Cosmic exergy-based ecological assessment for farmland-dairy-biogas agroecosystems in North China

This paper presents a comprehensive approach for evaluating agroecosystems based on an embodied cosmic exergy investigation. This novel methodology is applied to three distinctive systems: farmland-biogas (F-B), farmland-dairy (F-D) and farmland-dairy-biogas (F-D-B) systems. A comparison of renewability and sustainability among the F-B, F-D and F-D-B systems is conducted to demonstrate this framework. The results show that over 50% of the total cosmic exergy inputs for the F-D-B system can be ascribed to purchased and free renewable resources, which is much higher than the other two systems. The net present ecological value (NPEV) of the F-D-B system is approximately 6 times higher than that of the F-B and F-D systems. The sustainability of the F-D-B system is 2.76 and 2.08 times higher than that of the F-D and F-B systems, respectively. The economic benefit (EB) of the F-D-B system is the highest of all three systems. These results suggest that the F-D-B system is superior to the other two systems. This study contributes to providing a theoretical foundation for policy-making in the rural regions of China.