The goal with interseeding cover crops into corn and soybean early in the growing season is to allow for more time for a cover crop to be established. Having more time for establishment prior to harvest can aid in suppressing weeds, capturing excess nitrogen, providing additional nitrogen, increasing diversity and establishing forage for grazing. 

Thus far, we’ve shared CropWatch articles in 2023 on:

In this final article, we will share on cover crop species selection for interseeding cover crops into corn and soybean early in the growing season. The information shared here is the result of a partnership amongst The Nature Conservancy, Upper Big Blue NRD, Nebraska Extension, Kellogg’s, and cooperating farmers in the 2020-2022 growing seasons in Nebraska. We successfully achieved germination and establishment of a variety of interseeded cover crops (grasses, legumes, brassicas) using an interseeding drill to put the seed into the soil. Most of the fields we worked in were irrigated with center pivots. The soil moisture was excellent in 2020, resulting in good cover crop emergence. However, the soil surface was dry in 2021 and 2022, resulting in poor emergence without irrigation.

Our team used a variety of cover crop species in mixes. Our goal for multi-species mixes was to see what would germinate and establish, especially with different herbicide programs the farmers chose. In all cases, all species emerged in the farmers’ fields. Our cooperating farmers helped us evaluate the species contained in the mixes each year. Our goal was to keep the cost between $15-25/ac as the farmers felt that would be the range that other farmers would be willing to pay for the seed.

The following mixes were used from 2020-2022 and this video shares additional information.
In the soybean mix, we used winter wheat as a cover crop species. Had it survived the growing season into the fall, that can be problematic in creating a “green bridge” for the wheat curl mite in areas where wheat is often planted. In our studies, the winter wheat died during July, but if one wishes to err on the side of caution, a different grass species can be interseeded (or just interseed red/white clover) in areas where higher acres of wheat are planted.

Species Selection for Different Goals: Specific species depend on one’s goals. The following suggestions are based off on-farm research observations.

Goal of Weed Control:Cover crop biomass production is key for weed suppression. Buckwheat, cowpeas and forage collards/turnips/radishes are quick to emerge and shade the ground with large leaves.

Goal of Erosion Control:Grasses with their fibrous root system can greatly aid in erosion control. However, many cover crop species can help reducing wind/water erosion.

Goal of Providing Nitrogen:Cowpeas, other types of beans (mung), hairy vetch, clovers. The clovers and hairy vetch will survive the winter.

Goal of Forage:Brassicas such as forage collards/turnips/radishes/rape, annual/Italian ryegrass, clovers. We have had one grower try some sorghum with a lower population of corn (10,000-15,000 seeds/ac) in order to gain more forage. This could also be a consideration in 60-inch rows.

Goal of Scavenging Nutrients:Buckwheat scavenges phosphorus. Flax scavenges a number of nutrients. Grasses with fibrous root system will scavenge nitrogen.

Goal of Increasing Biodiversity:Buckwheat and Flax are great for pollinators. Flax is one of the best cover crops for increasing microbial biodiversity.

Goal of Overwintering:Clovers, annual and Italian ryegrass, cereal rye (need to increase the seeding rate otherwise winter survival is spotty), hairy vetch.

If you’re looking for only a few species, we’d recommend annual/Italian ryegrass, red clover and forage collards. Buckwheat is great for corn/corn but will go to seed if you’re in a corn/soy rotation. It will die with soybean POST herbicide, though. Our farmers always added some flax for the biodiversity aspect.

Final Thoughts for Success

  • Adding cover crops takes more management and a system’s approach. It helps to plan prior to the growing season and it’s important to know one’s goals to determine species.
  • Drill interseeding into V3-V4 corn and VC soybean is the development stages we’d recommend.
  • May need moisture shortly after interseeding to aid in emergence.
  • Herbicide recommendations were shared in this article.

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