Investigating Patterns of Nitrous Oxide Emissions in Corn Agriculture
Nitrous oxide (N2O) emissions in agriculture primarily come from the microbial processes of nitrification and denitrification in the soil, and they’re strongly influenced by nitrogen management practices, particularly the use of nitrogen fertilizers.
□ Why Crops Cannot Directly Utilize Atmospheric Nitrogen (feat. Nitrogen Cycling in Soil)?
■ Nitrification: The microbial process in which ammonium (NH4+), a form of nitrogen that's often applied as fertilizer, is converted into nitrate (NO3-). This process can result in the production of nitrous oxide as a byproduct, especially under certain soil conditions. ■ Denitrification: The another microbial process, but it occurs when soil conditions are anaerobic (i.e., without oxygen). In this process, nitrate (NO3-) is converted into various nitrogen gases including nitrous oxide. Denitrification is more likely to occur in wet, poorly drained soils.
These processes can lead to significant N2O emissions, especially after the application of nitrogen fertilizers, which provide a large source of nitrogen for the soil microbes to use in these processes. Other sources of N2O emissions in agriculture can include the decomposition of crop residues and animal manure.
N2O is a potent greenhouse gas (GHG), with a global warming potential nearly 300 times greater than that of (CO2) carbon dioxide over a 100 year period. It’s also a significant contributor to stratospheric ozone depletion. Thus, managing N2O emissions from agriculture is an important part of efforts to mitigate climate change and protect the ozone layer.
Various strategies can be used to reduce N2O emissions from agriculture, including optimizing the timing and rate of nitrogen fertilizer application, using nitrification inhibitors, improving soil management practices (e.g., crop rotation, cover crops, conservation tillage), and managing manure and crop residues more effectively.
Nitrous oxide (N2O) emissions from agricultural fields can occur throughout the entire growing season and even beyond. N2O is produced primarily through the biological processes of nitrification and denitrification in the soil, which are influenced by several factors including soil type, temperature, moisture content, and the availability of nitrogen.
Immediately after the application of nitrogen fertilizers (whether organic like manure or inorganic like urea or anhydrous ammonia), there is often a flush (N2O emission peak) of N2O emissions. This is due to the sudden increase in available nitrogen for soil microbes to use in the nitrification and denitrification processes. This flush typically lasts for a few days to a week, depending on the conditions.
After this initial peak, N2O emissions will generally decline but continue at a lower rate throughout the growing season as the nitrogen continues to be processed by the soil microbes. The exact length of time can vary significantly, but it’s not uncommon for emissions to continue for several months after sowing. These emissions can be influenced by the timing and amount of rainfall, the temperature, and the type and health of the crop.
In the Champaign area, we measured N2O gases in corn fields using ‘Gasmet,’ a portable gas analyzer, on a weekly basis. The gas emissions recorded over a certain period were then converted to cumulative Nitrous oxide (µg/m2 h). According to our data, after a month from sowing, the N2O emissions remained constant over time.
This result provides important insight into potential strategies for managing nitrogen fertilizer applications. For example, carefully timing and controlling the application of fertilizer could help to limit the initial peak in N2O emissions, as the data suggests that emissions stabilize after a certain period. Further, this consistent emission rate could also allow us to predict and effectively mitigate long-term N2O emissions. Additional strategies, such as utilizing nitrification inhibitors or other soil amendments, could be used in conjunction with this timing approach to further reduce N2O emissions. Understanding these emission patterns allows for the development of more targeted and effective nitrogen management strategies to mitigate N2O emissions from agricultural fields.
