Enhanced Belowground Nutrient Cycling Under Gradient of Increasing Cropping System Diveristy.

To address demands for sustained crop productivity and greater environmental quality, increased cropping system diversity may restore soil ecosystem processes that can achieve both goals.  We assessed microbially-driven, nutrient cycling across a gradient of increasing row crop diversity at the Kellogg Biological Station’s Long Term Ecological Research experiment in Michigan, USA.  Ranging from monoculture to rotations including corn, soy and wheat with multiple covers (up to six plants in rotation) and without external inputs, we measured pools and fluxes of nitrogen (N) and carbon (C), including trace gas flux, enzyme activities over the growing season, as well as structure and diversity of bacterial communities.  While increasing crop diversity enhanced belowground fluxes of C and N, the inclusion of cover crops maintained the greatest impact on nutrient cycling, bacterial community structure and crop productivity.  Indeed, after twelve years of the experimental rotations, total soil C and N pools did not show significant differences, while pools of labile C, mineralizable N, enzyme activities and gas flux all differed across the gradient and correlated most strongly with greater grain yields.  The results suggest, that particularly under cover crops, sustaining higher fluxes of nutrient cycling contributes to both higher crop yields potentially better environmental outcomes.