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

Project Overview

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

Annual Reports


  • Agronomic: corn, rye


  • Crop Production: application rate management, cover crops, crop rotation, nutrient cycling, tissue analysis
  • Production Systems: general crop production
  • Soil Management: green manures, nutrient mineralization, organic matter, soil analysis, soil microbiology, soil quality/health


    • Cultivation of cereal rye for cover crop seed offers the possibility of frost-seeding a legume into the standing rye crop in early spring, where the legume can produce biomass and fix N following rye harvest.
    • Farmer-cooperators Tim Sieren and Dick Sloan grew corn in rotation following cereal rye frost-seeded with red clover.
    • Iowa State University graduate student Will Osterholz quantifed N uptake by corn as well as two measures of N release from soil organic matter: net N mineralization and gross ammonification.
    • Key findings
      • Red clover did not improve corn growth, N content or grain yield compared to synthetic N fertilizer.
      • Soil N mineralization rates in August tended to be higher with red clover compared to synthetic N fertilizer, but differences were not statistically different.
      • Fertilization with supplemental N at planting could provide corn with early season N before clover decomposition can provide sufficient N to the corn crop in late summer.


    Corn (Zea mays) and soybean (Glycine max) rotations are the major land use in Iowa.  While these systems are highly productive, conventionally managed corn-soy systems usually require large applications of nitrogen fertilizer during the corn year to achieve high corn yields.  Most corn-soy systems lack a growing crop in late winter and early spring, which elevates the risk of nutrient losses to the environment, which in turn impacts farmer profitability and environmental quality.  Adding an overwintering small grain mixed with a frost-seeded legume to the corn-soy rotation may reduce mineral N fertilizer requirements and mitigate negative environmental impacts of this cropping system.  The small grain provides cover in the late fall to early spring period to reduce N losses, and the legume acts as an N source to the following corn crop.  Cereal rye (Secale cereale) has gained popularity in Iowa as a winter cover crop following soybean in corn-soybean rotations due to its ability to overwinter successfully.  Consequently, the increased demand for cereal rye seed has increased the price of rye grain, which may favor the economics of growing cereal rye for grain.  Cultivation of cereal rye for grain offers the possibility of frost-seeding a legume into the standing rye crop in early spring, where the legume can produce biomass and fix N following rye harvest.  Red clover (Trifolium pratense) is well adapted to frost-seeding into a small grain and can produce a large amount of biomass with significant N content following small grain harvest.   The clover biomass will decompose following termination, gradually releasing N during corn growth which could potentially replace part of the fertilizer required for corn. 

    While crops have traditionally been thought to utilize only mineral N that soil microbes fail to immobilize (i.e.net mineralization and nitrification), recent findings suggest that they can also successfully compete with microbes for actively cycling mineral N (i.e. gross mineralization and nitrification).  This suggests that N availability is controlled by both the pool size of mineral N in the soil as well as the gross rates of N cycling.  Diversified cropping systems that utilize legumes as a major N source could maintain high rates of gross N cycling, producing a stream of mineral N from a large organic N pool which is rapidly taken up by plants or microbes.  We proposed that including cereal rye/red clover in corn and soybean rotations will enhance both net N mineralization and gross N mineralization, and thus increase N supply to a subsequent corn crop.

    This project quantified N uptake, net N mineralization, and gross N mineralization in a corn crop following cereal rye/red clover.  Utilizing two established on-farm trials in eastern Iowa, we measured soil and plant N in the corn year of corn-soy-rye/clover rotations.  Results of this project were shared with farmers and researchers to improve awareness of the feasibility of utilizing small grain/legume mixes to diversify corn-soybean cropping systems and attendant effects on N cycling.  This information will contribute to the development and implementation of cropping systems that will enable farmers to better optimize N fertilizer application rates in diversified cropping systems, providing high levels of productivity with reduced input costs while simultaneously improving environmental quality in Iowa.


    Project objectives:

    Objectives met by this project included the development of knowledge by regarding the effect a cereal rye/red clover crop on N cycling in a subsequent corn crop. This project increased farmer and researcher understanding of the feasibility and desirability of diversification of corn-soybean rotations with a small grain/legume crop, and should encourage further research into this topic by farmers and researchers interested in this topic. The project outputs will contribute to the long-term goal of increasing Midwestern farmer adoption of diversified cropping systems in order to improve the environmental and economic performance of agroecosystems in the region.

    Primary outputs completed as a result of this project included a presentation at the 2015 Practical Farmers of Iowa cooperators meeting and a PFI research report that described our methods, results, and inferences made about the data collected. The research presentation shared results and conclusions drawn from this project, and was presented to 30+ farmers interested in innovative agricultural approaches from Iowa and neighboring states.  The research report has been made available to the public through the PFI website and has been printed for distribution at PFI events including the annual conference that draws over 800 attendees from across the Midwest.  Additionally, the results were presented by the graduate student to university researchers at a sustainable agriculture research symposium at Iowa State University.

    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.