Abstract
The United Kingdom currently reports nitrous oxide emissions from agriculture using the IPCC default Tier 1 methodology. However Tier 1 estimates have a large degree of uncertainty as they do not account for spatial variations in emissions. Therefore biogeochemical models such as DailyDayCent (DDC) are increasingly being used to provide a spatially disaggregated assessment of annual emissions. Prior to use, an assessment of the ability of the model to predict annual emissions should be undertaken, coupled with an analysis of how model inputs influence model outputs, and whether the modelled estimates are more robust that those derived from the Tier 1 methodology. The aims of the study were (a) to evaluate if the DailyDayCent model can accurately estimate annual N2O emissions across nine different experimental sites, (b) to examine its sensitivity to different soil and climate inputs across a number of experimental sites and (c) to examine the influence of uncertainty in the measured inputs on modelled N2O emissions. DailyDayCent performed well across the range of cropland and grassland sites, particularly for fertilized fields indicating that it is robust for UK conditions. The sensitivity of the model varied across the sites and also between fertilizer/manure treatments. Overall our results showed that there was a stronger correlation between the sensitivity of N2O emissions to changes in soil pH and clay content than the remaining input parameters used in this study. The lower the initial site values for soil pH and clay content, the more sensitive DDC was to changes from their initial value. When we compared modelled estimates with Tier 1 estimates for each site, we found that DailyDayCent provided a more accurate representation of the rate of annual emissions.
Highlights
Despite its relatively low atmospheric concentration, nitrous oxide (N2O) is an extremely important greenhouse gas (GHG) with a global warming potential of nearly 300 times that of CO2
DailyDayCent was able to provide a good estimate of annual emissions of N2O and a reasonable estimate of crop yields across the six cropland experimental sites
While data limitation and model processes can lead to uncertainty in our outputs in terms of overall performance, DDC performed well across a range of cropland and grassland sites, for fertilized fields, indicating that it is robust for UK conditions
Summary
Despite its relatively low atmospheric concentration, nitrous oxide (N2O) is an extremely important greenhouse gas (GHG) with a global warming potential of nearly 300 times that of CO2. For N2O emissions from soils, Tier 1 default reporting assumes that between 0.3 and 3% of any synthetic N applied to the soil is re-released as N2O–N (IPCC 2006) This methodology tends to produce a relatively large uncertainty of total emissions as it does not a) account for spatial variations in emissions, or b) allow for the inclusion of mitigation options other than those affecting total N application (Abdalla et al 2010, Saggar et al 2007). Process-based models such as DailyDayCent (DDC) have been considered for simulating GHG emissions across a range of different ecosystems and climate zones Use of these models aim to improve inventory reporting to Tier 2 or 3 levels, which could potentially reduce the uncertainty in total emissions, and adequately reflect N2O emission reduction through nitrogen management
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