Towards a UK Smart Greenhouse Gas Inventory for Agriculture
Dave Chadwick, Tom Misselbrook and Bob Rees.
In 2010, the UK Government and the Devolved administrations of Northern Ireland, Scotland and Wales initiated a programme of research that would deliver new country specific emission factors for nitrous oxide (N2O) and the associated activity data to generate a smarter greenhouse gas inventory that better reflected the soils, climate, nutrient management and ruminant systems of the UK.
The InveN2Ory project (AC0116) generated data to contribute to country specific N2O emission factors, filling knowledge gaps for the combinations of soil, nutrient source and climate. UK research groups (ADAS, AFBI, CEH, Rothamsted Research, and SRUC) conducted 37 (365 day) replicated plot-scale field experiments, following common experimental protocols for treatment applications, N2O static chamber deployment and soil, crop and gas sampling and analysis (Fig. 1; Chadwick et al. 2014).
Figure 1 Chamber measurements at an arable site in the East of Scotland
In parallel with the InveN2Ory project, a methane (CH4) project (AC0115) determined ruminant CH4 emissions from commonly used dairy, beef and sheep breeds and from typical diets, using a combination of calorimeter, SF6 and CH4 laser-based approaches, and a Synthesis project (AC0114) was responsible for integrating existing and new GHG emissions and mitigation data with agriculture statistics activity data to ‘drive’ the smart GHG inventory, and develop a robust structure for the smart GHG inventory for reporting and tracking change. All three projects contributed to a programme of work known as the UK’s GHG Platform programme.
Data from the InveN2Ory project was combined with existing (IPCC compliant) emission factor data from other studies and analysed statistically to generate the new country specific N2O EFs for: EF1 ammonium nitrate and urea fertilisers applied to grassland and arable land, EF3PRP urine and dung deposited by grazing livestock to grassland, and EF1 different manure types applied to crops. The resulting UK country specific N2O EFs from most of these N sources are less than those reported in the IPCC 2006 Guidelines, and some of the UKs new EFs, e.g. the EF3PRP, have contributed to the 2019 revisions of the IPCC 2006 Guidelines (Hergoualc’h et al. 2019; IPCC 2006) . Papers have been published synthesising the N2O EFs from the different N sources from the 37 plot-scale experiments (Bell et al. 2015; Cardenas et al. 2019; Chadwick et al. 2018; Thorman et al. 2020), and these data are publicly available from the UK’s AEDA data archive (http://www.environmentdata.org/).
The new analysis demonstrates a non-linear relationship between fertiliser N application rate and rainfall as predictors of N2O emissions (Fig. 2). This has allowed the new smart inventory to report spatially disaggregated emissions across the UK that reflect the rate and form of N applied and the long term average rainfall.
As a result of the UK GHG Platform projects, the UK now has an inventory for greenhouse gases that better reflects the UK farming systems, soils and climate. The new N2O EFs have resulted in a reduced contribution of this gas to the total CO2e emission from UK agriculture.
Figure 2 The response of the N2O emission factor (EF1) to changing rates of fertiliser N and rainfall as represented in the UK’s smart inventory (Kmietowicz & Thillainathan 2018).
Funding for this work was received from the UK Government Department for the Environment, Farming and Rural Affairs and from the Scottish and Welsh Governments, and the Department of Agriculture and Rural Development in Northern Ireland
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