Biomass and biomethane yield of cultivated and wild cardoon grown with zero input in the Mediterranean environment

The cardoon, both the cultivated (Cynara cardunculus var. altilis) and the wild one (C. cardunculus var. sylvestris), are suitable for energy production as they produce large amounts of biomass and minimize the demand for inputs. Furthermore, they are native to the Mediterranean basin and therefore well adapted to its environment, of which they make the most of its resources, escaping its harshness. The aim of the study is to provide a contribution of new knowledge on the production of biomethane in the Mediterranean environment starting from cardoon plants, which have not been supplied with fertilization, irrigation, weed control, or pest control. In the present work, two genotypes of cardoon have been compared. On the one hand ‘Altilis 41’, a cultivated cardoon genotype selected for its ability to produce biomass, on the other hand ‘Sylvestris Marsala’, a wild cardoon ecotype. The plants were 5 years old and were grown in a randomized block design. The plants’ regrowth was naturally allowed by rains at the end of September. Their epigeal biomass was collected at the flowering phenological stage, then ground and finally placed in silobags to simulate 3-month ensiling. ‘Altilis 41’ produced 19.8 t of dry biomass (DM) per hectare, while ‘Sylvestris Marsala’ produced under 9.5 t DM ha-1. Biomethane yield, obtained from the ensiled biomass subjected to anaerobic digestion for 27 days, was 178 Nm3 for ‘Sylvestris Marsala’ and 167 Nm3 for ‘Altilis 41’. However, the latter was more productive on a per hectare basis, due to its higher productivity in terms of biomass compared to ‘Sylvestris Marsala’ (3177 vs 1512 Nm3 ha-1).