체가 혼재되어 있으나, Bw층에서는 활성 Al이 주로 Allophane의 구성분으로 존재하고 있으며, 전 토층을 통하여 Allophane과 Ferrihydrite 함량이 높다. 습윤시 명도와 채도 값이 Ap, BA 및 Bw층 모두에서 2 이하이고, 유기탄소 함량이 각각 $125,\;115,\;42g\;kg^{-1}$이며, melanic index가 각각 1.53, 1.50, 1.55이다. 0 에서 72 cm 깊이까지 모든 층위에서 melanic 감식표층의 분류조건을 충족시키고 있다. 따라서 대군은 Melanudands로 분류된다. Ap, BA 및 Bw층에서 토양수분장력 1,500 kPa일 때 토양수분함량이 풍건 시료의 경우 각각 28.9, 29.1, 27.6%로 15% 이상이며, 비풍건 시료의 경우 34.2, 55.3, 48.7%로 70% 이하이다. 0~72 cm의 깊이에서 유기탄소 함량이 $60g \;kg^{-1}$ 이상이며, 습윤시 명도와 채도 값이 2 이하이므로 아군은 Pachic Melanudands 로 분류된다. 토양수분 제어부위에서 토양수분장력 1,500 kPa일때 토양수분함량이 풍건 시료의 경우 12% 이상이며, 비풍건 시료의 경우 30~100% 범위 내에 있으므로 대체 토성속은 medial에 속한다. 8 x acid oxalate 침출 Si(%) + 2 x acid oxalate 침출 Fe(%) 값이 광물속 제어부위에서 12.3~19.5로 5 이상이다. 또한 2 x acid oxalate 침출 Fe 값이 8 x acid oxalate 침출 Si(%) 값보다 크므로 광물속은 ferrihydritic에 속한다. 남원통은 thermic 토양온도상을 보유하므로 ashy, thermic family of Typic Melanudands가 아니라 medial, ferrihydritic, thermic family of Pachic Melanudands로 분류되어야 한다.

Keywords

References

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