The study examines the effects of Roundup (N-(phosphonomethyl)glycine) and N-Serve(2-chloro-6-(trichloromethyl)pyridine) on nitrifying organisms in static batch, perfusion soil columns, and a new continuous-flow soil column system. The continuous-flow method is new to nitrification studies and was shown to produce greater nitrifier activity than either static batch or perfusion techniques. Both products were shown to significantly inhibit nitrification in treated soils over untreated controls. N-Serve completely inhibited nitrification at concentrations less than 42 ug nitrapyrin/g dry soil, and Roundup significantly reduced nitrification at 6.8 and 68 mg glyphosate/g dry soil. Heterotrophic bacterial populations increased significantly in continuous-flow columns treated with 42 mg nitrapyrin and 68 mg glyphosate/g dry soil.