Biomass yield and energy balance of three perennial crops for energy use in the semi-arid mediterranean environment

Three different lignocellulosic energy crops (a local clone of Arundo donax L., Miscanthus x giganteus Greef et Deu. and Cynara cardunculus L. var. altilis D.C. cv. "Cardo gigante inerme") were compared over 5 years (2002-2007) for crop yield, net energy yield and energy ratio. In a hilly interior area of Sicily (Italy), two different irrigation treatments (75 and 25% of ETm restoration) and two nitrogen fertilization levels (100 and 50 kg ha-1) were evaluated in a split-plot experiment. In the fourth and fifth years of the field experiment (2005-2007) no fertilizer or irrigation was used. From crop establishment to the third year, above ground dry matter yield increased over all studied factors, in A. donax from 6.1 to 38.8 t ha-1 and in M. x giganteus from 2.5 to 26.9 t ha-1. Fifteen months after sowing, C. cardunculus yielded 24.7 t ha-1 of d.m. decreasing to 8.0 t ha-1 in the third year. In the fourth and fifth years, above ground dry matter yields of all crops decreased, but A. donax and M. x giganteus still maintained high productivity levels in both years. By contrast the yield of C. cardunculus yield fell to less than 1 t ha-1 of d.m. by the fourth year. Energy inputs of A. donax and M. x giganteus were higher in the year of establishment than that of C. cardunculus (34 GJ ha-1 for A. donax and M. x giganteus and 12 GJ ha-1 for C. cardunculus), mainly due to irrigation. Net energy yield showed low or negative values in the establishment year in A. donax and M. x giganteus. In the second and third year, net energy yield of A. donax was exceptionally high (487.2 and 611.5 GJ ha-1, respectively), whilst M x giganteus had lower values (232.2 and 425.9 GJ ha-1, respectively). M x giganteus attained its highest net energy yield in the fourth year (447.2 GJ ha-1). Net energy yield of C. cardunculus reflected energy output of the crop, being high in the first compared to subsequent years (364.7, 277.0 and 119.2 GJ ha-1, respectively for the first, second and third years). A significant effect of the different irrigation treatments was noted on all the studied parameters in all species. Conversely, only A. donax was affected by nitrogen fertilization.