减氮施肥对春玉米-晚稻生产系统碳足迹的影响

随着对气候变化和粮食安全的的日益认识,低碳农业引起了人们的广泛关注.低碳农业的研究需要综合考虑作物产量和温室气体排放,改进氮肥管理可能有助于减缓作物生产系统的温室气体排放,同时实现对作物稳产甚至高产的需求.本试验利用生命周期法研究了不同施氮量(150、225、300 kg N·hm^-2)对春玉米-晚稻轮作系统碳足迹的影响.结果表明: 随着氮肥用量增加,两季作物生产过程中温室气体和碳足迹增加.在春玉米生产过程中,氮肥生产和施用引起的温室气体排放对碳足迹贡献最大,占36.2%～50.2%;而在晚稻生产中,甲烷的排放贡献最大,占42.8%～48.0%,并且随氮肥用量增加甲烷排放增加.当氮肥施用量减少25%(225 kg N·hm^-2)和50%(150 kg N·hm^-2)时,春玉米生产的温室气体排放分别下降了21.9%和44.3%,碳足迹分别下降了20.3%和39.1%;晚稻生产的温室气体排放分别下降了12.3%和20.4%,碳足迹分别降低了13.7%和16.7%.氮肥减量对春玉米产量无显著影响,而晚稻产量在225 kg N·hm^-2施肥量下最高.因此,春玉米氮肥用量降低至150 kg N·hm^-2和晚稻氮肥用量降低至225 kg N·hm^-2不仅能够保持作物高产,而且还能大幅度降低作物系统的碳足迹.

Effect of reduced nitrogen fertilization on carbon footprint in spring maize-late rice production system

With the growing concerns on global climate change and food security, low carbon agriculture in food production attracts more attention. Low carbon agriculture needs to balance higher-level crop yields and lower greenhouse gas emission in production process. Improving nitrogen mana-gement may help mitigate greenhouse gas emission and achieve stable or higher crop yields in crop production systems. In this study, we investigated the effects of nitrogen application rates (150, 225, 300 kg N·hm^-2) on the carbon footprint of spring maize-late rice rotation system in paddy field using the life cycle assessment. The results showed that greenhouse gas emission and carbon footprint increased with the nitrogen fertilizer application rates in both crops. Nitrogen fertilizer was the most important contributor to carbon footprint of spring maize ecosystem, accounting for 36.2%-50.2%. Methane emission increased with nitrogen fertilizer input and contributed the most to the carbon footprint of late rice production, accounting for 42.8%-48.0%. When the nitrogen application rate was reduced by 25% (225 kg N·hm^-2) and 50% (150 kg N·hm^-2), greenhouse gas emission of maize production decreased by 21.9% and 44.3%, and the carbon footprint decreased by 20.3% and 39.1%, respectively. Meanwhile, the greenhouse gas emissions of late rice decreased by 12.3% and 20.4%, and the carbon footprint of late rice decreased by 13.7% and 16.7%, respectively. The reduction of nitrogen fertilizer rate had no significant effect on maize yield, with the treatment of 225 kg N·hm^-2 rate holding the highest yield in late rice ecosystem. The treatment of 150 kg N·hm^-2 rate in spring maize production and 225 kg N·hm^-2 rate in late rice production was the sustainable N fertilizer application rate for achieving high grain yield and reducing the carbon footprint in crop system.