# Disaggregated N₂O emission factors associated with deposition of sheep excreta in temperate grasslands

A. Mancia¹, D. Chadwick², S. Waters³, D. Krol¹

¹Teagasc, Crops, Environment and Land Use, Johnstown Castle, Co. Wexford, Ireland
Grange, Dunsany, Co. Meath

aude.mancia@teagasc.ie

²The School of Natural Sciences, Bangor University, Bangor, UK

³Teagasc, Animal and Grassland Research and Innovation Centre,

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## 1. Introduction

* Contribution of grazing ruminants to global warming through the deposition of urine and faeces onto soils

* Excreta patches → large nitrogen (N) inputs → increased N cycling rate and risk of N₂O emissions

* Default values for N₂O emissions from ruminants excreta deposition → IPCC 2019 Tier 1 emission factors (EFs) = 0,3 %

* Great spatial and temporal variations → need to develop country-specific EFs

## 3. Methodology

* Fully randomized block design trial on a well-managed lowland grassland in Athenry, Co. Galway (Fig. 1a)

* Parameters: N₂O and soil mineral N, measured for 365 days after each application (spring, summer, autumn)

* Treatments: control (C), sheep urine (U), sheep dung (D), artificial urine (AU) and sheep urine + nitrification inhibitor (UNI) for autumn experiment only

* Collection of excreta from local ewes for each season (Fig. 1b)

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## 2. Objectives

* To generate new EFs for N₂O emissions associated with sheep excreta deposition in temperate grasslands, by disaggregating emissions by type of excreta and season of application

* To assess climatic and soil factors influencing these emissions

## 4. Results

* N₂O flux peak after U and AU application for all seasons

* Significant effect (p<0,05) of treatments on cumulative N₂O emissions in autumn only, with AU ≠ C (Fig. 2)

* Overall seasons, mean partial EF = 0,05 % for urine and 0,02 % dung

<figure><img src="image_5.png" /><figcaption>Fig 2. Mean cumulative N₂O emissions calculated 15 weeks after treatments application in spring, summer and autumn. Vertical bars indicate standard error of the means (n=5).</figcaption></figure>

## 5. Conclusions

* Importance to refine IPCC Tier 1 EF which appears to be overestimated

* Similar experiment is being reproduced on an upland grassland with acid peat soil in Connemara, Co. Galway

**Acknowledgements:**

This research is financially supported by the Walsh Scholarships Programme