塔塔加與四圍山土壤物理化學性質的差異

Abstract

中文摘要 臺灣北部的四圍山與中部的塔塔加兩土壤剖面皆為具有淋澱化作用特徵的淋澱化土，兩地區在海拔高度、氣候條件與植被覆蓋上有許多差異，故針對兩土壤剖面之物理化學性質與黏土礦物方面進行研究，藉以了解在不同化育條件下兩淋澱化土壤之差異。進行的實驗包含土壤剖面基本理化性質分析、三二氧化物化學特性分析與黏土礦物鑑定。 在基本理化性質方面，兩土壤剖面皆為強酸性，並且交換性陽離子的含量，除了表層因為有機質的影響以外，其餘化育層含量都很低，另外由質地分析可發現兩剖面皆有明顯黏粒向下洗入移動聚積的現象，這是由於兩研究地區因高降雨量造成淋洗作用強烈，此外四圍山剖面總碳、總氮含量與碳氮比相較於塔塔加剖面則皆較低。 在三二氧化物化學特性方面，兩土壤剖面鐵、鋁氧化物皆有由土壤表層向下淋洗並累積在剖面下層的現象，而塔塔加的鐵活度比(Feo/Fed)值較四圍山高，且塔塔加剖面鐵氧化物結晶化指標(Fed-Feo)/ Fed)也較四圍山低，該兩指標顯示塔塔加剖面處於較還原的狀態。另外由鐵活度比可知塔塔加剖面淋澱化作用較四圍山剖面活躍，此外利用高梯度磁場分離機濃縮土壤中磁性物質後，再經X射線繞射儀鑑定土壤中的鐵氧化物後，發現兩土壤剖面皆含有鋁同構取代纖鐵礦(0.624 nm)與鋁同構取代針鐵礦(0.416 nm)。 在黏土礦物鑑定方面，四圍山土壤剖面中主要的礦物組成為綠泥石、伊萊石、高嶺石與三水鋁石，而塔塔加土壤剖面則為蛭石、伊萊石、高嶺石與三水鋁石，另外在塔塔加剖面的底層發現有氫氧基夾層蛭石(HIV)(1.41~1.01 nm)的存在，推測蛭石層間有氫氧化物的插入現象。由於四圍山與塔塔加土壤化育因子的差異，造成在塔塔加淋澱化作用較四圍山活躍，三二氧化物於剖面中向下移動現象明顯，並於剖面下方插入蛭石層間生成HIV。 關鍵詞︰淋澱化土、淋澱化作用、三二氧化物、鐵活度比、氫氧基夾層蛭石

Abstract Both Suweishan and Ta-Ta-Chia pedons are podzolic soils in Taiwan. There are a lot of different soil characteria with elevation, including climates and vegetations. This study aimed to identify soil physical, chemical properities and clay mineral compositions at different weathering conditions between the Suweishan and Ta-Ta-Chia pedons. Soil pH of the Suweishan and Ta-Ta-Chia pedons are under acidic conditions. Cation-exchange capacity except the surface horizon is because of high organic matter contents, the other horizons are low. These two study regions have high precipitation and intense leaching lead to clay contents increased with increasing soil depth. On the other hand, due to lower elevation of the Suweishan pedons, the total carbon, nitrogen contents and C/N ratio is lower than that of the Ta-Ta-Chia pedons. The sesquioxides leached from surface soils into subsoils and accumumated on subsoils. The iron activity ratio (i.e., Feo/Fed) on the Ta-Ta-Chia is higher than that of the Suweishan pedons and the iron crystallinity index (i.e., Fed-Feo/Fed) showed the reversed trend. From Feo/Fed and Fed-Feo/Fed values, it is indicated that Ta-Ta-Chia pedons with high clay contents are under higher activity of podzolization and redoximorphic condition than that of the Suweshan pedons. After high gradient magnetic separation (HGMS) treatments and X-ray diffraction analyses, both Suweishan and Ta-Ta-Chia pedons contained lepidocrocite and goethite. The clay fractions of the Suweishan contained chlorite, illite, kaolinite and gibbsite, and Ta-Ta-Chia pedon of vermiculite, kaolinite, illite and gibbsite. In addition, the hydroxyl-interlayered vermiculite (HIV) was found in subsoils of the Ta-Ta-Chia pedons. Formation of HIV in the Ta-Ta-Chia pedons are caused by the high higher activity of podzolization and redoximorphic condition during pedogenesis. Keywords: podzolic soils, podzolization, sesquioxides, iron activity ratio, hydroxyl-interlayered vermiculite (HIV)