In 2022, Steven Hines with the University of Idaho wrote an article for Ag Proud – Idaho on interseeding cover crops into silage corn. Hines shared lessons learned and research results from trials in Idaho during 2017-22. Concurrent research was being conducted in Utah around the same time frame. This article will revisit interseeding and discuss takeaways from the Utah studies.

Yost matt
Matt Yost
Agroclimate Extension Specialist / Utah State University
Matt Yost works in extension and the plants, soils and climate department at Utah State University.

First, a quick refresher on interseeding and its potential advantages and challenges in silage corn production. Interseeding refers to the practice of planting cover crops into an existing cash crop, such as silage corn, during the growing season. In this context, interseeding commonly occurs during early corn growth stages. By introducing cover crops in the early summer, farmers may be able to reap multiple benefits without negatively affecting silage yield.

Cover crops such as legumes (e.g., clover or vetch), grasses (e.g., rye or oats) and brassicas (e.g., radishes) are popular choices for interseeding into corn. These crops grow alongside the silage corn, providing a range of ecological and agronomic advantages. These include, among others:

  • Providing additional forage for grazing livestock after corn harvest
  • Improving soil health and fertility by increasing organic matter, enhancing soil structure and promoting microbial diversity
  • Reducing the need for synthetic nitrogen fertilizers when legume covers are used
  • Helping to suppress weeds by competing for space and light, thereby reducing the need for herbicides
  • Boosting farm resilience by increasing biodiversity, which helps protect against pests, diseases and extreme weather events

While interseeding cover crops into silage corn can offer several advantages, several challenges exist. Interseeded covers may compete with corn for moisture and nutrients, potentially reducing corn yield. Certain herbicides with residual effects may be restricted and specialized equipment, such as high-clearance or modified planters, is needed to drill cover crops. Furrow irrigation can be difficult with cover crops in the furrows, and planting cover crops of varying seed sizes in a mix can be challenging. Additionally, corn may need to be planted at lower densities to allow adequate sunlight for the cover crop. Managing weeds in the presence of cover crops is challenging, and successful cover crop establishment requires species that grow quickly, tolerate shade and develop extensive root systems to survive until corn harvest. In addition to these, interseeding adds additional costs (seed and labor) and another layer of complexity to crop management.

Most research on interseeding crops into standing corn has been conducted in the Midwest and eastern U.S. To better understand how interseeding cover crops affect silage corn production in the Intermountain West, a team of Utah State University researchers conducted trials to examine how cover crop planting time and corn populations influenced cover crop growth, corn silage yield and nitrate leaching.

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The results of the timing trial in 2021 at five Utah farms showed no detrimental effect on corn yield when cover crops were interseeded at the V2, V4, V6, V8 or V10 corn growth stages. However, it was noted that the V4 and V6 growth stages may be the most feasible selection. When attempting to interseed at the V2 corn growth stage, weed management strategies and furrow irrigation were challenging, and interseeding past the V6 growth stage was difficult to accomplish without physically damaging the corn.

Results from the corn population trials in 2022 indicated that reduced corn populations did not decrease corn silage yield but also did not significantly improve cover crop yields (Table 1). This indicates that reducing corn populations may not be necessary for successful interseeded cover crop production.

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A third trial in 2023 evaluated how an interseeded cover crop affected nutrient leaching in a field near Logan, Utah. Results showed that the interseeded cover crop cut the amount of nitrate leachate going below the root zone in half. This suggests that the cover crop was able to use excess nitrate and possibly increase fertilizer-nitrogen use efficiency in silage corn production, all without harming silage corn yield.

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Results from all three Utah trials need to be validated in additional trials, but they suggest that interseeding cover crops into corn silage can be an excellent option to enhance silage corn production and improve nitrogen use efficiency.

In addition to the research findings, the researchers and the participating farmer cooperators also learned valuable lessons about how to successfully interseed:

  1. Adequate soil moisture for cover crop germination and early growth is essential. Drought, low soil moisture and/or an inability to frequently irrigate cover crops will hinder their establishment.
  2. Early weed control is critical. Once a cover crop mix is planted, few to no herbicide options exist. Thus, a weed-free seedbed is essential for cover crop and corn silage success.
  3. Persistence is key. Even in ideal conditions, cover crops still sometimes failed or had poor growth. It may take several tries to be successful at interseeding cover crops. Small-scale experimental plots are recommended for beginners.
  4. Reach out for help. Local Natural Resources Conservation Service (NRCS) offices and soil conservation districts may offer assistance or resources for planting cover crops, including the rental of interseeder drills.

The author would like to thank the many farmers and researchers who led and participated in this research: Jacob Hadfield, Justin Clawson, Rhonda Miller, Michael Pace, Jody Gale, Cody Zesiger and Jenae Dean.