June 20, 2024

Biologicals bolster roots in high populations

CHAMPAIGN, Ill. — Increasing plant populations to hike corn yields also has a downside in the plant’s ability to take up nutrients.

Logan Woodward, a Ph.D. student working with Fred Below, University of Illinois plant physiologist, said biologicals are potentially a way to increase root biomass while keeping the same planting density.

“As we strive for higher yields, we’re going to have to find new ways to manage higher planting populations,” said Woodward at a crop nutrition field day hosted by The Mosaic Company.

“As we increase populations, we have smaller root systems. So, we have to find other ways to ensure that we have adequate nutrition for those growing plants — and the answer is add biologicals.

“The most important nutrient for corn is nitrogen and specifically nitrogen-fixing bacteria. We see biologicals as a new pool of available nitrogen. They’ll be fixing nitrogen from the air.”

Obviously, nitrogen is applied to the soil to supply the corn plants. The second source of nitrogen is through mineralized organic matter.

“Nitrogen-fixing bacteria is not necessarily a new technology because we’re aware of this rhizobia symbiosis with soybean plants. I’m trying to bring this type of scenario into a corn management system because I’m from Illinois where corn is king,” Woodward noted.

“As we strive for higher yields, we’re going to have to find new ways to manage higher planting populations.”

—  Logan Woodward, graduate research assistant, University of Illinois

Implementing biologicals into a nutrient management system offers multiple advantages including lowering nitrogen expenses and reducing field spatial variability.

“Growers would be happy if we can achieve greater yields with less nitrogen applied. With field spatial variability, within just 30 feet we have a different response to nitrogen fertility. Also, with weather events like rain we’re going to have a lot of nitrogen loss in our fields,” Woodward said.

Free Nitrogen

Air is 80% nitrogen that isn’t available for plants. Nitrogen-fixing bacteria utilize that nitrogen and puts it in an available form for the crop.

“Any way we can supply a new form of nitrogen being from the air, we can even out that variability and provide enough adequate nitrogen for those growing plants,” Woodward added.


Most of the commercial biologicals can be applied in-furrow at planting so they’re placed with the seed. The bacteria live along the root surface.

“These nitrogen-fixers growing on the roots are going to have the best effect on yield,” Woodward said.

A more robust underground plant system also will allow the roots to reach immobile nutrients such as phosphorous that don’t move much in the soil.

“One potential way to try to increase our root biomass or root surface area while keeping it the same planting density is with mycorrhizal fungi,” Woodward noted.

“We think of these as an extension of the root system. The mycorrhizal ‘pipes’ are going to be able to reach out into areas the roots aren’t able to go to and take up phosphorous, water and other important nutrients.”

Untying P

Woodward said a lot of the phosphorous in the soil is unavailable despite a larger root surface area.

“We have about 1,200 pounds of phosphorous in our soils, but the issue is only up to 0.1 pound is available at one point in time,” he said in reference to a study in Indiana.

“One way to make phosphorous available is with phosphorous solubilizing bacteria. A lot of the phosphorous in the soil is going to be fixed with heavy metal cation like aluminum, iron, zinc and calcium, but if we use phosphorous solubilizing bacteria, they give off organic acids and ultimately act as a chelating agent to try to break down those bonds and ultimately make phosphate available.

“This provides a very important interaction with the fertility that we’re applying because we see when we apply phosphorous solubilizing bacteria with phosphorous fertility, it can also act as keeping our phosphorous fertility available.

“The reason for that is as long as the bacteria are active, they’re able to keep chelating those heavy metal cation and keep the phosphorous fertilizer from being fixed. The idea is to try to get some synergy by applying both managements together.

“If we’re already applying phosphorous solubilizing bacteria in-furrow, why not try to also put a starter fertilizer in there and keep them in close proximity of each other so they can act on each other in positive ways.”

One of the phosphorous application options is with a strip-till application.

“If we’re placing that phosphorous fertility like MicroEssentials phosphate-based fertilizer in that band and plant right over top of that band with the bacteria, they’re in close proximity and able to keep phosphorous available for uptake almost all the way through the growing season,” Woodward said.

“As we’re striving towards higher corn yields, our populations are going to continue to increase resulting in smaller root systems and biologicals may be one potential way to try to either increase our root growth to get nutrients into the plant or keep that phosphorous or nitrogen fertility available throughout the season.”

Tom Doran

Tom C. Doran

Field Editor