Emergy analysis of ethanol production from low-input, high-diversity (LIHD) grasslands on degraded farmland

This research aims to analyze ethanol production from lignocellulosic biomass produced from low-input, high-diversity (LIHD) grasslands (often referred to as prairies) on degraded farmland by applying the principles of emergy analysis. This type of cellulosic biomass is an attractive alternative to traditional monocultural biomass sources such as corn because it requires less purchased inputs in the agricultural phase and can be grown on marginal lands such as degraded farmland, but has lower yields of biomass per hectare and is more difficult to process during ethanol production. To analyze this tradeoff, an emergy analysis was performed to quantify the amount of direct and indirect energy needed to make ethanol from the growth of the biomass through the production of ethanol from the biomass. Emergy metrics calculated are environmental yield ratio, environmental loading ratio, sustainability index, and fraction renewable, all of which indicate that LIHD ethanol is more attractive emergetically than corn and switchgrass ethanol. However, ethanol produced in this manner represents a small fraction of the current gasoline consumption in the US, suggesting that conservation measures are important in addition to the production of biofuels to ensure energy security. Other benefits of a LIHD grassland such as increased resilience to pests and disease as well as the use of marginal land are not captured explicitly by emergy analysis and would likely further increase the attractiveness of ethanol produced from LIHD systems.