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本省中南部沖積土不同形態鐵在剖面中之分佈及其對土壤磷吸著的影響

Disrtibution of Different Forms of Iron within Profiles from Alluvial Soils of Central-South Taiwan and Its Effect on Phosphate Sorption

摘要


本研究目的為明瞭沖積土中不同形態可抽出性鐵在水、旱田土壤剖面中之分佈特性,從不同形態之土壤剖面中探究與其有關之土壤化學性質的差異,及評估此性質對土壤磷吸著的影響。所得結果如下: 1.游離鐵(Fe(下標 d), Dithionite法)在剖面中之含量分佈大致與粕粒一致,唯受水田表土鐵之往下移動、地下水位上下起伏及剖面質地出現極不均的情形所影響。表土之Fe(下標 d)與粘粒含量二者呈極顯著正相關,且Fe(下標 d)含量呈旱田較高,排水良水田次之,而排水不良水田較低之趨勢。 無定形鐵(Fe(下標 o), Ammonium oxalate法)在剖面中之含量分佈則與粘粒無關而與有機質之分佈一致,即使表土具較低之Fe(下標 d)含量,Fe(下標 d)含量均以表土層最高,然後逐漸降低。表土之Fe(下標 o)含量受有機質含量及水田浸水影響,故表土之Fe(下標 o)與Fe(下標 d)不同,其與粘粒含量之相關僅呈5%顯著,且旱田者Feo含量明顯較水田低。 2,鐵活性比(Feo/Fed)在剖面中之分佈亦大致與有機質一致,而表土之鐵活性比,排水不良水田最高、排水良水田次之,旱田最低,故利用此比值可將此三種不同剖面形態之土壤區分。唯表土以下之灰斑層無法以此比值鑑定。 3.表土之土壤性質與土壤磷吸著的相關分析顯示土壤磷吸著僅與Fe(下標 o)含量成極顯著正相關,Fe(下標 o)對土壤磷吸著的重要性遠大於Fe(下標 d)。 4.土壤經浸水90天放乾後,僅經浸水處理的土壤,Fe(下標 o)含量較未浸水土壤增加,而添加1%有機質浸水處理者,增加幅度更大,且此效果,以旱田土壤明顯大於水田土壤。由此而導致土壤對磷吸著的增加趨勢亦同。經處理後之土壤利用草酸銨以抽出Fe(下標 o)後,磷吸著會明顯降低,且處理間磷吸著的差異亦因此而除去,顯示Fe(下標 o)確實是影響磷吸著的重要因子,唯各土壤間磷吸著的差異仍存在,表示土壤中除Fe(下標 o)外尚有其他成分參與磷的吸著作用。

關鍵字

游離鐵 無定形鐵 鐵活性比 磷吸著 水田 旱田 排水 剖面

並列摘要


The distribution of extractable forms of iron within profiles was described for rice soils and upland field from alluvial soils of central-south Taiwan. The different properties of profiles with various soil morphology was investigated and evaluated its effect on P-sorption. The results are summarized below: 1. The. distribution of free iron content (Fe(subscript d), dithionite-extractable) within soil profiles not completely concided with that of clay content, reflecting the influence of fluctuating water tables, downward movement of Fe(subscript d) in surface soil under paddy condition, and texture discontinuity within profile on the distribution of iron. There was the high correlation between Fe(subscript d) and clay content in sruface soils; however, the largest content of Fe(subscript d) was usually found in upland fields, followed by well drained paddy fields, and the lowest in poor drained paddy fields. The distribution of amorphous iron content (Fe(subscript o), oxalate-extractable) within profiles concided with that of organic matter content, but generally it did not correspond to clay content. The maximum for Fe(subscript o), however, was usually in the surface soil in spite of its Fed depletion. Fe(subscript o) content in the surface soil was affected by organic matter content and flooding, therefore Fe(subscript o) contern, differing from Fed, was correlated with clay content with 5 % significance. However. Fe(subscript o) content in surface soils of upland fields was much lower than that of paddy fields. 2. The active iron ratio (Fe(subscript o)/Fe(subscript d))decreased with depth down the profile and generally corresponded with organic matter content. The Fe(subscript o)/Fe(subscript d) ration in the surface soils could be used to separate well drained upland fields, well drained paddy fields, and poorly drained paddy fields. Layers below surface soils, exhibiting gley morphology, showed no difference in the Fe(subscript o)/Fe(subscript d) values, compared with their nongleyed counterpart, so that the FeO/Fed ratio could not be used to separate gleyed or nongleyed horizons below surface soils. 3. Among all the properties of the surface soils, only the Fe(subscript o) content was high correlated with soil P-sorption. The effect of Fe(subscript o) on P-sorption was much more important than that of Fe(subscript d). 4. The soils were ammended with o and 1% organic matter as cellulose and kept flooded for 90 days. Upon soil-flooding and draining, the Fe(subscript o) content increased in each soils. With the application of 1% organic matter at the time of soil flooding, the Fe(subscript o) content increased by a large magnitude. These effects for the soils from upland fields wewe much larger than those from paddy fields, there was the same trend for the effect on P-sorption. When the soils with or without organic matter treatment during flooding were drained, air-dried, and extracted with ammonium oxalate, P-sorption decreased. This extraction also eliminated the difference in P sorption due to prior flooding. These implied that Fe(subscript o) seemed to be responsible for the P sorption. The difference in P sorption among the soils, however, was not removed by this extraction. This indicated that soil properties other then amorphous Fe content of soil may also be responsible for the P sorptivity.

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