台灣坡地土壤冲蝕性及流失量之推估

SOIL ERODIBILITY AND SOIL LOSS OF TAIWAN AREA

10.29417/JCSWC.198611_17(2).0012

黃俊義(J. I. Hwang)

土壤冲蝕性指數 ； 降雨冲蝕指數 ； 土壤流失量 ； 質地 ； 坋粒含量 ； 保育措施 ； 永久農業 ； erodibility ； erosivity ； soil loss ； texture ； silt content conservation practice ； permanent agriculture

中華水土保持學報

17卷2期（1986 / 11 / 01）

139 - 154

繁體中文

土壤冲蝕性指數乃爲土壤對冲蝕之分離及搬運作用之抵抗能力，表示土壤內在忍耐冲蝕之難易程度。本文設定土壤冲蝕性指數K值小於0.20以下者爲低蝕性土壤，在0.20～0.40間者爲中蝕性土壤，在大於0.40以上者爲高蝕性土壤。台灣中部南投、台中、彰化等地區山坡地土壤，多爲中蝕性；嘉南地區山坡地土壤具有中高蝕性土壤之傾勢；台灣東北部之台北、基隆、宜蘭等地區山坡地土壤多屬低中蝕性。風化成土作用格外地影響土壤冲蝕性指數，紅壤偏向低、中蝕性土壤，而紅黃壤、黃壤、黃灰壤、灰壤因風化程度遞減，其冲蝕性指數有增高之趨勢。質地顯示着土壤冲蝕指數之特異性；細質地土壤屬低蝕性，中質地微粘重土壤表現爲低、中蝕性；中質地壤質土壤傾向爲中、高蝕性；土壤冲蝕性指數隨土壤坋粒含量增加有遞增之趨勢。土壤流失量乃屬嚴重，137處取樣地點中有50處流失量小於容許流失量，然而其值大多隣近臨界限界。舉凡土壤流失量大於容許流失量地區，大都是由於地形因子（坡度太大，坡長太長），或（及）內在因素（具有偏高冲蝕性指數），及（或）管理欠周所致，宜加強坡地之保育工作，以維持該地區之永久農業。

Soil erodibility is usually used as an indication of the degree of a soil to be eroded. It is the vulnerability or susceptability of the soil to erosion, which is the reciprocal of its resistance to erosion. A soil with a high erodibility will have higher erosion than that with low erodibility if both are exposed to the rainfall of same intensity. According to the designation given in earlier paper (Wann and Hwang, 1981), we found that soils of Central Taiwan are largely medium, those of Chia-Nan area are medium to high and those of Northeastern Taiwan are toward low to medium in erodibility. There is a trend that the erodibility increases inversely with the weathering degree of the soil. The role of soil texture has been indicated in erodibility. It was shown that large particles are resistance to transport because of the greater force required to entrain them and that fine particles are resistance to detachment because of their cohesiveness. The least resistance particles are therefore silt and fine sane fractions, thus soils with a high silt content are most erodible. Soil loss estimation was made using these K-values according to the Universal Soil Loss Equation (USLE) The results show that although some soils with low erodibility there were still greater soil losses than permitted. These sites need to adjust some parameter values for controlling erosion. The serious soil losses were partly due to intrinsic high erodibility, and/or partly due to too long in slope length, and/or partly due to the poor cropping management. Carefully and rigorously conservation practices should be made for the permanent agriculture in these areas.

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