Root-released organic acids are reported to increase phosphorus (P) availability in the soil. In this study a dynamic study of P release from soil was conducted to get more exact information of the organic acids role in P availability in soil. The results show that organic acids in different concentrations significantly affected P release. In a concentration of 10 mmol/L, no significant differences can be observed among citric acid, malic acid and acetic acid in terms of their effect on the release of soil P. However, when the concentration reduced to 1 mmol/L, both the total release amount and the maximum release amount of soil P significantly declined, and the decline degree were citric acid < malic acid < oxalic acid and acetic acid. When the concentration of organic acids was 0.1 mmol/L no P has been leached in the leaching solution of any of the four types of organic acids. The parabolic diffusion equation showed that organic acids can improve the migration rate of P in the soil, with the following order of citric acid > malic acid > acetic acid > oxalic acid. The higher the concentration of the organic acids was, the higher the migration rate of P would be. Given that the P needed by plants basically migrates by means of diffusion, under the condition of P deficiency of plants, improving the secretion amount of organic acids can effectively increase the biological utilization rate of P.
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