减氮和施生物炭对华北夏玉米-冬小麦田土壤CO_2和N_2O排放的影响

Effects of Reducing Nitrogen and Biochar Application on CO_2 and N_2O Emissions from Summer Maize-Winter Wheat Field in North China

2013年6月-2014年6月,在河南省新乡夏玉米-冬小麦试验田设置四种处理即农民常规施肥(F处理,250kg·hm^(-2))、减氮20%(LF处理,200kg·hm^(-2))、减氮20%+黑炭(LFC),以不施肥处理为对照(CK),采用静态箱-气相色谱法,对夏玉米-冬小麦生长季土壤CO_2和N_2O排放通量动态进行测定。结果表明:(1)夏玉米-冬小麦田的土壤CO_2排放通量为21.8~1022.7mg·m^(-2)·h^(-1),土壤CO_2排放通量主要受土壤温度和水分的影响,在夏玉米季受土壤水分的影响更为显著,而在冬小麦季则为5cm土层处的温度对其影响更为突出。减施氮肥20%处理和减氮加生物黑炭共同作用使土壤CO_2累积排放量显著降低,小麦生长季的减排作用尤为显著。(2)施肥和灌溉是影响土壤N_2O排放的最主要因素,施肥期间N_2O排放量分别占夏玉米季和冬小麦季累积排放量的73.9%~74.5%和40.5%~43.6%;施肥量主要影响排放峰的强度,灌溉主要影响排放峰出现时间的早晚且会影响不同措施的减排效果。在每季作物250kg·hm^(-2)施氮水平下减施氮肥20%使夏玉米季和冬小麦季的N_2O累积排放量分别降低15.7%~16.8%和18.1%~18.5%,是高产集约化农田减排N_2O的有效措施。在适宜施氮水平(200kg·hm^(-2))下施用生物黑炭,短期内对土壤N_2O排放无显著影响。(3)夏玉米-冬小麦田农民常规施肥水平的N_2O排放系数为0.60%,减氮施肥的N_2O排放系数为0.56%。在华北平原高产集约化农田适当减氮施肥不仅能降低农田土壤温室气体排放,且对作物产量无影响,是适宜的温室气体减排措施。

This experiment was conducted in Xinxiang, Henan province from June 2013 to June 2014. Four treatments were designed including farmers common practice（F, 250kg·ha^（-1））,80% F（LF, 200kg·ha^（-1））,80% F ＋ biochar（LFC） and no fertilizer（CK） to measure the dynamic emissions of CO_2 and N_2 O from a summer maize-winter wheat field using static chamber and gas chromatography method. The results indicated that,（1）soil CO_2 emission was 21.8-1022.7mg·m^（-2）·h^（-1） for this agriculture system and was significantly influenced by soil temperature and moisture. Soil moisture was more important for the N_2 O emissions during the summer maize growth period while N_2 O emissions during winter wheat growth period was more significantly influenced by the soil temperature. The cumulative CO_2 emissions under LF and LFC treatments were significantly lower than F treatment especially during the winter wheat growing season.（2）Soil N_2 O emission was significantly influenced by fertilizer application and irrigation. N_2 O emissions during the fertilization period accounted for 73.9%-74.5% and 40.5%-43.6% of cumulative N_2 O emissions in summer maize and winter maize growing season, respectively. The peak of emission fluxes was primarily affected by fertilizer rate while irrigation determined the occurrence time when emissions would peak and could affect the mitigation effect of practices. Reduce the nitrogen application rate to 200kg·ha^（-1） from 250kg·ha^（-1） could decrease cumulative N_2 O emissions by 15.7%-16.8% and 18.1%-18.5% during summer maize and winter wheat growing seasons, respectively, therefore decreasing nitrogen application is an effective N_2 O mitigation practice for high-yielding and intensive farmland. Biochar application did not show no significant influence on soil N_2 O mitigation of biochar application at suitable nitrogen level（200kg·ha^（-1）） in the short term.（3）N_2O emission factors of applied nitrogen were 0.60% and 0.56% for F and LF treatment, respectively, indicating that reducing the nitrogen application rate is an appropriate measure to mitigate greenhouse gas emissions without impact on crop yields in intensive farmlands in North China.