Research Highlights

When Planting Time is Short: Flexible Cover Crop Termination Strategies

In this article, you’ll find details on:

• Managing cover crops termination timing and residue can complicate soybean planting, especially in regions with a short growing season.
• Farmers in New England use a variety of strategies to terminate cover crops, and research shows that the best practice ahead of planting soybeans depends on the conditions of that season.
• Understanding the advantages and risks of each cover crop termination method and its interaction with soybeans equips farmers to choose the best method for each field situation.

By Laura Temple

When weather and field conditions narrow windows for spring fieldwork, farmers prioritize getting the crop in the ground. Cover crops complicate that process, especially when farmers are adjusting to new systems.

“We’ve found that flexibility and knowing how to respond to conditions help farmers manage cover crops before planting soybeans,” says Heather Darby, professor and agronomic and soils specialist with University of Vermont Extension. She explains that in the past several years, soybean acres have been increasing in New England. 

Her research has focused on helping farmers find solutions to their challenges as they incorporate soybeans into systems that traditionally focus on corn silage and hay, with critical soy checkoff support from the Eastern Region Soybean Board. Steep slopes, erodible soils and mandates require cover crops on many of those acres. 

She accepted the challenge of researching solutions that would allow farmers to manage cover crops ahead of short-season soybeans, establish cover crops following soybeans and more. Her research is heavily based on difficult experiences from farmers in the region. This research allows her to make mistakes and find solutions, reducing risks for farmers.

“We observed that soybeans planted into overwinter cover crops could experience yield depression of up to 10 bushels an acre,” she shares. “However, soybeans planted into cover crops that winter kill in our region, like oats and radishes, didn’t see any yield depression.”

In response, Darby designed trials that looked at cover crop seeding rates and residue. She planted soybeans into different amounts of cover crop residue. She compared no cover crop residue, achieved by tilling cover crops under, with low residue and high residue scenarios. Her initial research found the volume of spring biomass depends more on termination timing than cover crop seeding rate.

“We started to see soybean yields decline with biomass higher than 3 tons per acre, regardless of termination strategy,” she reports. “The amount of biomass produced mattered. While we are still researching to figure out why this is, we know cover crop termination timing and residue management is critical ahead of soybeans.”

Managing Residue Risks

Biomass accumulation depends heavily on growing conditions, like harsh or mild winters and moisture availability. The resulting residue offers the following soybean crop both benefits, like weed suppression and erosion prevention, and risks, like yield suppression and delayed planting.

Farmers in New England use a variety of strategies to terminate cover crops. 

• Choosing cover crops that winter kill saves time with termination in the spring, but this limits the benefits to those from the biomass accumulated prior to winter kill.
• Plowing cover crops under and tilling them into the soil ensures biomass breaks down quickly to add organic matter, while preparing fields for planting. However, this requires good conditions for spring fieldwork.
• Applying herbicide to halt cover crop growth allows farmers some flexibility in termination timing, depending on field conditions. Spraying early limits biomass, while allowing it to grow longer increases it.
• Rolling or crimping cover crops ahead of planting or just after soybean emergence protects soil from erosion and helps manage weeds.

Each method offers benefits and drawbacks.

Spraying to terminate cover crops gives farmers some ability to manage biomass quantity. However, most farmers rely on custom applicators for these applications, and variable spring weather limits when those applicators can get into fields and the number of acres they can cover. 

“With our short growing season, we don’t have big windows for any fieldwork, and cover crops add more risk to variable spring weather,” she says.

Planting green into cover crops is an option with both herbicide termination or rolling. However, Darby notes that sometimes a rye cover crop can get wiry and wrap around row cleaners.

Matching Practices to Conditions

Each growing season brings something different, and Darby is learning more each year.

“The take-home from the research so far is that the best termination option may depend on conditions,” Darby says. “It’s best for farmers to be flexible. Adaptive management is key to taking advantage of cover crops without impacting soybean yields.”

For example, during wet springs, more cover crop growth reduces excess soil moisture. However, under dry spring conditions, cover crops may have used most of the available moisture prior to the crop getting started, exacerbating current and any persistent drought issues.

“We’ve also seen that prior to hot, dry summers, rolling cover crop biomass keeps soils cooler and wetter,” she says. 

Based on this ongoing research, Darby encourages farmers to be ready to adapt each spring to select the best termination method for each field. In some cases, early herbicide termination may prevent high residue volumes. In other situations, planting green and rolling cover crops when soybeans have emerged may make the best use of the planting window.

“There are real risks and benefits to each option,” she says. “As we better understand how each one works with our short-season soybeans, we can equip farmers to adapt.”

Additional Resources: 

• Finding Best Practices to Maximize Yield and Environmental Stewardship – SRIN article
• When Harvest Time is Short: Interseeding Cover Crops in Short-Season Soybeans – SRIN article
• Soil Moisture is Key When Terminating Rye and Planting Soybeans – SRIN article
• Cover Crop Interaction with Soybean Planting Date – SRIN article
• GROW Resources on Cover Crops and Weed Suppression – GROW page 
• Cover Crops Do’s & Don’ts – Crop Protection Network page 
• Meet the Principal Investigator: Heather Darby

Published: Feb 24, 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.