Enhanced Efficiency Fertilizers (EEFs) & Nitrous Oxide

Written By: Derek Wilfing (Koch Agronomic Services)

In recent conversations in the agriculture industry throughout Canada, reducing nitrous oxide emissions associated with fertilizer use has become a hot topic after the Canadian Government announced a goal of reducing nitrous oxide emissions by 30% by 2030.

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.

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: Ploymer coated products are a nitrogen source that use a coating to delay available nitrogen in a controlled 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 N₂O 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 nitrificiation 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.

In a study published in Communications in Soil Science and Plant Analysis, it was found that the rate of dicyandiammide (DCD), an active ingredient in KAS’s SUPERU fertilizer, directly affects inhibition of nitrification which is needed to reduce N₂O losses^₅. 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 emissions⁶.

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 urea7. SUPERU contains a DCD concentration of 8,500 ppm which provides scientificatlly proven effective levels to inhibit nitrification.

Dual Inhibitor Products Offered By KAS

SUPERU - Backed by 25 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 N^₂O emissions by an average of 41%⁸.

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.

1 Research Studies: Frenzen et al., 2010; Kelly. 2009; Holcomb et al., 2010; Holt, 2008 2 Intergovernmental Panel on Climate Change 3 Fan et al. 2022. Global Change Biology. Global evaluation of inhibitor impacts ammonia and nitrous oxide emissions from agricultural soils: a meta-analysis. 28: 5121-5141. 4 Woodley et al. Soil Sci Soc Am J. Ammonia volatilization, nitrous oxide emissions, and corn yield as influenced by nitrogen placement and enhanced efficiency fertilizers. 202; 84: 1327-1341. 5 McCarty & Bremner. 1989. Communications in Soil Science and Plant Analysis. Laboratory evaluation of dicyandiamide as a soil nitrification inhibitor. 20:19-20, 2049-2065. 6 Eagle et al. 2017 Soil Sci Soc Am J. Fertilizer management and environmental factors drive N2O and NO3 losses in corn: a meta-analysis. 81: 1191-1202 7 Third party lab study—Roberts, University of Arkansas 2019-2020. 8 EPA EEF Challenge Submission data: 30% reduction - corn (Chatterjee et al, 2016); 34% reduction - corn (Chatterjee et al, 2016); 45% reduction - corn (Yang et al, 2016); 35% reduction - corn (Eagle et al, 2017); 48% reduction - irrigated no-till corn (Halvorson et al, 2010); 53% reduction - semi-arid irrigated corn (Dugan et al, 2017); 43.8% reduction - sandy loam soil (Awale and Chatterjee, 2017)