Can adjustments to nitrogen rates reduce corn yield drag and disease implications following a cereal rye cover crop? July 2023
Issue
Cover cropping is a practice that expands the time a living plant is present between harvest and planting of annual crops. Cereal rye is the most prevalent cover crop grown in Iowa because of its winter hardiness as well as its contribution to soil health and water quality. Greater cereal rye biomass increases the benefits received. However, there are tradeoffs associated with greater cereal rye biomass – most importantly for growers is the potential for corn yield drag.
The two most detrimental reasons for a reduction in corn yield following cereal rye include: soil nitrogen dynamics and seedling disease. To encourage the inclusion of cereal rye as a cover crop on the Iowa landscape for scavenging and recycling N, disease suppression and soil health, there is a need to understand the role of both N and disease as contributors to corn yield drag.
Objective
The goals of this proposal are to improve our understanding of the importance of seedling disease and N dynamics as influenced by cereal rye on corn growth and development. The knowledge gained from this research will:
- Improve understanding of cereal rye biomass effect on N dynamics and seedling disease.
- Decipher the ability to reduce corn yield drag by adjusting N application rates.
- Provide farmers with best management practices to ensure a successful corn production following cereal rye cover crop.
Approach
Researchers will establish an intense field trial at an ISU Research Farm in central Iowa and a less intense field trial at the Southeast Research Farm. Both trials will use six N rates under both cereal rye and no cereal rye cover crops. The trials will evaluate the N and disease interactions at three landscape positions.
Project Updates
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
September 2025
FINAL REPORT
The key research question this project hoped to answer:
Explore the impact of CR biomass accumulation on the corn yield drag, we will evaluate the effect of N at planting on: (i) corn seedling disease (ii) soil N dynamics, and (iii) corn growth, development, and yield.
Research findings:
One of the main findings is that we were not able to overcome the yield penalty caused by cereal rye by applying more N. Our results show that even with more N being applied at planting, the plots with cereal rye yield substantially less than the plots without cereal rye. Planting corn with a green cover crop is causing a yield penalty.
We also assessed N mineralization during the growing season. According to our data, the mineralization or immobilization of the N is being affected more by soil moisture (and precipitation) and N rate applied than by the presence or not of cereal rye biomass. The 0 N rate had a positive N net mineralization, meaning that more mineralization was occurring. The 200 N rate had basically a net mineralization of zero, meaning that immobilization and mineralization were happening at the same rate. The 300 N rate had a negative net N mineralization, meaning that more immobilization was occurring.
Root rot severity was greater for cereal rye compared to no cereal rye across all years (0.05). Root rot severity varied across nitrogen treatment and slope with no difference in root rot severity in the toeslope compared to the backslope and summit (0.05). This was unexpected as we hypothesized that more severe root rot would be present in the toeslope due to wetter conditions. We expected root rot severity to decrease with increasing nitrogen at planting. Greater root rot severity was found in 2022 than 2023 or 2024 (0.05), possibly due to significantly wetter conditions in 2022.
Related accomplishments and activities
1 Presentation: (planned) to ASA in Salt Lake City, Nov. 9-12, 2025 – Hillslope position affects soil nitrogen dynamics and maize needs following cereal rye cover crop
Publications from this project:
- Victorio Pessotto, M., McDaniel, M. D., Adjuik, T.A., Marcos, F.M., Matthiensen, R., O’Brien, P.L., Robertson, A., & Licht, M. A. Submitted. Hillslope position affects soil nitrogen dynamics and maize needs following cereal rye cover crop. Nutrient Cycling in Agroecosystems Journal
- Victorio Pessotto, M., Larson, A., McDaniel, M. D., & Licht, M. A. In Preparation. Robel Pole Methodology Can Estimate Cereal Rye Biomass Accumulation in Central Iowa. Agronomy Journal.
6 undergraduate students were employed as assistants on this project.
Leveraged dollars: Grant for $649,040: Getting to the ROOT of the corn-yield drag following cover crops: a cereal rye residue manipulation experiment. PI, A. Robertson. Co-PI, M. Licht, M. McDaniel, P. O’Brien. 2023-2025. USDA NIFA, Washington, D.C.
January 2025
In the summer/fall of 2024, between V6 and corn maturity, three in-situ mineralization tubes were placed and collected in two-week intervals at the Ames location, the last one being before corn harvest. Plant height was taken at VT. Final plant density and number of ears were collected before harvest. Similar to 2022 and 2023, the Ames location showed primary difference among landscape positions, but has differences between nitrogen rate and presence of cereal rye as well.
Related accomplishments and activities
2 presentations
June 2024
In the spring of 2024, cover crop biomass was collected in Ames twice. The first sample was on April 5 and the second at termination on May 14. Corn was planted on May 18, and the nitrogen treatments were applied on the same day. Three sequential in-situ mineralization tubes were placed and collected in two-week intervals prior to and following corn planting. One of the planned soil sampling was missed due to intense weather conditions (rain) in mid- to late May.
Three additional in-situ soil sampling periods will occur between V8 and corn maturity. Plant density, plant height and disease seedling samples were collected in June. The plots show differences between plots with and without cereal rye in plant height and plant density.
January 2024
In the fall of 2023, one research location was established with the drill seeding of cereal rye cover crop following soybean harvest. One fall cereal rye biomass sample was collected from all plots to determine the cover crop establishment. The Ames location is at the Kelley farm and has three landscape positions (summit, slope, and toeslope). Grid soil samples were taken to determine the baseline nutrient analysis for fertilizer application at planting and to characterize the soils.