Nitrogen loss from leaching, atmospheric exposure, and soil runoff can be costly. However, there are products designed to minimize that loss.
And according to Mario Tenuta, professor of applied soil ecology at the University of Manitoba, the stronger the product is, the better.
Why it matters: Nitrogen is an expensive input on farms and with increasing vigilance over the impact of excessive use of fertilizer, nitrogen efficiency products are gaining more interest.
How N-loss happens
Tenuta, in presenting to attendees at the Innovative Farmers Association of Ontario’s 2020 conference, explained ammonia loss at the soil surface starts to occur quickly, and is promoted by moisture.
Granular urea exposed to air (broadcast but not incorporated) leads to atmospheric loss. 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 makes its aerial escape.
Tenuta says crops prefer nitrate over ammonia. However, nitrate is very mobile, and nitrification proceeds rapidly in the soil — particularly when the soil is warm.
Enhanced efficiency fertilizers
As described by Tenuta, “enhanced efficiency fertilizers” refer to those treated with fertilizer treated with one of several different longevity-extending technologies. These include formulations that improve plant nutrient uptake (or make it easier for the plant to absorb the nutrient), reduce losses in the environment, and alter availability timing.
Stabilizing technologies combine nitrification inhibitors with fertilizer. Every time an organism dies, says Tenuta, its DNA forms urease enzyme, which promotes the nitrification process. Stabilizing 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.
Controlled-release products involve 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.
“If you have dry or cold soils these can be problematic,” says Tenuta. He also says Health Canada demands these products and potential plastic residues are small enough to pose no environmental hazard.
Slow-release products (such as 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.”
Tenuta stressed the need to employ 4-R nutrient management principals in using enhanced efficiency fertilizers. 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.
Overall, Tenuta believes enhanced efficiency fertilizers will get cheaper “and become the new norm” as new suppliers expand and refine the manufacturing potential of these products.