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Nitrogen inhibitors help reduce volatilization losses

These are key findings so far in research by Craig Drury, a soil biochemist at Agriculture and Agri-Food Canada’s (AAFC) Harrow Research and Development Centre.

Drury is in the second phase of field studies funded by AAFC’s Agro-Ecosystems Productivity and Health Science Strategy and the 4R Nutrient Research Network (Fertilizer Canada), analyzing the effectiveness of nitrogen inhibitors and nitrogen placement strategies. The study, which is a continuation of a previous two-year study, began in 2015 and will continue until 2017.

The goals of the study are threefold – Drury’s team, which includes Dan Reynolds, Xueming Yang and Wayne Calder, first aims to analyze how much nitrogen is lost from the soil as ammonia through volatilization or as nitrous oxide through the denitrification process. Second, they are assessing the effectiveness of different fertilizer application methods and how these could reduce losses and increase nitrogen uptake by corn.

They are also examining the effectiveness of nitrogen inhibitors – Agrotain, a urease inhibitor, and Agrotain Plus or SuperU, both urease and nitrification inhibitors.

Drury says the landscape has changed in terms of nitrogen fertilizer trends in Canada. “From 1980 to 2010, nitrogen fertilizer sales in Canada increased by a factor of 2.4. The amount of nitrogen fertilizer sold and used is increasing for many reasons.”

But that’s not all that’s changed. Drury says urea and UAN together account for 74 per cent of nitrogen sales in Canada, and that figure is increasing. “Right now, about 52 per cent of the nitrogen fertilizer sold in Canada is urea and 22 per cent is UAN,” he says. “The point is that we have seen over time a greater and greater percentage of nitrogen fertilizer being applied contains urea, whether it’s all granular urea or it’s 50 per cent urea in liquid UAN.”

The problem? Much of the fertilizer added to soils in Eastern Canada is lost to the environment – a problem both for the environment and the grower’s bottom line.

Drury says that when nitrogen is added to the soil as a fertilizer, as manure, through natural atmospheric deposition or nitrogen fixation via legume plants, it undergoes natural biological and chemical conversions. To be used by the plant, nitrogen has to be converted to ammonium and/or nitrate; but ammonium can easily volatilize and be lost to the atmosphere.

Under very wet conditions, negatively charged nitrate can leach out of the root zone through tile drains or it can be converted to nitrous oxide, which is lost to the air, where ultimately it contributes to the greenhouse gas effect.

“That is a problem on many levels – your nitrogen is going into the air or out of your tiles instead of the soil or the plant, so it’s a costly loss of the applied fertilizer,” he says.

Nitrogen inhibitors can help diminish this effect by slowing the conversion of urea into ammonium, which allows more time for the nutrient to move into the soil.

Findings
Drury’s study analyzed broadcast urea, UAN streaming and UAN injection, and used, in total, three separate fertilizer nitrogen sources: urea or UAN, urea or UAN plus a urease inhibitor and urea or UAN plus a urease and nitrification inhibitor.

The team used wind tunnels and air sampling instrumentation to measure ammonia losses.

The findings, so far, have been dramatic. Drury’s team found that 54 pounds per acre (lbs/ac), or roughly $3,200 for 100 acres of broadcast urea, was lost to volatilization, versus 23 lbs/ac or $1,500 for 100 acres of injected UAN.

Urease inhibitors decreased ammonia losses by 57 per cent (from 54 to 22 lbs/ac) for broadcast urea – $1,900 worth of savings for 100 acres. But even more notably, the use of urease inhibitors resulted in a whopping 97 per cent decrease in ammonia losses with the injection of UAN.

In total, Drury says, the combination of urease and a nitrification inhibitor also decreased nitrous oxide emissions by 21 per cent.

“If you have the opportunity to incorporate nitrogen into the soil through injection or immediate broadcast incorporation that’s certainly worth doing, and will get the nitrogen into the soil fast and efficiently,” he says.

But even with injection, the team still noted ammonium volatilization losses through the injection slot. “So with both broadcast urea as well as injection, it was still beneficial to include the urease inhibitor to decrease volatilization and have the nitrogen go into the crop,” Drury says.

These findings are not just about losses – Drury’s team also measured gains in yield. He says use of urease inhibitors increased yields by 5.5 bushels per acre with broadcast urea, and by 12.5 bushels per acre with the combination injected UAN. The benefit totaled $1,700 per 100 acres for broadcast urea, or $54 per acre, or $5,400 per 100 acres in the injected fields when urease inhibitors were also used.

“In all cases, it was very profitable, even when you consider the cost of the inhibitors. The revenue from the yield increase was far greater than the cost of the inhibitors,” he says.

“Clearly, there are ways of managing our fertilizers and our soils to reduce environmental losses and losses of expensive nutrients and have more of that nitrogen going to the crops and increasing yields.”

A previous version of this article originally appeared in the March 2016 issue of Top Crop Manager East.