不同耕作措施下小麦-玉米轮作农田温室气体交换及其综合增温潜势

摘要

Studies on the emissions of greenhouse gases and global warming potential (GWP) under different tillage systems have benefited scientific research on the effects of agricultural management on mitigating greenhouse gas emission and reducing global warming. Such studies have also laid the theoretical basis for establishing measures to reduce global greenhouse gas emissions. Long term tillage and straw return to soil experiments were set up in 2001 at the Luancheng Agro-ecosystem Experimental Station (LAES) of Chinese Academy of Sciences. The experiments included 5 treatments — no-tillage with whole maize residue mulching (M1), no-tillage with chopped maize residue mulching (M2), rotary tillage with chopped maize residue incorporation (X), mouldboard ploughing with chopped maize residue incorporation (F) and mouldboard ploughing with maize residue remove (CK, representing conventional tillage method). The experiment monitored N2O, CO2 and CH4 fluxes in wheat-maize rotation fields using the static chamber method / gas chromatography technique for the period from October 2008 to September 2010. Total greenhouse gas emissions and GWP were also estimated. Meanwhile, during the experimental period, the amount of fuel consumed by farm machines and power consumed during irrigation and fertilizer application were recorded and transformed to carbon equivalent using a transformation coefficient. In the study, crop yield and aboveground biomasses were measured and carbon sequestration calculated. The total GWP under the 5 tillage treatments were estimated based on the identified parameters of greenhouse effect. The results indicated that wheat-maize rotation fields served as the source of N2O and CO2, and also the sink of CH4. In M1, M2, X, F and CK treatments, total N2O emissions from soil were 2.06 kg(N2O-N)·hm-2·a-1, 2.28 kg(N2O-N)·hm-2·a-1, 2.54 kg(N2O-N)·hm-2·a-1, 3.87 kg(N2O-N)·hm-2·a-1 and 2.29 kg(N2O-N)·hm-2·a-1; total CO2 emissions from soil of 6904 kg(CO2-C)·hm-2·a-1, 7351 kg(CO2-C)·hm-2·a-1, 8873 kg(CO2-C)·hm-2·a-1, 9065 kg(CO2-C)·hm-2·a-1 and 7425 kg(CO2-C)·hm-2·a-1; and total CH4 sink of 2.50 kg(CH4-C)·hm-2·a-1, 1.77 kg(CH4-C)·hm-2·a-1, 1.33 kg(CH4-C)·hm-2·a-1, 1.38 kg(CH4-C)·hm-2·a-1 and 1.57 kg(CH4-C)·hm-2·a-1, respectively. GWPs in M1 and M2 treatments were negative, which indicated that farmland ecosystems under no-tillage with straw served as carbon sink, with annual carbon retention of 947–1070 kg(C)·hm-2after subtracting directly or indirectly carbon equivalent emitted from the system. GWPs for other treatments were positive, with GWPs for CK, F and X of 3364 kg(C).hm-2, 989 kg(C).hm-2 and 343 kg(C).hm-2, respectively. This suggested that for wheat-maize rotation system in the North China, chopped crop residue incorporation with rotary tillage was optimal tillage practice with relatively lower greenhouse effects and higher grain yield.%研究不同耕作措施下小麦-玉米轮作农田N2O、CO2和CH4等温室气体的综合增温潜势,有助于科学评价农业管理措施在减少温室气体排放和减缓全球变暖方面的作用,为制定温室气体减排措施提供依据.基于2001年开始的位于华北太行山前平原中国科学院栾城农业生态系统试验站的不同耕作与秸秆还田方式定位试验,应用静态箱/气相色谱法于2008年10月冬小麦播种时开始,连续两个作物轮作年动态监测了秸秆整秸覆盖免耕播种(M1)、秸秆粉碎覆盖免耕(M2)、秸秆粉碎还田旋耕(X)、秸秆粉碎还田深翻耕(F)和无秸秆还田深翻耕(CK,代表传统耕作方式)5种情况下冬小麦-夏玉米轮作农田土壤N2O、CO2和CH4排放通量,并估算其排放总量.试验期间同步记录每项农事活动机械燃油量、灌溉耗电量、施肥量,依据燃油、耗电和单位肥料量的碳排放系数统一转换为等碳当量,测定作物产量、地上部生物量,估算农田碳截存量,根据每个分支项对温室效应的作用估算了5个处理的综合增温潜势.结果表明,华北小麦-玉米轮作农田土壤是N2O和CO2的排放源,是CH4的吸收汇,每年M1、M2、X、F和CK农田土壤N2O排放总量依次为2.06 kg(N2O-N)·hm-2、2.28 kg(N2O-N)·hm-2、2.54 kg(N2O-N)·hm-2、3.87 kg(N2O-N)·hm-2和2.29 kg(N2O-N)·hm-2,CO2排放总量依次为6904 kg(CO2-C)·hm-2、7351 kg(CO2-C)·hm-2、8873 kg(CO2-C)·hm-2、9065 kg(CO2-C)·hm-2和7425 kg(CO2-C)·hm-2,CH4吸收量依次为2.50 kg(CH4-C)·hm-2、1.77 kg(CH4-C)·hm-2、1.33 kg(CH4-C)·hm-2、1.38 kg(CH4-C)·hm-2和1.57 kg(CH4-C)·hm-2.M1和M2处理农田生态系统综合增温潜势(GWP)均为负值,表明免耕情况下农田生态系统为大气的碳汇,去除农事活动引起的直接或间接排放的等当量碳,每年农田生态系统净截留碳947~1070 kg(C)·hm-2;其他处理农田生态系统的GWP值均为正值,表明温室气体是由系统向大气排放,CK、F和X每年向大气分别排放等当量碳3364 kg(C)·hm-2、989 kg(C)·hm-2和343 kg(C)·hm-2.故华北小麦-玉米轮作体系中,秸秆粉碎还田旋耕是最优化的耕作措施,其温室效应相对较低,而又能保证较高的经济产量.