Effects of fire and post-fire mulching for soil protection on N transformations were evaluated in the laboratory 4, 8 and 12 months after a wildfire in the 0-2-cm layer of a burned soil without (BS) or with straw mulch (BSM) and an unburned soil (US). The relationships between the gross N rates calculated with the FLUAZ model (Mary et al. 1998) and 19 soil characteristics were also explored. The gross N mineralisation (m) and NH 4 + immobilisation rates (ia) were similar and significantly correlated (p<0.001) and decreased during the incubation. Both m and ia were higher in burned than in unburned soils and, despite a reduction with time, differences were still 3-fold at t=12 months. Treatment explained half the variation of gross nitrification (kn), which was always low in US and nil in burned soils. Nitrate immobilisation (in) was the only gross rate that was (a) higher in unburned than in burned soils, (b) higher after 12 months than in previous samplings and (c) negatively affected by mulching. Both m and ia were positively correlated with soil pH, initial inorganic-N pools and extractable-Mn (p<0.05 to p<0.001) and negatively correlated with soil water-holding capacity and contents of total C, total N, extractable Cu and extractable Zn (p<0.05 to p<0.001). Both kn and in were negatively correlated with soil characteristics. Despite the strong correlations of pH and total C and N with the gross N transformations, the former variables were never included in the best multiple linear models for the latter. Besides the initial NH 4 + -N or NO 3 − -N contents, all but one best multiple regressions for m and ia included one or two available nutrients, in particular Cu, K, P and Mn. Multiple regressions of kn were only found for US and they included two nutrients (Ca and K, or K, Zn and electrical conductivity). Considering all samples and incubation intervals together, two thirds of in variance was explained by a model with the initial NO 3 − -N, the available Cu and P content. Mulching of burned soil gave a shortlived stimulation of m and ia and a sustained reduction of in.