Statewide study targets nitrogen inhibitors’ impact on nitrate loss
Farmers in the Midwest including Illinois routinely invest in nitrogen stabilizers designed to keep more fertilizer nitrogen available to crops and reduce the risk of losses to the environment. Yet despite how widely some of these products are used, surprisingly limited field-scale evidence exists to quantify their impact on nitrate losses under Illinois conditions.
A new research initiative led by the University of Illinois Urbana-Champaign aims to change that.
The four-year, $1.4 million project is funded by the Illinois Nutrient Research & Education Council (NREC). It is led by Andrew Margenot, professor in the Department of Crop Sciences, part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at U. of I. Researchers will conduct a statewide evaluation of nitrification and urease inhibitors across 12 research and on-farm sites spanning nine Illinois counties, from southern to northern Illinois.
Several of the same sites are also supporting nearly $1 million in additional research evaluating nitrous oxide emissions with Koch Agronomic Services, allowing researchers to examine multiple pathways of nitrogen loss at the same sites. Nitrous oxide emissions from fertilized soils are a major contributor to the carbon intensity (CI) scores being considered under the federal 45Z Clean Fuel Production Credit,and reductions of nitrous oxide, a potent climate-forcing greenhouse gas, may be achieved through the use of nitrification and urease inhibitors. To-date, few evaluations exist of comprehensive evaluation of yields, nitrate leaching losses via monitored tiles, and nitrous oxide gas losses, positioning the stacked projects to significantly advance understanding of nitrogen management.
The scale reflects how widely the products are already used. A recent Illinois Fertilizer and Chemical Association retailer survey found nitrification inhibitors were included in approximately 96% of fall anhydrous ammonia applications statewide. Yet researchers say surprisingly little field-scale data exists to quantify how much tile nitrate-N loss these products prevent under today's production conditions.
Much of the available evidence comes from a small collection of studies conducted in Illinois and Minnesota using data gathered more than two decades ago. The project team identified only 25 plot-years of monitored tile-drainage research across the Corn Belt that directly evaluated nitrate-N loss reductions from nitrification inhibitors. Those studies focused on a single inhibitor, used fixed inhibitor application rates despite a range of nitrogen fertilizer rates, and often reflected fertilizer practices that differ from those used by Illinois farmers today. The new project will increase the number of observations from 25 to more than 380, expanding the available information on this potential nitrate-loss reduction tool by more than 15-fold.
Nitrification inhibitors slow the conversion of ammonium fertilizer into nitrate, while urease inhibitors slow the conversion of urea into ammonium. Both are intended to keep nitrogen available to crops longer and reduce the risk of losses to the environment.
"This project is really about testing — and moving beyond — assumptions," Margenot said. "Farmers are already investing in these products, often for perceived yield or N use efficiency reasons. What we don't have nearly enough field-scale evidence on is how much they reduce nitrate-N loss through tile drainage, when those reductions are greatest, and how management influences their performance.”
The project brings together ACES researchers including Crop Sciences Professors John Jones and Giovani Preza-Fontes, as well as Natural Resources and Environmental Sciences Professor Zhongjie Yu, along with farmer collaborators and agricultural organizations such as the Illinois Corn Growers Association.
Unlike many previous studies, the work will rely heavily on monitored drainage systems that directly measure nitrate leaving agricultural fields through subsurface tile lines. Researchers will also evaluate crop nitrogen uptake, nitrogen-use efficiency, yield response, and economic returns, providing a more complete picture of how inhibitor performance affects both farm profitability and environmental outcomes.
Inhibitor performance can depend on weather, soil conditions, application timing, fertilizer source, and the active ingredient used — both the type and rate of active ingredient used. By collecting data across research farms and commercial fields throughout Illinois, researchers hope to identify the conditions that separate strong responses from little or no benefit.
Those differences matter to farmers because inhibitors add to the cost of a fertilizer application. Better information could help determine when that investment produces a measurable agronomic, economic, or environmental return.
The findings could also strengthen the scientific foundation behind Illinois nutrient-loss reduction efforts. The Illinois Nutrient Loss Reduction Strategy identifies nitrification inhibitors as a management practice for reducing nitrate losses, but current estimates of their effectiveness are not based on direct field measurements under modern Illinois production conditions.
Ultimately, the project aims to give farmers, crop advisers, and conservation professionals better evidence for deciding when and where nitrogen inhibitors can deliver enough benefit to justify their use.