Most row crop agriculture in the U.S. Midwest consists of rotations corn, soy and some wheat.  Increased demand for these commodities along with a desire for improved environmental benefits has resulted in calls to harness soil ecological processes and reduce external inputs by increasing cropping system diversity.  It is well-known that increasing rotational complexity, especially with cover crops, can improve crop productivity.  Research at the KBS-LTER Biodiversity gradient has shown that greater productivity in more diverse cropping systems is linked to rapidly cycling fractions of soil organic matter, especially potentially mineralizable N and labile soil carbon fractions.  Along a gradient of increasing rotational complexity from monoculture to crop rotation to rotation with cover crops, the structure of the soil microbial community also shifted according to increasing labile soil organic matter fractions.