CHICAGO — Increases in soybean yields over the past several
decades have come from a combination of genetic and agronomic improvements.
“Over the last nine decades, we’ve had a pretty good track
record in terms of yield across the U.S.,” said Shawn Casteel, soybean
agronomist for the Purdue University Cooperative Extension Service.
“The rate of gain has been from 0.14 bushels per acre per
year to 0.20 bushels per acre per year,” said Casteel during a presentation at
the Corn, Sorghum and Soybean Research Conference hosted by the American Seed
“We designed four agronomic studies to look at the genetic
and management gains, including planting date, the nitrogen component, seeding
rates and fungicide treatment,” he explained.
For the nitrogen study, researchers looked at maturity group
II and III soybeans and compared zero applied nitrogen to applying 500 pounds of
“The research totaled nearly 60 lines within each maturity
group,” Casteel said. “We put 200 pounds of nitrogen upfront, and we came back
prior to R1 and put on another 300 pounds.”
Research during 2010 and 2011 on the maturity group III
beans showed the rate of gain with no additional nitrogen was one-third of a
bushel per acre per year, in line with historical data.
“When we added 500 pounds of nitrogen and overloaded the
system, there was a fourth-tenths of a bushel per acre per year increase in the
rate of gain,” Casteel reported. “That was really interesting to see a 10 to 12
bushel gain with the new soybean lines. Although 500 pounds is not economical,
it gives us an idea what’s going on.”
The researchers also took biomass samples in the middle of
R6 to determine the vegetative nitrogen accumulation in the leaves and stems.
“With the 500 pounds of nitrogen, there was a remarkable
increase in the amount of nitrogen accumulation in the leaf biomass, as well as
the stems,” Casteel said.
Shawn Conley, state soybean specialist and associate
professor at the University of Wisconsin, said 50 percent of the on-farm yield
gain of soybeans has come from genetics.
“This experiment focuses on where the other 50 percent has
come from,” he said.
“We are looking at if we can exploit that agronomic impact
to push yields by looking at the interactions of breeding and agronomic
practices,” he noted.
The trend is towards earlier planting dates for soybeans.
“From 1980 to 2010, by May 1 from zero to 3 percent of
soybeans were planted and by 2010, 19 percent were planted by May 1,” Conley
reported. “For the 2012 season, that number was probably much higher than 20
Conley identified several consequences of delayed planting
for soybeans, including decreased yield, decreased plant height and decreased
The research shows, he said, the new genetics are doing a
better job of exploiting the yield gain by planting earlier.
“Not only do we see a decline in seed protein in both
maturity groups II and III, we also see a negative shift from our earlier
planting dates,” he explained.
“By planting earlier and our new genetics, breeders are
decreasing protein content and agronomists are doing the same thing by telling
growers to plant earlier.”
Through this study, Conley said, the data shows over the
last 90 years, there has been a decrease in the number of days the soybeans are
vegetative and a lengthening in the amount of days the soybeans are
“There is a shortened vegetative growth period and an
increase in the number of days the soybeans are reproductive by almost two
weeks,” he said.
“The purpose of the population study is to compare the
effects of high and low populations on the gain of genetic yield and to better
understand the characteristics that the plant canopy led towards yield gains,”
Researchers planted 180,000 soybean seeds per acre and
60,000 soybean seeds per acre.
“The interesting thing is for seed weight on the low
population, we seeing a three times increase in the amount of seed produced on
the newer varieties,” Conley reported. “We’re seeing a significant amount of the
yield coming from better branching.”
The yield gap for low populations has been narrowed by 4
“We’re taking the risk out for growers at low populations,”
“Plant breeders have selected cultivars that have increased
yield at both the high and low population densities,” he said.
“However newer cultivars have improved branching ability to
compensate for lower plant stands, so the penalty for lower seeding rates has
decreased by half.”