【目的】秸秆热解炭化-生物质炭基肥-生态农业产业体系正在中国兴起。炭基肥通过替代化肥产生可观的温室气体减排量并显著增加土壤有机碳库,其规模化发展具有参与我国正在实施的自愿减排碳交易项目的明显潜力。本研究探讨构建生物质炭基肥项目固碳减排计量方法,为其大规模农业应用参与自愿减排碳交易提供科学依据和方法学支撑。【方法】根据自愿减排项目固碳减排计量方法学和农田固碳减排计量的逻辑框架,基于秸秆炭基肥项目发展的实地调查、已有炭基肥试验的固碳减排案例监测及文献统计,并参考已备案的农业减排方法学,从项目合格性、基准线确定、边界选择、关键排放源和土壤碳库确定、系统泄漏到净碳汇计量方法等方面探讨开发炭基肥项目固碳减排计量方法学,以分析炭基肥项目进行碳交易的可行性。【结果】秸秆炭基肥项目计量方法学的基准线情景为农田常规施肥管理,但需针对不同农田经营模式而确定项目边界(例如分散农民为经营主体的田块模式和工厂-农田的集约化企业运营模式),分别考虑农田氧化亚氮和甲烷的排放和土壤有机碳库来审视项目的关键排放源和碳库,考虑项目的泄漏可能包括农民运输炭基肥导致的额外排放或原有秸秆利用方式发生改变导致的额外排放。农作物炭基肥案例分析表明:以农民为主体的炭基肥项目,单个生长季的冬小麦或水稻生产可分别产生1 440和282 kg CO_2-eq·hm~(-2)的减排量;而工厂-农田集约化模式中,在未对炭基肥生产工艺进行优化的条件下(副产物未被循环利用),炭基肥生产过程带来的温室气体排放将抵消部分炭基肥应用的农田碳汇量;如对优化炭基肥生产工艺后,单个生长季的冬小麦和水稻生产可分别产生1 479和340 kg CO_2-eq·hm~(-2)的净碳汇量。【结论】构建了一套用于量化炭基肥项目净碳汇量的计量方法,可以合理地量化炭基肥农田应用项目产生的净碳汇量。本研究发展的方法学适用炭基肥农业固碳减排项目,量化结果显示炭基肥项目可带来可观的减排量,且旱作农田的净碳汇效应高于稻作农田,优化炭基肥生产工艺条件下工厂-农田集约化运营模式获得的碳汇量显著高于未优化工艺条件下的农民主体的项目模式。研究表明未来应当关注和开发区域尺度不同类型炭基肥施用下氧化亚氮和甲烷减排因子以及土壤固碳因子。
英文摘要:
【Objective】Industrial system of straw pyrolysis-biochar compound fertilizer (BCF)-ecological agriculture is emerging in China. As a suggested measure which could promote soil organic carbon pool and mitigate greenhouse gas emissions through replacing chemical fertilizer, BCF application has the potential to participate in China's ongoing carbon trading of voluntary emission reduction (VER). Development of a measurable, reportable and verifiable net greenhouse gas (GHG) reduction quantification methodology is the basis for the implementation of VER carbon trading. The objective of this study was to discuss and develop a methodology for quantifying carbon sequestration and GHG emission mitigation in BCF project, which might provide scientific basis and methodology support for BCF project to attend the VER carbon trading. 【Method】Based on the theoretical framework of the methodology for VER projects, a discussion of how to develop a methodology for BCF project was performed from the aspects of project eligibility, baseline, boundary, carbon pool, key GHG sources, leakage and net carbon sink quantification by incorporating the recorded VER methodologies, the existing frameworks of carbon sequestration and GHG reduction quantification in cropland, and the BCF scientific research basis. In addition, a case study was conducted to quantify the net carbon sink in BCF project under different cropping systems by using the data from literature collection and field survey, which would assess the feasibility of the discussed methodology by this study. 【Result】Through analyzing and discussing, this study indicated that the baseline scenario of BCF project should be local conventional fertilization management in the methodology, and the boundary could be determined according to the difference of farmland operation mode, such as the boundaries of smallholder operated farmland and factory-farmland system intensive operated by enterprises. The key GHG sources and carbon pool considered in the methodology were suggested as farmland N_2O and CH_4 emissions, and soil organic carbon pools, respectively.