外源硝态氮对典型耕作土壤冻结过程N2O排放的影响

为明确外源硝态氮添加对典型耕作土壤冻结过程N₂O排放的影响,应用室内冰柜模拟土壤冻结过程,研究在室温-冻结过程中硝态氮添加(0、80、200和500 mg/kg)对3种典型耕作土壤(黑土、潮土和黄土)N₂O排放影响的特征. 结果表明:外源硝态氮的添加促进了黑土和潮土的N₂O排放,在200 mg/kg硝态氮添加处理下,黑土和潮土的N₂O排放通量比CK(对照)分别增加了849%和676%；但在添加高浓度(500 mg/kg)硝态氮时,黑土和潮土的N₂O排放通量分别比200 mg/kg处理降低39.3%和21.2%,表现为显著抑制. 随冻结过程的进行,黑土和潮土的N₂O排放通量均逐渐降低并接近零排放. 黄土N₂O排放通量在室温-冻结过程中变化范围很小,甚至出现负排放. 多因素方差分析结果表明,土壤类型显著影响N₂O累计排放量,而土壤pH和C/N是其中重要的影响因子. 根据室内培养试验结果,为减排N₂O,建议在深秋整地施肥时期尽量避免在潮土和黑土中施用硝态氮肥. 黄土的N₂O排放似乎对外源硝态氮的添加反应不明显,这有待在大田气候-植物-土壤综合条件下进一步验证. 

Effects of Nitrate Nitrogen Application on N2O Emissions from Three Types of Soil during Freezing Process

To understand the influence of nitrate nitrogen (NO₃--N) application on N₂O emissions from different soil types during the freezing process, a lab-simulated experiment was conducted to investigate N₂O production from black, fluvo-aquic and loess soils receiving different concentrations of NO₃--N:control (0), 80,0 and 500 mg/kg soil. The application of NO₃--N significantly increased N₂O emissions from the black and fluvo-aquic soils (P<0.05). Compared to the control treatment, the application of NO₃--N with 200 mg/kg soil increased N₂O emissions from the black and fluvo-aquic soils by 849% and 676%, respectively. However, N₂O emissions from the 500 mg/kg NO₃--N treatment soil were reduced by 39.3% and 21.2% compared to 200 mg/kg NO₃--N treatment soil in the black and fluvo-aquic soils, respectively. As the freezing proceeded, the N₂O fluxes from the black and fluvo-aquic soils gradually approached zero. Although there was no significant N₂O flux found from the loess soil, N₂O uptake occurred frequently in the soil. Multi-factor variance analysis showed that soil pH and soil C-to-N ratio were the most important factors driving N₂O emissions. The results implied that management strategies aiming to mitigate N₂O emissions from soil should avoid NO₃--N fertilizer application in black and fluvo-aquic soils during late autumn fertilization. Further studies to investigate the comprehensive relationship between N₂O emissions and variable field conditions involving climate, plants and soil conditions would be useful to expand this research.