Raising the bar on nitrogen efficiency

Every year, prairie canola growers spend $1 to $1.15 billion on nitrogen fertilizer.

At the farm level, an average grower is likely spending about $55 per acre just for the nitrogen component of fertilizer, based on Manitoba Agriculture crop production costs and a nitrogen rate of 120 pounds per acre.

That means a farmer with 1,500 acres of canola would have a nitrogen bill of $82,500.

Given that expense, farmers may be curious about how much of the nitrogen is used by the canola crop.

Across the Prairies, the average nitrogen use efficiency is close to 60 percent.

“What’s being removed in the crop is 59 percent of the nitrogen fertilizer being applied,” said Tom Bruulsema, chief scientist with the International Plant Nutrition Institute in Canada (IPNI).

That number is from 2018-20.

From 2011-13, Bruulsema pegged the nitrogen use efficiency of prairie canola at 52 percent. It has risen, mostly because the average canola yield in Western Canada has gone from 34 bushels per acre in 2011-13 to 41 bu. in 2018-20.

“Yields increased substantially over that period,” Bruulsema said from Guelph, Ont. “Nitrogen use seems to be increasing a little bit on the canola crop…. But the yields increased faster than nitrogen use.”

A number like 59 percent is only meaningful if you can compare it to something.

Bruulsema, who spoke at Canola Week, a virtual conference hosted by the Canola Council of Canada in early December, said the average nitrogen use efficiency for all crops in Canada is 70 percent.

But that includes things like soybeans and pulses, which fix most of their nitrogen. A crop with a nitrogen use efficiency of 100 percent will distort the overall average.

A group of scientists that make up the European Union Nitrogen Expert Panel, has said the optimal nitrogen use efficiency should be in the range of 50 to 90 percent. The current global average is around 45 to 50 percent, it said.

Prairie canola is above the global average, but is 59 percent good enough?

“I don’t know if we’ve thoroughly addressed it enough, specifically to canola producers… to know what their (nitrogen use efficiency) target ought to be,” Bruulsema said.

“(But) there is some room for improvement.”

If prairie canola growers could reach 65 percent, for instance, it would increase nitrogen efficiency by six percent and $100 million in nitrogen would actually make it into canola, rather than being lost.

Besides the economics, there is the environmental cost.

Nitrogen not taken up by canola can move from the soil to the atmosphere as nitrous oxide, a powerful greenhouse gas. It can also change to nitrate and pollute groundwater and surface water.

Globally, farmers use about 100 million tonnes of nitrogen fertilizer every year, meaning nitrogen losses from cropland can have a massive impact on the environment.

“For that reason there’s a lot of focus… on trying to improve nitrogen use efficiency,” Bruulsema said.

The easy way for a canola grower to improve is to apply less nitrogen. The canola crop will then use nitrogen available in the soil to get the necessary amount of nitrogen for plant development.

But that’s not a long-term solution.

“Good nitrogen use efficiency numbers are good, to a point,” said John Heard, soil fertility specialist with Manitoba Agriculture. “But if they’re really good that means you’re exploiting, or mining, the resource that’s there (in the soil).”

Which means growers need to strike a balance, where they use nitrogen efficiently but don’t draw down soil reserves.

Heard said corn growers are one group that keeps a close eye on nitrogen and how corn is using the applied fertilizer.

“They talk about how much nitrogen per bushel…. And a good value (for corn) is something between one to 1.2 pounds of (nitrogen) per bushel,” he said. “I don’t hear many other farmers talk about this. But maybe I’m just hanging out with corn (growers).”

Warren Ward, canola council agronomist in eastern Saskatchewan, also said few farmers talk about nitrogen use efficiency.

“It doesn’t come up in a lot of grower conversation that I have. But every grower is… going to want to use optimal nitrogen rates to produce their (canola).”

The canola council and provincial canola associations, along with the federal government, have committed $1.6 million to better understand nitrogen use efficiency in canola. Ag Canada scientists in Saskatoon are leading a five-year project with the goals of understanding:

  • how canola hybrids differ in their response to nitrogen
  • what happens in the soil, with root-microbial-soil nitrogen interactions
  • the influence of practices like fertilizer rate, timing, placement, type and seeding depth

“Through this study, breeders will be able to predict the nitrogen-response for canola lines… and longer term be able to pair canola lines with nitrogen-fertilizer agronomic practices that will reduce nitrogen loss,” the Manitoba Canola Growers website says.

The study will continue until 2023.

In the meantime, canola growers may want to compare their practices to a neighbour. If a nearby farmer is getting five bu. more per acre with the same amount of nitrogen fertilizer, maybe something can be done to improve NUE.

One possibility is better weed control, Ward said.

“If you’re doing everything right from a fertility standpoint, but maybe you’re spraying your weeds a little late… you’re actually losing yield because those weeds have taken up some of the nutrients you applied.”

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