Sweet, fibre and forage sorghum (Sorghum bicolor (L.) Moench) resilience to varying seeding time in view of supplying biomass for energy uses

To investigate the influence of varying seeding time on sorghum growth, yield, water use efficiency (WUE) and potential energy output, a three-year field experiment was carried in Northern Italy, comparing early (E; early April) and late seeding (L; mid May) in three sorghum genotypes (sweet, fibre and forage hybrid). L achieved about the same plant height as E, one month later. Differences among genotypes were more consistent (fibre = sweet > forage hybrid). Dry biomass yield outlined a similar picture: no substantial difference between E and L even in the year (2011) at strong summer drought, a circumstance which was expected to affect more L than E. WUE slightly decreased when passing from E to L in the two years (2009 and 2011) featuring high trait levels, possibly due to resuming rainfalls at the end of summer, too late for efficient water use. Given a similar fibre composition, potential energy output (electricity, bio-methane and 2nd generation bio-ethanol), assessed through coefficients and formulas, reflected dry biomass yield. The resilience to varying seeding time could be used to better exploit the potential for biomass production throughout the year, alternating or double cropping sorghum with other irrigated or rain-fed crops.