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Résumé :
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Published methods for calculating gross N rates differ in their assumptions and the method of calculation (algebrical equations or numerical methods). The calculation model presented here called FLUAZ considers the major N processes occurring in soil and enables testing of the importance of the various assumptions. It combines a numerical model for solving the mass balance equations and a non linear fitting program for optimizing the N rate parameters. It can be applied to a single 'paired' treatment(s) of an experiment in a bare soil. The model has been evaluated in two experiments made in the laboratory with wheat straw, each experiment involving two 'paired' treatments. When FLUAZ was applied to the 'paired' treatments, a good fit was obtained between the simulated and measured values of 10 variables (amount of NH4+ and NO3-, isotopic excess of NH4+, NO3- and organic N). This fit validated the compartmental model and enabled calculation of six N fluxes: mineralisation (m), ammonium immobilisation (i(a)), nitrate immobilisation (i(n)), nitrification (n), volatilisation (v) or denitrification (d) and remineralisation of recently immobilised N (r).
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