Sustainable biomass production: A comparison between Gross Energy Requirement and Emergy Synthesis methods

In this paper two methods for energy analysis and environmental accounting (Gross Energy Requirement and Emergy Synthesis) are critically discussed in order to explore their ability to provide a comprehensive evaluation of the performance and environmental sustainability of human-dominated production processes. In order to allow a quantitative comparison, two cropping systems, namely 1 ha of corn production in Italy, and 1 ha of willow production in Sweden, are investigated by means of the parallel application of both methods. The case studies are carried out by performing a quantitative inventory of both natural and economic input flows to the investigated cropping systems. Such input flows are then converted into embodied energy (MJ) as well as emergy (seJ) units. Finally, performance indicators representative for each method are calculated. Results provided by the two methods and their respective theoretical features are compared and discussed in order to point out limits and potentialities of both approaches. The study shows that the two methods account for different – although complementary – categories of input flows, use different conversion factors, and answer to different questions and concerns. Gross Energy Requirement focuses on fossil fuel use and is capable to support the development of more efficient use of commercial energy. Emergy Synthesis uses broader spatial and time frames and accounts for both natural and economic resources. In so doing, it takes into consideration different forms of energy, materials, human labor and economic services on a common basis, offering larger potentiality to explore the sustainable interplay of environment and economy.