台灣耕地土壤有機磷礦化作用之研究

Study on the Mineralization of Organic Phosphorus in Agricultural Soils of Taiwan

游逸凡(I-Fan Yu)

指導教授 ： 何聖賓

國立臺灣大學/生物資源暨農學院/農業化學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.00670

摘要

本論文針對台灣65種耕地土壤，評估及比較台灣耕地土壤總磷與有機磷測定方法之適用性；建立一簡單之方法來評估土壤原含有有機磷之礦化速率；以及探討有機磷被礦化後的無機磷在土壤中的動態等來瞭解有機磷之重要性，並探討各磷劃份與土壤性質間之相關關係以做有效性的管理建議。

有機磷和總磷的含量（r = 0.649, p < 0.001）有極顯著相關。65種土壤樣本藉由過氯酸消解法測得的平均總磷量為936 ± 866 mg P/kg；燒灼法測得的平均總磷為960 ± 833 mg P/kg。當土壤有較低的pH、黏粒量、CEC、有機碳、總磷低於500 mg P/kg及較高的游離氧化鐵、鋁時燒灼法所得的總磷量會被低估。雖然燒灼法測得的總磷比過氯酸消化法約有4.3％的低估，且變異甚廣，但前者可伴隨測得土壤有機磷，因此值得更進一步的研究並採納為常規步驟。透過複迴歸模式可知土壤總磷量和土壤性質彼此間之關係可藉由有機碳及有機磷含量較為精確的計算出總磷量（TPIgnition = 159 + 13.3 OC + 2.57 OP；TPHClO4 = 202 +13.9 OC + 2.51 OP）。

以常用的550℃燒灼法結果來評估65種土壤之有機磷平均為201 ± 159 mg P/kg。在燒灼法的比較中，燒灼溫度降低（450℃）在土壤有較低的游離氧化鐵、鋁、CEC，較高的有機碳及總磷大於500 mg P/kg時會造成有機磷的低估，而相同溫度下，改用濃度低的鹽酸萃取會造成無機磷的低估。

礦化過程中所釋放的無機磷之所以難以正確的測定與探討，乃因礦化磷被釋放後往往就迅速被吸附。我們發展一新方法，將孵育過程中會產生的無機磷溶解作用以及溶液磷生物固定化作用和有機磷礦化作用的總和分開來，以評估每個土壤的磷礦化速率。試驗設計中，一組為控制組，另一組則殺菌阻止微生物活性。所有的土壤樣品和陰離子樹脂混合均勻後，在通氣狀態下孵育，之後測定兩處理中的樹脂磷差異值則定義為磷的礦化速率。選定的12種土壤中，磷礦化速率平均分佈在0 - 0.18 mg/kg/day，無機磷溶解量則為0.02- 0.71 mg/kg/day。若土壤有機磷高於100 mg/kg的前提下，若土壤磷飽和指標（PSI）> 0.15，會得到較高的礦化磷。

各吸附體吸附磷的等溫吸附曲線約略符合Langmuir方程式，其最大吸附量依序為Dowex 1X8陰離子交換樹脂 > Dowex MSA 大孔隙陰離子交換樹脂 > 針鐵礦 > 赤鐵礦 > 水鋁氧。土壤背景溶液濃度的改變會改變樹脂磷的最大吸附量，當背景溶液濃度越高，益發增加溶液中的陰離子濃度（過氯酸根），進而與磷酸根競爭而降低了樹脂之磷最大吸附量，但會減緩反應中溶液pH值下降的幅度。

利用實驗室自行設計之三腔反應器進行離子交換樹脂與各吸附體對磷酸根離子的競爭性吸附。而吸附體親和力的不同，即使初始時控制競爭者吸附的能力相同，但最後所吸附的含量卻有所差異。除了針鐵礦、赤鐵礦等氧化鐵礦物競爭能力比樹脂高外，其餘的氧化鋁及土壤競爭能力比樹脂低。由於樹脂與植物根的吸收行為有良好相關，藉由這樣的結果，可推估植物根系從水溶液中吸收無機磷的能力比土壤組成份高。

關鍵字

有機磷 ； 過氯酸消解法 ； 燒灼法 ； 礦化作用速率 ； 競爭吸附 ； 陰離子交換樹脂 ； 土壤組成 ； 磷飽和指標

並列摘要

Mineralization of soil organic P (Po) plays an important role in soil P cycling. No direct methods presently exist enabling the determination of the organic phosphorus content of soil. Organic P is determined indirectly by either ignition or extraction methods. The Organic phosphorus is determined by measuring the differences in the extractable phosphorus in soil samples before and after treatment.

Organic phosphorus and total phosphorus are highly positive related. The average total phosphorus of 65 soils by HClO4 digestion method is 936 ± 866 mg p/kg. The result of using Ignition method is 960 ± 833 mg p/kg. These results showed that in soils with lower pH, clay contents, CEC values, and organic carbon contents, total P contents lower than 500 mg/kg and with higher amounts of CBD extractable Fe and Al, the total P contents obtained by the ignition method tended to be underestimated. Although the average amount of total P obtained by the ignition method was 4.3% lower than that obtained by the HClO4 method and variation was rather wide, the former method can concomitant use for the determination of soil organic P and is thus worthy of further studying and adopted as a routine procedure. On the other hand, stepwise regression selection procedure was adopted to relate the amount of total P content in soils to the selected soil properties. The results were as follows: TPIgnition = 159 + 13.3 OC + 2.57 OP; TPHClO4 = 202 +13.9 OC + 2.51 OP。

The average organic phosphorus for 65 soils is 201 ± 159 mg P/kg by ignition method at 550℃. Compare with the ignition method of 550℃, 450℃ or HCl extractant has tendency to underestimate the result.

Rates of P mineralization on native soil are poorly known due to the limitations of available analytical techniques. Quantitative information on the release of available inorganic P by this process is difficult to obtain because any mineralized P gets rapidly sorbed. We developed a new method to estimate P mineralization rate to each soil in order to separate the processes of mineral P solubilization and organic P mineralization and get rid of solution P immobilization. One set of soils was retained as control; the other set was sterilized to stop microbial activity. All sets of samples were then incubated with anion exchange resin mixed evenly under aerobic conditions. Difference in resin P among the two treatments was used to estimate P mineralization rates. Rates of P mineralization ranged from 0 - 0.18 mg/kg/day and the rates of solubilization of mineral P were 0.02 - 0.71 mg/kg/day for the twelve studied soils. If the value of phosphorus saturation index (PSI) is higher than 0.15 might cause the higher mineralized P. This new method is safer and simpler in operation than isotopic techniques.

The Sorption isotherms in soils and Fe- Al- oxides could be well described by the Langmuir equation. The phosphorus sorption maxima of all competitors decreased in the order Dowex 1X8 Resin > Dowex MSA Resin > Goethite > Hematite > Gibbsite. The adsorption of phosphorus by anion resins were affected by increasing the concentration of the background solution.

Competition in sorption of inorganic phosphorus between anion exchange resins and soil components was studied by using a special designed tri-chamber apparatus. Other than Goethite and Hematite, competitive sorption of Al2O3 and soils are lower than resin. With such a result, we can find the plant root system from the soil solution might have more ability to absorb the inorganic phosphorus than the soil.

並列關鍵字

organic phosphorus ； HClO4 Digestion method ； Ignition method ； the rate of mineralization ； competitive sorption ； Anion-exchange resin ； soil component ； phosphorus saturation index (PSI)

參考文獻

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Adams, M.A., and L.T. Byrne. 1989. 31P-NMR analysis of phosphorus compounds in extracts of surface soils from selected Karri (Eucalyptus diversicolor F. Muell.) forests. Soil Biol. Biochem. 21: 523-528.

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