Soil microbial communities play an important role in ecosystems in various ways to promote healthy and fertile soil. However, intensive agricultural practices with excessive tillage and fertilizer applications can affect the abundance and community structure of microbial communities in soil as well as their assembly and recruitment by plant roots. Using amplicon sequencing and microscopy, we have examined bacterial and fungal communities under different tillage and fertilizer treatments in a 34-year-old field-trial at the Carrington Research Extension Center of NDSU. We observed that fertilizer application has a significantly stronger effect than tillage on soil properties, as well as the overall soil microbial abundance and community structure. Significantly higher mycorrhizal colonization was found under organic manure application. Overall, the results of this study can improve our understanding of the effects of fertilizer application on soil microbial communities and how management practices can be optimized to reduce the imprints of intensive agriculture.