Stimulation of Autotrophic Ammonium Oxidation in Rice Rhizosphere Soil by the Insecticide Carbofuran

The application of the insecticide carbofuran (technical or formulated) to rice rhizosphere soil suspensions at 10 and 100 ppm (μg/ml) of active ingredient distinctly stimulated the autotrophic oxidation of ammonium. Evidence suggested that Nitrosomonas sp. was enriched in the presence of carbofuran. Formulated carbofuran (Furadan 3G) exhibited a more pronounced stimulation of ammonium oxidation than that exhibited by technical-grade (99.5%) carbofuran, a result which was attributed to the CaCO₃ present in the formulation.