Corn School: How much nitrogen is lost when applying in season?


How much fertilizer do farmers lose when they apply nitrogen in season? Is volatilization a significant problem? Could 4R nutrient management and urease inhibitors help?

On this episode of the RealAgriculture Corn School, University of Guelph researcher Josh Nasielski shares what he and his collaborators are learning about the best way to minimize in-season losses using a 4R nutrient management framework — right source, rate, time and place.

In research plots at Ridgetown, Winchester, and Elora, Ont., six different 4R treatments are being compared using a variety of nitrogen rates. Treatments include: urea broadcast with and without a urease inhibitor; UAN surface streamed with and without a urease inhibitor; and each source (urea and UAN) injected at a 2-inch depth. Ammonia volatilization losses are measured using the dosimeter method.

Nasielski notes that the number one pathway for nitrogen loss in-season in Ontario is volatilization. The goal of this research work is to measure volatilization across the different placement treatments and help growers better manage fertilizer nitrogen in corn.

While final conclusions will have to wait until yield data is available after the 2022 harvest, Nasielski says there are already significant insights available from 2021 data and what has been observed so far this season. (Story continues after the video.)

At locations in 2021, both injecting urea and UAN, and surface applying them with an urease inhibitor, reduced losses compared to surface application with no inhibitor. Those lower losses also translated into higher yields, including an 11-bushel response to using a urease inhibitor at Ridgetown.

For Nasielski, the research shows that inhibitors can pay. The story, however, is different for growers who farm more acidic soils. Here growers can expect lower losses from volatilization, which may not justify use of an inhibitor.

It’s important to realize that Ontario soils are different than the Corn Belt and other parts of Canada, says Nasielski. Ontario tends to have higher levels of calcium in its soil which can increase nitrogen losses. Compared to what happens in the U.S. Midwest and Quebec, volatilization is much more of a problem in Ontario.

“And even in Ontario it’s going to vary,” says Nasielski. Research trends suggest that urease inhibitors will reduce losses, but the amount is highly variable. It really does pay to test for soil pH and if growers are surface applying, they really do need to consider inhibitors, he adds.

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