Cumulative effects of long-term dual-inhibitor N-fertilizer use on yield, N2O emissions and soil microbiome function
Term: 4 years
Status: Ongoing
Researcher(s): Jennifer Town, Reynald Lemke, AAFC
SaskOilseeds Investment: $29,081
Total Project Cost: $116,325
Funding Partners: ADF, Sask Wheat
Objective
Determine the long-term maximum N-rate reduction with dual-inhibitor (DI) N-fertilizer that maintains optimal yields of canola and wheat.
Determine the cumulative N2O emissions-reduction achieved with a DI N-fertilizer compared to urea over long-term use.
Identify changes in soil microbiome composition after long-term application of DI N-fertilizer compared to standard urea.
Identify changes in N-cycling dynamics in response to long-term application of DI N-fertilizer compared to standard urea.
Project Description
Reducing greenhouse gas emissions has become a high priority for western Canadian producers. In 2020, the federal government established a target of reducing N2O emissions associated with fertilizer application by 30% below 2020 levels by 2030.
The need to identify approaches to maintain crop yields while reducing N-fertilizer application has led to greater adoption of 4R Nutrient Stewardship principles, including an increased use of enhanced-efficiency fertilizers (EEFs) that involve either urease or nitrification inhibitors or both. Research examining the efficiency of these products has shown variability in their effects due to soil conditions, crop selection and environmental factors, and their effects over several crop years is not well established.
We hypothesized that the greater N-use efficiency of EEFs would enable optimal crop yields at lower N application rates, minimizing N loss and maximizing both environmental and economic benefits. To that end, a rate response study was established in 2022 at the AAFC Research Farm near Melfort, SK. Data from 2022 and 2023 has shown that the use of EEFs has enabled lower N applications rates (down to 70% of soil test recommendation) with no significant yield loss. By extending the length of this study through 6 growing seasons, we will be able to quantify the cumulative effects of long-term EEF use on N2O emissions, grain yield and quality as well as soil microbiome diversity and N-cycling capacity.
One the most significant sources of N2O production is from inefficiencies in microbial N-cycling dynamics in the soil. When applied to the soil, urea fertilizer is converted to nitrate at a rapid rate which can result in N losses from volatilization of ammonia, leaching of excess nitrate and N2O emissions. By slowing the conversion of urea to ammonia and nitrate, EEFs can increase fertilizer use efficiency while reducing N losses from these pathways. The effects of EEFs compared to urea on soil bacterial and fungal populations has been variable, with crop selection, soil type and climate all playing a significant role. Understanding these microbial processes, and how the functional capacity of the soil is affected with long-term use of EEFs is important both for ensuring soil fertility as well as understanding the relationship between N formulation, microbial activity and N-cycling dynamics.
By examining the combined effects of enhanced efficiency N-fertilizer products and reduced N application rates, we aim to provide producers with concrete guidance and practical approaches to reducing N2O emissions while maintaining optimal yields.