Root structure impacts hybrid yields

FREEPORT, Ill. — Farmers may add root structure as another trait to consider when choosing corn hybrids for their operation.

“If you manage some hybrids the right way they really perform, and some if you manage the wrong way will really under perform,” said Connor Sible, research assistant professor in the Department of Crop Sciences at the University of Illinois.

“I think a lot of our hybrid variation is below ground and related to roots,” said Sible during a presentation at the Northwest Illinois Agronomy Summit, organized by the U of I Extension.

“When we’re looking at seed selections, we’re looking above ground at the ear and yield and we’re not really selecting for what’s going on below ground, but I think roots are going to be the next frontier,” he said.

The Crop Physiology department at the U of I conducts research at three locations — Yorkville, Champaign and Nashville.

“About five years ago, one of our students did root phenotyping to evaluate what type of root should be used in banding versus a broadcast scenario,” Sible said. “Another student has taken that further to look at what that means for planting population decisions.”

The U of I has developed a system to measure corn roots by looking at the angle of the roots and root ball depth.

“The root ball is 85% of the business end of the plant,” Sible said. “This is where the nutrients will be taken up so we are characterizing it.”

The SAAM is a rating system for the surface area, angle and mass of corn roots. This past year, the U of I students evaluated 3,216 roots.

“You can separate those into two groups — small and large for the surface area, narrow or wide on the angle and small or large on the mass, which is eight possible ratings to characterize a hybrid,” Sible said.

“There is a lot of variability of when you’re placing your fertilizer and we think this might matter to maximize response,” he said. “And plant population has the biggest effect on individual plant root mass.”

Planting density is driving the corn yield increase over time, the university professor said.

“Yields go up and down based on weather,” he said. “There has been a steady increase in yields and planting density and on average the U.S. plant population is increasing about 400 plants per acre per year.”

Changing the planting density impacts the root architecture.

“As you crowd more of them together in 30-inch rows, they start to sacrifice their root biomass because they’re putting a lot of resources into their above ground biomass,” Sible said.

“If you’re thinking about changing the plant density, that will probably influence your fertility program and placement becomes a lot more important.”

In 2024, the U of I researchers planted eight hybrids at 28,000, 34,000 and 40,000 plants per acre.

“The large surface area, wide angle hybrids had a good response going from 28,000 to 34,000 plants per acre, but they tanked going to 40,000 plants per acre,” Sible said.

“The wide angle hybrids with small surface responded to the first population jump, but there was no value going to the higher amount so the wide angle hybrids are not doing so well when we pack them together,” the university professor said.

“You get more return from population increases with narrow angle roots,” he said. “Roots don’t like to touch, so when you start wide and add more, the roots start to touch and they pull back.”

Wide angle hybrids respond better to split nitrogen applications, Sible said

“And narrow angle hybrids are better for stressed or sandier soils,” he said. “They don’t really hold the nutrients, so the nutrients move down and you want the root to chase them.”

There are a lot of nutrients in the soil. However, biology, chemistry and environment restrict how much of the nutrients are available to the plants.

“In the beginning of the season for the corn crop, the phosphorus uptake is in the leaves and the stalk and about halfway through the season the phosphorus is leaving the vegetation and it’s going into the grain,” Sible said.

“About 80% of the phosphorus uptake is in the grain, so if we want yields, we have to make sure we have phosphorus available.”

Fertility is important early in the season to set the yield potential for the corn crop.

“By the time the corn is waist high it has decided what it can do,” Sible said. “There is a short, three-week window in the middle of the season where corn needs the most available phosphorus per acre per day and most of that phosphorus was applied last fall.”

Early-season phosphorus availability does not determine a 160-bushel versus a 300-bushel crop, the university professor said.

“It’s the middle zone that separates the yield levels,” Sible said.

“We fertilize because it’s supplementing the soil supply especially during the phase of high nutrient demand,” he said. “That’s why split applications are working — it’s placing the fertilizer right there before the uptake.”

Planting soybeans is partially determined by the weather. However, research shows yields decrease by a half bushel per acre per day for every day soybeans are planted after April 23.

“Nodes are where the pods are and seed makes yield,” Sible said. “Higher soybean yields tend to be because you have more pods so with soybeans it’s all about the seed number and that’s why planting earlier works.”

Last year, it was beneficial to plant soybeans early.

“The early-planted soybeans were starting to seed fill in July and July was pretty wet,” Sible said. “The later planted beans were doing seed fill in August and September when it was really dry.”

Selecting the maturity group of the soybean variety may also impact yields.

“Data tells us if we go from 3.0 to 4.0 maturity group, I got a 4-bushel gain in 2022, an 8-bushel gain in 2023 and in 2024 it was worth 5 bushels so on average that’s 5.6 bushels,” the university professor said.

However, Sible does not recommend farmers go from a 3.0 to 4.0 maturity group on all their soybeans acres.

“Maybe go from a 2.5 to 2.8 and that would be about 3 bushels and don’t do your whole farm, but maybe a few acres and see what that value brings to you,” he said. “I think this is the lowest hanging fruit for increasing soybean yields.”