Trying to reduce the inescapable nitrous oxide emissions that come from farming.

While it’s inevitable that as grower you’ll have nitrous oxide (N2O) emissions, there are ways that you can control the amount you let out.

Nitrous oxide is emitted from the soil, which is something that can’t be avoided, Mario Tenuta said during a presentation at the Alberta Potato Conference and Tradeshow on Nov. 17, 2022. The nitrogen cycle results in emissions where nitrogen in the form of ammonium, which can from organic or synthetic fertilizers, is converted in soil into nitrate.

“That’s what we want to happen so that our crops or potato crop can take up nitrogen through the water. But in that process, bacteria and soil produce N2O, and it goes up as a gas to the atmosphere,” Tenuta, NSERC/WGRF/Fertilizer Canada Industrial Research chair in 4R Nutrient Stewardship and a professor of applied soil ecology at the University of Manitoba, added.

Mario Tenuta
NSERC/WGRF/Fertilizer Canada Industrial Research chair in 4R Nutrient Stewardship and a professor of applied soil ecology at the University of Manitoba

There are indirect ways that nitrous oxide is released into the atmosphere. If ammonia is spread on a field through an irrigation pivot, there’s some that will be released into the atmosphere as the ammonia will be converted into N2O by lightning or solar radiation. Nitrate leaching in soil into ground water is another way that N2O is indirectly released.

“You’ve heard talk about targets of reducing N2O omissions, right? All that discussion and talk of those targets, this is not even in the picture yet of reducing indirect emission, only being so far reducing the direct emissions from soil,” Tenuta said.

Direct sources of nitrous oxide emissions are when you spread nitrogen on a field. However, nitrous oxide makes up a small amount of nitrogen lost from a field with two to four pounds of nitrogen per acre being release into the atmosphere as N2O annually.

To study nitrous oxide emissions, Tenuta led a project a decade ago where boxes were placed on soils to collect N2O. For potatoes they put boxes on top of both the hills and furrows. The air would be collected in the boxes and then it would be analyzed for the amount of N2O released. The gases would have to be collected from the plots about 30 to 40 times during the growing season.

“The hills is where the nitrogen is, so we have to measure there. However, over time what we found is that nitrogen can actually pool in the furrow,” Tenuta explained. “We’ve been surprised in that we can get quite a bit of emissions of N2O even in the furrow, even though we did not apply nitrogen there.”

The second year however, the results were flipped with more nitrous oxide being found on the hills and not in the furrows.

“Nitrogen in the furrow was not providing nutrition to the crop. So, it’s something that we need to tackle with in potato production to keep the nitrogen in the hill,” he said.

The simplest thing that growers can do to reduce N2O emissions is to lower nitrogen rates, Tenuta said. You should optimize your nitrogen use by preventing excessive additions, use 4R nutrient stewardship and plant new potato varieties which take in more nitrogen.

The way that Tenuta discovered what reduces nitrous oxide emissions the most is using enhanced efficiency fertilizers — higher tech newer fertilizers that have either enzyme inhibitors embedded in them or are coated with polymer. Stabilized nitrogen inhibitors include urease, nitrification and double. Controlled release include polymer coated urea, aka environmentally smart nitrogen (ESN), and slow release include sulfur-coated urea, methylene urea, isobuylidene diurea, urea formaldehyde and urea triazone.

With Tenuta’s study being a decade old now and there being increasing pushes from the federal government to reduce fertilizer usage, Tenuta plans to start another study in 2023 as part of the Canadian Horticultural Council cluster projects funded by the Canadian Agricultural Partnership.

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