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


    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 and improving overall soil quality and 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, using cover crops that include legumes 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 social, environmental, and economic barriers. This project linked farmer input with principles of agricultural ecology to conduct an on-farm experiment with real world implications for cover crop management on Southeast Michigan grain farms. Our primary outcome was to increase farmer knowledge about the role of cover crops, particularly cover crop mixtures, in soil fertility management, which can reduce fertilizer inputs over time. 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 was to determine how multi-species cover crops impact cover crop biomass production, cover crop residue chemistry, soil N cycling processes, and resulting corn outcomes on grain farms in various stages of transition to cover cropping. We hypothesized that mixing legumes with grasses would alter total cover crop biomass and cover crop residue chemistry (e.g., carbon to nitrogen ratio (C:N)); improve synchrony between N release through decomposition and N uptake by the following corn crop via coupled N and C cycling; and result in either positive or no impact on the corn crop compared to a fallow or either cover crop grown alone. Across a nutrient management gradient on five grain farms and seven fields in Southeastern Michigan, we tested the impact of three different cover crop treatments – cereal rye, crimson clover, and a rye-clover mixture - on cover crop residue biochemistry, soil N cycling processes, and corn grain compared to a no-cover fallow. Input costs (seeds) were tracked for each treatment to conduct a cost-benefit analysis for different cover crops compared to leaving the field fallow over winter. Due to Covid-19 restrictions, we were only able to collect cover crop biomass and measure N mineralization rates following cover crop termination on 4 fields, but we were able to collect corn samples on all 7 fields.

    Generally, we found that underlying soil conditions varied significantly across farms and that those soil conditions lead to variability in cover crop production and resulting corn outcomes. One of the primary variables we measured, cover crop C:N, varied between treatments with significantly higher C:N in the rye treatment than the clover or mixture treatments across the four farms on which we collected cover crop biomass. Further, we found that soil properties such as particulate organic matter and micronutrient concentrations influenced rye C:N and clover biomass across farms. This suggests that initial soil properties could guide farmer decisions about which cover crop species to plant based on potential benefits. We did not find generalizable results regarding the impact of cover crops on N mineralization or corn yields. Our measurements of N mineralization rates showed different patterns across each farm with no significant differences between cover crop treatments. Corn yield was either positively impacted or not impacted by cover crops on all but one field. The latter field demonstrated the negative impact that cover crops can have on corn production with unfavorable spring weather conditions. This field also had the lowest soil fertility, with cover crops having less of an impact on corn production in higher fertility fields. We developed both farm level and general recommendations from our results.

    Farmers were consulted by phone during each phase of the project to plan the next phases. For example, farmer interviews determined the species we planted, the size of the plots, and fertilization methods. Focus groups were not conducted due to the pandemic. Instead, we communicated directly with each farmer over the phone throughout the project, and we are working with each farmer to provide them with a booklet with data and recommendations specific to their farm. I plan to share our results at farmer meetings and conferences over the next year and a half and engage in outreach through Michigan extension and local farmer outreach organizations in the counties where the study participants reside.

    The farmers who participated in this study are enthusiastic about continuing to grow cover crops and all of them agreed to participate in a follow up greenhouse study in the Blesh lab, which is assessing the potential for legume-grass cover crop mixtures to sequester carbon in soil. On one farm, we had a difficult experience terminating the legumes in a low fertility soil under unfavorable weather conditions. The legume biomass then stunted corn growth. Instead of being discouraged by this, this farmer proceeded to plant grass and brassica cover crop species for the next growing season, since we had better luck with the rye treatment on his farm given his specific soil conditions. We saw either positive or neutral impacts on corn production at all the other farms, which has helped to encourage the farmers to continue cover cropping. I plan to maintain relationships with these farmers and help them use what we learned from each of their field trials in their outreach. Several of the farmers in this study are influential public speakers in their county and may be able to leverage this experiment to increase cover crop adoption among other farmers in their communities.

    Project objectives:

    The study was 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 plant 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 soil nitrogen cycling. For example, legumes add new nitrogen to agroecosystems through biological nitrogen fixation. Other cover crops can retain and prevent nitrogen losses. Over time, farmers can apply nitrogen credits to cover crops, slowly reducing their fertilizer inputs. Since the study outcomes varied significantly from one farm to another, we are providing farm level data to each participant with recommendations for using cover crops on their specific soil in addition to a summary of aggregate results across all field sites. Our primary action outcome is increased adoption of cover crops that suit the needs of study participants' farms to meet their 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 through farmer-farmer interactions with participants in our study. The broader outcome is to reduce fertilizer application rates and N losses from Michigan grain farms (particularly in the Lake Erie watershed) 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.