16S rRNA gene libraries were constructed to evaluate the effects of natural and human disturbances on soil communities. The first study compared bacterial communities from agricultural and forest soils in the Southeast United States. Agricultural soils included conventional till or no-till regimes. Results showed that tillage regimes affect community structure, with conventional till populations being a subset of no-till. Forest soils from abandoned pasture communities were similar to nearby old-growth forest. Both forest communities differed from those of the agricultural plots. Bacterial communities from geographically distant forest soils at a second site resembled old-growth forest, but not the successional forest. Therefore, the impact of agriculture may be long lasting on bacterial populations. A second study compared the bacterial communities of soils associated with a rice-fallow rotation system. Community comparisons significantly differed across all treatments, showing both the flooded rice and pasture to be a subset of the never-tilled control soil. KEY WORDS: 16S rRNA, LIBSHUFF, Agriculture, Rice paddy, Bacterial diversity