Interseeding Cover Crops into Early Season Corn and Soybean: Species Selection

Interseeding video intro — It’s important to plan ahead of time and know your goals when adding cover crops to your operation. In this article, Nebraska Extension evaluates numerous cover crop species and provides guidance on how to choose the species that will best fit your production needs. This video shares additional information on cover crop species used.

April 27, 2023

Steve Melvin - Extension Educator Irrigated Cropping Systems

Nelson Winkel - Prescribed Fire Planning Specialist, Central Platte NRD

Mary Drewnoski - Beef Systems Specialist

Chris Proctor - Weed Management Extension Educator

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.

2020 Cover Crop Interseeding Mixes

**2020 Diversity Mix**
A 13 lb/ac seeding rate of this mix was seeded into V4-V5 corn at a cost of $16.86/acre
Species	Rate in Mix (lb)
Hairy vetch	4
Cat Jang cowpea	4
Red clover	1
Yellow blossom sweetclover	1
Red ripper cowpea	4
Annual ryegrass	3
Italian ryegrass	1
Smart radish	0.5
Impact forage collards	0.5
Mancan buckwheat	4
Golden flax	2
Mini pumpkins	0.5

**2020 Nitrogen Mix**
A 13 lb/ac seeding rate of this mix was seeded into V4-V5 corn at a cost of $18.16/acre
Species	Rate in Mix (lb)
Laredo forage soybean	4
Yellow blossom sweetclover	2
Red clover	1.5
Hairy vetch	4
Red Ripper cowpea	6
Pinkeye cowpea	4
Nitro radish	0.5
Impact forage collards	0.5
Mancan buckwheat	4

2020 Evaluation Notes: We chose to remove the red ripper cowpeas for the following season because they were too aggressive (grew up to the tassels in the corn and produced seed). The mini pumpkins were fun and families enjoyed collecting them in the fields, but they can also attract corn rootworm beetles, so we removed them for next growing season.

2021 Cover Crop Interseeding Mixes

**2021 Diversity Mix**
A seeding rate of 17 lb/ac was seeded into V4 corn at a cost of $22.15/acre
Species	Rate in Mix (lb)
MT hairy vetch	2
Iron & Clay cowpea	2
Red clover	1
Yellow blossom sweetclover	1
Winterhawk annual ryegrass (diploid)	5
Nitro radish	0.5
Impact forage collards	0.5
Mancan buckwheat	3
Golden flax	1.5
Laredo forage soybean	0.5

**2021 Nitrogen Mix**
The total rate seeded was 31.5 lb/ac into V4 corn and cost $46.21/ac. (We wanted to increase biomass with the higher seeding rate.)
Species	Rate in Mix (lb)
Laredo forage soybean	4.8
Yellow blossom sweetclover	3.3
Medium red clover	3.3
MT hairy vetch	4.8
Iron & Clay cowpea	8
Purple top turnip	0.43
Impact forage collards	0.54
Mancan buckwheat	6.4

**2021 Mix for Interseeding into Soybean**
The total rate seeded was 36 lb/ac into VC or V2 soybean and cost $26.50/ac.
Species	Rate in MIx (lb)
Hard red winter wheat	26
Medium red clover	10

2021 Evaluation Notes: We liked the Iron and Clay cowpeas as they weren’t as aggressive and didn’t go to seed compared to the red ripper cowpeas. We were concerned about how well the yellow blossom sweetclover survived the winter into the following spring and how aggressive it was to kill. The farmers chose to keep it for consistency for the 2022 season but felt it was not a species we should recommend in the future. Doubling the seeding rate for the nitrogen mix wasn’t worth the large seeding cost to the farmers and they recommended getting the cost down to the $20-25/ac range.

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.

2022 Cover Crop Interseeding Mixes

**2022 Diversity Mix**
A seeding rate of 13 lb/ac was seeded into V3 corn and cost $22.89/ac.
Species	Rate in Mix (lb)
Iron & Clay cowpea	2.5
Mung bean	2
Laredo forage soybean	3
Yellow blossom sweetclover	2
Medium red clover	4
Winterhawk annual ryegrass	4
Impact forage collards	0.5
Purple top turnips	0.5
Mancan buckwheat	3
Brown flax	2

2022 Evaluation Notes: The 2022 Diversity Mix is the mix we like going forward; however, we’d recommend removing the yellow blossom sweetclover and use red/white clover instead as a low-growing clover that form a mat.

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.

Helpful Resources

Rees, Jenny, Roger Elmore, Chris Proctor, Steve Melvin, Michael Sindelar. May 23, 2019. Interseeding Cover Crops into Corn or Soybean. UNL CropWatch. (Shares research from multiple universities).

Rees, Jenny. March 2023. Interseeding Cover Crops into Early Corn and Soy: What We’ve Learned. UNL Department of Agronomy and Horticulture Seminar.

Rees, Jenny, Steve Melvin, Laura Thompson, Taylor Lexow, Katja Koehler-Cole, and Mary Drewnoski. April 13, 2023. On-Farm Research Early-season Interseeding into Corn and Soybean Results (2019-2022). UNL CropWatch.

Rees, Jenny, Steve Melvin, Amit Jhala, and Chris Proctor. April 20, 2023. Herbicide Considerations When Interseeding Cover Crops. UNL CropWatch.

Midwest Cover Crop Council Selection Tool

Nebraska On-Farm Research Virtual Field Day Interseeding Videos: