Planting Date and Harvest Maturity Impact on Biofuel Feedstock Productivity and Quality of Sweet Sorghum Grown under Temperate Louisiana Conditions

Sweet sorghum [Sorghum bicolor (L.) Moench] is recognized as a promising biomass energy crop for meeting the increasing demand for bioenergy feedstocks. Field experiments were conducted at sites in northern and southern Louisiana for 2 yr to assess planting date and harvest maturity effects on yield from primary plantings and ratoon crops. The cultivar M81-E was evaluated using a split plot arrangement of treatments in randomized complete block designs. Planting date from mid-March to early July was the primary plot treatment. Harvest maturity at the early heading (EH) or hard dough (HD) stage was assigned as the subplot treatment. A range of planting dates from mid-March to early June produced substantial yields of biomass and fermentable sugar with appropriate harvest maturity and could support sugar mill operation for up to three additional months. However, sweet sorghum planted in early May and harvested at the HD stage produced 30 to 210% more fermentable sugar than other tested planting dates and maturity combinations. Ratoon crop production was not dependable showing inconsistent tiller growth with resultant low biomass yields. Correlation coefficients of sugar yield with biomass or other quantitative agronomic characteristics were higher than 0.79, while that with brix was only 0.32 (P < 0.0001). Production management in Louisiana from long season cultivars such as M81-E based on a single harvest 150 to 160 d from planting at the HD stage can provide more biomass and fermentable sugar than can production management targeting a ratoon crop.