Availability of dissolved organic carbon drives differences in microbial nitrogen-cycling processes between two sites with cover crops interseeded into corn

Interseeding cover crops into corn has been proposed as a technique to extend the cover crop growing window, but interseeded cover crops may reduce nitrogen (N) availability and compete with corn for available nutrients. To assess N-cycling dynamics in soils where cover crops have been interseeded into corn for 1 or 2 years, plots were established in duplicate at two sites in Michigan with differing edaphic properties. Annual ryegrass (Lolium multiflorum Lam.), crimson clover (Trifolium incarnatum L.), oilseed radish (Raphanus sativus L.), or a mixture of ryegrass and clover were interseeded into corn at the V3 or V6 stages of corn growth and compared to control plots that did not receive cover crops. We measured active carbon (C) and N pools during the growing season and after harvest as well as potential activities of microbially mediated nutrient-cycling processes via extracellular enzymes, nitrification, and denitrification. We found that after 2 years, interseeded cover crops had little to no effect on active pools of C and N or on microbial nutrient-cycling activities, but cover crop growth was severely limited in some site years. However, we observed major differences in these parameters between sites, with finer textured soils exhibiting increased dissolved organic C availability and greater peptidase activity compared to coarser-textured soils. Our results reveal important spatial and temporal trends that suggest greater C availability can lower the potential for N loss while maintaining a rapid flux of N through the N cycle. Microbial communities had distinct nutrient cycling strategies between two locations under similar management.Of the two soils used, the soil with more available C had more active N cycles but also less potential for N loss.Managing interseeded cover crops for maximal benefit requires an awareness of site-specific nutrient dynamics.