Excess phosphorus (P) has accumulated in Japanese paddy soils, due to fertilizer P inputs over crop requirement for several decades, and improvement of the excess of P is necessary in view of environmental conservation. This study aimed to evaluate the input/output balance of P related to soil P status in paddy rice systems, and to obtain a practical indication. , indicating no response to the P input. This was attributed to a large amount of plant-available Bray-and Truog-P in our soils. In our fields, paddy rice could be cultivated with no P-containing fertilizer or amendment. As a result, increase in the P input led to an increase in partial P balance (PPB). Cumulative increase in PPB resulted in the increase in soil total P, whereas cumulative decrease of PPB tended to decrease it. Excess accumulation of the soil P results in a loss of P into the environment. We concluded that P fertilization should be restricted to 20 kg ha -1 yr -1 (corresponding to 46 kg ha -1 yr -1 as P 2 O 5 ), based on evenly balanced P input with the rice P uptake. It is also important to include all of the P-containing fertilizers and amendments when determining the amount of application.