Measurement and modelling of N2O fluxes from Irish Agricultural Grasslands
Measurement and modelling of N2O fluxes from Irish Agricultural Grasslands
Greenhouse gases (GHGs) in the atmosphere keep the earth warm by absorbing infra-red radiation emitted from the earth's surface and preventing it from escaping to space.
The most significant greenhouse gases in the atmosphere are:
- Water vapour, H2O: the most abundant GHG, but as emissions of H2O are quickly recycled to the surface they do not have a lasting warming effect.
- Carbon dioxide, CO2: this is produced by the natural process of respiration in plants and animals and also by burning of fossil fuels such as oil, gas and coal.
- Methane, CH4: emitted by the digestion processes of ruminant animals such as cows, and from rice paddies and peat bogs and possibly from plants.
- Nitrous oxide, N2O: one of the main sources of this GHG is from the breakdown of nitrogen fertilisers and animal wastes in soils. The EPA estimates that up to 14% of total Irish GHG emissions are N2O from agricultural sources.
Nitrous oxide (N2O) is a powerful greenhouse gas. Although the amount of N2O emitted by soils is small compared to soil CO2 fluxes, it is still an important greenhouse gas as a gram of N2O has almost 300 times the warming effect on the atmosphere as a gram of CO2.
The concentration of N2O in the atmosphere is increasing: from 270 parts per billion in 1750 to 314 parts per billion today. The current rate of increase is approximately 0.8 parts per billion per year.
The average lifetime of a molecule of N2O in the atmosphere is estimated at approximately 114 years.
Agriculture and nitrous oxide
In Ireland, between 1% and 4% of nitrogen applied to the ground as synthetic fertiliser and animal waste is emitted as nitrous oxide. The amount of these fertilisers converted to N2O depends strongly on environmental conditions such as the soil temperature, soil moisture content and the amount of nitrogen available in the soil.
Agricultural activities lead to nitrous oxide emissions through the deposition of wastes from grazing animals and the use of synthetic nitrogen fertilisers and animal waste fertilisers to boost productivity.
In Ireland, approximately 14% of our total national greenhouse gas emissions from human activities are accounted for by nitrous oxide emissions from agriculture. Therefore agricultural greenhouse gas emissions are a very important area of scientific investigation. If we can understand the mechanisms of N2O generation in agricultural lands, we may be able to recommend measures to controlling these emissions and thus reducing national greenhouse gas emissions.
Nitrogen in the soil
Nitrification is a chain of oxidation reactions, starting with ammonium (NH4+) and ultimately leading to nitrate (NO3-). N2O is an intermediate by-product of nitrification.
Denitrification is a chain of reduction reactions, starting with nitrate (NO3-), leading to nitrogen (N2). N2O is an intermediate product and is readily emitted to the atmosphere.
Nitrogen is constantly cycling through the soil, being transformed by a series of chemical reactions. Nitrous oxide is produced in soils by two reaction pathways: nitrification and denitrification.
Sites and Funding
We are grateful to the owners of the following sites for co-operating with the project:
- Donoughmore, Co. Cork
- Teagasc Agricultural College, Darrara, Clonakilty, Co. Cork
- Salesian Agricultural College, Pallaskenry, Co. Limerick
- Sacred Heart Missionaries' Farm, Carraig na bhFear, Co. Cork
- Teagasc Research Farm, Solohead, Co. Tipperary
- Teagasc Kilworth Research Farm, Moorepark, Co. Cork
- Ballinhassig, Co. Cork
Soil moisture content, temperatures and rainfall are continuously measured at all sites. Soil nitrous oxide fluxes are regularly measured at all sites using the closed chamber technique. In addition, soil nitrous oxide fluxes are continuously measured at Donoughmore using the tunable diode laser trace gas analyser system.
Met information from Donoughmore station
Due to connection failure no data were collected since 14:15 on 19 Jun
N2O gas flux measurements
These will be measured at all sites using the closed chamber technique. A portable enclosure is placed over a small area (approx. 1500 cm2) of soil for a period of up to one hour. During this incubation time, N2O emitted by the soil is trapped inside the chamber, causing the concentration of N2O to rise, relative to the concentration outside. A sample of air taken from inside the chamber is brought back to the laboratory. The N2O concentration is determined using a gas chromatograph.
N2O fluxes are also measured using the eddy covariance technique at the Dripsey site. Three-dimensional wind speeds and N2O concentrations are continuously measured at 10 Hz frequency and these measurements can be analysed to yield fluxes of N2O, representative of an area of approximately 1 km2.
Soil temperature, soil moisture content and rainfall, all important influences on N2O emissions, are continuously measured at all sites.
N2O flux measurements will be analysed in order to look for underlying relationships with:
- Meteorological parameters: soil temperature and moisture
- Management: amount and timing of fertiliser applications and timing of grazing
- Soil parameters such as organic carbon concentrations and nitrogen availability.
Computer models of soil biogeochemistry will be used to simulate and predict fluxes of N2O and other trace gases and transport of other nitrogen compounds such as nitrate (NO3-) in the soil. The model inputs are meteorological data, soils data and management information. Models such as DNDC and CENTURY have been used with some success to simulate soil N2O emissions in several parts of the world.
Empirical models may also be derived from experimental observations and may be of use as predictive tools for N2O fluxes.
Once computer simulations have been verified using the data collected during the measurement phase of the project, it is possible to use the models to examine different management and environmental scenarios and simulate their effects on N2O emissions.
Among the scenarios which will be considered are:
- Climate change: increased temperatures, increased atmospheric CO2 and N2O concentrations, and increased incidence of extreme, [high and low] precipitation values.
- Less intensive management, e.g. reduced grazing densities and schemes such as REPS (Rural Environment Protection Scheme) and set-aside.
- Distinguishing peaks from background emissions of nitrous oxide in grassland ecosystem M. Mishurov, European Geosciences Union General Assambly, Vienna, Austria, 13-18 April 2008. Mishurov leahy kiely Presentation 2007
- Interannual variability of N2O emissions from a grazed grassland, Leahy P. and G. Kiely, Proceeding of the conference "Greenhouse gas fluxes in terrestrial ecosystems in Ireland", Delgany, Co. Wicklow, Ireland, September, 2007.Micrometeorological observations of N2O uptake by fertilised grassland, Proceedings of the Open Science Conference on the GHG Cycle in the Northern Hemisphere, Sissi-Lathiki, Greece, November, 2006. Leahy Presentation 2007
- Flux-tower measurements of N2O flux from Irish grasslands, Mishurov, M., Leahy P. and G. Kiely, Proceeding of the conference "Greenhouse gas fluxes in terrestrial ecosystems in Ireland", Delgany, Co. Wicklow, Ireland, September, 2007. Mishurov leahy kiely Presentation 2007
- Nitrous oxide flux studies at multiply grassland sites, Jimmy Casey, Proceeding of the conference "Greenhouse gas fluxes in terrestrial ecosystems in Ireland", Delgany, Co. Wicklow, Ireland, September, 2007 CaseyPresentation2007
- Please see the Centre's publications page for details of previous publications by the group on nitrogen cycling and N2O fluxes.