Abstract:

【Objective】Nitric oxide (NO) is not only a crucial precursor for tropospheric ozone formation but also participates in acid rain formation and nitrogen deposition processes, posing a severe threat to ecological security. Agriculture is a key anthropogenic source of NO. Given China’s substantial nitrogen fertilizer consumption, NO emissions from its agricultural soils warrant attention. Addressing the high uncertainty associated with current estimations that rely on global default emission factors (EFs) or a single national EF, this study aims to construct a localized EF dataset reflecting the characteristics of China's geographical regions, crops, and fertilizer types. Furthermore, it seeks to calculate the 2021 NO emission inventory for Chinese cropland soils and assess mitigation potentials, thereby providing a scientific basis for green agricultural development.【Method】This study systematically retrieved 54 field in-situ observation papers from the CNKI and Web of Science databases, extracting 440 pairs of full-growth period data. Three EF calculation methods—Maximum Likelihood Estimation (M1), Linear Regression With Intercept (M2), and Linear Regression Without Intercept (M3)—were compared. Adopting a “70% calculation+30% independent validation” mode, the optimal algorithm was screened to calculate localized EFs for China. By combining statistical data on crop planting areas and nitrogen application rates across provinces in 2021, the NO emission inventory for Chinese croplands was calculated, and uncertainty was quantified using the error propagation method. Finally, optimized management scenarios, such as fertilizer reduction and organic substitution, were established to predict NO mitigation potential.【Result】Independent validation results indicated that the M1 method yielded the highest prediction accuracy (R²=0.56). The calculated localized EFs demonstrated significant differences across crops and fertilization practices. Under sole synthetic fertilizer application, tea plantations exhibited the highest EF (1.91%), while rice paddies had the lowest (0.27%). Combined application of organic and inorganic fertilizers generally resulted in lower EFs compared to sole synthetic fertilizer application. Spatially, EFs presented a pattern of being higher in the southeast and lower in the northwest. It was estimated that the total NO emissions induced by nitrogen fertilizer application in Chinese croplands in 2021 were 150 kt NO-N, with an uncertainty of 9.1%. Regarding crop contribution, grain crops were the primary emission source, accounting for 49.9% of the total emissions. Among them, maize contributed the most (31.8 kt NO-N) due to its large planting area and high nitrogen application rates. Despite their smaller planting areas, tea plantations and sugarcane exhibited high emission intensities per unit area due to intensive nitrogen inputs, reaching 7.02 kg NO-N·hm^-2 and 2.55 kg NO-N·hm^-2, respectively. Regionally, East China contributed 40.9% of the total NO emissions from cereal crops nationwide (30.6 kt NO-N). Scenario analysis indicated significant mitigation potential for NO emissions from Chinese agricultural soils. Through the implementation of scientific nitrogen reduction and the promotion of organic fertilizer substitution technologies, the national NO mitigation potential could reach 24%, equivalent to an annual reduction of 36 kt NO-N. East, North, and Northeast China together accounted for 78.9% of the national mitigation potential from cereal crops.【Conclusion】By constructing a localized emission factor (EF) dataset based on field measurements, this study controlled the uncertainty of NO emission estimates from Chinese cropland soils to within 9.1%. However, due to the scarcity of field measurement data in regions such as Northeast and Northwest China, there remains some uncertainty in regional estimates. This study clarified the significant spatial heterogeneity and crop specificity of NO emissions from Chinese agricultural soils, identifying East China and high-nitrogen-input cash crops as priority areas for future NO mitigation and control. The findings confirm that optimizing chemical fertilizer application rates and implementing organic fertilizer substitution are effective pathways for reducing agricultural soil NO emissions. These results provide scientific support for formulating differentiated, region- and crop-specific agricultural nitrogen management policies and air pollution control measures.

Key words: NO emissions, emission factor, nitrogen fertilizer, soil, nitrogen management, environmental risk