Abstract Our objective was to model nitrification kinetics of ammoniated peat (AP), ammonium sulfate (AS) and peat supplemented with ammonium sulfate and hydrated lime (PAS), in four different surface soils. The peat source was an acid sapric peat of high ammonia retention capacity. Nitrification rate was influenced significantly by soil type, N carrier and N application rate. Nitrification of AP showed a lag lasting longer in coarse-textured soils than in fine-textured soils, whatever N rate was applied. No lag was observed in AS- and PAS-treated soils. Initial nitrification rate was lowest in AP-treated soils at low N application rates but increased with AP application rate. High application rates of AS and PAS reduced NO 3 − production considerably. N loss was higher for AS and PAS than for AP treatments. AP and PAS treatments significantly increased initial soil pH values. AP tended to decrease soil pH slightly at the end of the incubation. AP appeared to be an initially slow-release, thereafter a sustained-release N fertilizer.