若干臺灣耕地土壤中磷淋溶有關指標之比較

Abstract

本研究利用五種台灣代表性土壤進行孵育實驗，比較土壤溶液磷、Bray No.1萃取磷、Olsen萃取磷和磷飽和指標等與磷素有關的有效性指標，以作為對土壤中磷素有較好的管理。經選取將軍系 ( Cf )、二林系 ( Eh )、淇武蘭系 ( Ca )、平鎮系 ( Pc )、淡水系 ( TTs )等五種台灣代表性土壤，進行土壤等溫吸附試驗估測土壤磷的固定力，並以土壤溶液磷濃度為0.2 ppm之磷固定量為基準進行孵育實驗，以及分析孵育前後的土壤樣本之Bray No.1、Olsen萃取磷和磷飽和指標。 結果顯示，供試土壤最大吸附量範圍從89 到 1250 mg P kg-1，由大到小依序分別為淡水系，平鎮系，淇武蘭系，二林系，將軍系，其游離氧化鐵鋁含量越高，土壤之磷的最大吸附量也就越大。當土壤平衡溶液磷濃度為0.2 ppm時，各土系的吸附量分別為淡水系769 mg kg-1，平鎮系143 mg kg-1，淇武蘭系217 mg kg-1，二林系26 mg kg-1，將軍系11 mg kg-1，而此吸附量也與Bray No.1萃取磷、Olsen萃取磷和磷飽和指標呈顯著的相關。土壤孵育試驗結果不論是Bray No.1萃取磷、Olsen萃取磷或磷飽和指標，孵育時添加越高濃度的磷溶液所測得的值也會越高。在單一供試土壤以及所有供試土壤兩者情況下，Bray No.1萃取磷、Olsen萃取磷和磷飽和指標皆呈顯著的相關，單獨討論單一供試土壤時，Olsen萃取磷量與其他磷有效性指標皆有較高的相關性，但在討論所有供試土壤時，卻是Bray No.1萃取磷量與其他磷有效性指標有較高的相關性。五種供試土壤磷之平衡溶液濃度均低於0.2 ppm，意謂土壤磷有效性低，但Bray No.1萃取磷量和Olsen萃取磷量在大部分土壤皆達到需肥推薦的標準，這樣顯示此需肥推薦標準似乎已不再適用現今的土壤狀況，分級的標準須再詳細探討。

Comparisons of various methods for assessing the phosphorus (P) status of soils, i.e., soil solution P, Bray No.1, Olsen, and P saturation index method, were studied in this thesis in order for the better management of soil phosphorus. Five representative soils from Taiwan were selected for this study, i.e., Chengchung (Cf), Chiwulan (Ca), Erhlin (Eh), and Tansui (TTs) series. Phosphorus sorption isotherms were used to estimate P fixation of soils. The amount of P fixed to give a solution concentration of 0.2 ppm P was then used as the basis for the P application rate in the incubation experiments. Bray No.1 P, Olsen P, and P saturation index of soils were measured before and after incubation. The results showed that the P sorption maxima of the soils were in the range of 89 to 1250 mg P kg-1 and were decreased in the order of TTs＞Pc＞Ca＞Eh＞Cf with decreasing amounts of sesquioxide in soils. The amount of P fixed to give a solution concentration of 0.2 ppm P was 769, 217, 143, 26, and 11 mg P kg-1 for TTs, Ca, Pc, Eh, and Cf soils respectively and was negatively significant correlated to Bray No.1 P, Olsen P, and P saturation index. Bray No.1 P, Olsen P, and P saturation index were all increased with the increasing P application rate after incubation. The relationships among Bray No.1 P, Olsen P, and P saturation index were all significantly correlated both for each type of soils and for all types of soils. Olsen method seemed better for the same type of soil while Bray No.1 method is superior for all types of soils. Since soil solution P of the studied soils were all below 0.2 ppm P and Bray No.1 P, Olsen P of most soils were attained adequate level, the criteria for grading P status of soils needs further investigation.