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

Progress report for GNC18-255

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
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Project Information


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:

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. 


Materials and methods:

After spending a year attending meetings and recruiting farmers to participate in the cover crop experiment, I identified 10 fields on 7 farms that met our study criteria: (1)  fields were in wheat or fallow during summer 2019, and going into corn in summer 2020; (2) the farms were in Monroe and Lenawee counties, which are in the Lake Erie watershed and are within one hour driving distance of the lab where soil and plant samples are processed. Proximity to the lab facilitates accurate measurement of soil nitrate and ammonium concentrations; and (3) fields varied in soil health and duration of past cover crop use. On one end of the spectrum, we have a partnering farm that has historically been tilled and has no cover crops. On the other end of the spectrum, we have a field that has been in no-till with cover crops for several decades. This gradient supports our goal of testing how grass and legume cover crops impact the subsequent corn crop depending on differing initial soil conditions. During spring 2019, there were floods across all farms in the study, delaying our baseline soil sampling, but also showing us where the fields were prone to flooding so that we could choose a location were the cover crops were likely to grow well the following spring. We chose 12 fields for this experiment that spring, and sampled soil in each field by treatment using 20 cm x 2.75 cm soil cores (15 cores/plot). The experiment is replicated 4 times on each farm in randomized strips and there are four treatments: 1) sole crimson clover, 2) sole cereal rye, 3) crimson clover/cereal rye mixture, and 4) fallow. We decided to include a fallow treatment instead of an unfertilized cereal rye benchmark at the request of the farmer partners, who are interested in comparing the outcomes for the cover crops to no management. The baseline soil samples were air dried in the lab and analyzed for total organic matter, phosphorus, potassium, magnesium, calcium, cation exchange capacity, and pH by A&L labs in Fort Wayne, Indiana. In our lab at the University of Michigan we conducted tests for soil texture analysis, particulate organic matter – both free and occluded (i.e., physically protected inside aggregates), total organic C, and total N. When we planted the cover crops in August we took a second sample and immediately tested for nitrate and ammonium to get a baseline at the time of planting. 

We planted the cover crops on 10 fields in August. We had to drop 2 fields due to logistical constraints (notes below in spreadsheet).  Planting dates varied due to rain and wheat harvest timing. We visited all sites in late October to confirm that the cover crops had established in all fields. One farmer had accidentally plowed under one of the replicates on one of his two fields, but otherwise all experiments remained intact. We took pictures of each treatment in each replicate to create a record of growth – actual growth will be measured by clipping the biomass in a 0.25 m2 quadrat just before cover crop termination in the spring. 

The most challenging part of the study so far has been the weather. It rained frequently last spring, and didn’t get warm until late June. Then the rain started up again while we were trying to plant. I spent a lot of time cleaning the wheels on the grain drills and waiting for the soil to dry out so we could plant. 

Farm Code Date of Cover Crop Planting Planting Method/Notes
1 8/1/19

Planted field 1 with 15 ft John Deer No Till Drill into a field that never got planted due to flooding. Only field without wheat stubble – will compare to the wheat stubble fields. 

2 8/5/19 Planted fields 1 and 2 with 15 ft John Deer No Till Drill
3 8/7/19 Planted fields 1 and 2: Cereal Rye on 8/6/19, it started raining around noon, returned and finished planting 8/7/19; Planted with 10 ft Conservation District (CD) drill, We decided not to plant field 3 because we could not get the equipment there and the field was very difficult to access. The field also never got baled, so there was a heavy mat of wheat straw that would have made cover crop growth difficult. 
4 8/8/18

Planted by farmer with 10 ft CD Drill, added 2 replicates to field 1 after the farmer pulled field 2 from the study after deciding to start tilling it again to transition to organic. Farmer still very excited about doing experiment on field 1 though. 

5 8/8/19 Alison and the farmer planted field 1 with 10 ft CD Drill, added 2 replicates to field 1 after realizing we had more space than previously thought. The strips are narrower than other farms due to space limitations (10 ft).  
6 8/12/19 Alison planted field 1 with 10 ft CD Drill – borrowed tractor from farmer
7 8/26/19 Planted fields 1 and 2 with farmers’ 10 ft European, no till drill – clover was accidentally planted at double rate (28 lb/acre) in field 1 – will keep this data separate and compare to all the other fields planted at 14-16 lb/acre. 
Research results and discussion:

We have not collected any cover crop growth data or corn data yet, and therefore cannot conclude any results at this time. 

However, I have analyzed the baseline soil data from all sites and found that there is a statistically significant range in both occluded and free particulate organic matter pools across the field sites. This suggests that we successfully captured a soil fertility gradient, which should impact decomposition dynamics of the cover crop treatments, and potentially lead to variation in corn yield and nitrogen uptake. See box plots in attached file. 

Soil Data_Cover Crops_SARE_Report

Participation Summary
7 Farmers participating in research

Educational & Outreach Activities

1 Curricula, factsheets or educational tools

Participation Summary

7 Farmers
Education/outreach description:

We are planning outreach activities for summer 2020 – winter 2021 after we have some data to share. We plan to get the participating farmers together for a meeting in July 2020 so we can talk about cover crop termination and corn planting and then again in winter 2021 to talk about the outcomes and implications of the study. Broader outreach activities will also occur in winter 2021. I plan to host several meetings with Michigan farmers and go on a podcast to talk about my findings. The podcasts seem to have really taken off in the last year, and seem like a good place to reach a larger audience than an in-person meeting. 

We plan to present results at the Underground Innovations conference in December 2020, at the Midwest Cover Crop Council meeting in February 2021, and at the Ecological Society of America meeting in August 2021. We will also publish a paper in an academic journal. 

Project Outcomes

7 Farmers reporting change in knowledge, attitudes, skills and/or awareness
1 Farmers changed or adopted a practice
1 Grant received that built upon this project
7 New working collaborations
Project outcomes:

One of the farmers in the study has never grown cover crops and is learning a lot, I haven’t done the outreach part of this study yet though. 

As neighboring farmers and friends see what is happening with these cover crop experiments, it is possible that adoption will increase in the county creating a larger “innovation niche” of a conservation practice that is not currently widely used. This, combined with the more extreme weather we have had the last few years, and resulting payments from the government to plant more cover crops, will likely increase acres that are cover cropped. The community really seems interested in learning about cover cropping, and hopefully the data that comes out of this study will give the participating farmers more proof that cover crops can work to convince other farmers that it is worth trying. 

Knowledge Gained:

I have learned that in order to successfully implement research experiments on farms, close communication and building trusting relationships with farmers over many years is important. I started getting to know these farmers in 2017, when I first interviewed them about their management practices and have further developed relationships with all of them to the point that they trusted me coming on to their farms to take samples and use their machinery to plant cover crops.

I have learned a lot about farm management and associated logistics through this project. Several of the farmers generously spent a lot of time teaching me about their practices and why they plant certain cover crops on certain plots of land. I have learned a lot about planting green and how much easier it is to no-till drill into living plants rather than dead ones. I was really concerned the first time we planted the cover crops into a field of weeds that had been hit with roundup a few days before, but 2 weeks later, it looked amazing and the cover crops established really well. I think I have really learned that no matter how bad it looks, to just trust that it will be alright and that cover crops are strong and will grow. I have also learned how to calibrate and maintain a no-till grain drill and drive a tractor. 

Success stories:

The farmers who have experiments on their farms are all very interested in how the experiment will go and are generally very happy to hear from me when I call to discuss next steps. Since the experiment is only partially done, we expect to share success stories in the fall. 


Finding a no-till drill appropriate for planting the cover crops in research plots was tricky. It might be helpful to create a sort of tool bank or library/list to facilitate researchers accessing equipment to implement farm experiments. 

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.