Improved accuracy and reduced uncertainty in greenhouse gas inventories by refining the IPCC emission factor for direct N2O emissions from nitrogen inputs to managed soils
2021
Hergoualc’h, Kristell | Mueller, Nathan | Bernoux, Martial | Kasimir, Äsa | Van der Weerden, T. J. (Tony J.) | Ogle, Stephen M.
Most national GHG inventories estimating direct N₂O emissions from managed soils rely on a default Tier 1 emission factor (EF₁) amounting to 1% of nitrogen inputs. Recent research has, however, demonstrated the potential for refining the EF₁ considering variables that are readily available at national scales. Building on existing reviews, we produced a large dataset (n = 848) enriched in dry and low latitude tropical climate observations as compared to former global efforts and disaggregated the EF₁ according to most meaningful controlling factors. Using spatially explicit N fertilizer and manure inputs, we also investigated the implications of using the EF₁ developed as part of this research and adopted by the 2019 IPCC refinement report. Our results demonstrated that climate is a major driver of emission, with an EF₁ three times higher in wet climates (0.014, 95% CI 0.011–0.017) than in dry climates (0.005, 95% CI 0.000–0.011). Likewise, the form of the fertilizer markedly modulated the EF₁ in wet climates, where the EF₁ for synthetic and mixed forms (0.016, 95% CI 0.013–0.019) was also almost three times larger than the EF₁ for organic forms (0.006; 95% CI 0.001–0.011). Other factors such as land cover and soil texture, C content, and pH were also important regulators of the EF₁. The uncertainty associated with the disaggregated EF₁ was considerably reduced as compared to the range in the 2006 IPCC guidelines. Compared to estimates from the 2006 IPCC EF₁, emissions based on the 2019 IPCC EF₁ range from 15% to 46% lower in countries dominated by dry climates to 7%–37% higher in countries with wet climates and high synthetic N fertilizer consumption. The adoption of the 2019 IPCC EF₁ will allow parties to improve the accuracy of emissions’ inventories and to better target areas for implementing mitigation strategies.
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