Cover Crop Mixtures for Nitrogen Use Efficiency on Grain/Arms in Southern Michigan

Project Overview

Project Type: Graduate Student
Funds awarded in 2018: $11,970.00
Projected End Date: 04/30/2021
Grant Recipient: University of Michigan
Region: North Central
State: Michigan
Graduate Student:
Faculty Advisor:
Dr. Jennifer Blesh
University of Michigan


  • Agronomic: corn, soybeans


  • Crop Production: cover crops, crop rotation, nutrient cycling, nutrient management
  • Education and Training: on-farm/ranch research
  • Natural Resources/Environment: biodiversity

    Proposal abstract:

    Up to half of synthetic nitrogen (N) fertilizer applied to grain crops in the Midwest is lost from fields, resulting in environmental problems and economic losses for farmers. Including overwintering legume cover crops in crop rotations can reduce fertilizer inputs by adding biologically fixed N to the system and improving nitrogen-use efficiency (NUE). Combining legume and grass species in cover crop mixtures can supply new N while also improving soil N retention. Over time, greater NUE may increase farm sustainability, maintain or increase crop yields, and reduce fertilizer costs. Despite these potential benefits, adoption rates of cover crops in Michigan are low {<6%) due to a number of social, environmental, and economic barriers. The proposed project will provide practical recommendations on how to manage cover crops for NUE by linking farmer input with principles of agricultural ecology through on-farm experimentation and applied, outreach activities. Our primary outcome is to increase farmer knowledge about the role of cover crops in soil fertility management, which can reduce fertilizer inputs. Diversifying rotations with cover crops would ultimately reduce nutrient losses from farms in Great Lakes watersheds, with wider implications for water quality. Our research objective is to determine how multi-species cover crops impact cover crop biomass production, cover crop residue chemistry, and soil N cycling processes. We hypothesize that mixing legumes with grasses will alter cover crop residue chemistry (e.g., carbon to nitrogen ratio (C:N), lignin, and polyphenols); improve synchrony between N release through decomposition and N uptake by the following grain crop via coupled N and C cycling: and, increase NUE (i.e., field-scale N mass balance and N harvest index). Across a nutrient management gradient on twelve grain farms in Southern Michigan, we will test the impact of three different cover crop treatments - grass, legume, and a grass-legume mixture - on cover crop residue biochemistry, soil N cycling processes, and crop yield. 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. Through collaboration with farmers, results from this study will be translated into an accessible format and shared broadly with farmers through local conservation agencies.

    Project objectives from proposal:

    The study is designed to meet the needs of our primary intended audience: Michigan grain farmers who use, or are interested in using, cover crops. Farmers who already use cover crops may not be harnessing their full potential. For instance, we conducted interviews to solicit input from grain farmers who already grow cover crops, and learned that the connection between cover crops and soil nitrogen management is rarely being made. Our proposed learning outcome is to increase knowledge and understanding of the role of cover crops in soil fertility management. This includes understanding the connection between cover crops and accumulation of soil organic nitrogen and applying nitrogen credits for cover crops. The primary audiences for these learning outcomes are farmers who already plant cover crops and farmers who are considering growing cover crops to manage their soil. We will engage in educational activities with participants in the proposed field study as well as with a broader audience of grain farmers in Southern Michigan. Our primary action outcome is increased adoption of cover crop mixtures on study participants' farms to meet soil fertility management goals. The primary audience for this action outcome is farmers who participate in the on-farm study. Over time, we anticipate that a wider group of farmers will adopt these practices based on our educational outreach and farmer-farmer interactions with participants in our study. The broader outcome is to reduce fertilizer application rates and N losses from Michigan grain farms by using cover crops to manage soil nutrients. 

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.