Uncertainties in direct N2O emissions from grazing ruminant excreta (EF3PRP) in national greenhouse gas inventories

Aude Mancia; David R Chadwick; Sinéad M Waters; Dominika J Krol

doi:10.1016/j.scitotenv.2021.149935

Uncertainties in direct N₂O emissions from grazing ruminant excreta (EF_3PRP) in national greenhouse gas inventories

Sci Total Environ. 2022 Jan 10:803:149935. doi: 10.1016/j.scitotenv.2021.149935. Epub 2021 Aug 27.

Authors

Aude Mancia¹, David R Chadwick², Sinéad M Waters³, Dominika J Krol⁴

Affiliations

¹ Teagasc, Environment, Soils and Land Use Department, Johnstown Castle, Co. Wexford, Ireland; School of Natural Sciences, Bangor University, Bangor, Wales, UK; Teagasc, Animal and Bioscience Research Department, Animal and Grassland Research and Innovation Centre, Athenry, Co. Galway, Ireland.
² School of Natural Sciences, Bangor University, Bangor, Wales, UK.
³ Teagasc, Animal and Bioscience Research Department, Animal and Grassland Research and Innovation Centre, Athenry, Co. Galway, Ireland.
⁴ Teagasc, Environment, Soils and Land Use Department, Johnstown Castle, Co. Wexford, Ireland. Electronic address: dominika.krol@teagasc.ie.

PMID: 34487900
DOI: 10.1016/j.scitotenv.2021.149935

Abstract

Excreta deposition onto pasture, range and paddocks (PRP) by grazing ruminant constitute a source of nitrous oxide (N₂O), a potent greenhouse gas (GHG). These emissions must be reported in national GHG inventories, and their estimation is based on the application of an emission factor, EF_3PRP (proportion of nitrogen (N) deposited to the soil through ruminant excreta, which is emitted as N₂O)_. Depending on local data available, countries use various EF_3PRPs and approaches to estimate N₂O emissions from grazing ruminant excreta. Based on ten case study countries, this review aims to highlight the uncertainties around the methods used to account for these emissions in their national GHG inventories, and to discuss the efforts undertaken for considering factors of variation in the calculation of emissions. Without any local experimental data, 2006 the IPCC default (Tier 1) EF_3PRPs are still widely applied although the default values were revised in 2019. Some countries have developed country-specific (Tier 2) EF_3PRP based on local field studies. The accuracy of estimation can be improved through the disaggregation of EF_3PRP or the application of models; two approaches including factors of variation. While a disaggregation of EF_3PRP by excreta type is already well adopted, a disaggregation by other factors such as season of excreta deposition is more difficult to implement. Empirical models are a potential method of considering factors of variation in the establishment of EF_3PRP. Disaggregation and modelling requires availability of sufficient experimental and activity data, hence why only few countries have currently adopted such approaches. Replication of field studies under various conditions, combined with meta-analysis of experimental data, can help in the exploration of influencing factors, as long as appropriate metadata is recorded. Overall, despite standard IPCC methodologies for calculating GHG emissions, large uncertainties and differences between individual countries' accounting remain to be addressed.

Keywords: Disaggregation; Emission factor; Grassland; IPCC methodology; National inventory report.

Publication types

Review

MeSH terms

Animals
Greenhouse Gases* / analysis
Nitrous Oxide / analysis
Ruminants
Seasons
Soil

Substances

Greenhouse Gases
Soil
Nitrous Oxide