Cover Crops in Corn – a Good Match?

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Cover crops in corn Courtesy: Purdue University 

Cover crop use continues to increase as farmers learn and fine-tune how it fits in a corn and soybean rotation. The annual national cover crop survey among farmers in August 2020 showed small yield increases following cover crops in corn, soybeans and wheat.  

Overall, farmers cite that cover crops will deliver healthier soils, lower herbicide and fertilizer costs, reduce erosion and improve weed control, among other benefits.  

“I was pleasantly surprised to see 50% of these farmers [in the survey] plant some of their cover crops before harvest,” says Dean Baas, Michigan State University Extension educator in Sustainable Agriculture. “This is a good indicator that farmers seek ways to get cover crops established earlier than postharvest to improve cover crop benefits.” 

Northern Geography Limits Species 

Baas, who Michigan farmers rely on as their cover crop hotline expert due to the volume of phone calls he receives, says that cereal rye is the best species when seeding so late after corn grain harvest. “We’re kind of stuck with winter cereals when planting so late. But by seeding before harvest, there is more time to establish brassicas, legumes and other grasses,” he says. 

Ideally, cereal rye should be seeded no later than one week after the 50% frost date, which ranges from October 11 in northern Michigan to October 28 in southern Michigan. Seeding rates vary by method: drilled (45-60 pounds per acre) or broadcast with shallow incorporation (50-65 pounds per acre). Rates are based on high-quality seed with 85-98% germination. 

Michigan farmers are experimenting with interseeding in tall corn using Hi-Boy sprayers with cover crop seeders. “Some farmers are interseeding at the V3 to V5 growth stage, and so far, we’ve not seen any impact on corn yield after V2. The critical decision when interseeding early is to select residual herbicides whose residual carryover won’t kill or injure the cover crop species,” Baas adds. If cover crops will be grazed or fed to livestock, check herbicide label restrictions before applying. 

Termination is Critical

Baas gets a lot of questions about termination timing from farmers. “Our basic recommendation is to terminate cereal rye 10 days to two weeks before planting to reduce yield loss risk. If it’s a dry spring, we tell farmers to watch the weather forecast to decide if terminating early could save more moisture for the corn crop. No hard and fast recipe works year after year,” he says. 

To help corn get off to a good start, Michigan State University agronomists recommend a 2x2 application of 30-50 pounds per acre actual nitrogen starter fertilizer, since cereal rye can tie up nitrogen. 

Start Small

For farmers just beginning to manage this third crop in a corn-soybean rotation, Baas suggests starting on a small scale. “Pick a field with a problem like compaction or resistant weeds and seed a cover crop. Once you gain experience with cover crops, just like experience with cash crops, you learn how to make adjustments, so all crops succeed.” 

Baas often suggests that farmers look at cover crops like an insurance policy for better cash crop performance under abnormal weather conditions. 

“In abnormal years of too hot or cold or too wet or dry — which we're having a lot more of on a regular basis — cover crops will make your system more resilient,” Baas says. “In those years of heavy spring rains, growing cover crops can suck it [water] up and help you get out in the fields quicker. And if the weather turns dry after that, you end up retaining more moisture for use later into the season. So, there's just a lot of benefits that come from cover crops, especially during abnormal years.” 

For more information: 
Cover Crop Termination (MSU, 2021) 
Cover Crops for Sustainable Crop Rotations (SARE, 2015) 
Cover Crop Economics (SARE, 2019) 
Cover Crop Selector Tool (MCCC) 

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