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Research Highlights

Research Highlights
Proven soybean production practices help maximize yield, reduce input costs

By Carol Brown, USB database communications

In an ideal world, farmers would use all of the available inputs on each field to achieve the highest soybean yield possible. But this is far from a perfect world.

With checkoff support from the North Carolina Soybean Producers Association, researchers took this concept and applied it to a project to find which specific inputs or strategies result in the greatest yield increases or cost savings.

“Traditionally, researchers put plots in place and, one at a time, added inputs. We decided to take the opposite approach,” said Jim Dunphy, lead project investigator. “We put everything together and, one at a time, took them out as a way to evaluate what each input was contributing.”

A retired extension specialist at North Carolina State University (NCSU), Dunphy has been a national leader in soybean research for nearly 50 years. He began the maximum yield research project in 2015. When he retired in 2018, Rachel Vann took over Dunphy’s soybean research work including this project.

Vann, North Carolina state extension soybean specialist and assistant professor, said narrow row spacing had the greatest impact on soybean yield in their studies.

“The 15-inch rows yielded about 6 bushels an acre more than the 30-inch rows,” Vann said. “In many of the environments we tested, we saw a consistent yield benefit with the narrow row spacing.”

Changing row width comes down to cost, Dunphy reminded, as farmers may not have the capacity to switch planters to accommodate narrow rows or may have other reasons to retain the wider rows.

The ‘Cadillac’ approach to research

Dunphy said each research plot included everything except one input or strategy. They’d change row widths, seed populations, soybean varieties, or drop the fertilizer or fungicides. He referred to the treatment with all the inputs in place as the Cadillac treatment.

“There wasn’t an automatic name for it that I knew of, so I called it the Cadillac because it included everything that I could think of to improve yield,” he said. The name is comparable to the Cadillac car, which is known to include as many conveniences on the vehicle a driver could want.

Tests were done on private farmland with farmers all across North Carolina. Although the concept isn’t new, Dunphy said farmers remain interested in the outcomes from this type of research.

Greg Moxley, a Yadkin County farmer, had some of the research conducted on his farm.

“The more knowledge we have of anything that’s grown in the soil we’re working with, the better we all are,” Moxley said. “We have so much soil variation in this state that if you don’t do the research everywhere, we won’t know how things work in the different soils.”

Seed rates were one of the variables in the Cadillac test.

“We planted at regular rates and at 20 percent higher rates. These higher populations did not improve yields,” Dunphy said. “I didn’t expect it to, but I needed a way to convince farmers they don’t need to use the higher populations.”

For the population studies, they had more than 140 test environments between the May and June plantings. According to the research report, increasing plant population by 20 percent has a negligible impact on yield of less than one bushel per acre, indicating growers can save money by reducing seed populations to 120,000 seeds per acre or lower. Dunphy said the seed population test results have had an impact on farmers in North Carolina as well as other states.

“The farmers who were taught to plant as many seeds as they could are having trouble believing they don’t need that many. As seed gets more expensive, farmers need to take a serious look at how much seed they really need,” he said.

Based on Vann and Dunphy’s research, Moxley has made some management changes.

“I went to an earlier variety and lowered my seeding population,” Moxley said. “Rachel planted soybeans on my farm the last week of March, which is unheard of in North Carolina. But the beans looked good.”

Five years ago, he’d never considered planting soybeans before the last week of May. Based on the research done on his farm, Moxley said planting earlier can be considered a management option.

In addition to row spacing, maximal variety selection had a large impact on soybean yield. Growers should be intentional about selecting maturity groups, herbicide and disease resistance packages using high-quality yield data.

The researchers also looked at foliar fungicides, comparing three fungicides to no fungicide. Dunphy said the odds were stacked in favor of plots that included three fungicides, which were applied early, mid-season, and late-season.

 “When disease came in, we had a fungicide to deal with it,” Dunphy said. “But three different fungicide treatments are also more costly. Most farmers can’t afford all three.” Their research results showed that often using any fungicide fares better than none.

As farmers review the results of the North Carolina maximum yield study, they can work with their local extension agent to find the right combination of inputs and strategies to get the best outcome for their operation.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.