Harvest date effects on biomass quality and ethanol yield of new energycane (Saccharum hyb.) genotypes in the Southeast USA

Energycane (Saccharum hyb.) is a perennial bioenergy crop derived from sugarcane, but with higher fiber, greater biomass yields, and better cold tolerance than typical sugarcane. Two commercial sugarcanes, two high-sugar (Type I) energycanes, and five high-fiber (Type II) energycanes were planted at Tifton, GA, USA in a randomized complete block design with four replications. Beginning in October, 2008 (plant-cane crop year) five monthly samples were taken to assess the effects of delaying harvest on biomass composition and quality for ethanol production. The monthly harvests were repeated in the winter of 2010–2011 (second-ratoon crop year). Delaying harvest into the winter months resulted in minimal reductions in biomass moisture and N mass fractions, while K mass fraction decreased significantly. Free sugar mass fraction also decreased, thus causing the biomass to have an apparent increase in relative mass fractions of ash and neutral detergent fiber (NDF). The reduction in free sugars was more pronounced in the colder harvest season (2010–2011). The composition of biomass fiber (cellulose, hemicellulose, and lignin) was generally stable over time. A bench-top partial saccharification and co-fermentation (PSCF) protocol employing xylose-fermenting Escherichia coli was used to assess ethanol yields from the sequentially harvested biomass. Ethanol yield from sugarcanes and Type I energycanes was more variable over time, due to degradation of free sugars. Thus, early harvest is recommended to avoid loss of fermentable sugars. Type II energycanes can be harvested later during the winter months with little change in conversion properties.