Incubation and pot experiments were conducted to study changes in organic-P fractions in calcareous soils after application of pig slurry and monopotassium phosphate (MPP) and their contributions to Puptake by rye grass.The results indicated that: (1) Liable, moderately liable and moderately stable organic-P of soils increased markedly after the application of pig slurry and MPP, with the middle one being mostly increased; (2) The liable and moderately liable organic-P made greater direct contribution to the total amount of P uptake by rye grass and all the three organic-P fractions had some indirect contribution; (3) Based on their comprehensive effects on the amount of P uptake by rye grass, the three organic-P fractions ranked in such order: liable organic-P > moderately liable organic-P > moderately stable organic-P.