Research Highlights

Evaluating Early Soybean Planting to Fit Fieldwork Logistics

In this article, you’ll find details on:

• Maryland trials show that soybean planting dates interact with maturity group, population rate and the weather to determine yield.

• Understanding those interactions can help farmers manage soybeans within their overall crop rotation to handle fieldwork and optimize profits.

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By Laura Temple

As soon as spring conditions allow, farmers head to their fields. They have limited days to prepare fields, plant crops, apply fertilizer, control early weeds and more.

With many logistics to manage in limited time, farmers rely on data and experience to prioritize those tasks in the order most likely to maximize yields and profits. In recent years, headlines and coffee shop chatter have recommended planting soybeans earlier than in the past.

“Farmers on the Maryland Soybean Board had questions about timing for soybean planting,” recalls Nicole Fiorellino, assistant professor and extension agronomist for the University of Maryland. “They asked me to re-evaluate the University’s soybean planting recommendations.”

With Maryland Soybean Board direction and funding support, Fiorellino developed trials to do just that, starting in 2022. She chose to use the official state soybean variety trials, which she manages.  

At two variety trial locations, one in eastern Maryland and one in western Maryland, she duplicated plantings at two dates. Based on field conditions at each location, the early planting date occurred in mid to late April, roughly one month before average May timing. The goal was to get a snapshot of any yield differences across maturity groups and top varieties submitted by seed companies for the variety trials.

“Everything with soybeans is complicated, and investigating this question is no different,” Fiorellino says. “Results depend on the year, weather conditions, location, timing and more.”

She reports that in 2022, the team observed an overall yield increase with early planting at the western location, with a yield penalty from early planting seen in a few of the earlier maturing varieties. At the eastern location in 2022, more early maturing varieties, MG 3.1 to 4.4, experienced a yield penalty with early planting. At both locations in 2023, most varieties showed a yield increase or a minor yield penalty of less than 10 bushels per acre with early planting. 

“In the variety trials, early planting impacted maturity groups differently,” she explains. “For example, our experience with double-crop soybean systems shows that mid-MG 4 varieties are flexible enough in our region to yield comparably if planted in May or July.”

Exploring Other Influencing Factors

Fiorellino reported that initial, limited results indicated interactions between planting timing and maturity group.

• Early MG 3 varieties did not benefit from early planting. 
• Most varieties above MG 4.5 did benefit from early planting dates across years and locations. 
• Varieties ranging from mid-MG 3 up to MG 4.5 were less clear-cut, showing greater variation in yield between planting dates and locations.

Those trends prompted questions about increasing population rates at early planting dates to compensate for yield differences. 

“Because soybeans are complex, flexible plants, and because yields depend heavily on the weather and environmental conditions, I am hesitant to update University recommendations without multiple years of data,” she says.

To gather more data over multiple years, Fiorellino adapted the trials to focus on specific maturity group ranges. She started with MG 3 varieties in 2023 for the first of three years of trials. She notes that interest in earlier maturities is growing in the Mid-Atlantic region. These trials incorporate three planting populations: 80,000, 100,000 and 120,000 seeds per acre, at two planting dates about three to four weeks apart. 

“The first year of these trials showed no benefits to the population above 100,000 at the early planting date,” she reports. “It will be interesting to see if this holds true in the next couple years.”

After studying MG 3, she plans to focus on MG 4 varieties for a few years.

Optimizing Spring Logistics

“My hope is that this detailed research will help farmers figure out what soybean planting timing and maturity group combinations work best in their overall system and rotation,” Fiorellino says. “The data from these trials will help them decide how soybeans work best with their corn, small grains and cover crops, so they can prioritize fieldwork.”

For example, early maturing varieties may work well before winter wheat or barley. Choosing flexible soybeans that yield consistently regardless of planting may be best for farmers who need to get corn planted in a specific window. Planting longer-season varieties earlier may make sense for farmers committed to sowing a cover crop during harvest.

“I also expect this research to uncover any other variables we aren’t thinking about,” she adds. “I believe we have more potential to improve how soybeans fit into agronomic systems compared to the other crops grown in the region. Figuring out what combination of soybean planting date, maturity group and planting rate best fits into a rotation and workload will help farmers improve profitability and use time well.”

Published: Jun 3, 2024