Research HighlightsWhen Harvest Time is Short: Interseeding Cover Crops in Short-Season Soybeans
In this article, you’ll find details on:
- In New England, soybean acres have been increasing as farmers learn to incorporate them into their systems.
- Cover crops are mandated or highly desired in many New England fields to prevent soil erosion, but planting them into soybeans requires different management practices than silage or grain corn.
- Interseeding winter rye into soybeans after leaf drop allows time for the cover crop to be established before state and federal program cut-off dates without damaging the cash crop.
By Laura Temple
A century ago, U.S. farmers planted very few soybeans. Soybean acres have steadily risen, as farmers adopted them into crop rotations and learned how to make soybeans work in their climate and cropping system.
A decade ago, New England farmers planted very few soybeans, according to Heather Darby, professor and agronomic and soils specialist with University of Vermont Extension. Soybean acres are steadily rising here for diversification, self-sufficiency in livestock operations and similar reasons. Darby is exploring answers to farmer questions as they learn how to make soybeans work in their climate and cropping systems.
“In the Northeast, we have lots of mandates and regulations for water quality,” she says. “Farmers often have to plant cover crops to prevent soil erosion, so we are learning how to do cover crops in soybeans with our short growing season.”
With soy checkoff support from the Eastern Region Soybean Board, Darby has been researching ways to establish cover crops following soybeans, best planting practices for soybean following cover crops and more.
Farmers in northern New England typically plant soybeans from mid-May to mid-June, choosing varieties from Maturity Groups 0.6 to 1.5. Depending on the season’s weather, they often harvest in mid-September or October. In years like 2023, harvest happens in the snow.
“The goal is to plant cover crops before the last acceptable date to comply with federal or state programs,” Darby explains. “In Vermont, that’s October 10. There often isn’t time to harvest soybeans and plant a cover crop by then.”
She adds that winter rye is essentially the only cover crop option that will grow in the region at that time of year. The optimum date for planting that cover crop in the region is the third week of September.
Errors and Trials
Darby says that regional farmers successfully plant cover crops into corn when the crop is relatively small. Cover crops emerge, but then go dormant through the growing season until the canopy opens up later in the season.
“In soybeans, farmers started interseeding cover crops before they canopied,” she reports. “They soon learned that soybeans shaded out all the cover crop. It didn’t even get started.”
Because that didn’t work, Darby designed trials to identify when to time cover crop seeding with soybean leaf drop in the fall, while keeping program cut-off dates in mind.
“As soybean acres increase in the area, my research philosophy is to let me make mistakes to take the risks out of what farmers are doing,” she says.
She found that most seasons, shorter-season soybeans within the MG 0.6 to 1.5 range drop leaves by mid- to late-September in this region. Longer-season soybeans, closer to MG 2.0, don’t drop their leaves until early October.
“Regardless, if farmers are prepared to plant cover crops right after their soybeans drop leaves, they can get a cover crop planted before the cut-off date,” she says.
In her trials, she drilled winter rye between 30-inch soybean rows to ensure good seed-to-soil contact. In most cases, drilling after leaf drop didn’t damage the soybeans. And, the cover crop could emerge and grow before frost.
“The earlier the cover crop is planted, the better it gets established,” Darby explains. “However, the cover crop always emerged and grew in this system.”
She also discovered challenges that farmers may need to plan for or adjust management practices to still get cover crops planted following soybeans.
“In certain years with lots of rain and warm temperatures, soybeans can grow very lanky and lodge,” Darby notes. “Lodged soybeans prevent interseeding because they get caught in the drill.”
Management Recommendations
Darby wrapped up cover crop seeding trials following the 2023 season, determining that regional farmers had the basic knowledge to incorporate cover crops into systems following soybeans. They can continue to protect against soil erosion on sloped ground, even with the lower volume of residue soybeans provide compared to corn silage or grain corn. Her soybean research focus shifted to other cover crop management challenges.
Based on the trials, she encourages farmers to avoid planting soybean varieties that are prone to lodging or vining. If cover crops will be drilled, she recommends the 30-inch rows used in her trails. For farmers choosing to broadcast cover crop seed, other row spacings can work.
The seeding rates for planting cover crops after leaf drop remain the same as what would be used after harvest. Darby has seen the most success planting winter rye, but she notes that farmers can plant other species appropriate for that time of year.
“We now know that soybeans can be a cash crop option, while still including required or desired cover crops,” she says.
Additional Resources:
- Finding Best Practices to Maximize Yield and Environmental Stewardship – SRIN article
- Planting Cover Crops into Standing Soybeans – SRIN article
- Get More From Cover Crops: Seed Early – SRIN article
- Cover Crops and Soybeans can be a Good Combination – SRIN article
- Resources on Cover Crops and Weed Suppression – GROW web page
- Cover Crops Do’s & Don’ts – Crop Protection Network publication
- Meet the Principal Investigator: Heather Darby
Published: Jan 27, 2025
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.
