Development and application of a mechanistic model to estimate emission of nitrous oxide from UK agriculture
Introduction
Signatory states to the United Nations Framework on Climate Change (UNFCC) are required to produce an annual national inventory of nitrous oxide (N2O) emission from all anthropogenic sources. This inventory is intended to advise the magnitude and change in total emissions and gives an indication of which sectors of activity are responsible for the greatest emissions. Estimates of the contribution of agriculture to the total UK emission have indicated an increase over recent years as industrial sources (particularly adipic and nitric acid manufacture) have declined (Salway et al., 2001). Salway et al. (1999) estimated that in 1990 47% of the total UK emission was from agriculture (63.9 Gg N2O-N). In order to comply with the Kyoto Protocol on greenhouse gas emissions, 1990 levels of N2O emission from EU countries are required to be reduced by 8% in the period 2008–2012. Mitigation strategies require an agreed inventory against which measures to reduce N2O emissions from agricultural sources can be judged.
The framework that is used currently to estimate sources of N2O from UK agriculture is that produced by the Intergovernmental Panel on Climate Change (IPCC, 1997). This approach utilises emission factors (EFs) which specify the proportion of N input that is emitted as N2O, and are used with activity data (such as animal numbers, fertiliser use and crop areas) to calculate emission. These EFs are derived from field measurements at sites in a variety of countries, with different soil types, climate and crops (IPCC, 1997). Default EF values are provided, but each has a large range, which reflects the contrasting background conditions of the measurements and leads to a large uncertainty in the emission estimate (Brown et al., 2000). An approach is required which assigns some of this variation to its controlling variables by producing an estimate that takes into account factors such as soil, climate and fertiliser type. Possible approaches include the development and application of more detailed empirical relationships, which would account for such factors, or the use of a suitable mechanistic model to estimate emissions. This study used the rainfall-driven process-based model called DNDC (DeNitrification-DeComposition) (Li et al., 1992), originally written for USA conditions, to provide the basis for an improved UK N2O emission estimate. The development of this model for the UK, and the estimates of N2O emissions from agricultural land for 1990 derived from it, are discussed in this paper.
Section snippets
Model description
The DNDC model (Li et al., 1992) was selected to produce an annual UK emission estimate because it has reasonable data requirements, has produced robust estimates for other countries and is suitable for simulation at appropriate temporal and spatial scales for this exercise. DNDC is a process-oriented simulation model of C and N biogeochemistry in agricultural ecosystems, developed to assess nitrous oxide (N2O), nitric oxide (NO), dinitrogen (N2), ammonia (NH3) and carbon dioxide (CO2)
UK-DNDC-based estimates of N2O emission
The total N2O-N emission from UK current agricultural practice in 1990 was estimated to be 50.9 Gg, comprising 31.7 Gg from soil, 5.9 Gg from animals (this does not include emission from N deposited while grazing or from applied slurry and FYM, which are included in the soil sector) and 13.2 Gg from the indirect sector (Table 1). Of the emission from soil in the UK, 77% was attributed to fertiliser, 17% from applied animal waste and 5% due to emission from N deposited while grazing. The large
Comparison with IPCC estimate
The total emission estimate from current agricultural practice using UK-DNDC (50.9 Gg N2O-N) was smaller than the emission estimate of 87 Gg N2O-N obtained using the IPCC (1997) methodology with default values (Brown et al., 2000) (hereafter referred to as the IPCC (1997) methodology), and the 63.9 Gg N2O-N estimated by Salway et al. (1999). In the soil sector, emission from fertiliser represented a larger proportion and amount of the soil total than was predicted by the IPCC (1997) methodology.
Conclusions
- 1.
Development and application of DNDC (Li et al., 1992) to the UK produced a model capable of simulating the application of and N2O emission from both fertiliser and different forms of animal manures in agricultural land in the UK.
- 2.
This attempt to provide a national inventory of N2O emission based on the UK-DNDC model has a number of advantages over an IPCC-type approach. The greater detail of its calculations allows the effect of contrasting soils, crops, climates and farming practices to be
Acknowledgements
This work was funded by MAFF, London (Project No. OC9601). IGER, SRI and IACR are supported by BBSRC. We are grateful to Mark Rounsevell (now University of Leuven) for his part in initiation of the project. Input data were supplied by Crawford Jordan, John Wallace and Joe O’Reilly (DARDNI), Jim Gauld (MLURI), the British Atmospheric Data Centre, Ken Smith (ADAS), Clive Rahn (HRI), Brian Coulter (Teagasc), Keith Weatherhead (Cranfield University) and Ken Stewart (OSNI). Data for model validation
References (46)
- et al.
A UK inventory of nitrous oxide emissions from farmed livestock
Atmospheric Environment
(1999) - et al.
The influence of the first wave of colonising insects on cattle dung dispersal
Pedobiologia
(1995) - et al.
Carbon in the vegetation and soils of Great Britain
Journal of Environmental Management
(1997) - et al.
Ammonia emission factors for UK agriculture
Atmospheric Environment
(2000) - et al.
Nitrogen excretion by farm livestock with respect to land spreading requirements and controlling nitrogen losses to ground and surface waters. Part 1cattle and sheep
Bioresource Technology
(2000) - et al.
Nitrogen excretion by farm livestock with respect to land spreading requirements and controlling nitrogen losses to ground and surface waters. Part 2pigs and poultry
Bioresource Technology
(2000) - et al.
Nitrous oxide emissions from excreta applied in a simulated grazing pattern
Soil Biology and Biochemistry
(1998) Water retention properties of organic soils and the problems associated with laboratory measurements
(1986)- et al.
An inventory of nitrous oxide emissions from agriculture in the UK using the IPCC methodologyemission estimate, uncertainty and sensitivity analysis
Atmospheric Environment
(2000) - et al.
Hydrology of soil typesa hydrologically based classification of the soils of the United Kingdom. Report No. 126
(1995)