Abstract
An attempt was made to clarify the mechanisms of phosphate desorption using the anion exchange resin method for extraction of phosphorus from soil. It was shown that there is a linear dependence between the amount of phosphorus desorbed and the square root of the desorption time. Through theoretical examination it was concluded that the above-mentioned relation between the desorption and time is a result of the diffusion of phosphate from porous soil medium. Using this interpretation of the desorption curve as a basis, the activation energy of the phosphate desorption was calculated from the experimental results obtained with resin extraction at different temperatures. The activation energy values were 32—64 kJ/mol depending on soils involved. In application of the results, the mechanisms and rate at different steps of the desorption were examined.
Highlights
Pot experiments with oats (Aura 1978) indicated that the extraction of phosphorus from soil using anion-exchange resin and water seems to be a suitable method for measuring the phosphorus level of Finnish soils
The significance of the calculated activation energy may be interpreted in the following way
The step which determines the rate of diffusion is mainly the detachment of phosphate oxygen atom from Al + + + or
Summary
Pot experiments with oats (Aura 1978) indicated that the extraction of phosphorus from soil using anion-exchange resin and water seems to be a suitable method for measuring the phosphorus level of Finnish soils. The advantage of the resin method is apparently that the microstructure of the soil is not substantially changed by the extraction. When water acts as the extractant the sructure of the polymerous Fe- and Al-oxide in soil scarcely changes as the phosphate is desorbed from the surfaces of the oxides. The aim of this study is to clarify the rapidity and mechanisms of the release of soil phosphate to a strong base anion exchange resin. The studies of the desorption of phosphate help us to understand the processes which occur near the root surface when the plant takes up phosphorus from soil
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