Abstract:The desorption of phosphate from Al hydroxides by 0.01 mol/L KCl in the presence of different organic acids and from Al-OH, Al-P and Al-oxalate, Al-citrate complexes by organic acids were studied. The results showed: 1) When phosphate adsorbed on Al(OH)x in the presence and absence of oxalate was desorbed sequentially twice using 0.01 mol/L KCl, the total desorption rate with 0.5～2.0 mmol /L oxalate were 4. 10% ～4. 75%, however, without any organic acid, it was only 2. 05%; 2) The hlgher concentratlon of organic acld in adsorption solution, the more phosphorus was desorbed by 0.01 mol/L KCl to some extent. Some phosphate, which could not be desorbed by oxalate, would be desorbed by citrate at same concentration; 3)When phosphate was desorbed using a series of oxalate and citrate,the total rate of phosphate desorption from Al-oxalate complex was less than that from Al hydroxide, while the rate of phosphate desorption from Al-citrate complex was the highest; 4] Citrate could release the phosphate from Al-P complex, and the amount of phosphate desorption increased with the increment of citrate concentration. All these indlcated that the mechanism of phosphate desorption involved ligand exchange and dissolution by organic acid. Organic acids could obviously strengthen the desorption of phosphate and improve the efficiency of phosphate in acid soil.