Abstract: The paper proposed a method on keeping constant application rate of phosphorus by monitoring available-P in the soil and demonstraited feasibility of the method. The key points are as follows: * 1.A rational application rate was establised through long- term experiment to maintain the soil available-P within the critical level. 2.This application rate could maintain or increase soil avilable P, hence sustainable high yield and maximum effciency of the fertilizer were obtained. 3.Within a given application area under non-stressful soil conditions but with various soil fereility levels, this application rate could remain relatively stable for a considerably long period.