Collaborators: Brendan O’Neill, SEAS, University of Michigan (UM); Research partners who are providing data from long-term experiments

Funding: Environmental Defense Fund (EDF)

Agriculture directly contributes 10-14% of the emissions that cause climate change. A growing body of evidence indicates that diversified cropping systems have strong potential to restore soil organic C (SOC) while providing a suite of other ecosystem services. However, the potential to restore SOC varies at smaller scales with climate, soil type, land use history, and management practices. In addition, stable soil organic matter fractions have a typical C:N ratio of 10-12. Thus, realizing the 1200 Tg annual increase in soil C proposed by the 4 per mille initiative, for instance, would require an estimated 100-200 Tg N per year. If these N requirements are met through inorganic fertilizer additions, this may negate potential ecosystem benefits because of the embodied emissions in fertilizer production and the likelihood of exacerbating N leaching and N₂O emissions. Yet, current debates around the N needs of soil C accrual often miss key insights from ecology, including nuances related to N source (e.g., legume cover crops, fertilizer, manure) and the broader ecosystem context of N management, such as cropping system diversity.

To quantify the N demands of soil C sequestration, we are compiling and analyzing data from multiple long-term experiments testing management systems that span a diversification gradient in the Midwestern U.S. This research seeks to advance understanding of coupled C and N dynamics relevant to best practices for both soil C sequestration and N retention, while building a valuable database for further refinement to inform effective policies for more sustainable and resilient agricultural systems.