We will hear a lot more about nitrogen use efficiency

Nitrogen use efficiency (NUE) is a hot – and getting hotter – topic for agriculture in Canada and around the world. Nitrous oxide is a potent greenhouse gas, and climate change policy will aim to keep nitrous oxide emissions to a minimum – from fertilizer production on down to field application.

Tom Bruulsema is chief scientist with Plant Nutrition Canada, and chairs an independent Scientific Panel on Responsible Plant Nutrition supported by the International Fertilizer Association. Bruulsema says the simple calculation of NUE is to take the amount of nitrogen in crop yield at harvest and divide that by the amount of nitrogen applied.

Based on farmer surveys, canola NUE on the Prairies was around 51 per cent for 2018-20, Bruulsema says. Improving NUE for canola or on a whole-farm basis, and then comparing that to other regions and other countries, will benefit from a standardized system of measurement, Bruulsema says. “Right now, there is no standardized method to report inputs and outputs.”

While Canada and other countries work on a system to measure NUE, farmers can take steps to improve NUE and increase returns from their nitrogen investment.

“A great starting point is 4R,” Bruulsema says. “These nutrient practices are highly related to NUE, and they put the emphasis on things you can manage.”

These include steps that reduce nitrogen losses – such as banding in the soil or top-dressing just when the crop needs it.

The Canola Council of Canada (CCC) has a goal of 90 per cent of canola acres using 4R practices by 2025. “We see the value of maximizing fertilizer investments, while also being recognized for the environmental benefits that are achieved with 4R management practices,” says Warren Ward, agronomy specialist and fertilizer lead with the CCC.

Nitrogen stabilizers also help to reduce loss. “Inhibitors are remarkable for their efficacy,” he says, pointing to Canadian research on corn showing that nitrification inhibitors reduce nitrous oxide emissions by more than 30 percent and urease inhibitors reduced ammonia loss by 42 to 55 percent. He says global meta-analyses showed a drop in nitrous oxide emissions of 20 to 40 per cent when using a nitrogen stabilizer. (This is for higher risk situations and moist soils. “If you apply nitrogen close to when the crop needs it, you may not need a urease or denitrification inhibitor,” Bruulsema says.)

Growers can improve NUE through crop management as well, Bruulsema adds. Cultivar choice, seeding timing, seeding rates – really anything that contributes to higher yield – will also contribute to NUE, he says. “If a farm fertilizes for a usual crop but only gets two-thirds of a crop, NUE drops by two-thirds as well.”

With the fall election out of the way, the Government of Canada will probably resume action on the climate change file, which could include some guidelines on nitrogen use. As government policy evolves, the CCC will work with government agencies and researchers to answer key questions, including: What are the biggest factors for nitrogen loss? And what are the best ways to reduce losses and improve NUE?

We need more research. Michele Konschuh and Dilumi Liyanage, researchers from the University of Lethbridge, did a recent meta-analysis on NUE research. Using 730 comparisons extracted from 24 peer-reviewed publications, they concluded that simply adding more nitrogen did not improve NUE. They found only one situation from one study where NUE improved, and that situation included a combination of best practices that included right source, right place and right time.

Konschuh and Liyanage concluded that, “The lack of positive impacts for many management practices suggest that further research is required.”

Farmers need this research if they’ll be expected to make the right decisions to improve NUE.

“We can expect increasing attention on nitrogen use,” Bruulsema says. “Climate change as a political issue is getting stronger and stronger. Worldwide, countries are looking at incentives for action to reduce nitrous oxide emissions from fertilizer.”