Because the productivity of terrestrial ecosystems is directly related to microbial nutrient cycling, understanding the effects of chemical contaminants on soil microbial processes is important. The study examined the effects of two model chemicals - Roundup (glyphosate) and N-Serve (nitrapyrin) - on nitrifying organisms in static, perfusion, and continuous-flow culture systems. Experimental concentrations were approximately 1, 10 and 100 X the spot application rate. Both products were shown to inhibit nitrification in the treated soils. Roundup significantly reduced nitrification at 6.8 and 68 mg/g dry soil. N-Serve completely inhibited nitrification at levels greater than 42 mg/g dry soil in all cultural methods. In comparative studies with static batch and perfusion culture techniques, the continuous-flow system proved to be both reliable and useful in the culture of nitrifying bacteria. The method provides an alternative to traditional culture techniques in measuring chemical effects on microbial geochemical cycles and provides a new method for use in toxicity testing.