Effects of Cover Crop and Nitrogen Rate on Corn Grain and Silage Yield, Nitrogen Loss in Tile Drainage and Soil Health

Study author(s): Jeff Vetsch, University of Minnesota
Growing season(s): 2022, 2023, 2024, 2025
Minnesota location(s): Waseca

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2025 Growing Season2023 Growing Season2022 Growing Season

Introduction: Why This Study Matters

Corn needs nitrogen to grow well, but too much nitrogen can pollute water. Farmers in Minnesota and across the Midwest often use tile drainage to manage excess water, but this system can carry extra nitrogen (in the form of nitrate) into streams and rivers. This study, done at the University of Minnesota’s research center in Waseca, looks at how different cover crops and nitrogen fertilizer amounts affect corn yields, nitrogen losses in tile water, and soil health. It focuses on corn grown for grain or silage and compares cover crops like cereal rye and a mix of oats, peas, and radish.

Key Goals

  • Test how cover crops affect corn yield and nitrogen loss
  • Measure nitrogen levels in tile water and soil
  • See how different nitrogen rates interact with cover crops

Study Setup

Researchers set up 36 small tile-drained plots in Waseca on heavy clay soil. They tried:

  • Two nitrogen rates for corn (180 and 220 pounds per acre)
  • Corn grown for grain or silage
  • Cover crop options: no cover, cereal rye, or a blend of oats, peas, and radish

Cover crops were only planted after corn silage harvest, not after grain corn. Cover crop growth was often limited by Minnesota’s short fall season, but silage harvest allowed more time for them to grow.

Weather Impacts

Weather from 2021–2023 had a big effect:

  • 2021: Very dry; minimal nitrogen loss; below average corn yields
  • 2022: Wet spring, dry summer; decent corn yields but irregular rainfall
  • 2023: Wet spring, very dry summer; reduced corn yields.

Cover Crop Growth Results

  • Fall 2021: Cereal rye and the blend both established decently. Rye had slightly more biomass (296 lb/ac vs. 255 lb/ac).
  • Spring 2022: Rye biomass barely increased due to stand loss from wheel tracks and tillage.
  • Fall 2022 & Spring 2023: Extremely dry fall led to poor cover crop growth (<30 lb/ac of rye).
  • Fall 2023: The blend cover crop did much better (229 lb/ac) than rye (92 lb/ac). The blend also took up more nitrogen and had a lower C:N ratio, which is helpful for soil health.

Corn Yield and Fertilizer Results

Grain Corn:

  • Yields increased with nitrogen rate, peaking at 260 lb N/ac.
  • 180 and 220 lb N/ac produced similar yields; 260 lb N/ac was better, but this treatment wasn’t monitored for tile drainage.
  • The zero nitrogen control and 140 lb N/ac produced much lower yields.

Silage Corn:

  • Silage yields did not significantly increase between 180 and 220 lb N/ac.
  • All cover crop treatments produced similar yields when nitrogen was applied.
  • The control (no added nitrogen) had the lowest silage yield and quality.

Soil Health and Residue Cover

  • Silage harvest removes more plant material, leaving soil more exposed.
  • In 2022, cereal rye helped maintain over 30% residue cover—important for erosion control.
  • In 2023, all silage systems had less than 30% residue cover, even with rye, likely due to poor growth.
  • Grain corn left more residue, which helps soil but may reduce available nitrogen in spring due to slower decomposition.

Nitrogen in Tile Drainage Water

2022:

  • Most drainage occurred in April–June.
  • Cereal rye reduced nitrate concentration by 36% and nitrate load by a similar amount.
  • The annual blend reduced nitrate concentration by 21%.

2023:

  • Nitrate concentrations were higher especially for the corn silage system.
  • Cover crops had no effect—rye and blend had minimal growth.
  • Grain corn had lower nitrate levels than silage systems.
  • 180 lb N/ac lost less nitrogen to tile drainage than 220 lb N/ac, without reducing yields.

Soil Nitrogen Tests: – Fall 2022 and 2023

  • Grain systems left less nitrate in the soil than silage systems.
  • Cover crops didn’t significantly reduce soil nitrate, especially when fall growth was weak.
  • Applying 220 lb N/ac led to more nitrate remaining in the soil after harvest.

Takeaways for Minnesota Farmers:

  • Use 180 lb N/ac for corn silage: It’s enough and reduces nitrogen loss.
  • Cover crops after silage (especially cereal rye) can protect soil and reduce nitrate loss, but only if they grow well.
  • Weather matters a lot. Dry fall = poor cover crop growth = less benefit.
  • Grain corn needs more nitrogen and leaves more residue, which can affect spring soil temps and nitrogen availability.

This research gives Minnesota farmers clear guidance: if you’re growing corn silage, stick to 180 lb N/ac and try to get a good cover crop established in fall—especially rye—to keep your soil and nitrogen in place.

Missed Details and Why They Were Omitted:
  1. Statistical Methods (ANOVA, SAS procedures): Too technical for most farmers; does not affect application.
  2. Exact sample collection methods (e.g., how many cores per plot): Important for researchers but not farmers.
  3. Detailed data tables and standard errors: Too detailed; trends and averages are more useful for practical decisions.
  4. Exact nutrient removal numbers (e.g., lb of sulfur, potassium): Useful for precise fertilizer planning, but general trends suffice here.
  5. Soil health lab testing methods (POXC, CO2 burst): Not yet analyzed or relevant for immediate decisions.
  6. Flow-adjusted nitrate loss equations: Useful for scientists, but main point is which practices reduce loss.
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