Strong root systems contribute to corn, soybean yields

CHAMPAIGN, Ill. — Corn and soybean yields in Illinois for the 2023 growing season were higher than some farmers expected with the dry weather partially as a result of the outstanding root systems of these plants.

“We have to change what we think of as an ideal year for corn and soybeans,” said Emerson Nafziger, professor emeritus at the University of Illinois College of Agricultural, Consumer and Environmental Sciences.

“Corn hybrids and soybean varieties have been bred for yield and you can’t do that and not develop a highly competent root system,” said Nafziger during a presentation at the Farm Assets Conference, hosted by U of I Extension and the farmdoc team.

“We had some of the highest yields again this year than we’ve ever had in Illinois and it certainly didn’t look like the year to have that,” he said. “We got bailout rains in late June that made the corn crop and in the second week of August that made the soybean crop.”

Nafziger noted that there have been outstanding corn crops in 1984, 1994, 2004 and 2014.

“These set new yield records and next year is 2024,” Nafziger said.

“Cover crops were a problem for fields in 2023,” he said. “In this study, we had no-till, one pass and strip till, with and without cover crops and the cover crops dinged the yields in each case.”

The university has been conducting plant date studies in Illinois for many years. Corn is planted starting in the middle of April until the first week of June.

“For four of the last 10 years, we saw no significant effect of planting date on yield,” the professor emeritus said. “In two years, we planted the first week of June and got over 250 bushels per acre, so we have probably overestimated the danger of planting dates.”

The 2023 growing season was quite a year for nitrogen, Nafziger said.

“For the lowest rate of nitrogen at 58 pounds, the corn yield was about 185 bushels and with 50 more pounds of nitrogen the corn yielded 280 bushels per acre,” he said. “But we didn’t get any yield increase beyond that, which is pretty unusual, so we had a tremendous supply of nitrogen coming from the soil this year.”

Nafziger encourages farmers to stop using the yield-based system for applying nitrogen.

“That old idea is dead,” he said. “The increases in yield from genetic improvements have made the hybrids better at everything including taking up nitrogen from the soil.”

The dry June also helped the corn plants.

“They had really competent root systems that were well connected to the soil, so they pulled water from deeper in the soil,” Nafziger said.

“At the Monmouth research center this year we had corn following soybeans that yielded 233 bushels per acre with no nitrogen, and at 115 pounds of nitrogen, the corn yield was 309 bushels per acre,” he said.

Corn Rootworm Management

In Illinois, there are two different situations for corn rootworm.

“If you’re farming in Champaign County, I doubt insects are at the forefront of your mind,” said Nick Seiter, U of I Extension field crops entomologist.

“If you go to a soybean field looking for western corn rootworm, you don’t find them hardly at all, which is a far cry from what we saw 15 to 20 years ago in the days before pyramid Bt hybrids.”

It takes a pretty high population of corn rootworms for egg laying in a non-host crop to amount to much, Seiter said.

“The issues have largely gone away,” he said. “It is not nonexistent, but there’s not many in this part of the world.”

However, in northern Illinois, where there are fields of continuous corn, the situation is quite a bit different.

“In DeKalb, Kane, Ogle and Stephenson counties, we’re struggling to control those insects with pyramid Bt traits,” Seiter said.

“We’re starting to see higher populations in northern Illinois and we’re getting more concerned,” he said. “The best thing to do is work in some nonhost crops like soybeans to reduce the population because any egg that hatches in soybeans dies.”

One option for farmers to use is SmartStax PRO with RNAi varieties.

“That’s a new mode of action that is distinct from the Bt protein,” Seiter said.

“In our trials, we see a reduction in pruning when comparing SmartStax PRO to SmartStax, but we don’t see a reduction to zero from that new trait package,” the entomologist said.

“If you have a 10-year cornfield that has a problem with rootworm, we want to discourage people from using a RNAi trait and expecting to clean it up,” he said. “That’s not going to happen and like all traits we’ve got a high probability of developing resistance if we don’t practice proper stewardship.”

For farmers in east-central Illinois, Seiter said, they should go out in their fields and look for beetles.

“If you’re using a soil insecticide or Bt trait, see if that is justified because there is not a lot of risk for injury,” he said.