The partitioning of N from various sources within different parts of rice plant was studied. The result indicates the different N-supply characteristics of soils and fertilizers and the redistribution of soil-and fertilizer-N, which went into the plant "pool" in different times with different speed and intensity. The evaluation of fertilizing techniques are of practical meaning when the ratio of grain N% dff (or dfs) values to straw dff}dfs values which show the magnitude of contribution from different N sources to the rice grain, and the fertilizer N balance in the agricultural ecology were concerned. Fertilization increases both soil-N up-take and crop yield by changing the soil N supply characteristics. However, the "priming effect" may augment the soil N loss through volatilization.