Whether due to tighter margins or environmental pressures, more field crop farmers are considering using technologies that improve the efficiency of nitrogen fertilisers.
According to research from Canada’s University of Manitoba, the stronger those products are, the better. Mario Tenuta, professor of applied soil ecology at the University, says such technologies are specifically designed to limit the loss of nitrogen through leaching, atmospheric exposure, and soil runoff. “Enhanced efficiency fertilisers,” he says, refers to fertiliser treated with one of several different longevity-extending products – including formulations that help plants absorb nutrient more easily, reduce losses in the environment, and alter availability timing.
Understanding where fertiliser losses happen
Ammonia loss at the soil surface starts to occur quickly, and is promoted by moisture. In particular, Tenuta says granular urea exposed to air (broadcast but not incorporated) leads to atmospheric loss.
However, shallow banded granular urea can be lost to the atmosphere as well. This is because high concentrations of banded nutrient produce high concentrations of ammonium and bicarbonate – the latter breaking down to carbon dioxide and a high amount of base. That base subsequently turns ammonium into ammonia, which subsequently escapes into the air.
Despite generally feeding annual crops ammonia, Tenuta says they actually prefer nitrate. However, nitrate is very mobile, and nitrification proceeds rapidly in the soil – particularly when the soil is warm.
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Shallow banded granular urea can be lost to the atmosphere as well - Photo: Penn Communicatie
Stabilising technologies combine nitrification inhibitors with fertiliser. Every time an organism dies, says Tenuta, its DNA forms urease enzyme, which promotes the nitrification process. Stabilising additives slow down the process by lodging into those enzymes in place of urea. There is no concern of compromising too much urease enzyme since it is so easily created from once-living organisms.
“There is a ton of it in the soil naturally working to promote the nitrogen process,” he says, adding urea inhibitors alone can bring a 50 per cent reduction in losses.
Prevent ill-timed release of nutrients
Controlled-release products use polymer coatings that limit the exposure of nutrient to environmental conditions. These physical impediments stop the nutrient from dissolving immediately, then eventually allow moisture to permeate and dissolve the nutrient within.
Several weeks later, the nutrient solution moves out of the polymer and into the soil, though the time required for this process increases in colder, drier soils. Tenuta says this approach helps prevent ill-timed release of nutrients during adverse conditions, such as during a delayed planting season.
I always say go for the strongest
“If you have dry or cold soils these can be problematic,” says Tenuta. He also says Health Canada and other environmental bodies mandate such products and potential plastic residues are small enough to pose no environmental hazard.
Slow-release products (e.g. sulfur-coated urea) perform a similar function, and have been around for some time. Nitrification inhibitors comprise another long-standing category, though some newer technologies are still not yet available in Canada. “These are designed just to slow down nitrification,” he says. “I always say go for the strongest”.
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Mario Tenuta, professor of applied soil ecology at the University of Manitoba: “Don’t leave polymer coated products on the surface. It won’t work.”. - Photo: Courtesy of the Applied Soil Ecology Lab.
Good fertiliser application strategies
As with standard fertiliser use, Tenuta stresses the need to employ best management practices in using enhanced efficiency fertilisers. Timing and placement are also critical. For delayed-release products – and polymer coating products specifically – banding or incorporation after broadcast is imperative.
“Improper timing and placement can have major yield loss potential,” he says. “Don’t leave polymer coated products on the surface. It won’t work.”
Blending delayed-release products can be useful as well. Approximately three parts polymer-coated urea to one-part granular, for example, provides “an early shock” of nutrient while allowing the rest to remain in the soil until later in the season.
Is using more than one product worth the cost?
Summaries of Tenuta’s research findings were presented to North American farmers attending an environment and agronomy focused conference in Ontario in early 2020. During his session, he says their findings indicate there are yield increase opportunities when fertiliser and efficiency products are properly applied.
When asked if a combination of two different products would bring even greater nitrogen longevity, Tenuta was not entirely convinced. Yes, he says two products could be used simultaneously, but the benefits of doing so may not be worth the additional cost.
“It might be if the product on the surface provides early protection. Then once it wears off, the second inhibitor could help within the soil,” says Tenuta. He reiterates, though, it is hard to draw definitive conclusions.
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An agronomist working with the University of Manitoba’s Applied Soil Ecology Lab collects corn biomass to test nitrogen content. - Photo: Courtesy of the Applied Soil Ecology Lab.
Products not always available
Crucially for Canadian producers, though, not all nitrogen efficiency products are available on the market. While Canada’s regulatory system has been cited as a barrier for the proliferation of other agronomic technologies (e.g. nitrogen-fixing bacteria inputs), Tenuta says this is not necessarily the case. Instead, the small Canadian market (when compared to the United States or European Union, for example) means some companies are not rushing to complete Canadian regulatory paperwork.
Products like DMPP (a nitrogen stabiliser), for example, remain unavailable to Canadian growers despite fifteen-plus years on the market in other political jurisdictions. Other such as the stabiliser “Anvol” have only recently been made available.
Overall, Tenuta believes enhanced efficiency fertilisers will get cheaper “and become the new norm” as new suppliers expand and refine the manufacturing potential of these products.
Additonally, Tenuta says he and other university colleagues are planning to continue researching enhanced efficiency products in studies with corn and canola – examining sources, timing of application, as well as rate and placement depths. “I hope to start experiments in fall with nitrification inhibitors to anhydrous ammonia,” he says.