Goal is to match nitrogen supply with the crop’s demand

FREEPORT, Ill. — The nitrogen cycle is a complex process that makes it challenging to manage nitrogen for corn production.

“A lot of things happen after you apply nitrogen to soils,” said Giovani Preza Fontes, University of Illinois Extension field crops agronomist. “It’s also hard to predict because there’s a lot of biological, chemical and physical factors happening at the same time and they’re all interrelated.”

Nitrogen mineralization is the conversion of organic nitrogen to ammonium and nitrification occurs when ammonia is converted to nitrate.

“Nitrification happens very fast when it’s warm and wet,” said Preza Fontes during a presentation at the Northwest Agronomy Summit, hosted by U of I Extension.

Nitrate and ammonium behave differently in the soil.

“Ammonium is a positive charge, so it will be attached to soil particles and won’t move around in the soil,” Preza Fontes said. “Nitrate has a negative charge, so it doesn’t stick a lot to the soil and moves fairly easy with water.”

Farmers are concerned with nitrogen losses since nitrogen is a resource needed for crop production, but it is also a loss of investment.

“The more we pay for nitrogen, the more we lose with nitrogen loss,” Preza Fontes said.

The goal for corn production is to match the soil nitrogen supply with the crop nitrogen demand.

“By applying the nitrogen near the root zone so the roots have easy access to it and at the time the crop needs it the most will increase the nitrogen uptake by the crop and reduce the time the nitrogen stays in the soil,” Preza Fontes said. “Every time nitrate is in the soil, it is subject to loss.”

The agronomist talked about nitrogen rate trials from the past two years at the U of I research location at Monmouth.

“If it’s too dry early in the season and the crops are not growing very fast because of drought stress, the roots are not expanding that fast and they are not taking up water or nitrogen,” he said. “If it’s too dry early in the season, we reduce our yield potential.”

In 2022 and 2023, it was fairly dry during the growing season.

“We had good crop emergence, good stands and no damage from standing water,” Preza Fontes said. “That kept the nitrogen in place with little water moving through the soil profile, so the nitrogen stayed where we wanted it.”

In both years, there was timely rainfall in July and early August around pollination time.

“That set the kernel numbers and maintained the kernel numbers,” Preza Fontes said. “The rainfall in August also helped during the grain filling period, so the yields the past two years were more than we expected.”

The economic optimum nitrogen rate includes the price of grain and fertilizer.

“It is the last pound of nitrogen that produced enough yield to pay for itself,” Preza Fontes said. “In 2023, for corn following soybeans, 115 pounds of nitrogen produced 309 bushels per acre and for corn following corn, 161 pounds of nitrogen produced 294 bushels per acre.”

The corn following soybeans with no nitrogen application yielded 233 bushels per acre, and for corn following corn with no nitrogen application it yielded 217 bushels per acre, the agronomist said.

“We have good indication that we probably need to give more credit than we do for the soil’s ability to supply nitrogen,” he said.

In 2022, eight trials were done across Illinois that included two nitrogen rates of 185 pounds per acre and 242 pounds per acre.

“Adding the 57 pounds of nitrogen per acre averaged three bushels more of yield which was not enough to pay for the nitrogen,” Preza Fontes said. “On average, the loss was a little over $30 per acre and we only saw a positive return in one of the eight sites in southern Illinois.”

For the past four years, U of I researchers have conducted a project at Monmouth that looks at different nitrogen sources, placement and timing.

“We applied 150 pounds of nitrogen to the corn crop and it goes from applying everything at planting to combinations of planting and side-dress to all at side-dress,” Preza Fontes said.

“We only saw a significant effect of treatments in 2017 when we applied all the nitrogen by injecting UAN at planting, that had the highest yield,” he said. “The other three years we didn’t see any difference in terms of treatment, it didn’t matter how we applied the nitrogen, there were similar yields.”

That means farmers have a lot of opportunities for nitrogen applications.

“You have flexibility for when and how you apply nitrogen to the corn crop without compromising yield,” Preza Fontes said.

U of I researchers conducted a similar project at Urbana in 2022 and 2023.

“Last year, we needed 214 pounds of nitrogen to optimize yield,” Preza Fontes said.