27 November 2023

Spreading the good nutrients

Use of nitrogen-based fertilisers contributes heavily to greenhouse gas emissions. Research is underway at Teagasc Johnstown Castle to quantify the effect of alternative fertiliser formulations on nitrous oxide emissions.

Research at Johnstown Castle seeks to quantify the effect of fertiliser type on nitrous oxide emissions

Ireland’s Climate Action Plan 2023 set out a roadmap for taking decisive action to achieve a 51% reduction in greenhouse gas emissions by 2030 across its entire economy. The agriculture sector’s share of this reduction is 25%. The application of nitrogen fertiliser accounts for the largest source of anthropogenic nitrous oxide (N2O) emissions, with the emissions dependent on what fertiliser formulation is applied. Katie Scully, Postdoctoral Researcher at Teagasc Johnstown Castle, explains that different fertiliser types are currently measured according to different standards. “Ireland currently uses country-specific Tier 2 emission factors for straight nitrogen fertiliser. However, for compound fertilisers we use the Intergovernmental Panel on Climate Change default emission factor for N2O from soils. High N2O emissions tend to be associated with nitrate-containing fertilisers such as calcium ammonium nitrate compared to urea, particularly in wet temperate grassland soils, due to the immediate availability of the nitrate substrate for denitrification.”

Previous research has developed country-specific emission factors for three types of straight nitrogen fertiliser on the Irish market: calcium ammonium nitrate (CAN), urea and protected urea. Half of the nitrogen fertiliser in Ireland is spread as compound fertilisers, which contain a blend of nitrogen with other nutrients such as potassium (K), phosphorous (P) and sulphur (S). These fertilisers have different ratios of nitrate to ammonium, owing to their formulation. A preliminary field trial in 2020 showed that compound fertilisers with lower ratios of nitrate to ammonium could reduce N2O emissions by 40%, when compared to CAN.

A new research project is underway to quantify the effects of compound fertiliser types on N2O emissions. As Katie explains: “This will allow us to identify low-emission compound fertiliser formulations and produce national emission factors that can be included in the national inventory. “This collaborative study between the Agri-Food & Biosciences Institute and Teagasc will take place over two years at permanent pasture sites. Sites located at Johnstown Castle will allow for measurements of well-drained soil; by contrast, sites at Hillsborough allow measuring of poorly drained soil.” Nitrous oxide emissions are being measured from nine fertiliser treatments applied at 200kg N ha-1 in five equal splits, to simulate a typical grazed grassland. Katie explains: “Nitrous oxide emissions are being measured using the National Soil Greenhouse Gas Test Platform funded by Science Foundation Ireland. This experiment’s high-frequency monitoring method with low-labour intensity will generate high-resolution measurement of N2O emissions to robustly account for events, such as rainfall, that drive high emissions.” This type of high-resolution data helps paint a clearer picture of real emissions levels in Ireland, creating a better baseline for choosing fertiliser formulations.

Further Information:

Youtube Link: Technologies for Reducing Greenhouse Gases and Ammonia - Karl Richards & Gary Lanigan

Funding

This research is financially supported under the National Development Plan, Research Stimulus Fund, Department of Agriculture, Food and the Marine (2021R550). The National Soil Greenhouse Gas Test Platform was funded by Science Foundation Ireland (21RI9642).

Contributors

Karl Richards
Head of Teagasc Climate Centre, Teagasc Johnstown Castle.

Katie Scully
Postdoctoral Researcher, Teagasc Johnstown Castle.
katie.scully@teagasc.ie

[pic credit] Teagasc