Cover Crop Commentary: Addressing the Risks of Corn After Rye
Pro: reduce weed pressure. Con: soil nitrogen may be tied up. Pro: reduce soil erosion. Con: potential for allelopathy. Pro: increase organic matter. Con: increased insect pressure. We could pro-con list cover crops all day with their potential for both positive and negative impacts. Which leads to the need for some perfecting of their management even though this conservation practice was introduced in American agriculture in the 1860s (White, 2014).
In 2014, Bob Hartzler with the Department of Agronomy at Iowa State noted that, albeit inconsistent, under certain conditions, corn yields may be reduced when planted into the residue of a rye cover crop with many chalking it up to rye allelopathy. Allelopathy, or the release of chemicals by one plant that inhibits the growth of adjacent plants, is what makes rye a great weed suppressor. But its effect on corn? While one research study showed reduced corn root length as a negative effect of allelopathic chemical extracts from rye, another found no similar effects (Rees et al, 2021). Both studies were conducted in laboratories, so it comes as no surprise that additional in-field research is very limited.
Nitrogen Tie Up
High surface residue can temporarily tie up nitrogen fertilizer (Geist, 2017). The higher the C:N ratio of a plant, the more nitrogen microbes take from the soil to decompose the residue (Vieira Branco Ozorio et al, 2022). Cereal rye residue typically has a higher C:N ratio and may tie up soil nitrogen more than other cover crops. As residue decomposes though, some nitrogen is released back into the soil within a few weeks after termination.
Soil water availability can also be negatively impacted by cover cropping, especially in a dry spring. Cover crops need water too and may compete with some row crops or dry out the seed bed. We know that cover crops increase transpiration when alive and decrease evaporation when dead, but once again research is conflicting when it comes to the impact of cover crops on available soil water and crop yields (Kaspar & Singer, 2015).
Insect & Disease Pressure
Increased pest pressure may also be a negative effect of utilizing cover crops. In 2017, University of Nebraska Extension educator, Jen Rees, found wheat stem maggots migrating from late-terminated cereal rye to emerging corn plants (Rees et al, 2021) with other rare incidences of this occurring in corn by South Dakota State University and Kansas State University (Rees, 2017).
Disease and pathogen pressure can also be an issue especially if successive plants belong to the same plant family. A USDA study published in 2016 assessed the potential for cover cropping to increase inoculum of corn seedling pathogens. While the study proved that there was an increased density of four common corn seedling pathogens in rye roots, there would have to be close contact between the corn seed or roots and the infected rye roots (Bakker et al, 2016).
Cover Crop Management & Termination
Looking back, we’ve seen a rise in cover crops when the idea first was implemented in American agriculture, a fall in the late 1950s with the introduction of synthetic fertilizers (White, 2014) and then a rise again with the introduction of funding programs. While we’ve discussed a lot of potential issues cover crops can bring, it’s still important to remember all the benefits cover crops provide from reducing soil erosion, decreasing nutrient loss, and improving soil quality. Are these benefits worth the risk? To be honest, it’s hard saying. Our little literature review above shows that data is inconsistent and somewhat outdated.
However, what we can tell you is that with proper management, the rewards can outweigh the risks. Timely termination can help eliminate many of these negative impacts. Early 2010s suggestions all follow a 14-day pre-plant termination of cover crops. However, new approaches suggest that “planting green” may offer easier planting, corn seedlings that look less yellow or sickly, and increased early-season weed suppression (Rees et al, 2021).
Our approach is to work with you on an individual and field-by-field level to make sure you’re able to avoid yield loss without limiting the beneficial characteristics of cover crops. From selecting your cover crop seed to determining the method and timing of termination, our agronomists are staying on top of today’s information to give you viable cover crop options that work here in southeast Iowa.
Bakker, M. G., Acharya, J., Moorman, T. B., Robertson, A. E., & Kaspar, T. C. (2016). The potential for cereal rye cover crops to host corn seedling pathogens. Phytopathology®, 106(6), 591–601. https://doi.org/10.1094/phyto-09-15-0214-r
Geist, L. (2017, May 30). Cover crop residue can complicate nitrogen management in corn. University of Missouri Extension. https://extension.missouri.edu/publications/g4161
Kaspar, T. C., & Singer, J. W. (2015). The use of cover crops to manage soil. Soil Management: Building a Stable Base for Agriculture, 321–337. https://doi.org/10.2136/2011.soilmanagement.c21
Rees, J. (2017, June 12). Corn concern in wheat/rye cover. JenREESources’s Extension Blog. https://jenreesources.com/2017/06/05/corn-concern-in-wheatrye-cover/
Rees, J., Proctor, C., Koehler-Cole, K., & Jhala, A. (2021, April 8). Cover crop termination tradeoffs. CropWatch. https://cropwatch.unl.edu/2021/cover-crop-termination-tradeoffs
Vieira Branco Ozorio , D., Basche, A., & Koehler-Cole, K. (2022, September 14). How much nitrogen does my cover crop take up and when do I get it back? CropWatch. https://cropwatch.unl.edu/2020/how-much-nitrogen-does-my-cover-crop-take-and-when-do-i-get-it-back
White, P. A. (2014, August). The Growing Business of Cover Crops. National Wildlife Federation. https://www.nwf.org/~/media/PDFs/Wildlife/A-G/TheGrowingBusinessofCoverCrops-