Evaluating Manure Application and Cover Crop Planting Timing to Maximize Water Quality Benefits in Corn
Issue
This project aims to provide valuable insights into the impacts of different cover crop systems and manure application methods on water quality and corn yield.
Objective
Overall, this project seeks to enhance sustainable agricultural practices by providing comprehensive data on the interactions between cover crop systems, manure application methods, water quality and corn yield.
Approach
Specifically, the research will directly compare water quality and corn yield performance between a winter annual cover crop system, using cereal rye, and a perennial ground cover system with Kentucky bluegrass. This comparison will help determine which cover crop system is more effective in promoting sustainable agricultural practices.
Additionally, the project will examine the outcomes of hand-interseeded cereal rye (used as a proxy for aerial seeding) versus post-harvest drilled cereal rye. By evaluating the establishment timing of these cover crops, the study aims to identify the most effective method for improving water quality and maximizing corn yield. Furthermore, the research will assess the drainage water quality associated with Poa bulbosa ground cover, providing crucial insights into the impact of this ground cover on water resources.
The project will also finalize the optimal timing for manure application when used with cover crops. It will evaluate the performance of cover crops with spring manure application, comparing results to data collected in previous studies for early fall and late fall manure applications. This analysis will help determine the best practices for integrating cover crops with manure application to enhance soil health and crop yield.
Finally, the study will evaluate the effectiveness of split manure application, specifically applying 100 pounds of nitrogen manure in the fall and 50 pounds of UAN (urea-ammonium nitrate) as a sidedress. This approach aims to optimize nitrogen use efficiency and minimize environmental impacts.
Project Updates
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
July 2025
Year 1 (funded by Iowa Pork Producers)
Tile Flow and Nutrient Concentrations. Rainfall began in April, with significant accumulation during the early growing season followed by a dry summer and fall. Tile flow was about 30% of precipitation, consistent with the site’s long-term average. Nitrate levels were consistently higher in spring across most systems, reflecting an initial flush of water, more precipitation and limited water uptake by crops during this period. All cover crop treatments – cereal rye, KBG and RHb – reduced nitrate concentrations by 30–50% compared to treatments without cover crops, though some reductions were not statistically significant.
Erosion. Erosion was monitored for two treatments: SM-CR-C, which had no-cover during the growing season and SM-RHb-C system. Early in the season, the no-cover treatment experienced significantly higher soil loss (13 t/ha) compared to the RHb groundcover system (2.5 t/ha), reflecting an 81.5% reduction in erosion by the PGC system. As the growing season progressed, erosion rates declined in both treatments due to canopy development and limited precipitation, converging to 0.26 t/ha and 0.22 t/ha for the no-cover and RHb treatments, respectively, by late September.
Yields. In the continuous corn plots, average grain yields varied slightly across treatments, with cover crops showing a slight positive effect. The FM-CR treatment (fall manure with cereal rye drilled after harvest) produced the highest yield at 194.5 bushels/acre, followed by FM-ESCR (fall manure with early interseeded cereal rye) at 187.9 bushels/acre and FM-KBG (fall manure with Kentucky bluegrass PGC) at 187.6 bushels/acre. The FM treatment (fall manure with no cover crop) recorded the lowest yield at 186.7 bushels/acre. In the corn-soybean rotation plots, significant differences emerged. The spring manure with cereal rye drilled after harvest achieved the highest average yield at 189.2 bushels/acre, closely followed by spring manure with no cover crop) at 188.9 bushels/acre. In contrast, spring manure with RHb PGC recorded the lowest yield at 124.6 bushels/acre, suggesting resource competition between Radix Hybrid bulbosa (RHb) and corn. The low yields in the RHb plots may be due to competition as no cropping zone was created and the PGC grass went dormant a month later than anticipated. This was unsurprising in light of the non-conforming nature of this PGC plot (see footnote for details). The Split-N treatment (fall manure with sidedress UAN) yielded 174.2 bushels/acre, indicating the split nitrogen strategy was less effective than spring-applied manure.
Year 2
The Rhb groundcover is strong but was suppressed on time. Rye cover crop had low growth but established well. Rye plants seeded early last fall had more fall growth, but drilled had more biomass this spring. Plots planted and growing well, water and soil sample collection on pace. Study progressing well.
Related activities and accomplishments
4 presentations.
2 publications:
- Assessing the Impacts of Manure Timing and Innovative Cover Cropping Techniques on Crop Yield and Drainage Water Quality (Iowa State University Northeast Research and Demonstration Farm Report)
- The Design and Testing of a Field Operations Visualizer, Rockson, P., Andersen, D.S. Licht, M., Raman, D. Raj. AgriEngineering 2024, 6(4), 4620-4638; https://doi.org/10.3390/agriengineering6040264
3 related proposals submitted:
- Iowa Pork Producers, Manure Application Timing and Cover Crops, Looking at Other Soils (In Review) ($50,120)
- Iowa Water Center, Impact of Perennial Ground Covers and Cereal Rye on Water Balances using Lysimeters (funded) ($27,744 in new funding, $28,578 in cost share)
- Pre-proposal to FFAR: Engineering Integrated Relay-Forage Systems to Enhance Nutrient Capture and Feed Self-Sufficiency in Midwest Livestock Agriculture (~$0.8 million cost share and $0.8 million funding request)
Planning 1 field day at this location in fall 2025, 2 additional field days related to perennial ground covers July 10, field day with Iowa Soy on 4Rs related to this work.
Have an REU student this summer working on this project evaluating row variability in perennial ground cover plots (and will have a poster).