Calculating greenhouse gas emissions from all the vehicles in Canada is a simple task: take the number of cars and trucks in Canada and multiply that figure by the average emission per vehicle.
Calculating emissions from agriculture is not so easy.
“When (we) talk about greenhouse gas emissions in Canada, the sector that has the most uncertainty of emissions is agriculture…. The un-certainty is like plus or minus 40 percent,” said Mario Tenuta, a University of Manitoba soil scientist.
“We know the emissions from the oil and gas (sector). We know emissions from industry. It’s the emissions from soil that we don’t (know) because we have few studies.”
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Tenuta, who runs the soil ecology laboratory at the U of M, is leading several studies to get a better handle on greenhouse gas emissions from agricultural cropland in Canada. Tenuta is particularly interested in nitrous oxide (N2O) emissions from soil.
The U.S. Environmental Protection Agency says agricultural soil contributed 74 percent of that country’s total N2O emissions in 2013. The percentage is likely similar in Canada, which is why provincial and federal governments want to identify the best agricultural practices to mitigate N2O emissions.
“Policy-makers are very interested in this work because very little of it has been done,” said Tenuta, who spoke at a U of M faculty of agriculture seminar in April.
“We need as many studies as possible… so we have confidence in (the results)…. You don’t want to develop policy on one study. Need multiple studies, over multiple years in different weather conditions”
Tenuta is focusing his research on fertilizer because increased use of nitrogen fertilizer is driving greenhouse gas emissions higher.
“If you look at (Canadian) agriculture as a whole, in terms of greenhouse gas emissions, it went up nine mega-tonnes (from 1990-2012),” he said.
“The increase has been seven mega-tonnes of CO2 equivalent from synthetic fertilizer N20…. That means fertilizer use is (responsible) for about 80 percent of the increase in greenhouse gas emissions from agriculture in the last 22 years.”
Statistics Canada data indicates that the amount of nitrogen fertilizer used in Canada doubled from 1981-2011. Tenuta said there is a linear relationship between the greater use of nitrogen fertilizer and the rise in N2O emissions from soil in Canada.
The trend is worrisome because nitrous oxide is a potent greenhouse gas. Climate Change Connection, a Manitoba Eco-Network program, says the global warming potential of N2O is 298 times greater than carbon dioxide.
Based on research conducted at the U of M Glenlea Research Station and other locations, Tenuta has discovered that N2O emissions peak at certain times in the spring — during the thaw period and following a spring rain.
Enhanced efficiency fertilizers, such as ESN, can reduce the severity of emission spikes after a spring rain and decrease the amount of nitrous oxide released from the soil.
“We’re starting with this hypothesis that the rate of nitrification, as it increases, increases the N2O emissions,” Tenuta said.
“That ESN, with the polymer coating, slowed down the release of the nitrogen and, as a result, we had less N2O.”
Tenuta’s data shows that the benefits of enhanced efficiency fertilizers, or practices like fertilizer banding, are minimal in dry years.
“We (might) have 60 to 70 percent (emission) reductions in one year, another year might be nothing,” he said. “Usually when we find there is no effect of the management practice in reducing N2O emissions, that was a low year in general for emissions because it was too dry.”
Tenuta and his colleagues are also studying fall application of nitrogen compared to spring application.
Fall application can increase N2O emissions during the thaw period, but emissions following a spring rain were minimal.
“The fall application didn’t seem to be that bad in terms of N2O emissions. If anything… it’s much lower.”
Tenuta also wants to study the combination of late fall application and the use of enhanced efficiency fertilizers.
“What we don’t know now is if we used more efficient fertilizers, or these intelligent fertilizers, what they would do with the thaw emissions?”
Tenuta’s research may be interesting to Canadian policy-makers, but identifying practices that mitigate emissions could have global implications.
North American farmers use an immense amount of nitrogen fertilizer, but the growth is small relative to places like China, Tenuta said.
“The majority of fertilizer use increase in the world is in China and Asia,” he said. “China is like 45 percent of the increase in (global) demand.”
