The nitrogen cycle includes inputs to the scene via fertilization, irrigation, deposition, fixation by crops, and the water table.

Nitrogen fixation by trees is also modeled.

Nitrogen exports from the scene include crop and tree harvests, leaching via natural and artificial drainage, nitrification, denitrification, and volatilization of fertilizer.

Management of humus, crop residues (mineralization, humification, etc.), and the fate of nitrogen fertilizers are simulated by STICS.

Nitrogen competition in the soil is computed by integrating the matrix flux potentials over the whole simulated scene (De Willigen et al, 2000).