Objective  To reveal the action mechanisms of organic acids, and provide a scientific basis for raising the utilization rate of accumulative phosphorus(P) in acidic red soil.

Method  Laboratory simulation experiments were conducted to study the effects of low-molecular-weight organic acids, represented by oxalic acid, citric acid and malic acid, on P form in lateritic soil.

Result  During the whole incubation period, citric acid inhibited resin-P(P₁) desorption, while water (control), oxalic acid and malic acid enhanced resin-P(P₁) desorption. At the earlier stage of incubation, all three organic acids inhibited the activation of NaHCO₃-extractable inorganic P(P₂), with citric acid having the highest inhibition effect and oxalic acid having the lowest. Three organic acids activated NaHCO₃-extractable organic P(P₃) during the whole incubation period, and oxalic acid showed the strongest activating effect. Three organic acids enhanced the activation of NaOH-extractable inorganic P(P₄) and oxalic acid displayed the strongest activating effect. Three organic acids inhibited the activation of NaOH-extractable organic P(P₅). During the whole incubation period, three organic acids inhibited the activation of dilute HCl-extractable P(P₆), dense HCl-extractable inorganic P(P₇), dense HCl-extractable organic P(P₈) and residual-P(P₉).

Conclusion  Three organic acids showed different effects on soil P forms at different times of incubation. Oxalic acid showed the strongest activating effects, followed by malic acid and then citric acid.