Abstract: Paddy soil samples applied with different rates of P fertilizer were incubated and examined for changes in contents of OlsenP and CaCl₂-P at different time periods.Results show that in 200 days,soil Olsen-P decreased by about 50% in all the treatments.When P application rate was low,the content of CaCl₂-P was low and did not varied much.But when P application rate exceeded 400 kg·hm^-2,the content of CaCl₂-P rose rapidly.With the increasing P application rate,the proportion of the applied P entering into the P pool of residual P was decreasing,whereas those into the pools of dissolved P and Olsen-P were increasing,so the probability of P losing into water that may induce non-point pollution is increasing.The "change point" value of Olsen-P content that can indicate soil P loss into surface runoff and rapid increase in P content in subsurface drainage is 81.3 mg·kg^-1,and the corresponding P application rate is about 524 kg·hm^-2.So,if P application is above 500 kg·hm^-2,the possibility of soil P loss in different ways is increasing.

Key words: paddy field, soil, application of fertilizer, P, leaching, control