Agronomy Update
Agronomy Update: Enhanced efficiency fertilizers cut nitrous oxide emissions in spring wheat

Environment and Climate Change Canada has set a goal to reduce the amount of greenhouse gas emissions from nitrogen (N) fertilizer by 30 per cent below 2020 levels by 2030. Reducing nitrous oxide N2O emissions will be a key strategy in meeting this goal while maintaining or increasing crop yields.

A cross-Canadian Prairie research study examined the effect of fall and spring application timings of urea and anhydrous ammonia treated with enhanced efficiency fertilizers (EEFs) on spring wheat performance and N2O emissions. Mario Tenuta, senior industrial research chair in 4R nutrient management and professor of soil ecology at the University of Manitoba, summarized the Manitoba research that evaluated the impact of using multiple EEF sources compared to conventional urea, and fall and spring application timings, on spring wheat yield and protein content over three years, along with the impact on N2O emissions.

Research was carried out in southern Manitoba at Warren and Glenlea in 2015, Carman and La Salle in 2016 and Kelburn and Ridge in 2017. All sites had residual nitrate-N soil test levels less than 89 pounds per acre (100 kg/ha) and were on soybean stubble.

Nitrogen fertilizer sources compared were an unfertilized control, untreated urea and four EEFs including urea plus a urease inhibitor (Limus); polymer-coated urea (environmentally smart nitrogen [ESN]); urea plus a nitrification inhibitor (eNtrench); and urea plus nitrification and urease inhibitors (SuperU). Application timing included late fall banding at one to two inches (2.5 to 5 cm) depth and spring banding at seeding in a one-pass operation at one to two inches, both treatments done in a mid-row band placement.

Fertilizer rates were based on provincial soil test recommendations. All plots were seeded to AAC Brandon and were managed with standard agronomic practices.

At five of six site years, wheat yield and protein content were not affected by N fertilizer source. The only site where N source impacted yield and protein content was Kelburn-17. At this site, the controlled-release product ESN produced significantly higher yield than urea and urea + Limus. It also produced grain protein content significantly higher than urea, SuperU and urea + Limus.

The impact of application timing on wheat yield and protein content was variable. Three of six site-years had lower yield with fall application compared to spring application, while one site had higher yield with fall application and the other two sites had similar yields with fall and spring applications. Four of six sites had similar protein content for both spring and fall application, while fall application had lower protein content at the other two sites.

Urea + Limus did not significantly reduce N2O emissions compared to untreated urea. ESN also did not significantly reduce emissions.

However, products containing a nitrification inhibitor significantly and consistently reduced N2O emissions. Urea + eNtrench reduced cumulative N2O emissions by 47 per cent to 64 per cent at four of six site-years irrespective of application timing. SuperU also reduced N2O emissions by 37 per cent to 57 per cent at three of six site-years. ESN significantly reduced emissions at Warren-15 by 44 per cent compared to untreated urea, but reductions were variable at other site-years.

Application timing also impacted N2O emissions. Overall, fall application produced 33 per cent to 67 per cent higher N2O emissions at three of six site-years compared to a spring application. This was mainly due to emissions during the spring thaw. There wasn’t any interaction between source and timing at five of six site-years.

Overall, compared to untreated urea across all site-years, the products containing nitrification inhibitors significantly reduced cumulative N2O emissions by 38 per cent for urea + eNtrench, and 43 per cent for Super U, irrespective of application time. The effectiveness of these nitrification inhibitor products was attributed to the slower conversion of NH4+ to NO3-, reducing nitrification and subsequent N2O emissions.

The research provides guidance to policymakers on developing cost-share programs to encourage the use of EEFs to reduce N2O emissions. Currently, under the On Farm Climate Action Fund program, dual-inhibitor products are eligible for incentives, but single nitrification inhibitor products have not qualified to date. The results of this study show that single nitrification inhibitors are as effective as dual inhibitors for urea fertilizers.

The study also advances the understanding of 4R nutrient management as it relates to N management practices and how EEF fertilizers can play a role in helping to reduce greenhouse gas emissions. However, since few yield or protein content benefits were found in the research, other policy mechanisms to encourage the use of EEFs need to be investigated.

Bruce Barker divides his time between CanadianAgronomist.ca and as Western Field Editor for Top Crop Manager. CanadianAgronomist.ca translates research into agronomic knowledge that agronomists and farmers can use to grow better crops. Read the full Research Insight at CanadianAgronomist.ca.