Nitrous oxide is no laughing matter when it comes to climate change and agriculture delivers its share of N2O
Nitrous oxide emissions from Canadian crop production can be reduced significantly with the use of advanced efficiency fertilizers, but these products don’t provide enough agronomic benefits to warrant a wide scale adoption by growers, according to a study on slow and controlled released nitrogen products on the Prairies.
Richard Farrell of the University of Saskatchewan’s College of Agriculture and Bioresources, who is involved in the ongoing study, said farmers likely need a financial incentive to increase their use of advanced efficiency fertilizer products but that a significant reduction in nitrous oxide (N2O) emissions is within reach.
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He said farms do a lot more than produce food, including ecosystems services.
“Society and government want to see ecosystem services protected, but you can’t pass that cost on because you don’t control what you get paid, basically,” Farrell said during his presentation at the 2020 Soils and Crops workshop in Saskatoon.
“So since you can’t pass those costs on and if you want to get paid for those things, there has to be some sources of money coming in.”
He said the extra money to pay for the N2O emission reductions likely won’t come from a free market system because food companies source the cheapest food possible.
“If you want to get that (N20 emission reductions), there has to be a pool of money that can be paid into it. If you are charging people who are large emitters, that money comes back to farms to pay for these ecosystem services. I think that’s the way to go,” Farrell said.
He said nitrous oxide is a potent greenhouse gas with an atmospheric lifetime of more than 100 years and almost 300 times the global warming potential compared to carbon, so it’s an obvious place to look for greenhouse gas emission improvements.
He said Canada’s doesn’t have high N2O emissions, but they do have a high impact.
“The ag sector accounts for typical 80 to 90 percent of the N20 that’s emitted altogether, 80 percent nationally, up to 90 percent in Saskatchewan. Soil-emitted N20, basically from fertilizers, accounts for 80 to 88 percent of all the nitrous oxide that’s put out there. So that’s another reason why we’re interested in it,” Farrell said.
Crops don’t use all of the nitrogen fertilizer that’s applied, and the leftover nitrogen is susceptible to gas off as N2O.
“Cereal crops in Western Canada have a nitrogen use efficiency of about 50 percent. Oilseed crops like canola have lower efficiency, so 30 to 40 percent, which means a lot of the nitrogen being applied is just left in the soil during the year that it’s applied,” Farrell said.
He said research in the United States and Canada has shown that adopting best management practices, including the 4R nutrient stewardship principles, can improve nitrogen use efficiency by 10 to 20 percent.
It’s important to understand how to reduce nitrous oxide emissions in crop production, but there are concerns within the agriculture industry that just focusing on environmental goals will negatively impact agronomic goals.
Farrell said he’s heard people say that if the goal is to reduce emissions of N2O, growers should just reduce the amount of nitrogen fertilizer they apply.
However, this perspective doesn’t take into account how a fertilizer reduction would affect productivity, or if N2O emissions on a per bushel basis would also improve.
The collaborative study Farrell presented has researchers from the University of Manitoba, Agriculture Canada and the University of Alberta measure N2O emissions from western Canadian crop production.
The goal of the study is to improve agronomic and environmental performance by increasing nitrogen use efficiency, and to do this they try to understand how to synchronize nitrogen availability and crop demand.
“We really need to have less nitrogen in there two to three weeks after the plants emerge,” Farrell said.
“When you put the nitrogen, at first there are no roots there to take it up so the only thing that can happen is it’s basically there to be lost or transformed by micro-organisms in the soil.”
Advanced efficiency products can help match nitrogen availability to the needs of the crop, which will out-compete soil micro-organisms for the coveted nutrient.
Other than water, nitrogen is the most limiting element for plants in the Prairies, which is why it’s the most applied nutrient in crop production.
In the study, researchers measured N20 emissions on fields that were fertilized with slow release and control-released products, as well as with straight urea.
One of the slow release products has urea granular coated with elemental sulfur, which reacts with water and starts to oxidize when in the soil.
“Water gets into the granular and then diffuses out and then controls the release of the urea into the soil. Rates are variable, it depends on a lot of factors so it’s not very predictable,” Farrell said.
A second slow release product has urea coated with a polymer coating which Farrell said is more predictable.
“(The coating) controls the amount of water coming into the granular first, creates a solution inside the little pellet, and then depending on soil and temperature it is released but it is released at a predictable rate.”
The second group is stabilized fertilizers that have a urease inhibitor, a nitrification inhibitor or both.
“The urease inhibitor just delays the hydrolysis of urea to form ammonia, and the nitrification inhibitors inhibit just the activity of the ammonium-oxidizing bacteria to form nitrate,” Farrell said.
For products in this group, when the inhibition process gets exhausted, nitrogen is released into the soil and suffers no further inhibitions and is immediately available to plants.
The study had nitrogen applied in a mid-row band in spring and fall, and N20 emission measures were taken on and off band.
“We can find significant N20 emission reduction in both rain-fed and irrigated systems, using an advanced efficiency fertilizer,” Farrell said.
“The largest emissions reductions and the most consistent emissions reductions were always achieved using products that had a nitrification inhibitor, whether it was spring or fall applied.”
Products with urease inhibitors significantly reduced nitrous oxide emissions, but only if they were applied in the spring.
Polymer-coated products were the least effective at reducing N2O emissions, but they still achieved significant emission reduction compared to straight urea.
Farrell said despite clear environmental benefits of using advanced efficiency products, researchers were unable to detect any significant agronomic benefits.
“Between the three provinces we had 12 site years and in 12 site years there was only one site year where there was an effect on yield. It was 2017 in Manitoba and ESN had higher yields then the other products,” Farrell said.
He said this was partly because nitrogen application rates were applied based on soil test recommendations, and they were meant to meet crop demands.
“Usually with an advanced product you would cut back, you would drop 20 or 30 percent lower than the soil test recommendation,” Farrell said.
“For this study we didn’t want to confuse the effect on N20 emissions because you get reduced emissions if you put less nitrogen on.”
He said crops were fertilized at the top end of the yield response curve, so any increase in nitrogen use efficiency is basically a little bit of luxury consumption by the crops, which is why yields were comparable across all treatments.
He said he’s been increasingly asked about applying nitrogen in the fall as farms try to reduce the logistic burden during the spring planting season.
“Fall fertilization isn’t recommended, but if you’re going to do a fall application, an enhanced product is the way to go,” Farrell said.
“You might consider doing a fall application and maybe something at seeding, a small amount.”
Farrell said a recent meta analysis on advanced efficient fertilizers products in the U.S. showed these products enabled a 20 to 30 percent yield increase in grasslands and forages, but yields in wheat and corn systems improved only by two to three percent.
“So it’s more about lowering your inputs to keep a yield than it is to improve a yield by using an advanced product,” he said.
The study Farrell presented also examined anhydrous ammonia fertilizer.
“We used a nitrification inhibitor applied with the anhydrous, and we didn’t see any real reductions with N20 emissions and no effect on yields at all. This basically just suggests there is a limited benefit in using advanced efficiency products with anhydrous,” he said.
