Long-term evaluation of biomass production and quality of two cardoon (Cynara cardunculus L.) cultivars for energy use

Cardoon (Cynara cardunculus L.) is an herbaceous species indicated as one of the most suitable energy crop for southern European countries. The aim of this work was to outline the productivity of two cardoon cultivars, Bianco Avorio (BA) and Gigante di Romagna (GR), over 11 years of cultivation in rain fed field conditions in the temperate climate of Central Italy. The quantitative and qualitative aspects of its biomass (calorific value, ultimate and proximate analyses, ash composition) as well as its energy balance (energy efficiency, net energy yield) have been determined. Crop dry yield was not different between the two cultivars and it was rather stable with a mean value (averaged from year 3 to 11) of 14 and 13 t ha-1 for GR and BA respectively. Furthermore the biomass dry matter content was higher in BA than GR (51% vs 42%). The chemical analysis of cardoon biomass showed a similar composition in both cultivars with good calorific value (15 MJ kg-1) but with an ash content (13.9% d.w.) higher than other herbaceous energy crops. The total energy input was higher in the establishing than in the following years, however from the planting year onward, both cardoon crops were characterised by a positive energy balance. Even if its mean net energy is lower than other perennial energy crops (182 GJ ha-1 year-1), cardoon can be easily propagated by seed with important advantages for crop management and production costs. The results confirmed cardoon's good biomass yield and favourable energy balance even in cultivation systems characterised by limited water input. Moreover future works are necessary in order to improve cardoon biomass quality and to evaluate the possibility of using it in blends with other biomass sources.