What factors should you consider when planting a cover crop before corn?

A corn cover crop is not as simple as a soybean cover but with proper planning, you can achieve great success. 

In our Cargill RegenConnect™ program, we've heard many different reasons why growers don't use a corn cover crop. While a corn cover crop is not as simple as a soybean cover, with proper planning you can successfully integrate cover crops into your corn cropping program. Let's look at some options that you should consider before implementing a corn cover crop.

What is your goal with implementing a corn cover crop?

Knowing the reason behind why you are implementing a cover crop is the first step in proper seed selection.

• Soil health and erosion control

While all cover crops will add organic matter to the soil, some are more prolific than others in their biomass production. Biomass will cover the soil to reduce evaporation, slow erosion, and keep the soil cool in summer heat. If you are dealing with tight soils or tillage pans, consider adding a cover crop with a deep tap root to help break through the compaction layers.

• Weed suppression

A cover crop with rapid growth in the fall or spring will help suppress weeds, but be mindful of the crop's C:N ratio as this will tie up nitrogen for the corn. A starter fertilizer will be necessary to give the corn a jumpstart.

• Increase fertility

Adding a legume cover crop can help increase N in the soil but it comes with considerable hurdles for success.

Summer annual legumes add the most N but would not fit in a corn/soybean rotation. These would, instead, be a great option after harvested wheat.

Winter annual legumes, such as hairy vetch and clovers, can easily be inter-seeded or planted after early soybeans. In doing this, they would need a fair amount of spring growth for significant N production.

Many legumes can also pose issues for planting due to their viny nature. If you decide to use a legume, make sure your planter can combat the residue.

What should you consider when selecting seed for a corn cover crop?

Planting date and termination

Planting date is most likely the biggest factor when planning a corn cover crop. For winter kill cover crops, ensure a minimum of four weeks before your first average frost to give your cover plenty of time to grow. To achieve this, inter-seeding into the current crop may be necessary. This is best done when the crop is just starting to yellow and drop leaves. Another option is planting a shorter maturity crop to allow for an earlier harvest in the fall.

A winter-kill cover crop is a great option to consider for someone just starting to implement corn cover crops. Cover crops such as oats won't require termination and can be implemented with little change in current management practices if early seeding is possible. When seeding covers early, be aware of any residual herbicide still present in the soil that could affect germination.

While winter-hardy crops offer more benefits with their longer growing season, proper termination planning is important to ensure success. Planting green will help reduce the risk of terminated cover holding moisture in a wet year. This could also potentially allow you to plant earlier due to the moisture the cover uses in the spring. Terminating before planting can be done successfully, but make sure to terminate at least 10-14 days before planting and when plants are no taller than eight inches. This will reduce the amount of nitrogen tie-up and residue covering the soil.

Proper herbicide selection is important to ensure complete cover crop termination. Always use labeled rates of chemical and consider increasing the amount of water applied to ensure coverage in heavy stands of cover crops. 

What cover crops should you consider?

• Cereal grain crops
  • Oats - Oats have rapid fall growth and will winter-kill once cold temperatures set in. Make sure to plant as early as possible (early September) to leave potential for the most growth.
  • Cereal rye - This crop is a great biomass producer for increasing organic matter and helping in weed suppression. Rye has a high C:N ratio so a starter fertilizer will be necessary to give the corn a jumpstart.    
• Brassicas
  • Radish and turnips - Either of these crops are great options to help improve soil health as their deep roots break up hardpans and help cycle nutrients to the top of the soil profile.
  • Rapeseed and kale - Both of these are broadleaf cover options that can be planted later and are more tolerant of cold weather. These plants offer a smaller taproot than a radish but also have a great fibrous root system to improve upper-level soil structure.
• Legumes
  • There is a long list of legume cover crops that can help add N to the soil before corn. Clover, vetch, and peas are all good options if you are looking to add N. Keep in mind that corn planting may need to be delayed for maximum N credit.

For further information on cover crops for corn, or information on inter-seeding into standing cash crops, please refer to the additional links posted below or reach out to a Cargill RegenConnect™ agronomist near you.

 

https://extension.purdue.edu/extmedia/ay/ay-353-w.PDF

https://www.360yieldcenter.com/2017/04/dont-tie-up-your-nitrogen-3-tips-for-managing-the-carbon-penalty/#:~:text=Corn%20residue%20has%20a%20high,is%20unavailable%20to%20your%20crop.

https://extension.umn.edu/cover-crops/early-season-cover-crop-interseeding-corn

https://cropwatch.unl.edu/2016/planting-corn-cereal-rye-cover-crop