In no-tillage systems, crop residues are left on the soil surface and form a mulch, which can result in the stimulation of N2O emissions through various processes. As a consequence, the accurate description of mulch decomposition and the associated N2O emissions by soil-crop models is essential to help manage the potential impacts of mulches on the environmental performances of these agroecosystems. Here, we combined the use of a soil-crop model (STICS) and published experimental data to develop a new model representation of mulches (with various masses and qualities) and their decomposition, the carbon (C) and nitrogen (N) dynamics, and effects on N2O emissions. We used a published dataset from southern Brazil combining two residues with distinct chemical characteristics (vetch, Vicia sativa L., and wheat Triticum aestivum L.) and four rates of mulch addition (0, 3, 6 and 9 Mg dry matter (DM) ha 1) decomposing over one year. The STICS model with its default parameterization overestimated the remaining mulch masses, particularly at high DM inputs, and underestimated the N2O emissions. The evolution of the STICS soil and decomposition modules led to two major results: i) we modified the mulch module parameterization, by representing that the whole mulch is accessible to decomposers, whatever its initial mass and thickness; ii) a new potential denitrification function was proposed, which uses simulated CO2 fluxes associated from both soil humus and residue decomposition as proxy for C readily available to denitrifiers. With these new representation and parameterization, the model then accurately reproduced the very large range of magnitudes and the temporal variability of C and N fluxes observed for the two residues and the four mulch masses. These results are promising and the conceptual formalisms generic enough to be potentially developed in other soil-crop models. The next step is now to extend and generalize them to other conditions.