关键词: 碳交易, 农业固碳减排, 炭基肥, 方法学, 气候变化, 秸秆热解炭化

Abstract:

【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 N₂O and CH₄ emissions, and soil organic carbon pools, respectively. The extra GHG emissions induced by the transportation of BCF or the changes in original straw utilization method could be considered as leakage. According to the case study, the net carbon sink of 1 439.77 kg CO₂-eq·hm ^-2 and 281.58 kg CO₂-eq·hm ^-2 for the growing seasons of winter wheat and rice production could be obtained, respectively, when the boundary was set as smallholder operated farmland. However, in the boundary of factory-farmland system intensive operated by enterprises, the carbon sink obtained in the farmland might offset by the GHG emissions in the process of BCF production, and the net carbon sink of 1 479.01 kg CO₂-eq·hm ^-2 and 340.43 kg CO₂-eq·hm ^-2 for the growing seasons of winter wheat and rice production could be obtained, respectively, once the BCF production process was optimized. Given these, the optimizing of BCF production process by recycling the by-products would make the carbon trading of VER by BCF project feasible. 【Conclusion】A theoretical framework and a set of methods were proposed to quantify the net carbon sink for BCF project. The case study indicated that the developed methodology could be well applied into the quantification of net carbon sink for BCF project, and it was found that dry cropping system had the higher net carbon sink than paddy rice cropping system under BCF project, while optimizing the production process of BCF was an important pathway to obtain the considerable amount of carbon sink under factory-farmland system operated by enterprises. This study indicated that a national or industry standard of BCF should be established as soon as possible to provide a theoretical basis for project eligibility identification; meanwhile the attentions should be paid to the development of regional specific N₂O and CH₄ emission reduction factors and soil carbon sequestration factors for different types of BCFs applied.

Key words: carbon trading, agricultural carbon reduction, biochar compound fertilizer, methodology framework, climate change, straw pyrolysis