Experimental data showed that the addition of rice straw,pig manure,and milk vetch could increase the resin-P but decrease the P adsorption of soils with different properities.The former was ettri3uted to the dis solution and complexing effect of organic acids prnduced when incubation of organic manure with s oils,and,the later was believed to he due to some phosphorus adsorbing sites of soil masked by the carbohydrates in organic manure.This assumption was supported by the data that the removal of soil organic matter increased the P adsorption of soil and water soluble organic matter extracted from organic manures has the ability to compete with phosphate for adsorption of soil.