Abstract: Quantitative descriptions of N-inputs through fertilizer application,N-fixation,precipitation and irrigation and N-outputs through harvest,leaching,run off,denitrification,ammonia volatilization and direct loss from plant leaves are presented and analysed in reference to dealing with nitrogen cycling in modern agroecosystem.Asimplified approach has been suggested to establish the nitrogen balance model under certain soil conditions and agricultural practices.

Key words: Broadleaved Korean pine forest, Spectral solar radiation