Comparative environmental performance of three different annual energy crops for biogas production in Northern Italy

Bioenergy is becoming increasingly important for agriculture. However, the use of first generation crops for biofuels and bioenergy production is controversial due to their competition with food and feed. The cultivation of three different energy crops – wheat, maize and triticale – for biomass in order to produce biogas in Lombardy, in the Po Valley (Italy), was evaluated in this study to quantify their environmental profiles and identify the best biomass source from an environmental perspective. The choice of these cropping systems was based on the fact that they are well-known and extensively cultivated for energy purposes in Italy. The standard framework of the Life Cycle Assessment (LCA) was followed in this study and detailed inventories for these crops were designed. The environmental profile was analysed in terms of abiotic depletion, acidification, eutrophication, global warming, ozone layer depletion, photochemical oxidants formation, human toxicity and ecotoxicity. In addition, an energy analysis was performed using the cumulative energy demand method. According to the results, the selection of the best biomass source depends on several factors such as the functional unit and biomass yield. Therefore, a sensitivity assessment was done in order to identify these differences. Moreover, the most critical processes throughout the life cycle of the cropping systems were identified and improvement alternatives were proposed, specifically for the mineral fertilization (one of the most important hot spots). Thus, different scenarios built on alternative nitrogen based fertilizers were assessed in detail and discussed, resulting in the identification that the use of calcium ammonium nitrate instead of urea should improve the environmental profile regardless of the energy crop. Finally, the combination of triticale or wheat with maize classes 300, 400 and 500 in rotation systems was done in order to achieve similar biomass yields, per ha, to the maize classes 600 and 700, which were also evaluated. The best results were obtained for maize classes 600 and 700 regardless of the functional unit considered in all the categories assessed except in GWP, where triticale with maize 400 and with maize 500 were the best options.