Assessing sorghum (Sorghum bicolor (L.) Moench) biomass potential under different harvrst schemes

Biomass sorghum has an attitude to re-grow after cutting, which is exploited in forage production. To investigate potential benefits for energy production, two genotypes (B133, fibre sorghum; Trudan Headless (TH), forage sorghum), two harvest schemes (single harvest (SH) at physiological maturity (September); double harvest (DH) at blooming (July) plus October re-growth) and two irrigation levels (rainfed and irrigated, with a different timing between SH and DH) were cross-tested in Northern Italy. Determinations included: dry biomass yield (DB), plant moisture, water use efficiency (WUE), potential energy output, economic assessments. The two genotypes had a close DB in all harvests, despite morphological differences (TH with shorter plants, several tillers and thinner, more resilient stems). TH had a somewhat higher moisture. DH yielded about 20% more than SH; DH average DB (30 Mg ha-1) was equally split between the two harvests. Irrigation raised DB by 10% in SH; by 20% in DH (irrigated during re-growth). Irrigation always involved decreases in WUE. Energy output (biogas, heat, 2nd-generation ethanol) was uninfluenced by genotype (similar fibre composition) and directly related to DB. In financial terms, irrigation and, to a lesser extent, DH hardly proved affordable in a year with a favourable weather course (wet springtime).