台灣中部一極育土中鐵瘤的生成

The Formation of Iron Nodules in an Ultisol in Central Taiwan

蔣先覺(Hsien-Chueh Chiang) ； 許正一(Zeng-Yei Hseu) ； 陳尊賢(Zueng-Sang Chen) ； 胡弘道(Hung-Tao Hu)

《台灣林業科學》 11卷4期 (1996/12) Pp. 385-391

https://doi.org/10.7075/TJFS.199612.0385

摘要

鐵瘤是土壤中不規則形的堅硬鐵濃縮物質，通常出現在乾濕交替頻繁的土壤中。鐵瘤的存在與否雖然不會影響土壤的分類結果，但其形態特微與化學性質卻能直接反應土壤生成化育的環境。本研究選擇台灣中部低海拔丘陵地區之－極育土剖面，描述其形態特徵並進行各種化學分析，試圖探討鐵瘤的生成與化育機制。結果顯示，鐵瘤的粒徑與含量會隨剖面深度而遞增，且其游離鐵含量高於土壤基體，但Feo-/Fed-比值則極低，顯示主要為結晶性較佳的氧化鐵。本研究中生成鐵瘤的主要機制乃是腐石在原處經頻繁變動的乾濕交替作用後，崩解風化而化育生成，而洗入型的氧化鐵則為生成鐵瘤的次要力量。

關鍵字

鐵瘤 ； 游離鐵 ； 腐石

並列摘要

Iron nodules with irregular shapes are hard cemented materials with high concentrations of Fe oxide, and generally occur in soils associated with frequent wetting/drying cycles or with poor drainage. The presence or absence of iron nodules does not affect the taxa of soil classification, but they always indicate the soil genetic environments. An Ultisol located on a low-elevation terrace in central Taiwan was selected in this study to investigate the morphological characteristics, chemical properties, and pedogenic processes of iron nodules. The results indicate that the sizes and amounts of iron nodules increase with increasing soil depth. Free iron contents in the iron nodules are higher than those in the soil matrices, but the Feo-/Fed-values in the iron nodules are very low. The major driving force promoting the formation of iron nodules is in situ weathering from saprolites by frequently alternating wetting/drying cycles, while illuviated iron only played a minor role in this formation.

並列關鍵字

iron nodules ； free iron ； saprolite