| Summary: | 博士 === 國立臺灣大學 === 農業化學研究所 === 96 === 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.
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