Shawn Casteel, soybean agronomist for the Purdue University Cooperative Extension Service, hopes farmers in the new year resolve to read the variety tag, take stand counts and harvest grain above 13 percent moisture.
Shawn Casteel, soybean agronomist for the Purdue University Cooperative Extension Service, hopes farmers in the new year resolve to read the variety tag, take stand counts and harvest grain above 13 percent moisture.

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 Trade Association.

“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 nitrogen.

“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 percent.”

Conley identified several consequences of delayed planting for soybeans, including decreased yield, decreased plant height and decreased pods.

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 reproductive.

“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,” he added.

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 percent.

“We’re taking the risk out for growers at low populations,” Conley noted.

“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.”