Diversification of Corn-Soybean Rotations with Cereal Rye/Red Clover: Impacts on Nitrogen Availability in Corn

2015 Annual Report for GNC14-193

Project Type: Graduate Student
Funds awarded in 2014: $9,144.00
Projected End Date: 12/31/2015
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Graduate Student:
Faculty Advisor:
Dr. Matt Liebman
Iowa State University

Diversification of Corn-Soybean Rotations with Cereal Rye/Red Clover: Impacts on Nitrogen Availability in Corn


This project’s objective is to measure N availability in the corn year of rye/ red clover-corn rotations by quantifying N uptake by corn as well as two measures of N release from soil organic matter: net N mineralization and gross ammonification.

Research was conducted on Dick Sloan’s farm near Rowley in Buchanan County in NE Iowa and Tim Sieren’s farm near Keota in Washington County in SE Iowa. On both farms, the experimental treatments consisted of a diversified rotation with corn following cereal rye/red clover, and a corn crop that did not follow clover but which received synthetic N fertilizer within a conventional N fertilization strategy. Soil nitrogen levels in all treatments were measured using the Late Spring Nitrate Test (LSNT), and synthetic N fertilizer was side-dressed on the synthetic N corn only using the results of the LSNT. The farms employed side-by-side strips between 300 and 750 ft in length to compare treatments. The sampling scheme entailed sampling 4 replicates of 2 treatments at 2 sites, for a total of 16 experimental units for each of the measurements. Net N mineralization and gross N mineralization were measured in a laboratory at ISU. Nitrogen uptake in the corn crop was measured by sampling corn plants at two dates on each farm. Corn was analyzed for biomass and N content. Measurements were completed in 2015.

Spring terminated red clover did not significantly enhance soil N cycling rates in a succeeding corn crop on the two cooperating farms. Corn yields in this study were less when following a spring terminated red clover cover crop compared to corn fertilized with synthetic N. Corn plant N results, however, suggest that the decomposing red clover was able to provide significant late season N to the corn. Conceivably, moderate fertilization at corn planting could enable the young corn crop to overcome early season N limitation and enhance corn yields following red clover.

Objectives/Performance Targets

Measurements and interpretation of results was completed in 2015. Outreach began in late 2015  and continues into 2016.


Results of the project were presented orally at the Practical Farmers of Iowa Cooperator’s Meeting to a group of approximately 30 farmers who are actively involved in PFI’s on-farm research projects. The group was composed primarily of corn and soybean farmers, and included many individuals with experience testing and adopting innovative farming techniques. Thus the project results were presented to farmers with an open-minded, yet critical view towards innovative practices such as the practices examined in this project.

A PFI research report titled “Timing of Nitrogen Supply to Corn from Spring Terminated Red Clover” was written and published in conjunction with the PFI research coordinator Stefan Gailans and the cooperating farmers, Tim Sieren and Dick Sloan. The research report highlighted important results of this research, as well as the insights of the cooperating farmers regarding the pros and cons of the farming practices investigated by the project. This report will be made available in paper format at future PFI events including field days and the PFI annual conference that is typically attended by more than 400 farmers, researchers, and other interested parties. Additionally, the report is currently available for free on the PFI website, and was highlighted in a blog post written by Stefan Gailans on 12-16-15.

A future outreach activity will be a poster presentation of research results at the Iowa State University Graduate Program in Sustainable Agriculture’s research symposium on April 20, 2016. The symposium highlights research done by graduate students in the GPSA program, and is attended by researchers involved in sustainable agriculture research at ISU.

Impacts and Contributions/Outcomes

Published a research report highlighting important results of this research.

Presented results to a group of innovative grain farmers interested in alternative management.



Richard Sloan

3046 Harrison Ave
Rowley, IA 52329
Office Phone: 3195586934
Dr. Matt Liebman

Professor of Agronomy
Iowa State University
1401 Agronomy Hall
Iowa State University
Ames, IA 50011
Office Phone: 5152947486
Tim Sieren

1320 Hwy 92
Keota, IA 52248
Office Phone: 3195609508