Research Highlights

Testing Varieties for Ultra-Late Soybean Production on the Coastal Plain

By Laura Temple

The long growing season and late average frost date in the Coastal Plain of the Southeastern U.S. supports a unique soybean production system – ultra-late soybeans.

Soybeans can be planted in early August, following the harvest of irrigated corn. The addition of nitrogen to get the crop off to a good start allows it to grow and flower quickly. Narrow rows, typically 7.5 inches apart, allow for rapid canopy closure. Though the soybeans only reach 18 inches or so in height, they can yield at least 20 bushels per acre. However, the goal for the system is to reach yields between 30 and 50 bushels per acre when harvested in December.

“Varieties that do well in this system don’t necessarily do well in our full-season variety tests,” explains Daniel Mailhot, director of Statewide Variety Testing for University of Georgia Extension. “As more farmers in this region adopt this ultra-late soybean production system, they need to know what varieties will work.”

With soy checkoff support from the Georgia Agricultural Commodity Commission for Soybeans, Mailhot has added ultra-late soybeans to the state variety trials. About 45 varieties are included in these trials each year. 2020 trials were located in Attapulgus and Camilla, Georgia. Past trials have also been done in Midville. 

“We are screening as many varieties as possible for this system,” he says. “Maturity group doesn’t seem to matter, but there are very large differences between varieties. It’s critical that varieties grow tall and nodulate quickly.”

Farmers in the Coastal Plain of southern Georgia began developing this system about 15 years ago. The corn–soybeans–winter fallow rotation each year works well for those who don’t raise peanuts. If corn is planted in late-February to very early March, it can be harvested early enough to allow soybeans to be planted between August 1 and August 10. 

“Currently most farmers are using one old soybean variety that has worked reasonably well in this system,” Mailhot says. “However, we are finding several varieties that out-perform it. In 2019, we found eight varieties that yielded more than 30 bushels per acre. In 2020, we observed early defoliation and lower yields. However, 13 varieties exceeded 20 bushels per acre, including a public variety from Missouri with the off-patent Roundup Ready 1 herbicide tolerance trait.”

University of Georgia Extension publishes the results in their annual online reports, with the ultra-late production system results near the end of the summaries. 

Initial variety screening for this system has focused on determinate soybean varieties, which grow to a certain size and then start to flower. However, Mailhot plans to include indeterminate varieties in future trials.

“We are helping to improve the ultra-late production system,” he says. “Our goal is to eventually identify eight to 10 soybean varieties that will be very good options for Georgia soybean farmers and others in the Coastal Plain.”

Published: Feb 8, 2021