Emissions on sheep farms – greenhouse gases and ammonia
Dominika Krol and Aude Mancia, Teagasc Research staff, look at the main emissions, including nitrous oxide, from sheep production. They discuss their promising initial results, as well as ways to further reduce these emissions.
- Greenhouse gases and air pollutants are the main emissions to the air from sheep production systems
- Ongoing research investigating nitrous oxide emissions from sheep excreta deposited on pasture show low emissions from these production systems
- Estimated nitrous oxide emissions from sheep excreta applied on a lowland grassland pasture are low, and may be even lower in an upland grassland
- Ways to further reduce emissions include improved animal health, soil fertility and nutrient use efficiency, and grazing management
Agricultural emissions are divided into two main categories-greenhouse gases and air pollutants (Fig. 1). Greenhouse gases (GHG) have negative impact on climate change and agriculture contributes over 30% of our national emissions. The gases are methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). In agriculture the first two are the most important. Methane represents around two-thirds of all emissions and nitrous oxide the other one-third.
The other type of emissions are air pollutants like ammonia (NH3). Ammonia is a gaseous form of nitrogen, which negatively impacts on human and animal health while also damaging ecosystems. In Ireland agriculture is responsible for 99% of all ammonia emissions.
Sheep excreta as a source of a greenhouse gas nitrous oxide
Nitrous oxide is a very prominent GHG originating mainly from agriculture. It is naturally produced by soils, through microbial activity, which is moderated by nitrogen inputs to the soil and by surrounding environmental factors. Ruminants such as sheep have poor nitrogen use efficiency and excrete between 70 and 95% of ingested nitrogen. Due to these large nitrogen inputs, sheep excreta patches represent hotspots for nitrous oxide production. In sheep production systems, excreta deposited during grazing can be a major source of nitrous oxide, however these emissions have never previously been measured in Ireland. As ruminant grazing systems represent the dominant agricultural activity in Ireland and grasslands account for approximately 60% of total land use, it is important to accurately estimate nitrous oxide emissions associated with excreta deposition of grazing ruminants.
A recent field study has been set-up on a well-managed lowland grassland, in Teagasc Research Centre in Athenry, Co. Galway in order to estimate nitrous oxide emissions after sheep urine and dung applied to the soil during three seasons (spring, summer, autumn) representing early, mid-season and late grazing. Initial results show low nitrous oxide emissions from both sheep urine and dung. The emissions are much lower than those recently estimated for cattle excreta on Irish grassland soils. A similar field study is currently reproduced in an upland grassland in Connemara (Oorid, Recess, Co. Galway), characterised by peat soil. On this grassland, nitrous oxide emissions are expected to be even lower than on the managed grassland due to soil properties.
Conclusions and implications
Initial research results are promising and indicate that sheep excreta deposited on grasslands do not to contribute as much nitrous oxide as previously estimated using international data. However, emissions are still a concern for overall sustainability of the sector. There are number of ways to further reduce emissions such as through improved animal health, soil fertility and nutrient use efficiency, and grazing management.