减氮及硝化抑制剂对菜地氧化亚氮排放的影响

利用静态暗箱—气相色谱法,周年监测集约化菜地四种蔬菜种植过程中N2O的排放和蔬菜产量变化,探究减氮(640、960 kg hm-2 a-1)以及施用硝化抑制剂氯甲基吡啶(CP)对菜地N2O排放的影响。结果表明,与常规施氮(Nn)处理相比,减量施氮(Nr)在不显著降低产量的情况下平均降低菜地N2O排放27.1%;与仅施用尿素的处理相比,在减量和常规施氮水平的基础上添加硝化抑制剂又分别能降低菜地N2O排放总量29.4%、26.0%,降低N2O排放系数60.9%、42.4%,而对蔬菜产量没有显著影响,因此显著降低菜地单位产量N2O排放量32.1%、30.3%,以减氮结合CP(CP-Nr)处理减排效果最佳。因此,减氮结合CP应用于集约化蔬菜生产是一种有效的菜地减排农业措施。

Effects of N Reduction and Nitrification Inhibitor on N2O Emissions in Intensive Vegetable Field

Objective] A one-year-round field experiment,monitoring nitrous oxide (N2O) emissions during the growing seasons of four consecutive vegetable crops and yields of the crops,was conducted to investigate effects of reduced application of nitrogen (N) fertilizer and application of chlorinated pyridine (CP),a kind of nitrification inhibitor,on N2O emission and vegetable yield.Method] During the observation period from May,2015 to May,2016,four different species of vegetables were cultivated one by one,namely,amaranth,water spinach,cilantro and baby bok choy.The experiment was designed to have two treatments in N input i.e.640 and 960 kg hm-2 a-1,or a reduced N dose (Nr) and a normal N dose (Nn).Urea was applied as N fertilizer coupled with CP (CP-N) or without CP (N).Phosphate and potassium fertilizers were applied in the form of calcium/magnesium phosphate (12％ P2O5) and potassium chloride (60％ K2O) at a rate of 960 kg hm-2 a-1.All the fertilizers were evenly distributed among the four crops.Each treatment had three replicates.N2O fluxes were monitored with the static-closed chamber method and gas phase chromatography.Air samples were collected normally once a week and once every two or three days during the 7 ～ 10 days after the application of N fertilizer.Result] Results show that N2O flux varied significantly with the season in all the treatments,showing a trend of rising higher in the period from May to September and staying lower in the rest of the year.The N2O flux during the growing season of water spinach was the highest and reached N 6 426 μg m-2 h-1 soon after N fertilization,which could probably be attributed to the high temperature in the season.But no apparent peaks were observed during the growing seasons of cilantro and baby bok choy,when the highest N2O flux reached N 664.9 and 914.9 μg m-2 h-1 respectively.N2O flux was found significantly and positively related to soil water content and soil temperature (p ＜ 0.05) and to N fertilizer application rate too.In treatment Nr,CP-Nr,Nn and CP-Nn,N2O flux varied in the range of N 3.2 ～ 4 280,5.0 ～ 3 293,3.2 ～ 6 427 and 1.2 ～ 6 097 μg m-2 h-1,respectively.During all the four vegetable growing seasons,treatment Nr was always lower than treatment iNn in N2O flux.Compared with treatment Nn,treatment Nr could reduce cumulative N2O emission by 27.1％ on average without significantly affecting yield of the crops (p ＜ 0.05).In the treatments equal in N application rate,amendment of CP reduced cumulative N2O flux,which indicates that CP is capable of mitigating N2O emission in the vegetable field.During the year of the experiment,treatment Nn was found to be the highest in cumulative N2O emission,reaching up to N 59.2 ± 4.4 kg hm-2,while treatment CP-Nr the lowest,getting down to 31.2 ± 2.2 kg hm-2.Comparison between treatments equal in N application rate,CP amendment reduced total cumulative N2O emission by 29.4％ and 26.0％,N2O emission factor by 60.9％ and 42.4％,and yield-scaled N2O emission by 32.1％ and 30.3％,respectively,in treatment CP-Nn and CP-Nr,without significantly affecting crop yield.In the soil of the vegetable field,the content of NH4+-N and NO3--N varied in the range of 10.8 ～ 803.9 and 0.9 ～ 520.0 mg kg-1,respectively.The average NO3--N content in the soil of treatment Nr,CP-Nr,Nn and CP-Nn was 31.6,33.2,35.7 and 43.3 mg kg-1,respectively,and the average NH4+-N content,51.0,50.9,53.8 and 60.4 mg kg-1,respectively.Obviously,with rising N application rate,the content of inorganic N gradually increases in all the treatments.Conclusion] Taking into account cumulative N2O emission,N2O emission factor,yield and yield-scaled N2O emission,Treatment CP-Nr is capable of reducing N2O emission and getting high vegetable yields simultaneously.Hence,the practice of reducing N fertilizer application rate by one third coupled with CP amendment can be used as an effective vegetable field management measure in intensive vegetable production to mitigate N2O emission and maintain crop yield.