Application of multi-metric analysis for the evaluation of energy performance and energy use efficiency of sweet sorghum in the bioethanol supply-chain: A fuzzy-based expert system approach

This study uses a fuzzy-based expert system to assess the impact of soil treatment (conventional tillage vs. no-till) and mineral nitrogen supply (0, 75, 150 kg N ha−1) on the energy performance and efficiency of sweet sorghum in the bioethanol supply chain. The different agronomic strategies were compared using four energy indicators: energy yield, net energy gain, energy use efficiency and energy return on energy invested. The highest productivity in bioethanol and energy yield required the full energy input management, while conventional tillage without N fertilization resulted in the best agronomic strategy in terms of net energy gain. The highest energy use efficiency was achieved from the lowest-agro-energy-input cropping system (no-till without nitrogen fertilization). Uncertainty and vague information resulted from the investigation of multiple different metrics. As a consequence, aggregating information into a single multi-composite indicator can be useful. The multi-metric indicator based on the fuzzy-based expert system clearly indicated the behavior of a cropping system in optimizing the energy performance and efficiency of the sweet sorghum-bioethanol chain in a specific pedo-climatic context. The optimization between energy input and output was achieved by the agronomic strategy that combined conventional tillage without nitrogen fertilization, while no-till with 75 kg N ha−1 was inefficient. The proposed method is flexible in building a synthetic index to assess the sustainability of biomass production for energy purposes. An operative module for evaluating the energy performance and energy use efficiency of a cropping system through a multi-composite metric is also provided in this paper.