秸秆还田对冬小麦-夏玉米农田土壤固碳、氧化亚氮排放和全球增温潜势的影响

Effects of Stalk Incorporation on Soil Carbon Sequestration, Nitrous Oxide Emissions, and Global Warming Potential of a Winter Wheat-Summer Maize Field in Guanzhong Plain

旱地农田温室气体净排放(以全球增温潜势表示)主要取决于土壤固碳速率和氧化亚氮(N_(2)O)排放量.基于长期定位施肥试验,综合分析2010~2017年表层(0~20 cm)土壤有机碳含量和2014~2017年N_(2)O排放通量的观测结果,定量评价秸秆还田对关中平原冬小麦-夏玉米农田土壤固碳速率、N_(2)O年排放量和全球增温潜势的影响.田间试验设置传统施肥(CF)和传统施肥加玉米秸秆(CFS)处理及不施肥对照(CK).CF和CFS处理施入等量尿素,冬小麦季和夏玉米季施氮量分别为165 kg·hm^(-2)和188 kg·hm^(-2);CF处理在两季作物收获时均保留本小区地上约10 cm高根茬,CFS处理在冬小麦收获时保留相同根茬,而在玉米收获时保留全部秸秆(含氮量约40 kg·hm^(-2)).CK全年不施化肥,秸秆管理方式与CF处理一致.结果表明,CK土壤有机碳含量变化小、N_(2)O排放量低,其全球增温潜势变化范围为0.04~0.11 t·(hm^(2)·a)^(-1).CF和CFS处理土壤有机碳含量均随施肥年限呈线性增长(P<0.001),其固碳速率分别为0.69 t·(hm^(2)·a)^(-1)和0.97 t·(hm^(2)·a)^(-1);两处理N_(2)O排放量分别在1.65~5.36 kg·(hm^(2)·a)^(-1)和3.08~7.73 kg·(hm^(2)·a)^(-1)之间,CFS处理N_(2)O年排放量较CF处理偏高43%~94%,但仅在2015~2016年有显著性差异(P<0.05).CF和CFS处理全球增温潜势分别在-1.95~-0.28 t·(hm^(2)·a)^(-1)和-2.59~-0.35 t·(hm^(2)·a)^(-1)之间,CFS处理3 a累计全球增温潜势较CF处理偏低42%.本研究的冬小麦-夏玉米农田在传统施肥管理方式下已是温室气体的汇;尽管土壤固碳速率和N_(2)O排放量存在消长关系,但全量玉米秸秆还田仍然更有利于温室气体减排.

The net greenhouse gas emissions from upland soils,as indicated by global warming potential(GWP),mainly depend on the soil carbon sequestration and nitrous oxide(N_(2)O)emissions.The annual changes in surface(0-20 cm)soil organic carbon(SOC)content from 2010 to 2017 and the N_(2)O emissions from 2014 to 2017 were measured within a long-term fertilization experiment.The objective was to quantify the effect of stalk incorporation on the soil carbon sequestration,annual N_(2)O emissions,and GWP of a winter wheat-summer maize field in the Guanzhong Plain.The field experiment included three treatments:conventional fertilization(CF),conventional fertilization plus maize stalks(CFS),and an unfertilized control(CK).The CF and CFS treatments received the same amount of urea per year,with nitrogen(N)input at 165 kg·hm^(-2) and 188 kg·hm^(-2) in the winter wheat season and summer maize season,respectively.The CF treatment retained the stubbles(about 10 cm above ground)when harvesting the winter wheat and summer maize crops.The CFS treatment retained the same wheat stubbles and all maize stalks(containing approximately 40 kg·hm^(-2) of N).The CK treatment was unfertilized throughout the year,with the stubble management the same as that in the CF treatment.The results showed that the CK treatment displayed few changes in SOC content and low N_(2)O emissions,with GWP varying from 0.04 to 0.11 t·(hm^(2)·a)^(-1).The SOC contents in the CF and CFS treatments increased linearly with the fertilization years(P<0.001),and their SOC sequestration rates were 0.69 t·(hm^(2)·a)^(-1) and 0.97 t·(hm^(2)·a)^(-1),respectively.The N_(2)O emissions from the CF and CFS treatments varied from 1.65 to 5.36 kg·(hm^(2)·a)^(-1) and from 3.08 to 7.73 kg·(hm^(2)·a)^(-1),respectively.The annual N_(2)O emissions from the CFS treatment were 43%-94%higher than those from the CF treatment,whereas the difference was only significant between 2015 and 2016(P<0.05).The GWP of the CF and CFS treatments varied from-1.95 to-0.28 t·(hm^(2)·a)^(-1) and from-2.59 to-0.35 t·(hm^(2)·a)^(-1),respectively.The cumulative GWP of the CFS treatment was 42%lower than that of the CF treatment between 2014 and 2017.In summary,the studied winter wheat-summer maize field acted as a sink of greenhouse gases under the conventional fertilization regime.The stalk incorporation further favored greenhouse gas mitigation despite the trade-offs between SOC sequestration and N_(2)O emissions.