Addressing nitrogen fertilizer uncertainties in corn production

WEST LAFAYETTE, Ind. — This perennial question puzzles farmers and agricultural researchers alike: How much nitrogen fertilizer do corn fields need to ensure optimal yields? Uncertainty blurs the answer.

A new Purdue University-led study published in Nature Communications suggests that properly accounting for this uncertainty can lead to improved crop production, increased profits and lowered environmental costs.

“You can call it a triple win,” said Ignacio Ciampitti, a professor of agronomy at Purdue University who co-led the study with former postdoctoral scientist Francisco Palmero. “You can optimize agronomy. You can increase profits because you are saving on fertilizer. And you can reduce your environmental footprint.”

The researchers based their study on field trials conducted in eight U.S. Corn Belt states (Illinois, Indiana, Iowa, Minnesota, Missouri, Nebraska, North Dakota and Wisconsin). The database was assembled by a public-industry partnership that conducted experiments on corn yield response to nitrogen fertilization from 2014 to 2016.

Their statistical analysis of the database determined that nitrogen fertilizer application uncertainties in corn production spawn environmental and social costs amounting to hundreds of millions of dollars. Their analysis demonstrated that nitrogen reductions of 12% to 16% could lead to air and water quality enhancements worth between $230 to $350 million.

Researchers have spent decades assessing optimum nitrogen application rates to corn fields. They have paid far less attention, however, to understanding the uncertainties involved. “No one has been looking at how much wiggle room we have on fertilizer advice,” said Ciampitti, who also co-directs Purdue’s Institute for Digital and Advanced Agricultural Systems.

AVOIDING RISK

The Nature Communications study offers a solution that embraces uncertainties in optimum nitrogen application rates so that farmers avoid unacceptable risk.

“Giving farmers information on uncertainty in nitrogen rates and the risk of yield loss when reducing rates is key to more flexible decision-making,” said Palmero, now a faculty member at Universidad Católica de Córdoba in Argentina.

The uncertainty stems from the complexity on how corn nitrogen demand is co-regulated by weather and soil nitrogen processes, impacting crop growth and soil nitrogen supply. If these supply-and-demand processes fail to synchronize, complications arise.

“It’s never constant. It’s a very complex co-regulation,” Palmero said. The nitrogen “goal posts” are constantly moving within the same field. “That’s a challenge. You cannot say, ‘I know how to manage this year after year.'”

Soil organic matter, soil type, crop rotations and cover crops, among several other factors, can also affect the optimum nitrogen application rate. “They really influence the synchrony or balance between supply and demand,” Ciampitti said. “Everything that you throw into the system can impact how that same part of the field behaves next year.”

APPLICATION PHASES

The study considered various scenarios of fertilizer application phases. During the initial, over-application phase, cuts come easily because they do not affect yields. But in the second phase, where farmers more skillfully manage their nitrogen applications, the fear of yield losses rises. Farmers need high-yield corn to  pay their bills, Ciampitti noted. Nitrogen fertilizer contributes to their costs, now more than ever.

The U.S. produces nearly one-third of the global corn crop, with the U.S. Corn Belt accounting for more than three-fourths of that amount, according to the U.S. Department of Agriculture. Just doing the minimum nitrogen reductions in the U.S. alone could have a huge impact, Palmero noted.

“The best way to start moving in that direction is to help farmers reduce risk. Using uncertainty-based decision making helps farmers manage the risk when choosing nitrogen rates,” Palmero said.

Over the last century, crop-yield improvements to feed the world’s burgeoning population have become increasingly dependent on the Haber-Bosch process, which draws nitrogen from the atmosphere to produce fertilizer. “It’s a process that is energy-intensive. Every time you produce fertilizer, you leave a footprint on the system,” Ciampitti said. “At this moment, when natural gas prices are going up, the cost of fertilizer is going up because of that, too.”

Achieving nitrogen fertilizer reductions will require helping farmers to overcome their fear of losing profitable yields. “Initially, we’re going to need some incentives to move in that direction,” he said. In a separate study published last December, Ciampitti and his associates proposed a market-based insurance approach as one possible incentive.

“Strong policies and programs, such as carbon or insurance schemes, are needed to support farmers in this shift, helping them choose nitrogen rates while balancing profit, uncertainty, and environmental and human health,” Palmero said.

The new study documents the science while also emphasizing more effective policy options. “We are demonstrating that this is not only an issue for farmers,” Ciampitti said. “This involves everyone.”