Abstract: In this paper, the typical kind of soil in the Three Gorges Reservoir region was taken from Kaixian County to make two types of soil samples (original soil sample and floodeddried soil sample), to examine the relationship between alternative floodingdrying condition and the isothermal adsorption of the P from the soil samples, and to compare the P release patterns of the floodeddried soil samples with original soil samples. The maximum P adsorption capacity (Xm) from Langmuir isotherm equation was first studied in this paper, and then the two types of soil samples were treated by KH2PO4 of 0% Xm, 30% Xm, 50% Xm, and 80% Xm. All the treated soil samples were deposited for 15 days before the subsequent flooding experiments. The adsorption capacity of the soil can be enhanced by flooding and subsequent airdrying condition. The adsorption capacity of the P increased from 256 mg/kg (original soil samples) to 625 mg/kg (flooded and dried soil samples), and the EPC0 was from 0.46 mg/L to 1.47 mg/L respectively after flooding condition. The ratio of desorption of the soil samples decreased from 73.3%~80.3% to 67.3%~69.6% after flooding. It is predicted that phosphorus adsorbed by the soils in drawdown area of Three Gorges area may then be released under the conditions similar to the flooding conditions employed in the present study. The release amount of P will vary synchronously with the P amount absorbed by soils before flooding. The alternative floodingdrying condition will cause the soil release more phosphorus.

Key words: drawdrown area of the Three Gorges Reservoir, floodingdrying, adsorptiondesorption, release of phosphorus