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Biologicals require new management approaches

Willie Vogt Logan Woodward shows the difference in root size for a corn plant at 30-inch rows and 30,000 and 35,000 population
ROOT SIZE MATTERS: Rising plant populations mean smaller roots, which limit the ability of nutrient uptake. Doctoral student Logan Woodward shows the difference in root size for a plant in a 30-inch row at a 30,000 population (left) and one at a more common 35,000 population.
New forms of plant nutrition offer opportunities to boost yield, but managing them matters.

Logan Woodward offered an observation on biologicals during a recent University of Illinois field event: “There is one common occurrence with every single one of them. And the worse they smell, the better they work.”

Woodward is a Ph.D. student working with Fred Below, U of I plant physiologist, exploring ways to put biologicals to work. He has been studying biologicals for more than five years.

The rise of biologicals across crop production has accelerated in the past five years, and achieving consistent results will matter for the investment farmers make. Biologicals, properly deployed, can bring a boost to plants beyond traditional mineral crop nutrient sources.

During the field day, Below showed the trend of rising corn yields, which also correlates to a rise in plant populations. He noted that plant population rises on average about 400 plants per year (across all corn acres) over time, which helps boost yields, yet brings new challenges for crop nutrition.

“Planting more plants per acre means each plant will have smaller roots,” Below said. A smaller root system has less capacity to take up mineral nutrition. That’s where the potential promise of biologicals lies.

Woodward delved into the challenge of smaller plant roots and biological use. “We’re trying to find other ways to help ensure that we have adequate nutrition for those growing plants, and the answer is biologicals,” he noted.

Nitrogen fixation and corn

Earth’s atmosphere is 80% nitrogen, but it’s in a form that’s of no use to plants. N-fixing bacteria offer the potential to pull that nitrogen out of the air and convert it into a plant-available form. It’s essentially a living Haber-Bosch process happening underground.

“Nitrogen fixing bacteria isn’t necessarily new technology,” Woodward said. “We’re aware of the symbiosis with Brady rhizobia and soybean plants.” The key is working to bring that type of scenario to the corn management system.

Bringing nitrogen to plants through mineral fertilizer is a challenge as root systems get smaller. Also, rising prices can hinder returns for farms. Another issue is the spatial variability in an average cornfield.

“We see that within just 30 feet in a field where we have a different response to nitrogen fertility, and there can be weather events like rain that limit availability,” he said. “We’re going to have a lot of nitrogen loss in our fields.”

Bringing nitrogen-fixing biologicals into the mix could help mitigate that nitrogen loss while making more N available to plants when needed. An added benefit of the biological approach is that even the smaller root system from higher plant populations can benefit.

In the microbiome, roots provide carbon and exudates that help feed the bacteria, which then fix nitrogen right at the root. With those rising plant populations, smaller root systems having access to mineral nutrition may be more limited.

Beyond nitrogen

Some nutrients, like phosphorus, are often tied up and immobile in the soil, and those smaller roots create another problem. But Woodward points to a solution there too: mycorrhizal fungi. This fungus populates on the root system, colonizing in a way that increases root mass even in higher plant populations. These fungi “reach out” to phosphorus in the soil, making it available in a plant-usable form. The fungi can also take up water and other crop nutrients.

Woodward discussed a public study from Indiana that found on similar soils, there’s about 1,200 pounds of phosphorus in the soil per acre, but only about 0.1 pound is available at one point in time. “So how are we going to be able to make some of that phosphorus available for crop uptake?” he asked.

Beyond the mycorrhizal fungi, there are phosphorus solubilizing bacteria that can increase the mineral P availability by acting as a chelating agent to free phosphorus, which is tied up with heavy metals in the soil.

Woodward said it appears that phosphorus-solubilizing bacteria when used with applied P can help keep that nutrient from getting tied up in the soil. That would help maximize available P each season.

Placement of fertilizer and biologicals matters. Woodward is researching the impact of a banded application of P, in this case Microessentials from Mosaic, and then planting over the top of the band with the added bacteria. “With that, we’re going to keep that phosphorus available, or uptake almost all the way through the growing season,” he said.

As corn population rises and root systems get smaller, biologicals may be the key to maximizing use of available nutrients in the soil.

TAGS: Fertilizer
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