Differences in soil N₂O emission coefficients of different land use types in red soil hilly areas in southern China

【Objective】 To clarify the differences in soil N₂O emission coefficients of different land use methods and assess regional N₂O emissions, to provide basic data and basis for evaluating the N₂O emission inventory of red soil hilly areas in southern China.【Method】 This paper selected four common land use methods(Camellia oleifera forest, dry farmland, rice field and pine forest) in the red soil hilly region of southern China, and calculated the emission coefficient by analyzing the difference in the N₂O emission rate and amount when the soil was not fertilized and when nitrogen was applied, and ¹⁵N isotope was used. The labeling method explored the relative contribution of nitrification and denitrification to soil N₂O emissions.【Result】 There weregreat differences in soil physical and chemical properties among different land use methods, and the total nitrogen content of paddy fields was the highest(2.22 g/kg), which was significantly higher than others(P<0.05, the same below). When the soil was not fertilized, the N₂O emission rate was 0-227.80 μg/ (kg·h), and when the nitrogen application rate was 200 kg·N/ha, the N₂O emission rate was 0-4213.27 μg/ (kg·h). The soil N₂O emission coefficients of the four land use methods all increased with the increase of water content of soil porosity(WPFS). When the WPFS was 75%, the soil N₂O emission coefficients of paddy field, dry farmland, C. oleifera forest and pine forest were 2.47%, 0.39%, 2.31%, 0.91%, respectively. The N₂O emission coefficients of the four land use methods were mainly affected by total nitrogen content, and accumulated N₂O emissions were significantly positively related with potential denitrification potential, except paddy fields, N₂O cumulative emission of the other three land use methods was significantly positively related with potential nitrification potential. The relative contribution of denitrification with NO₃^--N as the substrate to N₂O emissions was more than 90% on average, which was much higher than nitrification.【Conclusion】 In red soil hilly areas in southern China, the denitrification with NO₃^--N as the substrate dominates N₂O emission. The application of amino nitrogen fertilizer may effectively reduce the loss of nitrogen fertilizer N₂O emission and provide technical support for the national implementation of carbon neutral policy.