Biomass yield, water use efficiency, energy content, and energy return on investment of diverse perennial grasses in autumn and winter harvest regimes in the mediterranean area

The main objective of the present study was to assess the biomass dry matter yield (DM), the water use efficiency (WUE), the energy content (EC) and the energy return on investment (EROI) at the farm gate of several perennial grasses grown at the experimental farm of the University of Catania, Italy. Field trials of Arundo donax, Miscanthus x giganteus, Saccharum spontaneum spp. aegyptiacum, Sorghum halepense, Oryzopsis miliacea and Cymbopogon hirthus grown under low-input practices in an autumn and a winter harvesting regime were used. From February 2014 to February 2015 (winter harvest regime), and from October 2014 to October 2015 (autumn harvest regime), the dryness index (P/ET) was computed. Main results suggested that Saccharum was the outstanding species. Across species there was no difference in DM between autumn and winter harvests. On the other hand, WUE was higher in autumn than winter harvest, due to the lower dryness index in the autumn (0.32) than in the winter regime (0.53). The EC, although significantly different, was in the range of 1.0 MJ kg-1 between the most (Miscanthus, 15.9 MJ kg-1) and the least (Oryzopsis, 14.9 MJ kg-1) species. All species can be considered sustainable from the energy point of view as the EROI ranged from 120:1 in Saccharum to 20:1 in Cymbopogon.