春玉米-晚稻与早稻-晚稻种植模式碳足迹比较

量化作物生产的碳足迹有助于为农业生态系统温室气体减排提供理论依据。利用生命周期法研究了我国南方地区稻田春玉米-晚稻水旱轮作种植模式和早稻-晚稻连作种植模式下粮食生产的碳足迹，并定量分析粮食生产过程中各种碳排放源的相对贡献。结果表明，与早稻-晚稻的连作模式相比，春玉米-晚稻轮作模式的单位面积碳排放降低了6724 kg CO₂-eq/hm²，单位产量的碳足迹降低了0.56 kg CO₂-eq/kg。春玉米比早稻少排放6228 kg CO₂-eq/hm²；与早稻-晚稻模式中晚稻碳排放相比，春玉米-晚稻轮作模式晚稻碳排放降低了497 kg CO₂-eq/hm²。早稻-晚稻种植模式的碳足迹主要来源于甲烷（CH₄），其碳排放为9776 kg CO₂-eq/hm²（54.8%），氮肥生产和施用的碳排放为2871 kg CO₂-eq/hm²（16.1%），灌溉电力消耗的碳排放2849 kg CO₂-eq/hm²（16.0%）。春玉米-晚稻轮作模式的碳足迹主要来源于CH₄的碳排放4442 kg CO₂-eq/hm²（39.9%），氮肥生产和施用的碳排放2871 kg CO₂-eq/hm²（25.8%），灌溉电力消耗的碳排放1508 kg CO₂-eq/hm²（13.6%）。该模式中晚稻的碳足迹组成情况与春玉米-晚稻模式的碳足迹相似。但是，对于春玉米而言，其碳足迹主要来源氮肥生产和施用的碳排放1436 CO₂-eq/hm²（50.1%），氧化亚氮（N₂O）的碳排放为579 kg CO₂-eq/hm²（20.2%），CH₄的碳排放为378 CO₂-eq/hm²（13.2%）。同时，相比于早稻-晚稻中晚稻的产量（6333 kg/hm²），春玉米-晚稻轮作模式下的晚稻产量（7270 kg/hm²）提高了14.8%。因此，引入春玉米-晚稻轮作模式有利于提升稻田生产力，降低稻田连作系统碳排放和碳足迹。

Comparison of carbon footprint between spring maize-late rice and early rice-late rice cropping system

Quantifying the carbon footprint of crop production can help provide a theoretical basis to mitigate greenhouse gas emissions in agro-ecosystem. In this study, the life cycle assessment was used to assess the carbon footprint of two cropping systems (early rice-late rice continuous cropping system and spring maize-late rice rotation systems) and quantitatively analyze the relative contribution of various carbon sources in grain production in paddy field of Southern China. The results showed that the spring maize-late rice rotation reduced the carbon emissions per unit area by 6724 kg CO₂-eq/hm² and the carbon footprint per unit yield by 0.56 kg CO₂-eq/kg compared with the continuous cropping of early rice-late rice. The carbon emissions from the production of spring maize were less 6228 kg CO₂-eq/hm² than in early rice. The carbon emissions of late rice in spring maize-late rice rotation system were decreased by 497 kg CO₂-eq/hm², when compared with that in early rice-late rice system. The main components of carbon footprint in the early rice-late rice planting system were derived from the carbon emission of methane (CH₄) from paddy field (9776kg CO₂-eq/hm², 54.8%), nitrogen fertilizer production and application (2871 kg CO₂-eq/hm², 16.1%), and electricity consumption (2849 kg CO₂-eq/hm², 16.0%). While the main part of carbon footprint came from the carbon emission of CH₄ (4442 kg CO₂-eq/hm², 40.0%), nitrogen fertilizer production and application (2871 kg CO₂-eq/hm², 25.8%), and electricity consumption (1508 kg CO₂-eq/hm², 13.6%) in the spring maize-late rice rotation system. The composition of carbon footprint of late rice in this system were similar to that in the spring maize-late rice system. However, the main part of carbon footprints of spring maize were mainly derived from the carbon emission of nitrogen fertilizer production and application (1435 CO₂-eq/hm², 50.1%), nitrous oxide (579 kg CO₂-eq/hm², 20.2%), and CH₄ (378 CO₂-eq/hm², 13.2%). Meanwhile, compared with the yield of late rice (6333 kg/hm²) in early rice-late rice cropping system, the yield of late rice (7271 kg/hm²) was increased in the spring maize-late rice rotation system. Accordingly, introducing spring maize-late rice rotation system is conducive to improving rice paddy productivity and mitigating carbon emission and carbon footprint in continuous rice systems.