Enhanced‐Efficiency Fertilizer Impacts on Yield‐Scaled Nitrous Oxide Emissions in Maize

Abstract

Core Ideas Enhanced‐efficiency fertilizers reduced N2O compared with anhydrous ammonia in two of three years. SuperU reduced both area‐ and yield‐scaled N2O emissions in two of three years. Soil inorganic N concentrations were not correlated with daily N2O fluxes. Fertilizers ESN, SuperU, and UAN + nitrapyrin did not increase yield or grain N recovery efficiency. Balancing efforts to mitigate nitrous oxide (N2O) emissions from crop production while increasing grain yields is an important challenge for agriculture. The objectives of this study were to assess N2O emissions, soil inorganic nitrogen (N) concentrations, grain yield, and grain N content for three enhanced‐efficiency nitrogen fertilizers (EENFs) compared with anhydrous ammonia in a rainfed corn system in Illinois over 3 yr (2015–2017). Treatments included a control (check) and four N sources applied at 202 kg N ha−1: injected anhydrous ammonia, stabilized urea containing urease and nitrification inhibitors (SuperU, Agrotain International), polymer‐coated urea (ESN, Agrium Advanced Technologies), and injected urea‐ammonium nitrate (UAN) + nitrapyrin. Significant reductions in N2O emissions were observed for several EENFs compared with anhydrous ammonia, but results were not consistent across treatments and years. SuperU reduced area‐ and yield‐scaled N2O emissions in two of three study years compared with anhydrous ammonia, while ESN had no N2O mitigation benefit. Injected UAN + nitrapyrin had the highest emissions in the first year but significantly decreased emissions in the second 2 yr. No treatment significantly improved yield or grain N content compared with anhydrous ammonia. In light of efforts to broadly promote EENFs in the US Midwest, these results demonstrate there is some promise for N2O mitigation, but the lack of clear crop productivity benefits combined with inconsistent N2O mitigation effects do not support the conclusion that EENFs inherently improve agronomic and environmental outcomes.

How 4R nutrient stewardship research helps us interpret sustainability science

“…While there is research that demonstrates the ability of EEF‐treated fertilizers to reduce N 2 O loss by as much as 32% (Eagle et al, 2017), details within the paper reveal that critical aspects necessary for EEF selection were not considered within the assumptions and calculations used to arrive at the concluded policy action. Rainfall, soil moisture, air temperature, and soil temperature can all impact the performance of nitrogen fertilizer treated with an EEF product (Barker and Sawyer, 2017; Eagle et al, 2017; Graham et al, 2018) and should be considered when assessing the environmental impact of EEF use.…”

“…A recent meta‐analysis reported that a 1°C change in average July temperature was equivalent to the difference in losses related to the use of nitrification inhibitors with higher losses as temperature increases (Eagle et al, 2017). Research conducted in Illinois through the 2015, 2016, and 2017 growing seasons compared three EEF nitrogen products to no N fertilizer and the standard practice of injecting anhydrous ammonia (Graham et al, 2018). Nitrous oxide emissions from the plots, which received the same rate of 180 lb N/ac, varied within and across years for the three products (Graham et al, 2018).…”

“…Research conducted in Illinois through the 2015, 2016, and 2017 growing seasons compared three EEF nitrogen products to no N fertilizer and the standard practice of injecting anhydrous ammonia (Graham et al, 2018). Nitrous oxide emissions from the plots, which received the same rate of 180 lb N/ac, varied within and across years for the three products (Graham et al, 2018). For example, in 2015, UAN with nitrapyrin, a nitrification inhibitor, had significantly higher N 2 O emissions than SuperU, urea treated with nitrification and urease inhibitor products, but in 2016 and 2017, emissions from these two products were not statistically different (Graham et al, 2018).…”

“…Nitrous oxide emissions from the plots, which received the same rate of 180 lb N/ac, varied within and across years for the three products (Graham et al, 2018). For example, in 2015, UAN with nitrapyrin, a nitrification inhibitor, had significantly higher N 2 O emissions than SuperU, urea treated with nitrification and urease inhibitor products, but in 2016 and 2017, emissions from these two products were not statistically different (Graham et al, 2018). While reducing nitrogen losses is a component of farm management decisions, the crop response and potential return on the use of the product is also an important part of the evaluation.…”

“…While reducing nitrogen losses is a component of farm management decisions, the crop response and potential return on the use of the product is also an important part of the evaluation. Yield response to the use of an EEF product also varied across the years of the project, with no difference across products in 2015 and 2017 but significantly lower yield with UAN with nitrapyrin in 2016 (Graham et al, 2018). The dependence of N 2 O loss and crop yield response on weather and soil conditions when a nitrogen fertilizer is treated with an EEF product would make it difficult to achieve the desired N 2 O emission reduction outcome using the Kanter and Searchinger (2018) proposed policy.…”