Comprehensive evaluation and optimization of agricultural system: An emergy approach

China's agriculture is facing a series of severe challenges such as increasingly tight resource constraints and deteriorating environmental problems. The intensive utilization of agricultural resources and sustainable development of agricultural have been paid more and more attention by the Chinese government. Hence, an emergy approach is employed in this study to comprehensively evaluate economic benefit, environmental pressure and sustainability performance of agricultural system in Gaomi city. The results showed that the emergy yield ratio (EYR), the environmental loading ratio (ELR) and the emergy sustainable index (ESI) of the agricultural system are 2.25, 1.91 and 1.18 respectively. To further improve the sustainable development level of the agricultural system, the sensitivity analysis is used to identify key emergy flows restricting its sustainable development. On this basis, tracing the source to find the key substances. Finally, according to the position of key substances in the agricultural system, the Reduce-Reuse-Recycle (3R) principle of circular economy is introduced to design three optimization scenarios. The results showed that if all the three optimization scenarios proposed in this study are realized, the sustainable development level of the agricultural system in Gaomi city can be increased by 52.51%. The emergy optimization methodology system based on 3R principle proposed in this study can provide a new perspective of an industry evaluation.