Gaseous nitrogen losses in agricultural sources and mitigation

• Solutions to emissions - suite of GHG and ammonia mitigation measures
• Recent research into reducing gaseous N losses and improving farm sustainability 
• Current research into reducing gaseous N losses and improving farm sustainability

Agricultural emissions to air are divided into two main categories - greenhouse gases and air pollutants (Figure 1). Greenhouse gases have a negative impact on climate change and agriculture contributes 36% of our national emissions. The gases are:

• methane (CH4)
• nitrous oxide (N2O)
• carbon dioxide (CO2).

In agriculture, the first two are the most important. Methane represents around two-thirds of all emissions and nitrous oxide the remaining third.

When it comes to emission sources, nearly 60% come from animals and 30% from soils that were fertilised by manures or synthetic fertilizer or animals grazing pasture. The remaining 10% comes mainly from management of animal manures like housing during indoor feeding periods and slurry storage.

The Climate Action and Low Carbon Amendment Act 2021 seeks to reduce Irish greenhouse gas (GHG) emissions by 51% by 2030 with agriculture set a reduction target of between 22% and 30%. Achieving these targets pose significant challenges for agriculture across the island of Ireland, especially in the context of sustained economic and GHG emissions growth since 2011.

Air pollutants

The other type of emissions are air pollutants like ammonia. Ammonia is a gaseous form of N which can significantly reduce the N available for grass growth when lost from N fertilizer and slurry. Ammonia negatively impacts on human and animal health, while also damaging ecosystems. Ireland has committed to reducing ammonia emissions, however, we have been exceeding our EU targets in recent years.

In Ireland, agriculture is responsible for 99% of all ammonia emissions so any national reduction will have to come from agriculture, primarily from how we manage our N fertilizer and slurry. Ammonia comes mainly from management of animal manures (housing, slurry storage and land spreading) but also from grazing animals, and finally from spreading of synthetic fertilizer.

Figure 1. Gaseous emissions from agricultural sources.

Solutions to emissions - suite of GHG and ammonia mitigation measures

Teagasc assessed a number of options to reduce nitrous oxide and ammonia emissions on Irish farms using Marginal Abatement Cost Curves (MACCs; Figures 2 and 3). The MACCs compare options based on cost to implement at farm level and their effectiveness at reducing emissions. MACCs indicate that there are many measures to reduce emissions while improving on-farm efficiency and profitability.

Figure 2. Cost and abatement potential of greenhouse gas mitigation from Irish agriculture. From An Analysis of Abatement Potential of Greenhouse Gas Emissions in Irish Agriculture 2021-2030 (pdf) 

Table 1 simplifies the MACCs presenting a suite of ‘win-win’ solutions that can easily be implemented and deliver good results for GHG and ammonia mitigation. Improvements in beef genomics, including improving maternal traits such as higher fertility or terminal traits such as improved live weight gain as well as improved animal health can reduce the carbon footprint of beef whilst also enhancing profitability.

Other measures such as extended grazing, and reducing the age of slaughter by one month can provide benefits mainly through reducing animal methane emissions. Other presented measures focus on N use efficiency and resultant N losses. Optimization of soil fertility and inclusion of clover in grass sward, including as a component of multi-species swards, allow for lower N fertilisation rates without a yield penalty. Similarly, choosing fertilizer sources such as protected urea substantially reduce N losses to the air while sustaining quantity and quality of yields.

Remaining measures focus on manure management, either through extending animal grazing season and thus reducing quantity of animal manure being stored and land spread, or through mitigating emissions during storage and land spreading by using slurry additives or low emission spreading technologies. The mitigation of N losses during storage and land spreading results in a higher retention of N, which can then support plant growth. Reducing the crude protein of animal rations reduces farm input costs, while also reducing ammonia emissions. Protected urea and low emission slurry spreading (LESS) are the two most effective options to reduce ammonia emissions and can deliver up to 80% of the reduction required to meet our EU ammonia targets.

Table 1 - Various measures mitigating greenhouse gas and ammonia emissions 

Figure 3. Cost and abatement potential of ammonia mitigation from Irish agriculture. From An Analysis of the Cost of the Abatement of Ammonia Emissions in Irish Agriculture to 2030 

Recent research into reducing gaseous N losses and improving farm sustainability

Work carried out in Teagasc, Johnstown Castle shows that a long-term low soil phosphorus level results in high N2O emissions from N fertilizer application. When applied to grassland low in soil phosphorus, N is not incorporated into plant biomass and is lost to the environment. This highlights the importance of discerning exactly what is limiting the system as in this case any applied N is a waste because it cannot be recovered in herbage yield and results in both financial losses and environmental damage. Such N loss occurs regardless of the form of N-fertilizer and the application rate (potassium nitrate, ammonium sulphate, ammonium nitrate, urea and high or low application rates.)

Recently published research from Teagasc Johnstown Castle shows that N2O emissions from fertilizer applied to soils, which are at the upper end of the recommended agronomic range, are reduced by 39%. Therefore, farmers who improve soil pH for agronomic benefits, can also reduce N2O emissions. This represents a ‘win-win’ for the farmer and the environment.

Current research into reducing gaseous N losses and improving farm sustainability

Teagasc Johnstown Castle is carrying out a number of research projects seeking to improve our knowledge of processes and quantification of gaseous N losses, as well as investigating new and novel ways of mitigating emissions.

Abating Ammonia in Agriculture

This project seeks to investigate novel strategies for abating ammonia emissions to add to a suite of options available to Irish agriculture. The research will produce reliable emission factors associated with slurry spreading techniques and amended slurries during storage and after land spreading to improve national accounting of mitigation. The socio-economic barriers hindering the adoption of ammonia abatement measures will also be investigated during the project.

Environmental and economic sustainability of biogas / biomethane production in Ireland through anaerobic digestion of slurry and various grass feedstocks

Research at Teagasc Johnstown Castle is looking into greenhouse gas and ammonia emissions associated with using digestate as fertilizer for grasslands, while also exploring the agronomic performance of those grasslands.

Land-Use, Agriculture and Bioenergy Measures for the Abatement of Climate Change and inclusion in Marginal Abatement Cost Curve

This project seeks to build on the previous MACC and quantify mitigation associated with a range of new measures that:

• reduce N2O emissions
• enhance carbon sinks via land-use
• displace fossil fuel emissions via closed farm nutrient loops using enhanced production of bio-based products.

This research will refine emission factors nationally so that the mitigation measures can be incorporated into national inventories and enable farmers to receive credit for emissions reduction. It will also evaluate the economic and mitigation consequences of incorporation of abatement measures into production systems and help develop farmer decision support tools.

The project will focus on knowledge transfer and the delivery of timely messaging and demonstration to farmers using the Signpost farms programme. The project will generate new projections of GHG emissions out towards 2050 and a new MACC analysis will be generated incorporating the new measures evaluated in this project and other current and future projects to identify the pathways for agricultural to become climate neutral by 2050.

Dominika Krol, Gary Lanigan, Rosie O’Neill, Ali Sultan Khan, Maxwell Owusu-Twum and Karl Richards 
Teagasc, Environment, Soils and Land Use Department, Johnstown Castle, Co. Wexford