Cutting nitrous oxide emissions without cutting the crop

Glacier FarmMedia – Canadian agriculture is being pushed to looking for a new balance when it comes to nitrogen emissions.

It’s a critical nutrient, essential to life and agriculture, but its byproduct, nitrous oxide (N2O), is also powerful greenhouse gas, one that federal government has aimed to slash.

Canadian farmers aren’t the only ones getting pushed. Green regulations, including those targeting agricultural greenhouse gas emissions and nitrogen application, have caused significant tension in places like the European Union.

Kate Congreves, an associate professor at the University of Saskatchewan and researcher, has been researching how to improve crop production while limiting nitrogen emissions as part of the second Diverse Field Crops Cluster (DFCC). The most recent five-year research cluster started in 2024.

Preliminary results keyed in on the mix of different fertilizer application techniques and products that resulted in more efficient nitrogen management.

“Nitrogen fertilizers are the largest source of anthropogenic N2O emissions,” she said during a March presentation. “… What this means (is), if fertilizers and fertilizer applications are a large source of N2O emissions, anthropogenic N2O emissions, that means our adjustments to fertilizer and fertilizer management do have an impact on reducing emissions.”

DFCC focuses on research on diverse crops such as camelina, carinata, flax, sunflower and mustard. As such, these crops form the focus area of the researcher’s project. Spring wheat is tapped as a control.

One of her hopes is to identify “double wins,” high-value crops associated with the lowest emissions.

The Diverse Field Crops Cluster is a research project examining how to improve crop production while limiting nitrogen emissions. Crops such as camelina, carinata, flax (seen here), sunflower and mustard are the focus area of the project. Photo: Greg Berg

Win-wins on farm nitrous oxide

The project builds on nitrogen emission test results and practices established in Nitrous Oxide Emission Reduction Protocol (NERP), created in collaboration with Fertilizer Canada. NERP forms a set of guidelines, with a goal of helping the producer hone their nitrogen management, reduce emissions, but also protect their crop production.

There are three levels for NERP – basic, intermediate, and advanced. Levels relate to the amount of fertilizer and how it’s applied.

Basic uses ammonium-based fertilizer applied at seeding, with a rate established from soil testing information. Intermediate expands management to include options like enhanced efficiency fertilizers, applied at a reduced rate (around 75 per cent of the basic rate), since less would be presumably needed for the same crop effect. Advanced NERP guidelines utilize enhanced efficiency fertilizer as well, but applied with split application between seeding and in-season.

These guidelines are followed closely in the DFCC project. Congreves uses SuperU at the intermediate level as the enhanced efficiency product, and SuperU with split application at the advanced level. Intermediate treatments band at 75 per cent rates of the basic treatments, and advanced bands a 75 per cent of intermediate (totalled between applications), the first of which occurs at seeding and the second at crop emergence. The in-season application was done with backpack sprayers to ensure uniformity of application and to reduce the risk of altering emission metrics.

The project has three research sites in Saskatchewan, each of which includes DFCC crop species tested under the different fertilizer practices. Each site is on clay loam soil with similar levels of organic matter and pH. Background soil nitrogen, however, is varied. The sites are categorized as having low, moderate or high existing nitrogen levels.

“The background nitrogen levels, they do have an influence on nitrogen cycling,” Congreves said. “And soil priming effects how much nitrogen that would subsequently get released from soil organic matter, for example, and then you’ve got nitrogen from the fertilizer. So you actually have some synergistic or additive effects going on.”

These background levels were one of the factors that went into determining the plots’ treatment levels. Others were consultation of crop fertilizer guidelines, review of estimates for soil mineralized land potential during the growing season and what NERP guidelines had to say.

Sampling for N2O

Seeding across all sites was underway in mid to late May 2024, and bases that would allow the team to measure greenhouse gas emissions were installed immediately following seeding and fertilizer passes. Bases were placed in every plot, maintained throughout the season and sealed at the surface of the soil. Chambers were then attached to the top of the bases to capture gases to be measured. Samples were taken several times a week, but more frequently right after seeding and rainfall events, as these periods see the most flux (the rate that greenhouse gases are added or removed from the air).

“We go in and seal the chamber air tight and we collect our gas samples… with a syringe,” Congreves said.

Samples are taken at various points after the chamber is sealed.

To measure the sample, the team uses gas chromatography, a technique that separates organic or inorganic substances from a gas to be analyzed. With this method, the researchers are able to see the N2O concentrations in the emitted gas.

Findings are paired with data kept on soil moisture, temperature, weather conditions and crop production, as well as information from soil and plant samples, to determine the effects of nitrogen management practices.

Looking at the results from mustard, Congreves noted that, at the side with moderate levels of background nitrogen, there were incremental “additive” amounts of N2O throughout the growing season.

“What we’re seeing is N2O emissions are indeed greater with basic, and then incrementally lower with intermediate, advanced, and then our unfertilized control,” she said.

The site with high background nitrogen levels saw larger daily fluxes at application time, but not as many during the growing season. Following this pattern, the site with the lowest background levels had the lowest major emissions.

Congreves said that she’s not yet seen any major yield differences associated with the practices. Her 2024 yields had normal rates of variability that were on par with other small plot agronomy trials and aligned with 2024 crop averages.

The other crop data sets have also been analyzed, and show similar patterns of emissions.

However, the research is far from wrapped up yet. Spring thaw is a major point of emissions. When the spring 2025 emissions are measured, the cumulative emissions will be adjusted to officially cap off the first year of the project.

“I was really happy with how the data is turning out,” Congreves said. “So far we’re indeed seeing, for most crops, the same pattern… so far, based on 2024 preliminary data, improving the nitrogen management practice does tend to practically reduce (cumulative) N2O emissions.”

Project next steps

Going forward, Congreves noted they plan to link nitrogen use efficiency metrics to N2O data to get a “fuller picture” of what occurs with the gasses and the crops together.

All completed data will be essential to the validation and calibration of current models used to predict emissions, and to compare region-specific data to information from current models. It can also be used to improve the current models by extrapolating data to apply to various sites, conditions and scenarios, the researcher said.

– This article was originally published in the April 3, 2025 issue of the Manitoba Co-operator.