The main species cultivated in SRC are: poplar (Populus x euroamericana)
[10], willow (Salix spp) [11] and black locust (Robinia
pseudoacacia H.) [12].
Farmers may also produce biomass using annual crops [13],
which require higher input [14] than multiyear crops but have a
shorter cycle, giving to the farmer the possibility to change the
crops every year in function of the market demand [15].
The most common annual crops are: wheat (Triticum aestivum
H.), triticale (Triticosecale hybrid), and maize (Zea mays H.) [16]. In
the last years, also forages [17] and many sorghum (Sorghum bicolor
L.) hybrids [18,19] have been tested for biogas production. In Italy
[20] and in Europe [21] the maize is the most widely used crop as
feedstock for anaerobic digestion