旱作覆膜春玉米高产体系的温室气体排放及净温室效应研究

To simultaneously realize high yield and low greenhouse gas (GHG) emissions of dryland crops under water-limited conditions is the hotspot and focus area in dryland farming research worldwide. Plastic film mulching is an effective strategy in semi-arid areas of the Loess Plateau because it can improve crop yield by increasing top soil temperature and moisture. However, side effects of the plastic film mulching such as its influence on GHG emissions are still hardly investigated. Therefore, an understanding of the trade-offs among crop productivity, plastic film mulching and GHG emission is an essential requirement for developing management strategy that maximize crop yield while reducing GHG emissions. To determine whether the film mulching affects GHG emissions, we conduct two experiments: first, comparing N2O, CH4 and CO2 emissions of plastic film mulching spring maize and non-mulched spring maize; second, assessing the effects of N application rates on GHG emissions. The N2O, CH4 and CO2 emissions and the impact factors (soil inorganic nitrogen, soil temperature and moisture, etc.) will be monitored to reveal the emissions and characters of three GHG at different growth stages and the whole growth season. In addition to direct GHG emissions from soils, we will calculate emissions during the production and transportation of fertilizer, plastic film, pesticides, and the use of diesel fuel in farming operations during the whole life cycle of crop production. On the basis of these, we calculate the net global warming potential (Net-GWP) and the GHG intensity (i.e., GHG emissions per unit yield) of the plastic film mulching spring maize system to identify a preferable management practice to simultaneously obtain a high grain yield and low GHG intensity.

覆膜是目前黄土高原旱作农业提高产量的重要措施。覆膜通过提高土壤温度，保持土壤湿度等促进玉米生长并影响玉米对土壤氮素的吸收，从而直接或间接影响土壤温室气体产生、传输和排放过程。本研究以不覆膜春玉米体系为对照，拟通过连续三年定位高频率温室气体排放及其影响因子（土壤无机氮、土壤温度和土壤湿度等）监测，研究覆膜春玉米高产体系N2O、CH4和CO2在不同生育期以及周年的排放特征，同时揭示关键影响因素。在此基础上通过研究施氮水平对该体系温室气体排放的效应，确定产量、效益相对较高，而温室气体排放较低的氮素供应水平；同时应用生命周期评价法计算由化肥投入、地膜投入、机械燃油、农药施用等产生的等当量CO2，最终明确该体系的净温室效应、温室气体排放强度及各因素对CO2当量的贡献份额，为实现该体系作物高产和低环境代价双赢提供理论指导。

覆膜通过提高土壤温度，保持土壤湿度等促进玉米生长并影响玉米对土壤氮素的吸收，从而直接或间接影响土壤温室气体产生、传输和排放过程。本研究以旱作春玉米为研究对象，研究覆膜春玉米农田土壤剖面温室气体浓度分布特征以及覆膜和施氮水平对地表温室气体排放特征的影响，并在此基础上应用生命周期评价法明确该体系的净温室效应和温室气体排放强度。取得的主要结论有：（1）明确了覆膜春玉米农田土壤剖面温室气体浓度特征，土壤剖面中CO2浓度呈现出较强的季节波动，且随土层深度增加而增加，与裸地处理相比，种植玉米显著提高土壤剖面CO2浓度和扩散通量，种植玉米处理中，施氮增加了玉米生育期土壤总扩散通量，同时提高来源于植物的CO2扩散通量；土壤N2O浓度没有呈现出季节变化规律，土壤剖面中N2O浓度随着土壤深度增加而增加，氮肥的施入显著增加了土壤剖面的N2O浓度，与裸地处理相比，种植玉米显著减少了10-40 cm剖面的N2O浓度；（2）明确了覆盖措施和施氮水平对春玉米农田地表温室气体排放的影响，N2O排放随着氮肥施用量的增加而显著增加，地膜覆盖没有显著增加N2O累积排放量，但改变了春玉米不同生育阶段的N2O累积排放比例；地膜覆盖显著增加了春玉米生长季农田CO2累积排放量，改变了春玉米不同生育阶段的CO2累积排放比例；（3）建立了基于LCA方法计算覆膜旱地玉米农田净温室效应的参数，对春玉米从原材料投入到玉米收获整个生命周期温室气体的排放进行了评价，当施氮量为250 kg ha-1时，春玉米单位籽粒温室气体排放强度可降低至245.9 kg·CO2-eq·Mg-1，可实现产量和低碳排放的协同。本研究为调控温室气体排放及实现作物高产和低环境效应双赢提供理论依据。