Abstract: The ~(15)N labelled ammonium sulfate or rape residues applied alone, and ammonium sulfate and rape residues in combined application (crosswise tagged) were studied. The experiment dealt with the transformation and distribution of fertilizer ~(15)N in the soil and rice plant at different stage of the rice growth. The mineralization rate of organic N, the f'xation rate of inorganic N and the variation of soil biomass were also discussed.It has been well lllustrated that the combined fertilization has many advantages.