Abstract: The phosphorus distribution in paddy soil and its pollution risk to water body were studied in a 23-year long-term experiment,which was designed to have 14 treatments with 3 replicates and has been carried out under a rice-wheat cropping system.The 14 treatments consisted of no fertilizer（C₀）,N（C_N）,NK(C_NK),NP(C_NP),PK(C_PK),NPK(C_NPK),Straw+N(C_RN),Manure（M₀）,Manure+N（M_N）,Manure+N+K(M_NK),Manure+N+P(M_NP),Manure+P+K(M_PK),Manure+N+P+K(M_NPK),and Manure+Straw+N(M_RN).Compared with no P treatments,all P treatments showed significant increase in total P（TP）,Olsen P（Olsen-P）and inorganic P（I-P） in the plow layer（0—15 cm） and only M_NP,M_PK,M_NPK and C_PK did in organic P（O-P）.Significant TP accumulation in M_NPK and Olsen P in M_NPK and C_NP were found at the depth of 30 cm in soil profile,and I-P in M_NPK,M_NP,M_RN and M_N at the depth of 25 cm.P accumulation in the plow layer and P downward transport in the soil profile were related to application rate,fertilization pattern（fertilizer P,manure P,single fertilizer application and mixed fertilizer application） and form of P.I-P plays a very important part in P downward transport in the profile and I-P from manure went deeper than that from fertilizer.The treatments varied in P pollution risk to water body,with M_NPK being the highest.The risk is higher to surface water than to groundwater,in the rice season than in the wheat season,and in years with excessive rainfall than in those with normal rainfall.

Key words: Taihu Lake area, Huangni soil, phosphorus, accumulation, water body, pollution, risk