Collaborators: Alison Bressler, University of Michigan

Funding: North Central Region Sustainable Agriculture Research and Education (NCR-SARE) Graduate Student Grant

Up to half of nitrogen fertilizer applied to grain crops in the Midwest is lost from fields, resulting in environmental degradation and economic losses for farmers. Overwintering legume cover crops can reduce fertilizer inputs by supplying biologically fixed nitrogen and improving nitrogen retention in soil, particularly when legumes are combined with grasses in cover crop mixtures. Despite these potential benefits, adoption rates of cover crops in Michigan are low (<6%) due to a number of social, environmental, and economic barriers. In this project, led by PhD student Alison Bressler, we are providing practical recommendations on how to manage cover crops for improved nitrogen retention by linking farmer input with principles of agricultural ecology through on-farm experimentation and applied, outreach activities. We are also conducting a case study of the Cover Crop Champions program to understand strategies for overcoming structural constraints to cover crop adoption in the Midwest.

The overall objective of the project is to determine how multi-species cover crops impact cover crop biomass production, cover crop residue chemistry, and soil N cycling processes through an experiment on grain farms in southern Michigan. We hypothesize that mixing legumes with grasses will: (i) alter cover crop residue chemistry (e.g., carbon to nitrogen ratio (C:N), lignin, and polyphenols); (ii) improve synchrony between N mineralization and N uptake by the following grain crop via coupled N and C cycling; and, (iii) increase nitrogen use efficiency (i.e., improved field-scale N mass balance and N harvest index). Input costs (seeds, labor, fertilizer) and yield will be tracked for each treatment to conduct a cost-benefit analysis for different cover crops compared to leaving the field fallow over winter. Evaluation will be conducted at each phase of the project by soliciting farmer feedback through interviews and focus groups, and sharing results broadly with farmers and regional conservation organizations. Diversifying rotations with cover crops could ultimately reduce nutrient losses from farms in Great Lakes watersheds, with broader implications for regional water quality.