IPCC Emission Factor Overestimates N<sub>2</sub>O Emissions from Agricultural Ditches
Wenxin Wu, Sophie Comer‐Warner, Mike Peacock, Xingxing Han, Si‐Liang Li, Xiaotang Ju, Cong‐Qiang Liu, Pete Smith, Zhifeng Yan
Abstract
Agricultural ditches emit disproportionate amounts of nitrous oxide (N 2 O), but their contributions to regional or global N 2 O emissions remain unclear due to limited data. The Intergovernmental Panel on Climate Change (IPCC) recommends using emission factors (EFs) to estimate indirect N 2 O emission, but the EF for ditches (EF 5g ) is categorized as groundwater, which potentially introduces a significant bias. This study conducted a regional-scale campaign in the North China Plain, one of the world’s most intensive agricultural regions, and calculated the EF 5g values from agricultural ditches by the concentration method (N 2 O–N/NO 3 – –N). The results found that the regional-scale mean EF 5g value (0.0028) was less than half of the IPCC default value (0.006), illustrating that the current IPCC methodology significantly overestimates N 2 O emissions from agricultural ditches. Despite the relatively small EF 5g values, agricultural ditches exhibited a high mean N 2 O concentration (3.36 μg L –1 ) and a large regional emission (1.14 ± 0.86 Gg N 2 O–N yr –1 ), which is equal to 3.8 ± 2.9% of direct N 2 O emission from the croplands in the North China Plain. Since ditches are ubiquitous in agricultural regions and are likely to expand under climate change, refining EF 5g is crucial to accurately assess their contribution to global N 2 O budgets.