Enhanced Efficiency Fertilizer Can Cut Emissions, But Soil Type Matters
New NC State research sheds light on the economic and environmental effects of adding inhibitors to synthetic fertilizers. Corn yields didn’t change much, but emissions of ammonia and, in some cases, nitrous oxide, were lower.
A three-year study on nitrous oxide and ammonia emissions from North Carolina corn fields is giving NC State University researchers a better handle on when and where using enhanced efficiency fertilizers could benefit the environment and what that means for farmers’ bottom lines.
Since 2023, Alex Woodley, an associate professor in the Department of Crop and Soil Sciences and an N.C. Plant Sciences Initiative faculty affiliate, has been studying the effects of one kind of these fertilizers on emissions and crop yields at 18 North Carolina farms that lie between Greensboro and the coast.
While conventional synthetic fertilizers significantly boost yields, allowing farmers to produce more food on less land, they’re expensive. Not only that, only 40-60% of nitrogen fertilizer is actually taken up by crops. And when plants don’t use that nitrogen, it can be converted to nitrous oxide and ammonia. Nitrous oxide is a potent greenhouse gas that can deplete the ozone, and ammonia can harm air and water quality and degrade ecosystems.
Video: Woodley describes trials to see when and where enhanced efficiency fertilizers help
The type of enhanced efficiency fertilizer Woodley is studying is designed to get around these problems. Called a dual urease and nitrification inhibitor, it is added to conventional fertilizers to slow the conversion of two forms of nitrogen, urea and ammonium, giving plants more time to access the nitrogen while it’s in their root zones.
Findings from Woodley’s Beyond Yield study could help farmers more accurately weigh the financial costs and benefits of using inhibitors, while providing policymakers with data to determine if governments should offer farmers incentives to offset those costs.
“What this research will do is allow farmers to have a couple things on paper. If it works, they can reduce their nitrogen inputs and apply the nitrogen they do need more effectively,” he says. “What it can also do is potentially unlock economic incentives in the future for more sustainable nitrogen use.”
Soil Type Matters for N2O Emissions
Funded by the U.S. Department of Agriculture’s Natural Resources Conservation Service, the Beyond Yield study involved 18 North Carolina farms with varying soil types. Crop and Soil Sciences faculty members Luke Gatiboni, Deanna Osmond, Josh Heitman and Rob Austin also worked on the project.
While inhibitors have been shown to help with ammonia emissions in other places, not much is known about how they work in North Carolina’s hot, humid conditions and coarse soils.
Woodley’s team took weekly measurements in corn plots where the inhibitor was used and in plots where it wasn’t. They found that it cut ammonia emissions on nearly every farm where it was used, while nitrous oxide emission results were mixed, depending on soil type.
As Woodley explained, “We saw pretty strong trends coming out. We always want to make these big, broad-brush recommendations, but there’s a lot more nuance. With nitrous oxide, on heavy-texture soil, like clay and loam, where it gets wetter and saturated longer, we saw the inhibitors work, but on really sandy soils, we saw less effectiveness.”
Yield Effects Were Small
The team also found that cutting down on the amount of fertilizer used didn’t have a significant impact on yield in most of the fields evaluated.
“We’re seeing some impacts, but basically we applied a little nitrogen before planting, and then at side-dress, when the corn is knee-high, we either use nitrogen at a full rate, whatever the farmer normally does, versus a half rate,” Woodley says. “In a lot of the cases, what we found is the yields aren’t very different between that half application versus the full application, regardless of inhibitor.”
In terms of straight agronomic economics, using inhibitors may not be worth the money, but we will be running scenarios around carbon crediting systems.
As Woodley and his team dig deeper into the data as they prepare to publish their results, they’re collaborating with Rod Rejesus, an NC State agricultural economist and N.C. PSI faculty affiliate, to see how yield effects shown in the N.C. corn crops would balance out against inhibitors’ cost.
Right now, Woodley says it may not make sense for farmers to use inhibitors solely as a strategy for ensuring good yields.
Still, he contends they could have a place on North Carolina farms.
“In terms of straight agronomic economics, using inhibitors may not be worth the money, but we will be running scenarios around carbon crediting systems,” Woodley says. “The goal is to consider what types of subsidies or support programs you might need to make their use profitable or neutral, if society deems that we need to lower these ammonia and nitrous oxide emissions.”
This post was originally published in Plant Sciences Initiative.
