In part one of this series, panelists University of Illinois soil fertility specialist John Jones, University of Illinois agricultural economist Gary Schnitkey, and Illinois Corn Growers Association water quality specialist Laura Gentry at the December Farm Assets Conference explained how the Corn Nitrogen Rate Calculator identifies the profitable nitrogen range.
In the second half of the conversation, the focus shifted to what happens when nitrogen rates exceed that range and what farm-level data reveals about those decisions.
The “insurance nitrogen” mindset
Drawing from data collected through Precision Conservation Management (PCM), Gentry explained that many farmers apply nitrogen above the MRTN rate. In some years, average nitrogen applications have exceeded MRTN by 25 to 40 pounds per acre.
While those additional pounds are often viewed as “insurance,” Gentry noted that the MRTN model has consistently predicted profitable nitrogen rates in the years she reviewed. In fact, she emphasized that it has not underestimated the nitrogen rate needed to maximize economic return. “It’s a conservative estimate,” she said, meaning it is unlikely to result in under-application. Schnitkey said that when farms spend more than necessary in one area, they often do so in others, too, such as making extra field passes or adding more inputs, which raises overall costs.
A leaky system
Jones described Illinois cropping systems as inherently “leaky.” Nitrogen follows water, whether through tile drainage, surface runoff, or volatilization under certain conditions. He also clarified that not all nitrogen found in tile drainage originates directly from fertilizer. A significant portion comes from mineralized organic matter in the soil.
However, research shows that once nitrogen rates exceed the economic optimum, losses increase more rapidly. The additional pounds applied above MRTN are more likely to contribute to nutrient loss than to yield.
That relationship reinforces the connection between agronomic efficiency and environmental efficiency discussed in the blog post How MRTN works and the economics behind nitrogen rates.
Timing and field passes
The panel also addressed nitrogen timing and application methods. Jones shared research comparing fall and spring applications of anhydrous ammonia. While yield differences were minimal, spring applications sometimes required slightly lower optimum nitrogen rates.
He noted that environmental conditions play a major role in nitrogen availability and loss risk, making timing decisions complex.
Schnitkey reminded listeners that every pass across the field carries a cost. He explained that multi-pass systems, including split applications, may provide flexibility but also increase fuel, labor, equipment wear, and, in some cases, stabilizer expenses. “Every time you go across the field, there’s a cost,” he said.
According to the panel, the key is aligning nitrogen timing and rate decisions with overall profitability rather than assuming that more applications automatically improve outcomes.
Using data to guide decisions
Gentry highlighted that programs such as Precision Conservation Management allow farmers to evaluate field-level data and compare nitrogen decisions with anonymized regional benchmarks. Participation is voluntary and confidential, and the goal is to provide farmers with information to support their own decision-making process.
Jones added that soil testing and on-farm research trials can help identify areas of fields that may not require additional inputs, particularly in tighter economic years when return on investment becomes even more important.
The bottom line
Across the discussion, the message remained consistent:
- The nitrogen rate that maximizes yield is not always the rate that maximizes profit.
- Applying nitrogen above the profitable range increases cost and can increase the risk of nutrient loss without delivering meaningful yield benefits.
As Schnitkey summarized: “Maximize profits, not yields.”
Explore more
To listen to the entire discussion, go to Episode 79 of the Illinois Nutrient Loss Reduction Podcast.
- Corn Nitrogen Rate Calculator (MRTN)
- Precision Conservation Management
- Episode 76: Addressing nutrient loss through conservation: Precision Conservation Management
- Blog: Addressing nutrient loss through conservation: Precision Conservation Management
About the authors
Rachel Curry is an Agriculture and Agribusiness Educator specializing in agriculture and watershed education, and she is part of the Illinois Extension's Nutrient Loss Reduction Strategy implementation team. She holds a B.A. in Environmental Studies from Knox College and an M.S. in Environmental Science and Soil Science from Iowa State University, with a focus on soil fertility. Her work centers on education and outreach related to the Illinois Nutrient Loss Reduction Strategy, promoting agricultural conservation practices that reduce nutrient loss while enhancing water quality and soil health across Illinois.
Nicole Haverback serves as a Watershed Outreach Associate and is an Illinois Extension team member implementing the Nutrient Loss Reduction Strategy. She holds a B.S. in Agricultural and Rural Policy Studies from Iowa State University. In her role, Nicole coordinates watershed management efforts to reduce nutrient losses in two nitrate-nitrogen priority watersheds, provides expertise on best management practices to minimize nutrient losses, and leads outreach initiatives promoting agricultural conservation practices outlined in the Illinois Nutrient Loss Reduction Strategy.
Luke Zwilling serves as a Watershed Outreach Associate and is an Illinois Extension team member implementing the Nutrient Loss Reduction Strategy. He grew up on a farm in Jasper County and earned a B.S. in Agriculture and Biological Engineering from University of Illinois. Luke coordinates watershed-based activities to reduce nutrient loss in two phosphorus-priority watersheds, provides expertise on best management practices for nutrient loss reduction, and conducts outreach on agricultural conservation practices in the Illinois Nutrient Loss Reduction Strategy.
About the blog
At Illinois Extension, we’re working to improve water quality at home and downstream. Every month, our Watershed Outreach Associates will bring you stories highlighting agricultural conservation practices, current research projects and results, and from the field farmer interviews. The Nutrient Loss Reduction blog covers conservation practices recommended by the Illinois Nutrient Loss Reduction Strategy, timely updates, farm safety, and new decision tools to help farmers and producers reduce the nutrients leaving their fields.