蓮華池地區不同植被土壤的水力特性

Abstract

為了探討不同植被下土壤的水力傳導度、孔隙水通量及導水孔隙率的差異，本論文研究地點位於南投縣魚池鄉林業試驗所蓮華池研究中心轄區，選擇台灣杉人工林（台灣杉林）、檳榔園與香蕉園三種植被，使用張力滲透計對表層與深度20 cm土壤進行現地滲透試驗，測定不同壓力水頭下的水力傳導度，並計算不同壓力水頭區間之土壤孔隙水通量與導水孔隙率。同時，採取不擾動土樣進行室內實驗，測定孔隙率等物理性質，供分析土壤物理性質與水力特性的關係。土壤孔隙率試驗結果，三種植被之不擾動土樣的總孔隙率，以及使用加壓排水法測定之大孔隙率（壓力水頭＞–3 cm）、中孔隙率（壓力水頭–3 cm ~ –100 cm）、小孔隙率（壓力水頭–100 cm ~ –500 cm），皆以台灣杉林為最高。經變異數分析，三種植被之土壤總孔隙率、大孔隙率、中孔隙率、及小孔隙率皆呈現顯著差異。滲透試驗結果，三種植被之表層土壤平均飽和水力傳導度皆高於深度20 cm，且台灣杉林的平均飽和水力傳導度為最高。在壓力水頭＞–10 cm時，三種植被之表層水力傳導度皆大於深度20 cm；壓力水頭為–10 cm時，表層與深度20 cm的水力傳導度幾乎相同；而壓力水頭＜–10 cm時，則深度20 cm的水力傳導度高於表層之水力傳導度。 土壤孔隙水通量與導水孔隙率分別表示在不同壓力水頭區間的水通量及實際參與水分傳導之孔隙比率。孔隙水通量計算結果，台灣杉林、檳榔園及香蕉園表層土壤分別有70.30%、82.45%及80.70%的水流經壓力水頭＞–3 cm之大孔隙，深度20 cm則分別有63.84%、72.16%及68.58%。其次，使用Watson and Luxmoore（1986）（WL 方法）以及Bodhinayake et al.（2004）（BSX 方法）兩種方法計算相當於壓力水頭–0.6 ~ –3 cm的導水大孔隙率，WL方法計算結果，台灣杉林、檳榔園、香蕉園表層的導水大孔隙率分別為0.056%、0.023%、0.027%，深度20 cm分別為0.031%、0.006%、0.007%；BSX方法之表層的導水大孔隙率則分別為0.019%、0.006%、0.007%，深度20 cm分別為0.010%、0.002%、0.002%。三種植被土壤之大孔隙水通量及導水孔隙率皆以表層大於深度20 cm。以BSX法計算之導水大孔隙率約為加壓排水法所測得之大孔隙率的1%左右，顯示實際參與水分傳導的大孔隙僅屬少部份，其餘不連續的大孔隙對水分傳導並無直接影響。

The purpose of this research was to investigate soil hydraulic conductivity, soil pores water flux, and water-conducting porosity under conditions of different vegetation types. Related experiments were executed on three vegetation types, Taiwania plantation, Areca palm plantation, and banana plantation, and both soil surface and depth of 20 cm, which were located beside on the Medicinal Botanical Garden of Lienhuachih Research Center, Nantou. Tension infiltrometer was used to measure soil hydraulic conductivity under different water pressure head in situ. Meanwhile, pore water flux ratio and water-conducting porosity were calculated on the basis of specified water pressure head range. Besides, undisturbed soil samples were extracted for physical properties analysis including porosity and et al., that the data also was used to probe the relationship to soil hydraulic properties. From the soil porosity analysis, Taiwania plantation had higest total porosity, and macroporosity (pressure head >−3 cm H2O), mesoporosity (pressure head range −3 to −100 cm H2O), and miniporosity (pressure head range −100 to −500 cm H2O) measured by Ceramic Plate Extractor in three vegetation types. Those mean were significant difference between vegetation types by ANOVA. Secondly, from the tension infiltration test, the estimated saturated hydraulic conductivity of soil surface was higher than soil depth of 20 cm in each three vegetation types. The estimated unsaturated hydraulic conductivity of soil surface was higher than soil depth of 20 cm under the conditions of pressure head > –10 cm H2O, but lower under the conditions of pressure head < –10 cm H2O. The pore water flux and water-conducting porosity are ways to express the water flux ratio under specificed water pressure head range and the porosity that really participate conducting water. The water flux ratio of macropores (pressure head > –3 cm H2O) of soil surface in Taiwania plantation, Areca palm plantation, and banana plantation were 70.30%, 82.45%, and 80.70% respectively, and soil depth of 20 cm were 63.84%, 72.16%, and 68.58% respectively. Besides, there were two approach, Watson and Luxmoore (1986) (WL approach) and Bodhinayake et al. (2004) (BSX approach), were used to calculate water-conducting porosity. Water-conducting macroporosity (pressure head range 0.6 to –3 cm H2O) of soil surface calculated by the WL approach in Taiwania plantation, Areca palm plantation, and banana plantation were 0.056%, 0.023%, and 0.027% respectively; and soil depth of 20 cm were 0.031%, 0.006%, and 0.007% respectively; and soil surface calculated by the BSX approach in Taiwania plantation, Areca palm plantation, and banana plantation were 0.019%, 0.006%, and 0.007% respectively; and soil depth of 20 cm were 0.010%, 0.002%, 0.002% respectively. Both soil macropore water flux ratio and water-conducting macroporosity of soil surface were higher than soil depth of 20 cm. Besides, the results of water-conducting macroporosity calculated by BSX approach were far less than those measured by Ceramic Plate Extractor. This revealed that the actual water-conducting macroporosity was only about 1% of total macroporosity, and the remaining unconnected macropores which was helpless for water conduction.