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As sustainable crop management systems are developed, an assessement of the effects of these practices on the soil microflora is essential to ensure maximum productivity. A 3-year field study was established to determine the effects of crop residue burning, no-till management and four preemergence herbicides on soil microorganisms. Numbers of actinomycetes, algae, bacteria, fungi and nitrifiers were evaluated during the soybean [Glycine max (L.) Merrill] growing season in a wheat (Triticum aestivum L.)-soybean double-cropping system. Residue burning and tillage had no effect on numbers of bacteria and nitrifiers. Non-disturbed (non-burned or no-till) plots had greater numbers of actinomycetes, algae and fungi 7 days after herbicide application each year, but the increases generally did not persist through the season. Herbicide application had no effect on microbial numbers. This is particularly important with recent increased emphasis on protection of soil and water resources from pesticide contamination. As new management systems are developed, their effects on biological properties must be carefully assessed, since the soil microflora play such a vital role.