不同耕作方法和施氮量对旱作农田土壤CO2排放及碳平衡的影响

全膜双垄沟播技术是近年来黄土高原旱作玉米主要的生产技术之一，其采用的耕作方法包括深松耕、免耕、旋耕和翻耕，因此，研究不同耕作方法下旱作玉米农田土壤CO₂排放特征对农田生态系统固碳减排的综合评价和管理措施的选择具有一定的重要意义。本研究采用田间定位试验，研究4种耕作方式（深松耕、免耕、旋耕和翻耕）结合两种传统施氮量（300和200 kg·hm^-2）处理下旱作玉米农田土壤CO₂的排放规律及碳平衡。结果表明，土壤CO₂日排放速率最大值和最小值分别出现在12：00-14：00和4：00-6：00，趋势与大气温度变化一致；生育期内各处理土壤CO₂排放速率均随生育进程呈先增后降的变化趋势，各处理波动规律基本一致，峰值出现在拔节期、大喇叭期与花期交替期，谷值出现在成熟期，翻耕措施下土壤碳排放总量和作物碳排放效率均显著高于其他耕作方式（P<0.05），其他耕作方式间差异不显著（P>0.05）；施肥量为300 kg·hm^-2时土壤CO₂排放总量显著高于200 kg·hm^-2（P<0.05）；农田净生态系统生产力、固碳潜力在耕作方式间差异显著，深松耕处理显著高于其他处理（P<0.05），施氮量间差异不显著（P>0.05）。综上，从固碳减排的角度，深松耕措施和传统施氮量（200 kg·hm^-2）相结合是黄土高原旱区玉米较好的管理模式。

Effects of different tillage practices and nitrogen application rate on carbon dioxide emissions and carbon balance in rain-fed maize crops

Full-film double furrow sowing technology is one of the main production technologies of dryland maize on the Loess Plateau in recent years. Study of the influence of different tillage methods on soil CO₂ emission from dryland maize farmland is highly relevant to understanding of carbon cycling， reducing emissions， and selection of appropriate management measures in farmland systems. This research evaluated the CO₂ emission and carbon balance of dryland maize farmland under four tillage methods （subsoiling， no-tillage， rotary tillage and ploughing）. combined with two commonly used nitrogen application rates （200 and 300 kg·ha^-1） in field experiments. It was found that the variation in soil CO₂ emission rate reflected variation in atmospheric temperature. The maximum and minimum values occurred around 12：00-14：00 and 4：00-6：00， respectively. The soil CO₂ emission rate during the growth period showed a trend of initial increase and then decrease with increasing plant maturity. The pattern of variation in each treatment with time was basically the same. The peak soil CO₂ emission rate appeared in the stem elongation， head emergence and flowering periods， and then decreased to the lowest rate in the ripening period. The total carbon emission and carbon emission efficiency over the entire growth period were significantly higher in the ploughing treatment than other treatments （P<0.05）， and there were no significant differences （P>0.05） between the other tillage methods. The total soil CO₂ emission at a fertilizer application rate of 300 kg·ha^-1 was significantly higher than 200 kg·ha^-1 （P<0.05）. The net ecosystem productivity and carbon sequestration potential of the maize field cropping system were significantly higher under subsoiling than other treatments （P<0.05）， but the two nitrogen rates did not differ significantly （P>0.05）. In conclusion， based on these results， the combination of subsoiling and the traditional nitrogen application rate （200 kg N·ha^-1） is the preferred management mode for maize in the Loess Plateau arid region， from the perspective of carbon sequestration and emission reduction.