Research Highlights

Cover Crop Interaction with Soybean Planting Date

By Laura Temple

Years of research have confirmed that planting date is the management practice that most influences soybean yield. Another body of research has documented the value a cover crop can add to production systems.

“In Ohio, we’ve seen that soybeans planted after the last week of April can have yield reduced as much as 0.5 bushels per acre per day,” says Laura Lindsey, Ohio State University Extension specialist for soybeans. “However, research involving cover crops with an early planting date is lacking.”

To learn about the impact of cover crops at different planting dates, Lindsey designed a research trial that is being funded by Ohio Soybean Council checkoff funds.

“The concept for the trial was inspired by a farmer who planted soybeans into a rye cover crop early in 2019,” she explains. “The young seedlings were exposed to a late frost, but the field still maintained a decent yield.”

Based on this experience, she started this small plot study with a rye cover crop planted prior to the 2021 growing season.

“Remember, with cover crops, every season is unique,” Lindsey says. “The initial results are interesting, but we need data from multiple years to fully understand how planting dates and cover crops influence soybean yields. We have a cover crop planted to repeat this trial during the 2022 season.”

Trial Variables

Lindsey conducted trials at two Ohio locations: Wooster in the northeast, and South Charleston in the west-central region. Temperatures tend to be cooler and the growing season shorter in the northern part of the state, while west-central Ohio is similar to the majority of the Midwest Corn Belt.

Her study includes three planting date ranges, two cover crop termination practices and a control with no cover crop. Exact planting date and cover crop termination dates were dictated by weather conditions. The rye cover crop was planted on October 14 and 15, 2020, at a rate of 1.4 to 1.6 million seeds per acre. Soybeans were seeded in 15-inch rows at a rate of 120,000 seeds per acre.

At the South Charleston trial location in west-central Ohio, cover crops had no impact on soybean yield at different 2021 planting dates. Trials planted in April yielded between 74 and 76 bushels per acre, while plots planted in late May averaged just 64 bushels per acre.

“Based on conditions in 2021, planting early does boost yields,” Lindsey says. “In this environment, farmers can incorporate cover crops using the practices that best fit their operation. However, they should be aware of potential challenges we saw in northeast Ohio.”

Soybean Stands Link to Yield

Trials at the Wooster location in northeast Ohio demonstrated the potential for notable interaction between cover crops and planting date. Preliminary results correlated cover crop influence with soybean stands, which translated to yield differences.

“The ultra-early plantings with no cover crop had a stand of 80,000 plants per acre and yielded 73 bushels per acre,” Lindsey says. “However, with cover crops, ultra-early stands were just 20,000 plants per acre, and that impacted yield.”

She theorizes that cover crops may have kept soils moist and cool longer, making it hard for soybeans to emerge. Slug damage may also have been a problem, though they weren’t visible when the plots were checked during the day.

“The early plantings all yielded well, between 70 and 76 bushels per acre regardless of cover crops,” she explains. “This timing appeared to provide strong yields and the benefits of cover crops.”

However, the normal planting in northeast Ohio, which happened to be in late May due to weather, yielded less with cover crops. Lindsey thinks the large amount of cover crop biomass may have played a role in reducing soybean stands.

“In May 2021, we had snow and frost damage, and it was worse in northern Ohio,” she adds. “Soybeans grew very slowly, regardless of planting date.”

Another interesting result Lindsey found was that soybeans planted early can have poor stands, as low as 50,000 plants per acre, and still yield really well.

“Soybeans can branch out and fill in space really well later in the season,” Lindsey says. “If farmers cannot let the eyesore of a poor early stand bother them, they may get excellent yields without replanting. That also supports profitability.”

Regardless of cover crop practices, she recommends looking at stand counts carefully before making decisions about replanting. She expects that 2022 data will provide a different picture and more information about how cover crops and early planting dates interact.

“I am very happy this study is being funded,” Lindsey says. “We are gathering unique information that will help farmers make better decisions about planting and replanting soybeans, especially when incorporating cover crops.”

Published: Feb 21, 2022