基于能值理论的循环复合农业生态系统发展评价——以福建省福清星源循环农业产业示范基地为例

Evaluating the ecosystem sustainability of circular agriculture based on the emergy theory:a case study of the Xingyuan circular agriculture demonstration site in Fuqing City,Fujian

循环农业是当前农业可持续发展理念的具体运作模式。对能值分析方法优化,使其更适合循环复合生态系统的应用上进行优化,并以福建省福清星源循环农业产业示范基地为例验证,评价复合生态系统的可持续发展程度和经济效益。结果表明改进的能值分析方法对循环复合农业生态系统的可持续发展评价更科学,复合系统的可持续发展指数比单纯的生猪养殖提高23.44%—33.86%,在4种组合的循环模式中以"生猪养殖-沼气工程-有机肥生产-种植业"循环复合生态系统整体效益最佳,其可持续发展指数最高,环境负载率最低,净能值产出率仅略低于"生猪养殖-沼气工程-种植业"复合系统。

Since the introduction of the Circular Economy in the 1990s, the management practice of circular agriculture has been rapid advancement. Based on the principles of sustainable agricultural development, circular agriculture has been the subject of numerous reports, which have evaluated and studied the development of this new agricultural practice at different scales. However, one of the most widely used methods of accounting for different forms of energy and resources-the emergy theory-has yet to be employed in evaluating circular agriculture. Emergy describes one kind of available energy that is used up in transformation, directly or indirectly, to make a product. It measures quality differences between forms of energy that are generated by transformation processes in nature, and that support work in natural or human dominated systems. In this study, the emergy analysis method was partly modified and specifically tailored for circular agriculture systems, and then used to evaluate the sustainability and economic benefits of ecosystem development. To validate the feasibility and quality of the improved emergy analysis method, we conducted assessments in four complex circular systems at Xingyuan circular agriculture demonstration site in the city of Fuqing, Fujian Province. We found that total production input could be substantially overestimated under the traditional emergy theory, as the systematic feedback emergy was accounted into total inputs. Further, the environmental stresses from the tremendous amount of wastes generated in the studied systems were notconsidered in the traditional emergy theory, and as a result, the sustainability of the conventional ＇ pig-only＇ farm was estimated to be 2.8%-11.52% higher than that of the studied circular systems. In contrast, the improved emergy analysis method could evaluate the sustainability of the circular systems more efficiently and accurately, as the most important advantage of circular agriculture-decreasing the total inputs and reducing environmental stresses by converting the systematic wastes into renewable resources-were factored into the new analysis. Furthermore, the improved emergy theory recognized the circular system as a whole by carefully defining the boundary conditions and energy fluxes in and out of the system, which reflects the real production processes both by design and in practice. According to our evaluation using the improved emergy method, the emergy sustainable indices （ESI） of the circular systems were improved by 23.44%- 35.86% compared to that of conventional pig farming. The circular system of ＇ pig farm-biogas system-compost productioncultivation＇ had the highest overall benefit among the four circular systems, as demonstrated by the highest ESI, lowest environment load ratio （ELR）, and second highest emergy yield ratio （EYR）, which was only slightly smaller than that of the circulating system of ＇ pig farm-biogas system-cultivation＇. The circular agricultural system is essentially an interactive combination of multiple sub-systems. Its ecological benefits should be measured by the system efficiency rather than the length of the production chain. This is supported by our evaluation using the modified emergy theory： the ＇ pig farm-fire damp-compost production-mushroom farm-cultivation＇ system, with the longest chain in all four studied systems, had the least ecological benefits. Further investigations into the model efficiency are required to improve flexibility and applicability of the improved emergy theory in larger areas or more complex systems.