Diversifying cover crops to sequester carbon in agricultural soil

Collaborators: Kent Connell, University of Michigan; Timothy James, University of Michigan; Julie Doll, Michigan State University

Funding: The Graham Sustainability Institute’s Carbon Neutrality Acceleration Program

Agriculture contributes between 10-14% of global greenhouse gas emissions. Cover cropping is a management practice that reduces carbon emissions from agriculture, yet cover crops are planted on few farms despite wide interest by stakeholders. Cover crops are nonharvested plants that sequester carbon by building soil organic matter (SOM). However, the breakdown of SOM releases nutrients, reducing the need for synthetic fertilizers manufactured using fossil fuels. This “soil carbon dilemma” may be solved by building two functionally distinct fractions of SOM.

Particulate organic matter (POM) is a fraction of SOM that releases nutrients through microbial decomposition, while mineral-associated organic matter (MAOM) accumulates through plant-microbe interactions and is associated with long-term carbon storage. We hypothesize that a legume-grass cover crop mixture will build both fractions due to complementary plant traits, but it is unknown how real-world variability in soil properties and microbial communities moderates the impact of cover crop mixtures on soil C storage.

We are using a stable isotope tracer to track the transfer of carbon from cover crops to microbial biomass and these two distinct SOM fractions in soils collected from working farms across Michigan. Failing to account for field-to-field variability within management recommendations is a significant barrier for cover crop adoption. Therefore, we are also hosting roundtable discussions with agricultural stakeholders to develop strategies that can enhance their adoption and carbon sequestration. Adopting cover crops in only 10% of corn and soybean fields in the Midwest would be equivalent to avoiding the emissions from over one million cars each year.