For thousands of years, humans have known that regular crop rotation can keep soils productive. But we’re just beginning to understand how microbes in soil make that possible–including viruses. A new study unearths how viruses orchestrate vital changes in soil rotated with rapeseed and wheat. Researchers probed three areas for both DNA and RNA viruses: bulk soil, soil near roots, and roots themselves. Their search revealed 683 new genera and 2,379 new species of viruses and effectively quintupled the number of known genomes belonging to Leviviricetes, a relatively new and underexplored class of viruses. Most of the viruses were lytic phages, which hijack and then kill bacteria for their own replication. Driving bacterial turnover in this manner could be one way soil viruses control bacterial diversity across both space and time. For example, in relation to crop rotation, the team observed a “viral priming” effect, whereby the number of active viruses seemed to increase in continuously cropped soils (orange) vs. rotated soils (blue), suggesting an adaptation mechanism. These findings highlight the critical roles played by viruses in agriculture and how they might be harnessed to improve productivity.