Understanding Emissions From Applied Nitrogen Fertilizer

Nitrous Oxide (N₂O) formation is not only a result of using synthetic fertilizers, but is also formed when soil organic matter, manure, and crop residues go through the nitrogen cycle. It is produced during the nitrification process when ammonium converts to nitrate or the denitrification process when nitrate is converted to nitrogen gas (N₂ and N₂O).

Two of the largest influencing factors of N₂O emissions are soil properties and weather. Because weather can be unpredictable, the amount of emissions produced each year can vary, and growers may look for more sustainable options to utilize on their farms to reduce nitrogen loss and N₂O emissions. An effective way to do this can include the use of enhanced efficiency fertilizers (EEFs), which align with Fertilizer Canada’s initiative, the 4R Nutrient Stewardship (4R) program.

The 4R Nutrient Stewardship Program

The 4R program provides a framework that has been deemed effective in improving nitrogen efficiency from cropping systems while maintaining crop yield. The framework incorporates the right source of fertilizer at the right rate, right time and right place. Under the 4Rs, the implementation of best management practices is required to optimize the efficacy of fertilizer use and ultimately, reduce nitrogen loss from fields.

Enhanced Efficiency Fertilizers (EEFs)

EEFs fall within the scope of the 4R management as they are an alternative to applying a commodity fertilizer (right source). There are several modes of action within the EEF category, but all act to reduce nitrogen loss by either slowing availability or keeping the nitrogen in a form where the risk of loss is lessened. When the chance of loss is decreased, the crop’s uptake and utilization is increased.

Currently, there are four categories of EEFs available:

1. Urease Inhibitors: Urease inhibitors reduce nitrogen loss to ammonia volatilization by inhibiting the conversion of urea to ammonia by blocking the urease enzyme. Volatilization losses can be up to 40% when urea or UAN is not adequately incorporated¹, leading to significant yield reductions if nitrogen is limiting. Examples of products containing these inhibitors are Koch Agronomic Services (KAS) brands, AGROTAIN^® and ANVOL^® nitrogen stabilizers.

2. Nitrification Inhibitors: Offering protection from leaching and denitrification, nitrification inhibitors reduce the activity of nitrifying bacteria in the soil. These bacteria are responsible for converting ammonium to nitrate. While ammonium is available to the plant, it is tightly bound to the soil clay and organic matter, so it is not subject to leaching. Ammonium is also not subject to denitrification losses, which happens when soils are near saturation. Denitrification and leaching can also lead to nitrogen loss, but generally 1% or less of the applied nitrogen is lost as N₂O². KAS’s CENTURO^® nitrogen stabilizer is an example of a product containing a nitrification inhibitor.

3. Dual Inhibitors: A combination of both urease and nitrification inhibitors, dual inhibitors protect against all three forms of nitrogen loss, providing protection against ammonia volatilization, leaching and denitrification. KAS currently offers two dual inhibitor products in Canada—SUPERU^® and TRIBUNE^®.

4. Polymer Coated: Polymer coated products are a nitrogen source that use a coating to delay available nitrogen in a slow-release form.

Research Proven Products in N₂O Reduction

According to a 2022 meta-analysis in Global Change Biology, all EEFs tested were shown to reduce N₂0 emissions with the most consistent category in preventing total loss being dual inhibitors. Within this study, nitrification inhibitors showed the largest reduction in N₂O emissions; however, using a nitrification inhibitor by itself with surface applied urea increased ammonia volatilization under the studied conditions. Treatments that contained dual inhibitors significantly reduced both ammonia volatilization and denitrification which lead to an increase in crop yield³. Also, in a study published in the Soil Science Society of America Journal, urease inhibitors were found to reduce N₂O emissions when compared to straight urea, but dual inhibitors were shown to be the more effective option⁴.

Because urease inhibitors reduce ammonia volatilization of surface applied urea, significantly more nitrogen is left in the soil compared to untreated urea. If a study does not account for the volatilization loss of the untreated urea, then the higher soil nitrogen concentrations, caused by limiting volatilization, can cause an increase of N₂O emissions depending on soil conditions, post-application weather and nitrogen placement. An example of this can be found in a 2017 Agriculture and Agri-food Canada study where N₂O emissions were increased with a broadcast application of urea with a urease inhibitor compared to untreated urea. In this same study, a dual inhibitor was shown to be effective in reducing N₂O emissions compared to untreated urea⁵.

Each of these studies use scientifically demonstrated rates of urease and nitrification inhibitors. The rate of the active ingredient in a product will directly influence the efficacy, whether its volatilization loss or N₂O emissions from nitrification. One such active ingredient that has been proven effective in mitigating N₂O loss, is dicyandiamide (DCD).

In a study published in Communications in Soil Science and Plant Analysis, it was found that the rate of DCD, an active ingredient in KAS’s SUPERU fertilizer, directly affects inhibition of nitrification which is needed to reduce N₂O losses⁶. In fact, in another meta-analysis published in Soil Science Society of America Journal, 25 comparisons of SUPERU versus untreated urea and discovered SUPERU was the most effective nitrogen source in reducing nitrous oxide emissions⁷.

This data shows the impact the right rate and concentration an active ingredient can have on product effectiveness. Other third-party research indicates that products with DCD concentration lower than 1,500 parts per million (ppm) showed no statistical difference when compared to untreated urea⁸. SUPERU contains a DCD concentration of 8,500 ppm which provides scientifically proven effective levels to inhibit nitrification.

Dual Inhibitor Products Offered by KAS

SUPERU — Backed by 30 years of research and hundreds of trials, SUPERU guards against all three forms of loss, ammonia volatilization, leaching and denitrification, showing how it can enhance nitrogen efficiency and optimize yields. Produced primarily in Brandon, Manitoba, SUPERU contains the highest concentration of nitrogen available (46%) in a stabilized, finished fertilizer product. Across seven third-party studies, SUPERU reduced N₂O emissions by an average of 41%⁹.

TRIBUNE — Containing both a urease and nitrification inhibitor, TRIBUNE guards against volatilization, denitrification and leaching. Dual active ingredients NBPT and Pronitridine come together to protect urea ammonium nitrate (UAN) in a nonvolatile, true-liquid formulation.

To learn more about SUPERU, DCD, and how to reduce nitrous oxide emissions, contact your KAS sales rep or find a sales rep today.