玄武岩黑土與黑色灰土理化性質之比較-臺灣黑色土之研究(II)

Abstract

(一)為研究臺灣黑色土究係趨向於核粘土型，抑係黑色石灰土型，乃選擇由玄武岩風化之黑土剖面一個與由石灰岩所生成之黑色石灰土剖面二個進行理化分析，以比較其成土作用及成土趨向，併檢討其分類方法。 (二)從剖面形態觀之，玄武岩黑土與黑色石灰土二者雖均屬暗棕色，但玄武岩黑土之構造體屬核粒狀，結構強而硬，塑性甚大，乾時裂隙甚寬；黑色石灰土則構造體主要團粒狀，結構柔軟，塑性小，乾濕時乏伸縮性。 (三)物理分析結果示黑色石灰土之粘粒量、真比重均低於玄武岩黑土，碎石含量與分散度則顯較高；而水份當量玄武岩黑土受黏土含量之影響甚明顯，黑色石灰土則主要受有機質之影響。 (四)化學分析結果示二者之鹽基置換能量，不飽合度與粘土中之矽鐵鋁率頗相似，但黑色石灰土之母岩與土壤含多量之碳酸鈣，土壤全量中之矽、鈣與鎂均高，而矽鋁率及矽鐵鋁率母岩低於土壤甚多。玄武岩黑土之矽鐵鋁與鹽基等各成分母岩與土壤之差異甚小。 (五)二種土壤之流失成份、ba值、β值與Sa值均有甚明顯之不同，玄武岩黑土在成土過程中鐵鋁顯有積聚，而黑色石灰土則呈集矽之現象，示二種土壤之成土過程與趨向有所不同。 (六)依THORP等之分類方法，玄武岩黑土與核粘土頗為相似，而在土壤新分類第七草案中可以歸屬於Vertisols土綱，Aquerts亞綱，Mazaquerts大土類，Haplic Mazaquerts亞類，黑色石灰土則屬於Mollisol土綱 Remoll亞綱與大土類 Typic Remoll亞類。 The purpose of this paper is to compare the soil properties and genesis of Black Soils and Rendzinas in Taiwan and to find out the proper categories of these soils in Soil Classification of 7th Approximation. Soil morphologies and physico-chemical properties of three soil profiles, one deriving from basalt being called Black Soils, and two others deriving from limestone being classified as Rendzinas are studied.The results may be summarized as follows: By comparing the soil morphologies, both soils are dark brown to black in colore throughout the profiles, but Black Soils are of strongly moderate to fine blosky structure, extremely hard, very firm, very plastic, and also forming large cracks when dried. However, the Rendzinas are of moderate to large granular in structure, friable, slight plastic, and small cracks when dried. Data from physical measurement show that, clay content, specific gravity and apparent specific gravity of Black Soils are higher than those of Rendzinas. However, the reverses are found in the contents of gravels and degree of dispersion. The moisture equivalents of Black Soils are evidently influenced by the contents of clay in the profile, while Rendzinas are dominantely changed with the contents of organic matter. Data from chemical analyses indicate that the exchange capacity, base saturation and the silica to sesquioxide moleculars ratio of clay fractions in these profiles are similar to each other. Judging from the chemical composition data, it has been found that Rendzinas contain more calcium, magnesium and carbonates but fewer iron and alumina than Black Soils. In addition, in Rendzinas, the soil bodies have especially high content of residual silica in comparison with their parent material. However, slight difference was found between them in Black Soils. The loss of gaining soil constituents were calculated from their parent materials as a basis. From which the Black Soils have lost more kinds but fewer amounts of elements than those of Rendzinas. The ba values, β values and sa ratios indicate slight leaching out of bases and accumulating some alumina in some horizons of Black Soils; in Rendzinas, a large amounts of bases were lost, but a lot of silicate were accumulated. These indicate that the forming processes of these two soil groups are very different. From the morphologies and physico-chemical properties, Black Soils are more similar to the Grumusol rather than the Rendzinas. According to the soil classifying system of 7th Approximation the Black Soils which derived from basalt may be classified in Vertisol order, Aquert suborder, Mazaquert great group, and subgroup of Haplic Mazaquert, wheras the Rendzinas have been classified in mollisol order, Remoll suborder and great group and Typic Remoll subgroup.