The concentration of ammonium-nitrogen (NH₄⁺-N) frequently exceeds that of nitrate-N (NO₃^--N) in Australian wet tropical sugarcane soils. The amount of mineral N in soil is the net result of complex processes in the field, so the objective of this experiment was to investigate nitrification and ammonification in these soils under laboratory conditions. Aerobic and saturated incubations were performed for 1 week on 2 wet tropical soils. Net NO₃^--N increased significantly in both soils during both types of incubation. A second series of aerobic incubations of these soils treated with NH₄⁺-N and inoculated with subtropical nitrifying soils was conducted for 48 days. Nitrification in the wet tropical soils was not significantly affected by inoculation, and virtually all added N was nitrified during the incubation period. Mineral N behaviour of the 48-day incubations was captured with the APSIM-SoilN model. As nitrification proceeded under laboratory conditions and was able to be captured by the model, it was concluded that nitrification processes in the wet tropical soils studied were not different from those in the subtropical soils. Processes that remove NO₃^- from the soil, such as leaching and denitrification, may therefore be important factors affecting the proportions of NH₄⁺-N and NO₃^--N measured under field conditions.