台灣北部烘爐山森林土壤之特性化育與分類

烘爐山(Honglu Mountain, HL)屬於大屯火山亞群，約在40萬年前停止噴發，為一座由高鋁玄武岩所構成的截頂狀火山錐。由於母質特殊且尚未調查，根據地形土序在該地區山頂(HL-1)、上背坡(HL-2)與下背坡(HL-3)位置選擇土壤樣體，研究其土壤特性、化育作用與分類。土壤剖面呈現棕色，且不具有典型灰燼土具有的黑瘠表育層。研究區域屬亞熱帶氣候，茂盛的植被提供大量有機質來源，而豐富的可交換性鋁增加了土壤酸度，強烈的淋洗作用造成低鹽基飽和度。選擇性化學抽出指出，土壤中的活性鋁主要以鋁‒有機質複合物為主，而鋁英石在酸性環境下不易生成(pH < 5)。微形態特徵顯示樣體無明顯的黏粒洗入現象，再以質地分析結果判斷得知，研究樣體無黏聚層(argillic horizon, Bt)，B化育層均為火山灰土壤常見的變育層(cambic horizon, Bw)。礦物分析結果顯示黏土礦物以高嶺石、水鋁氧含量最多，石英次之，方矽石含量最少，HL-2及HL-3有中量的綠泥石及水化層間蛭石，HL-2及HL-3樣體有相對較多的2:1型礦物。研究區域土壤受母質影響為火山灰土化作用，且氣候與時間因素使得化育於火山母質的土壤逐漸脫離火山灰土壤性質，在此轉變的過程有鹽基離子流失、結晶性鐵氧化物變多、無定形物質減少、總體密度上升、黏粒含量變多、高嶺石等黏土礦物的生成等。地形對於本研究區域土壤化育的影響不大，但各樣體間受到坡度、坡向等微地形的影響，因此在物理及化學性質間仍有些許差異。所研究的三個樣體在物理及化學性質上皆未能完全符合美國土壤分類系統中火山灰土壤性質(andic soil properties)之定義，在海拔385–650 m間地形土序上的HL-1及HL-2其亞類為灰燼型低鹽基濕潤弱育土(Andic Dystrudepts)，HL-3所受的風化程度最大其亞類為典型低鹽基濕潤弱育土(Typic Dystrudepts)，地形土序上的變化不大，皆屬於弱育土(Inceptisols)。

關鍵字

灰燼土；弱育土；土壤化育；火山灰土壤性質；玄武岩；安山岩；鋁–有機質複合物；地形土序

並列摘要

Honglu Mountain belongs to Tatun volcano subgroup with the extinction of eruption approximate 0.4 million years ago. Previous studies have explored the pedogenesis and soil classification in most areas of Yangmingshan national park, but Honglu Mountain is not investigated and only an Al-enriched basalt composite cone in Tatun volcano group. Three soil pedons are selected along a toposequence including summit (HL-1), upper backslope (HL-2), and lower backslope (HL-3) landscape positions. The soil color is brown and the diagnostic epipedon is ochric epipedon for all the studied three pedons. Dense vegetation supplies large amounts of organic matter to the soils in this subtropical climate, but exchangeable cations were leached out of the soils due to the very high rainfall of 4800 mm per year. However, large amounts of exchangeable Al are generated in the soils to increase the soil acidity. The results of selective chemical extractions indicate that the active Al are dominantly formed as Al -humus complexes in the soils. Allophane is not identified in such an acidic condition (pH< 5). The soil micromorphology shows that clay illuviation is unobvious in B horizon and the particle-size analysis indicates that B horizon are cambic horizons (Bw). X-ray diffractometer analysis shows that the mineralogical compositions of the clay fractions are major with kaolinite and gibbsite, minor with quartz, and fewer with cristobalite. The pedogenesis processes of the studied soils are predominant andosolization and subsequent de-andosolization, which forming Inceptisols via the factors of climate and time. This implies the base loss, increases of crystalline iron oxides, bulk density, and clay contents, decreases of non-crystalline materials, and formation of kaolin minerals. The factor of topography did not significantly affect the pedogenesis, while the differences between physical and chemical properties of the three soil pedons can be attributed to micro-topography. The chemical and physical properties of the studied pedons can’t completely meet the criteria of andic soil properties of USDA Soil Taxonomy. The pedon HL-1 and HL-2 can be classified as Andic Dystrudepts, and pedon HL-3 can be classified as Typic Dystrudepts. The studied pedons are all classified as Inceptisols along the toposequence.

並列關鍵字

Pedogenesis ； Andic soil properties ； Inceptisols ； Andisols ； Al-humus complexes ； Basalt ； Andesite ； Toposequence

參考文獻

陳春泉。1979。土壤調查手冊。台灣省農業試驗所。

鄭亦均。2014。兩個不同風化時間的地形序列中火山土壤特性比較。國立臺灣大學農業化學研究所碩士論文。

Asio, V. B and Z. S. Chen. 1998. Study of andesite weathering in northern Taiwan using micromorphological approaches. Taiwan J. For. Sci. 13(4): 259-269.

Juang, W. S. 1993. Diversity and origin of Quaternary basaltic magma series in northern Taiwan. Bull. Natl. Mus. Nat. Sci. 4: 125-166.

Bascomb, C. L. 1968. Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups. J. Soil Sci. 19: 251-267.

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台灣北部烘爐山森林土壤之特性化育與分類

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