Biogas production is a key technology for the sustainable use of agricultural biomass as a renewable energy source and maize ( Zea mays L.) is the most commonly used energy crop in Italy. However, maize as an energy crop shows several negative aspects such as high environmental impact and a possible adverse effect on the price of food and feed commodities. For these reasons several perennial crops, and in particular miscanthus ( Miscanthus × giganteus Greef et Deu.) and giant reed ( Arundo donax L.), have recently generated wide interest because they are considered positive for environmental loads and footprint and already recognized as very high-yielding crops for Mediterranean environments. In order to evaluate the biogas yield potential of these crops, local accessions of arundo and miscanthus were cultivated, at very low inputs, in a northeastern area of Italy, harvested in summer and fall and submitted to an ensilage process, in comparison with maize. All ensiled biomasses were then submitted to anaerobic digestion, utilizing a 2:1 inoculum to substrate ratio (I:S) of volatile solids, through a laboratory Methane Test System. The perennial species can be stored as traditional silage with no need for additives, assuring a suitable biomass dry matter content at silage time (no more than 43%). Although arundo and miscanthus showed a significantly higher biomass yield at the fall harvest time with respect to maize, the latter gave an about 30% higher methane yield per hectare due to the very low biochemical methane potential (BMP) of both perennial species. Efforts have to be made to improve biodegradability and, consequently, the BMP of these perennial species in order to bridge the methane yield gap with respect to maize. In fact, the adoption of the perennial crops as energy crops for bio-methane production, could avoid the negative impact on environmental sustainability and depletion of limited resources (water), shortcomings evidenced by maize as an energy crop.
