Nitrogen Credits and Fertilizer Dollars Saved: Identifying benefits for seeding diverse legume-based cover mixes into or after winter small grains

Progress report for ONC23-132

Project Type: Partnership
Funds awarded in 2023: $49,054.00
Projected End Date: 03/31/2025
Grant Recipient: Michael Fields Agricultural Institute
Region: North Central
State: Wisconsin
Project Coordinator:
Dr. Nicole Tautges
Michael Fields Agricultural Institute
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Project Information


Among grain growers in the Midwest, interest is growing in cultivating winter small grains followed by a legume cover crop to take advantage of the growing window after small grain harvest in July. By eliminating this late summer fallow, the soil is protected by maintaining plant cover and farmers can take advantage of nitrogen (N) fixation to benefit the following crop in rotation while contributing to soil health by keeping living roots in the soil and feeding microbes. Growers assume the legume cover is providing an N credit to the following corn crop, although research-backed estimates for these credits are not widely available and have mostly focused exclusively on red clover. We have convened a network of growers using more diverse legume mixes after winter grains who need good estimates of N credits to reduce their fertilizer inputs and costs. This project convenes growers, a nonprofit-based agroecologist, and a UW Extension Educator to identify cover biomass N, soil health benefits, N credits to the following corn crop (via an N fertilizer yield response experiment) and fertilizer dollar value for six different cover crop mixes on 6 farms. Results will be published in case studies, factsheets, and presented at grower conferences.

Project Objectives:
  1. Quantify biomass production, N fixation, and soil health benefits of several legume-based cover mixes by collecting data on 6 collaborating farms and describe via 3 case studies.
  2. Identify N credits of legume-based mixes to the following corn crops by measuring corn yield in N fertilizer response field trials on each collaborating farm.
  3. Develop Extension factsheet reporting legume biomass, N credit values, and corresponding fertilizer $ values, among legume-based cover crop treatments, to aid grower decision making.
  4. Present results and disseminate published products alongside collaborating growers at 2 on-farm field days and at 3 annual grower conferences.


Click linked name(s) to expand/collapse or show everyone's info
  • Sandy Syburg
  • Will Fulwider (Researcher)
  • Andrea Hazzard
  • Aaron Shotliffe
  • Karl Sime
  • Ben Grove


Materials and methods:

This project will use a nitrogen fertilizer series applied as a split-plot treatment in corn following summer cover crops after wheat harvest, with plus cover crop and minus cover crop as the whole plot treatments, replicated four times on each participating farm. Project leaders met with growers frost seeding red clover in February 2023, and with growers planting summer cover crop mixes after wheat harvest in June 2023, to develop plot layouts to deploy whole-plot cover crop and no cover crop treatments in four replicates. Growers using red clover as the cover crop excluded cover crop seeding from the no cover crop strips, and seeded over the rest of the area of their winter wheat fields. Growers using summer cover crop mixes similarly excluded seeding the mixes in the no cover crop strips but planted across the rest of the area, following wheat harvest. At the time of planting, project personnel collected baseline soil samples in depth increments of 0-12 inches and 12-24 inches, which were subjected to a soil health panel analysis that included physical indicators (soil texture, soil water holding capacity, aggregate stability), chemical indicators (water soluble nitrate, phosphorus, potassium, sulfur, and pH), and important biochemical indicators (total carbon, organic matter, active carbon/POXC, and mineralizable nitrogen/ACE protein). Resampling of soil will occur at the end of the project to assess cover crop impact on soil health indicators. In late fall just after the first frost (around beginning of November), fall cover crop biomass was collected in 0.5-m2 quadrats, two per plot, dried, and weighed to analyze biomass production of cover crops. Biomass was submitted to an analytical lab to measure total nitrogen content of the aboveground biomass, as an indicator of nitrogen input to the soil of the cover crop.

Spring planning with collaborating farmers is currently underway. Meetings have been conducted with each farmer to plan for deployment of the nitrogen fertilizer series (0, 40, 80, 120, 160 lb N/acre rates), to be applied in split plots within the +/- cover crop whole plots. Farmers are planning to calibrate their spreading equipment accordingly, and at some sites with smaller plot sizes, project personnel will apply the fertilizer by hand. Nitrogen fertilizers will be applied in the form of urea ammonium nitrate (UAN) as sidedress at the corn growth stage V5-V6 on conventional farms; on organic farms, the nitrogen fertilizer applied will be an OMRI-approved product called Naturesafe with a composition of 13-0-0, to apply nitrogen only and to avoid confounding effects of additional phosphorus, potassium, or other nutrients that could come in other organic fertilizers. Prior to cover crop termination, project personnel will collect biomass samples by hand, using the same methods described above for fall, to assess spring biomass production by the cover crops. Biomass will be dried, weighed, and analyzed using the same methods as previously described. Project personnel will also collect soil samples in

Research results and discussion:

In fall 2023, we collected soil samples from 0-12 and 12-24 inches in eight plots per farm (+/- cover crops, in 4 replicates) on six farms, and analyzed the soils for total aggregates (%), large macroaggregates (%), small macroaggregates (%), microaggregates (%), water-holding capacity (percent moisture at 0.3 bar pressure and 15 bar pressure), organic matter content (%), carbonates (%, to perform adjustments in total carbon for organic matter-based changes), total carbon (%), pH, total nitrogen (%), nitrate (ppm), Bray-phosphorus (ppm), potassium (ppm), sulfate (ppm), active/permanganate-oxidizable carbon (POX-C; ppm), mineralizable nitrogen/ACE protein (mg per gram), and texture (%sand, %silt, %clay). Data is entered and statistical analysis is ongoing; however, these are baseline values and the real value of analyzing these data will be in comparison to endpoint values to assess how cover cropping in the wheat-corn part of the rotation affects soil health physical, biological, and chemical indicators. Fall biomass accumulation of different cover crops was measured and analysis is ongoing; we are still receiving dry biomass total nitrogen values from the analytical lab. We began consultations with farmers regarding the results of these analyses, but have not completed all analysis yet.

Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

5 On-farm demonstrations
1 Tours
1 Workshop field days

Participation Summary:

5 Farmers participated
3 Ag professionals participated
Education/outreach description:

The first round of soil sampling to conduct baseline soil health analyses on cooperating farms has been conducted and results have undergone a preliminary analysis. We are in the process of developing reports for each farmer to give them an idea of the status of their soil health panel results on the field undergoing study. For two farmers in particular, we identified soil pH and other low fertility issues that indicate the field would benefit from remediation; we conducted consultations with these growers to discuss fertility management options to remediate these potential issues and to boost productivity of the fields.

Six research trials/demonstration sites have been established on cooperating farms' fields. Each trial/demonstration site is field-scale, consisting of 1/2 acre to multiple acres, depending on the farm and field. We are in the process of planning for field days at at least two of the six farms, one field day is set for July 19, 2024 at Hazzard Free Farm, and the other field days are still in early planning stages with the other farmers. The goal is to hold at least three field days this summer to discuss cover cropping under or after small grains in rotation, to offset nitrogen input requirements to corn, and to build soil health. We will be able to share preliminary cover crop nitrogen and preplant available nitrogen results with field day attendees in summer 2024.

Given the scope and replicated nature of the six trial sites, the data generated from this trial will be sufficient for publication in a peer-reviewed agronomy research journal. Data is being collected, managed, and analyzed to enable such analysis, presentation, and publication in the future, but data to complete such a publication will not be complete until the end of 2o24. Manuscript preparation will begin in early 2025.

Learning Outcomes

6 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • nitrogen crediting; nutrient management

  • cover cropping

  • nutrient cycling

Project Outcomes

5 Farmers changed or adopted a practice
1 Grant received that built upon this project
5 New working collaborations
Project outcomes:

This project will generate: 1) published tables of cover crop N production, N credit values for corn after winter grains, and dollars saved on off-farm fertilizer purchases for diverse cover crop mixes vs. frost-seeded red clover; 2) published description of soil health indicator changes
after winter grains plus cover crop; 3) three case studies published via Michael Fields web channels (and other web channels) that provide storytelling and description of how farmers implement this system and capture its benefits; 4) at least 2 field days featuring this work; and 5) Extension factsheet and 3 conference presentations.

Impacts of the project include a growth in the number of farms using legume-based covers, a decrease in off-farm fertilizer purchase quantities and costs for corn after winter grains, and digital resources available for perpetuity on the web (via Michael Fields and UW Extension websites).



One of the on-farm cooperator sites listed on the proposal was Granor Farm; the farm managers who originally signed on as a collaborator is in the process of leaving Granor Farm to take a new position; I am working with him to attempt to hand the on-farm trial/project off to his successor in the farm manager position, but the status of the collaboration is unclear at this point. I am hopeful I can keep the site.

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.