不同水旱轮作模式全生命周期温室效应及经济效益评价

以不同水旱轮作稻田为研究对象，对比分析不同轮作模式温室气体排放特征，挖掘关键影响因素，并将温室效应和成本-收益计量相结合，通过综合评价筛选环境友好、经济效益高的轮作模式。基于大田小区试验，设置休闲-水稻、紫云英-水稻、小麦-水稻、油菜-水稻、青饲小麦-水稻、蚕豆-水稻6种水旱轮作处理，采用静态箱-气相色谱法，于2020年6月—2021年5月进行CH₄和N₂O排放原位监测，通过结构方程模型挖掘影响CH₄和N₂O排放的关键因素，采用全球增温潜势和成本-收益计算方法，评价不同轮作制度的环境和经济效应。结果表明：不同水旱轮作模式CH₄累积排放量为95.6~173.3 kg·hm^-2，排放量与冬茬秸秆还田量和水稻产量有关；N₂O累积排放量为1.5~2.5 kg·hm^-2，受施氮量、冬茬秸秆还田量、水稻产量和土壤有机质含量影响。增加氮肥施用量不仅可增加N₂O排放量，而且会导致土壤有机质含量的降低；冬茬秸秆还田量、水稻产量的变化会导致CH₄和N₂O排放的此消彼长，即秸秆还田量和水稻产量与CH₄排放量呈正相关，而与N₂O排放量呈负相关。青饲小麦-水稻轮作模式的经济效益为10 139元·hm^-2，高于其他轮作模式。对比单位经济效益的温室气体排放量发现，尽管青饲小麦-水稻轮作模式周年N₂O排放量最高、土壤固碳量低，但其单位经济收益的温室气体排放量仍最低（0.41 kg CO₂e·元^-1）；紫云英-水稻轮作分别比油菜、小麦、休闲、蚕豆与水稻的轮作方式低51%、33%、20%和4%。不同水旱轮作方式下的稻田周年温室效应有显著差异，紫云英-水稻轮作的综合温室效应（3.1 t CO₂e·hm^-2）显著低于小麦-水稻轮作（5.4 t CO₂e·hm^-2）。研究表明，与其他轮作模式相比，紫云英-水稻和蚕豆-水稻轮作在保证较高经济收益的同时温室气体排放量相对较低，冬茬秸秆还田量、绿肥还田生物量是环境效应和经济效益协同的重要影响因素。

Life cycle assessment on greenhouse effects and economic benefits for different paddy rice-upland rotation systems

This study aimed to investigate the characteristics of greenhouse gas emission from paddy fields based on different paddy rice-upland rotation systems and explored their key influencing factors by evaluating the effects and cost benefit of the greenhouse and comprehensively assessing the best rotation system with friendly environment and high economic benefit. In the field experiment, six rotation systems such as fallow-paddy rice, Chinese milk vetch-paddy rice, wheat-paddy rice, oilseed rape-paddy rice, green forage wheat-paddy rice, and broad bean-paddy rice were set up. Field CH₄ and N₂O emissions were monitored from June 2020 to May 2021 using static chamber-gas chromatographic techniques, and the driving factors for CH₄ and N₂O emissions were analyzed using structural equation model. In addition, the environmental and economic effects of different rotation systems were evaluated. The cumulative CH 4 emission from paddy-upland rotation ranged from 95.6 kg·hm^-2 to 173.3 kg·hm^-2, and the CH₄ emission intensity was related to winter straw returning amount and rice yield. The cumulative N₂O emission ranged from 1.5 kg·hm^-2 to 2.5 kg·hm^-2 and was affected by nitrogen application rate, winter straw returning amount, rice yield, and soil organic matter. Besides, nitrogen fertilizer application did not only increase N₂O emissions but also led to the reduction of soil organic matter. The change in winter straw returning amount and rice yield had contrary effects on annual CH₄ and N₂O cumulative emission, which had a positive correlation with CH₄ emission and a negative correlation with N₂O emission. Green forage wheat-paddy rice rotation had the highest economic income with a value of 10 139 yuan·hm^-2 and was higher than that of other rotations. Despite generating the highest N₂O emission and having weak soil carbon sequestration capacity, the greenhouse gas emissions per unit economic benefit of green forage wheat-paddy rice rotation was the lowest with a value of 0.41 kg CO₂e· yuan^-1. The value of Chinese milk vetch-paddy rice rotation decreased by 51%, 33%, 20%, and 4% compared with that of oilseed rape, wheat, fallow and broad bean-paddy rice rotation, respectively. Paddy-upland rotations significantly affected the greenhouse effect for paddy field, and the global warming potential of Chinese milk vetch-paddy rice rotation(3.1 t CO₂e·hm^-2)was significantly lower than that of wheat-paddy rice rotation(5.4 t CO₂e·hm^-2). Compared with other rotation systems, Chinese milk vetch-paddy rice and broad bean-paddy rice rotation systems could both ensure high economic benefits and relatively low greenhouse gas emissions. Winter straw returning amount and green manure biomass were the important factors to realize the synergy of environmental effects and economic benefits.