The results of our field experiments demonstrated that maize yield was not significantly affected by reducing the application rate of P fertilizer, except when no P fertilizer was applied. Relative early growth rate was a useful measure for evaluating the effect of reduced P fertilizer application on maize yield. P fertilizer application rates that did not result in reduced yield were different depending on factors such as soil type, available phosphorus content, and AMF colonization. Based on relative early growth rate, we tentatively determined that P fertilizer application rates could be reduced by 20% of the present standard in fields where maize is continuously cultivated.