Reducing Nitrous Oxide Emissions from Excess Fertilizer Usage in Agriculture
Funded through the Biological GHG Management Program in 2014, the long-term objective of the project was to reduce nitrous oxide emissions from agricultural landscapes where manure is applied. This project generated new data to support the application of carbon credits for greenhouse gas (GHG) reduction in Alberta’s carbon offset market and provided farmers with options on how to use liquid manure while reducing environmental risks and optimizing the efficient use of nutrients.
Nitrous oxide is a potent GHG with a global warming potential nearly 300 times that of carbon dioxide (CO2) over a 100-year period. In Alberta’s agricultural industry, an estimated eight million tonnes of GHGs come from nitrous oxide emissions every year, with the majority occurring in cropping systems where synthetic nitrogen fertilizer or manure is recurrently added to the soil.
This project, completed in 2017, involved identification and development of management practices that can decrease nitrous oxide emissions from cropland receiving liquid manure. In Alberta’s agricultural industry, an estimated 8 million tonnes of GHGs per year come from nitrous oxide emissions. Most of these emissions occur in cropping systems where synthetic nitrogen fertilizer or manure is recurrently added to the soil, and the portion unused by plants is often lost to the environment in the form of GHGs. The researchers tested the application of liquid manure at different times of the year, in early fall vs late spring, in combination with two nitrification inhibitors (NIs) – called nitrapyrin and dimethylpyrazole phosphate (DMPP) – mixed with the liquid manure. NIs are compounds added to a nitrogen-based fertilizer to limit greenhouse gas emissions and nitrogen run-off, thus reducing risk of harm to the environment from fertilizer use. Nitrapyrin and DMPP are effective NIs that are widely used in agriculture already; however, more strategically applying these NIs based on the seasons may help farmers to further reduce emissions.
Seasonal Impact of Nitrogen Inhibitor Effectiveness
The researchers found that fields where NIs were used showed a sharp reduction in GHGs compared to fields where they were not, but that there was a seasonal impact to when these NIs were applied. For instance, fall manure treated with DMPP reduced annual nitrous oxide emissions by 81 per cent, and nitrapyrin reduced emissions by 58 per cent. The emission reductions caused by NIs were also evident in the spring manure field treatments, but the reduction magnitudes were typically smaller. Additionally, compared to the spring manure application, manure without NIs applied in the fall resulted in an approximate two-fold increase in emissions. This was due to major nitrous oxide fluctuations following the early spring snow melt, which accounted for at least 65 per cent of the annual emissions that year.
What’s next?
This project is one of many efforts to assess the effectiveness of NIs in reducing GHGs associated with fertilizer application. The researchers conducted a follow-up project to quantify the effects of varying nitrification inhibitor rates on nitrous oxide emissions where the liquid manure is treated with these nitrification inhibitors. This inhibitor rate project is a key follow-up on this concluding manure project to reduce nitrous oxide emissions during the early spring following soil thawing and snow melt. Nitrapyrin and DMPP remain the most widely used NIs, however, there are many on the market with various success rates. Uptake of the technology to date has been low in Alberta, primarily due to the cost. The product has good potential with high value crops including malt barley or sugar beets, but more piloting may be needed in these areas.