Research on soybeans experiencing a flood event during early reproduction stages showed no significant impact on seed composition, and some variety variability.
How Flooding Soybeans in Early Reproductive Stages Impacts Yield, Seed Composition
By John Lovett University of Arkansas System Division of Agriculture Arkansas Agricultural Experiment Station
With an increasing frequency and intensity of flooding events and an eye to capitalize on a common rice production technique, soybean breeders are on a quest to develop varieties with flood tolerance at any stage in the plant’s development.
Farmers who use zero-grade fields for rice as their main production system are also interested in flood-tolerant soybean varieties for crop rotation, said Caio Vieira, assistant professor of soybean breeding and a researcher for the Arkansas Agricultural Experiment Station, the University of Arkansas System Division of Agriculture’s research arm. Zero-grade fields are leveled to minimize drainage, a water-conservation strategy that has become a key sustainability practice in rice production.
Vieira is the lead author of a study offering more insight into how soybean plants respond to flooding in the critical early reproductive
stage when the plant begins to flower. The study, “Impact of flooding at the early reproductive growth stage on soybean yield and seed composition,” was published in the journal Crop Science.
“Flooding research has focused on the early reproductive stage simply because it is when the stress is most pronounced and causes the greatest yield loss,” Vieira said. “Across the Mid-South, soybean is most susceptible to flooding at the R1 stage.”
R1 is the name given to the early flowering stage in soybean growth. There are eight stages of soybean plant reproductive growth, from R1 — beginning blooming — to R8 — full maturity.
Vieira said that temperature changes in the United States have allowed earlier soybean planting dates so that shifting rain patterns are also resulting in additional stress on the soybean plants. Soybeans are also highly sensitive to flooding during seed germination, the study explains.
“The intensity and frequency of rain has been shifting to earlier in
Cover photo by Carla Trantham
the season,” he added. “We're pretty much getting the potential for ooding throughout the season. It's been tougher.”
Typically, soybeans in Arkansas are planted from early April to mid-May, which puts the R1 stage in late June to early July. As growers see the bene ts of earlier planting, including improved yields, Vieira said, naturally, the early reproductive stage would also shi .
“It can be hit or miss,” Vieira said. “You can get a year where that period is a full-on drought, or you can get a year where that typical R1 period is completely wet with intensive rains. It's hard, hard to predict.”
Experiment station researchers have also worked to improve drought tolerance in soybeans.
Trend Toward Early Planting
Jeremy Ross, professor and Extension soybean agronomist for the University of Arkansas System Division of Agriculture, said he has noticed more farmers planting earlier — at the end of February or early March instead of April and May.
“ ere’s been a big push to plant a month earlier than 10 years ago because we have data showing it leads up to 10 percentage points better production,” Ross said.
Early planting, Ross added, made possible by a shi in weather patterns, may assist in avoiding late-season insect problems and possibly outrun some hotter temperatures in July. An earlier harvest has also allowed those early planters to prepare their elds for the following season when the ground is dry in the fall. Unless, of course, remnants of hurricanes roll through Arkansas, as happened twice in September 2024.
Seed Composition Discovery
While grain yield losses from ooding stress have been well documented, Vieira said there has been a gap in literature on the impact of ooding on soybean seed composition.
e study was conducted at the Division of Agriculture’s Rice Research and Extension Center in Stuttgart and compared 31 soybean genotypes over the 2019 and 2020 growing seasons. e plants were exposed to non- ooded and ooded conditions to look at yield and seed composition — speci cally its oil and protein content.
A surprising discovery, Vieira said, was that four-day ooding in the early reproductive stage did not signi cantly alter the soybean seed composition of any of the varieties tested compared to the non- ooded control group.
Looks Can be Deceiving
Visual inspection of ood-damaged soybeans has been useful, Vieira noted, but it doesn’t tell the whole story. e study found that some genotypes visually classi ed as “moderately tolerant” to ooding had higher yields than those classi ed as “tolerant.”
“Although ood tolerance has been shown to provide yield security under short-term ood exposure, losses are still observed in tolerant genotypes, and little is known regarding the stability of tolerance and the multitude of environmental e ects of the trait,” the study noted. “ e limitations of subjective visual scoring, combined with spatial variability, emphasize the need for novel and improved methods to accurately classify genotypic responses.”
On average, for each unit increase in ood damage score, the study showed that grain yield decreased by 17.4%. Tolerant genotypes experienced roughly 33% yield losses between ooding and non- ooding treatments, while “moderately” tolerant and “susceptible” genotypes experienced 44% and 51% yield losses, respectively.
Vieira said the study will help his team identify and incorporate ood-tolerant characteristics into future soybean genetics, potentially mitigating ooding-induced yield losses across diverse environmental conditions.
Soybean breeder Caio Vieira is the lead of the Arkansas Soybean Breeding team, a professor in the crop, soil, and environmental sciences department, and a researcher for the Arkansas Agricultural Experiment Station.
Co-authors of the study included Arkansas Agricultural Experiment Station program associates Chengjun Wu, Liliana Florez-Palacios, Andrea Acuna, and Derrick Harrison; program technician Daniel Rogers; former experiment station faculty member Leandro Mozzoni; and John Carlin, director of the Arkansas Crop Variety Improvement Program. Henry Nguyen and Grover Shannon of the University of Missouri plant science and technology department were also co-authors. e study was supported by funding from the United Soybean Board under a project titled “Improving Soybean Flood Tolerance for Sustainable Production,” grant number 2413-209-0201, and the Mid-South Soybean Board under the project “Screening soybean germplasm and breeding soybeans for ood tolerance.”
Learning More
In research that followed, Vieira and his team have worked to identify which potential genes are regulating the response to stress under ooded conditions and if the genes are the same in the vegetative and reproductive stages. From what they can tell, they are not the same.
“ e second step of this work is that we must combine the favorable genetics for each growth stage, so we have season-long ood tolerance,” Vieira said. “We have developed soybean varieties with ood tolerance, including a new commercial release from 2024 called R19C-1012 that has been tested in over 40 environments across the Mid-South.
“In normal irrigation, it performs extremely well; when you introduce the ooding stress, it substantially outperforms the ood-susceptible commercial checks in the same maturity group. e data shows over 75% yield advantage — that's a gigantic di erence.”
Missouri Soybean Farmers Strengthen Trade Ties with Mexico and Panama
Adelegation of Missouri soybean farmers and industry representatives recently traveled to Mexico and Panama to strengthen trade relationships, engage with agricultural leaders, and explore new market opportunities for Missouri-grown soybeans.
The Missouri Soybean Merchandising Council organized the trade mission in partnership with key industry stakeholders and the U.S. Soybean Export Council. The mission reinforced Mexico and Panama’s status as key partners in the U.S. soybean supply chain.
“Mexico remains a top customer for U.S. soy, and this mission allowed us to engage directly with buyers, processors, and feed industry leaders,” said Aaron Porter, MSMC past chair and demand committee chairman. “By understanding their needs and demonstrating the value of Missouri soybeans, we can continue building long-term partnerships that benefit both Missouri farmers and Mexican agribusiness.”
Missouri soybean farmers met with feed manufacturers, soybean processors, and industry leaders to discuss supply chain logistics, sustainability, and the importance of high-quality soybean meal. In Mexico, the delegation learned that 26% of one major soybean crush company’s imports come directly from Missouri, highlighting the state’s critical role in international trade.
In Panama, the team explored growth opportunities for U.S. soybeans, as the country imported 240,000 metric tons of soybean products in the marketing year 2023/24. With its strategic location and reliable transportation infrastructure, Panama serves as a key access point for global soybean exports.
“In a typical year, the U.S. soybean industry moves 600 million bushels through the canal, making it a critical part of the global soybean supply chain.”
“The Panama Canal plays a vital role in getting Missouri soybeans to international markets,” said Brad Arnold, MSMC director from Drexel. “In a typical year, the U.S. soybean industry moves 600 million bushels through the canal, making it a critical part of the global soybean supply chain.”
Missouri Soybeans continues to prioritize international market development to support farmer profitability and global trade partnerships. By fostering direct relationships with buyers and processors, Missouri farmers are securing long-term demand for their soybeans and reinforcing the state’s reputation as a trusted supplier.
“At the end of the day, everything we do comes back to supporting our farmers and ensuring they have strong, reliable soybean markets,” said Gary Wheeler, Missouri Soybeans CEO and executive director. “Mexico and Panama have been, and will continue to be, key partners for Missouri farmers, and we’re committed to building on that relationship for years to come.”
This information is provided by Missouri Soybeans.