With fertilizer prices remaining historically high, farmers continue to seek ways to get the best bang for their buck when it comes to crop nutrients.
Nitrification and urease inhibitors are a popular and practical option. They can be applied with nitrogen-based fertilizers to improve nutrient use efficiency and they can also potentially limit greenhouse gas emissions and nitrate leaching. That, in turn, can reduce the risk of environmental harm from fertilizer use.
Nitrification inhibitors work by slowing the conversion of ammonium to nitrate in the soil, a process known as nitrification. This reduces leaching of nitrates into groundwater and controls denitrification, mitigating the loss of nitrous oxide. Nitrification can lead to loss of any soil N, including organic amendments or from legume N fixation. Inhibitors can be added to urea and anhydrous ammonia to slow the process.
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Urea is one of the most commonly used forms of nitrogen fertilizer. The risk is that an enzyme in the soil and thatch converts urea to ammonia and carbon dioxide, which can be lost to the atmosphere through volatilization as the reaction produces an increase in pH, resulting in this loss.
Urease inhibitors reduce the activity of that enzyme and slow the rate at which urea is broken down, so rainfall or tillage can move it into the root zone.
“To the farmer, there are two reasons to consider them,” says Lyle Cowell, the senior agronomist, Canada, for Nutrien.
“One is you don’t want to lose nitrogen in any form. A nitrification inhibitor will help prevent the loss of nitrates from fertilizer the farmer has purchased. And, of course, we would like to reduce the risk of greenhouse gases from nitrogen fertilizers. Those are two valid reasons to use them.”
Cowell says nitrification and urease inhibitors provide obvious benefits when it comes to fertilizer management, but they may not be right for every farm.
Make a plan
Before using them, Cowell says farmers should first ensure they have a basic 4R nutrient management plan in place.
“I think farmers should consider sitting down with a trusted agronomist, someone that they value, and go over their fertilizer use plans in a 4R context. It can help confirm that you are using the right rate of fertilizer for each crop, make sure you are using it at the best time and place, and, in some cases, make sure you are using the right products to make sure you produce a good crop,” he says.
He also recommends that farmers do some homework before jumping into enhanced efficiency products (EEP) such as nitrification and urease inhibitors.
“There is no point … if you haven’t used an inhibitor before just starting off blindly and expecting a response every time on every acre. It’s no different than any other product you buy for the farm. Take the time to learn and understand why you are using them,” he says.
Biggest benefit
Cowell says it’s important for farmers to understand when and where nitrification and urease inhibitors are most likely to provide the greatest benefit.
“If you are going to invest in something, you want to invest in something that will have an economic benefit to your farm,” he says.
“Nitrification inhibitors are always going to have the most value if you are applying your fertilizer well ahead of when the crop will utilize it, especially in the case of fall application. You’ll generally see the greatest response when you apply fertilizer well ahead of when the crop starts to grow.”
Rigas Karamanos, a retired soil scientist and former director of the Saskatchewan Soil Testing Laboratory, says EEPs such as inhibitors can be particularly helpful in situations where farmers shallow-band (one to 1.5 inches) or surface-apply fertilizer where loss is likely to occur.
Conversely, he recommends against using inhibitors in cases where deep-banded fertilizer is applied two and a half inches or more below the surface.
“The same reaction will occur (in the soil). But with deep banding, all those gases that are being generated, instead of flying into the atmosphere they are being absorbed by the soil as they go up,” he says.
“The moral of the story is you don’t generally need (inhibitors) if you are deep banding.”
Location is everything
As with real estate, proper use of nitrification and urease inhibitors often comes down to location, location, location. Cowell says farmers are most likely to get the best response from inhibitors when they are used in conjunction with a fall fertilizer application in a wetter or low-lying area or one with a heavier textured soil.
“When looking for the first place there’s going to be a response, that’s where it’s going to be,” he adds.
Karamanos says nitrification and urease inhibitors can also be effective when applied in conjunction with top dressing soon after planting, especially when fertilizer is broadcast on the surface.
The value of nitrification inhibitors tends to decline the closer they are used to seeding, adds Cowell. That said, they do retain value in spring applications, especially if conditions are fairly wet at seeding time when significant nitrification or leaching losses of nitrates can occur.
“If you are getting into a situation in spring where it’s very wet, then a nitrification inhibitor on some fields or even all fields can be a great benefit.”
Cool idea
Winter can arrive quickly and with little warning in Western Canada. The good news is cold conditions can essentially stop nitrification because bacteria in the soil aren’t active. But an early winter can make for an extremely narrow window of time in which to apply fall fertilizer, since it’s best to do it when soil doesn’t have snow covering but has cooled to below 10 C.
Cowell says nitrification inhibitors can delay the conversion of ammonium to nitrates in the soil even when it hasn’t cooled sufficiently.
“It can be a tool for us to comfortably apply nitrogen a little bit earlier in the season. Instead of using the cold soil to slow the process, we can use a nitrogen inhibitor to do that for us.”
When is the use of an inhibitor not warranted? Karamanos says that if a farmer is already using the necessary best management practices, they are unlikely to see much difference when using an inhibitor.
However, if they are using best management practices such as spring banding and still want to use an inhibitor, they should consider applying fertilizer at a reduced rate of 70 or 80 per cent.
“If you are using the same amount of fertilizer and you are getting the same amount of yield, then you are paying a heck of a lot more money and you are not gaining anything, to be honest.”
Karamanos also suggests that farmers determine the concentration rate of nitrification or urease inhibitors before using them.
While some manufacturers make claims about their products, he says there are no rules forcing them to prove efficacy. Karamanos recommends working with people at the retail level who are trustworthy, knowledgeable about the products they sell and have their clients’ best interests in mind rather than their own.
Cowell says there is no harm in using nitrification and urease inhibitors but it really comes down to choice.
“Every farm is somewhat different in terms of management, soils are different, the environment is different, fertilizer management practices are different,” he says.
“There’s no one best answer for every farm in Canada; that’s not realistic. The best thing is to take that base level knowledge of what these products can do and then sort out with a 4R plan where they can be the most effective.”
