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GHG Platform - Nitrous Oxide Emissions Factors - AC0116

"Reductions in GHG are required from agriculture, in common with all other sectors, in order to meet the reduction targets set by the UK Climate Change Act 2008, as detailed in the Low Carbon Transition (LCT) Plan recently published by DECC. The current methodology for estimating nitrous oxide (N2O) emissions from UK agriculture estimates that emissions from soils account for more than 50% of GHG emissions from agriculture, with fertiliser N applications, grazing returns (urine) and manure applications to land being the predominant sources (c. 80% of total N2O emissions from UK agriculture). There is an urgent requirement to improve the national agricultural inventory for N2O emissions to better reflect management systems within the UK, to take account of the range of soil types and climate and future proof the inventory structure to take account of potential mitigation methods, thus enabling Defra to track N2O emissions against the LCT plan targets. This entails a move from what is essentially a Tier 1 structure (with some country specific activity data) to a Tier 2 structure using country specific emission factors (EFs)and improved activity data, and eventually towards a Tier 3 approach. Whilst project Defra AC0112 has been designed to improve the structure of the inventory along these aspirational lines, its scope is limited to generating Tier 2 EFs where possible using literature data and to disaggregating the inventory to regional scale and an annual time step. This project will build upon the desk based review of country specific EFs in project AC0112 by the generation of measured EFs for direct (and some indirect) emissions of N2O from N fertilisers, manures and grazing returns of both dung and urine from a range of soils, farming systems and climatic zones of the UK. Nine field sites, four tillage and five grassland, have been selected based on knowledge of recently completed and current projects where N2O measurements have been made from grass and tillage land uses, contrasting soil types and climatic situations. A prioritisation phase at the start of the project will assess in more detail if these sites are the most appropriate ones to cover the required range of soil and climate for each major land use. At the experimental field sites, N2O EFs will be measured from the following key N sources: N fertilisers, manures, and dung and urine deposition by grazing stock. In order to quantify effects of potential mitigation methods on N2O emissions for these N sources, additional aims will include quantifying the effect of fertiliser types, fertiliser timings, as well as the effects of urine and dung deposition timings on N2O EFs. Applications of fertiliser N in excess of crop requirement will lead to increased N2O emissions, particularly if applied under conditions conducive to elevated emissions i.e. ‘wet’ and warm soil conditions. 'Little and often' policies and the use of nitrification inhibitors to reduce N2O emissions will be studied. Limited studies have shown that the relationship between fertiliser N application rate and N2O emission is non-linear. More frequent applications of smaller amounts of fertiliser N in close synchrony with crop requirements would minimise soil mineral N levels at risk from elevated N2O losses at any point in time, including those when conditions are conducive to high N2O emissions. The measurements made as part of project AC0116 will provide essential data to generate a series of country specific EFs. This project will extend the number of sites (to Northern Ireland, Scotland and Wales) where the effect of nitrification inhibitors will be assessed, i.e. adding to the sites in planned project AC0213. The effect of slurry application techniques on N2O emissions will also be assessed to generate EFs for a future proofed inventory which may need to reflect methodologies aimed at reducing ammonia emissions from slurry spreading. Also, much needed emissions from solid manure applications will be made at most livestock manure experimental sites. Indirect N2O EFs associated with leached nitrate will be assessed from drainage/runoff and groundwater samples from the three Defra DTCs. The N2O concentrations in drainage and ground water from the three Defra DTCs will be quantified. The EFs derived from the experimental work will be used to generate Tier 2 country specific emission factors via project AC0114 and then incorporated into the improved N2O inventory model for UK agriculture (project AC0112). Models will be used to interpolate between missing data at the measurement sites and to assess the attribution of flux measurements to different drivers for defining Tier 2 EFs. Tier 2 EFs will also be estimated through modelling (e.g. soil, climate, region, crop, rotation, fertilizer specific) and we will quantify the confidence of (or uncertainty about) EFs. Spatial modelling (Tier 3 runs) will estimate N2O emissions for the whole of the UK. The project will also develop and assess the use of proxies which could be useful (to both policy makers and modellers) in assessing the impact of changes in agricultural practices and soil and climatic conditions on N2O emissions at national, regional, farm and field levels. 'Blind' modelling will be used to test the predictive capacity of the proxies identified. Although some mitigation will be tested experimentally, potential mitigation methods will also be assessed through modelling. Verification of measured and modelled emissions of N2O will occur at a range of temporal and spatial scales. We will assess potential uncertainty of using static chambers to address spatial and temporal variation in N2O emissions using fast-flux and automated chambers. Upscaling from emissions measured using chambers to the field scale will be assessed via comparison of static chambers and eddy covariance methodologies, whilst modelled emissions will be assessed seasonally through continued high resolution sampling at the field scale. Inverse modelling will be used to verify emissions at the regional and national scales. Through the combination of N2O emission measurements, verification and modelling, this project will provide Defra with a robust evidence base to underpin the improved N2O inventory at appropriate spatial and temporal scales."
Project Documents
• EVID4 - Final project report : Final Report AC0116: Improvements to the national agricultural inventory - Nitrous oxide   (2741k)
• ANX - Annex : AC0116 Appendix 1.1. Prioritisation Phase Appendix E Nitrous Oxide Protocols Report June 2011   (2558k)
• ANX - Annex : AC0116 Appendix 1.2. Joint Experimental Protocols for Fertilisers, Manures and Urine Dung   (1032k)
• ANX - Annex : AC0116 Appendix 2.1. Intercomparison of blind gas samples for N2O analysis   (85k)
• ANX - Annex : AC0116 Appendix 4.1. Site Sensitivity and Uncertainty Analysis   (3346k)
• ANX - Annex : AC0116 Appendix 4.2. Modelling with L-DNDC   (814k)
• ANX - Annex : AC0116 Appendix 4.3. Site Simulation of N2O fluxes using Daily DayCent   (3026k)
• ANX - Annex : AC0116 Appendix 4.4. Spatial Simulation of N2O Emissions from UK Crop and Grassland   (1410k)
• ANX - Annex : AC0116 Appendix 6.1. Automatic monitoring of urination events from grazing cattle   (832k)
Time-Scale and Cost
From: 2010

To: 2015

Cost: £6,689,724
Contractor / Funded Organisations
University - Scottish Agricultural College, University - Aberdeen, North Wyke Research, Centre for Ecology and Hydrology, University - East Anglia, Agri-Food and Biosciences Institute, ADAS UK Ltd.