We studied the effects of irrigation and non-irrigation on barley (Hordeum vulgare L.) after one year under tillage and no-till and an established Conservation Reserve Program on soil aggregation, investigated the community structure of the predominant, culturable, and heterotrophic bacterial species inhabiting microaggregates (0.25-0.050 mm diameter) from the different practices, and determined the soil aggregative ability of these species using image-based reflectance to measure in vitro the sedimentation of soil particles (less than 0.050 mm) by pure cultures of individual species. Soil was a Lihen sandy loam (sandy, mixed, frigid, Entic Haplustolls). In both irrigation systems, the amount of soil present in the large macroaggregates (4.75-2.00 mm class) and the mean weight diameter were higher with barley under no till than the other treatments, indicating an increase in soil aggregation and aggregate stability. Regardless of irrigation, the percentage of isolates (regardless of species) with ability to aggregate soil were higher under no till than till (under irrigation, 32.84 % vs. 21.13 %, respectively; under no-irrigation, 23.53% vs. 7.14 %, respectively) and a greater percentage of species, among all the taxa identified from each treatment, were soil aggregators under no-till compared to till (under irrigation 21.52 % vs. 13.92 %, respectively; under no irrigation 13.92 % vs. 5.06 %, respectively), suggesting that tillage management has an impact on  the growth and survival of the dominant soil aggregating bacterial communities in the microaggregates. Furthermore, the total number of the soil aggregating isolates and species of the irrigated treatments was higher than in non-irrigated treatments indicated that conditions under irrigation favor the presence of these beneficial bacteria. This study indicates that there were underlying differences in the composition of the predominant species with ability to aggregate soil in vitro which may have been related to differences in community function leading to soil aggregation.