Management of Sweet Sorghum for Biomass Production

Sweet sorghum [Sorghum bicolor (L.) Moench] has been suggested as a biofuel feedstock due to its high productivity, low N requirements, and drought tolerance but little data exist on its management in the Midwestern US Corn Belt. In 2005 and 2006 in central Iowa, USA, plots were seeded with ‘Top 76-6’ sweet sorghum on three dates; late May, early June, and late June, at rates of 4.5, 11.2, and 17.9 kg ha⁻¹ with row widths of 20, 38, and 76 cm, and fertilized at either 84 or 168 kg N ha⁻¹ to determine how sweet sorghum yield and plant composition respond to changes in management. Yields were highest when sweet sorghum was planted in 20 cm row widths in late May (26.3 Mg ha⁻¹) or early June (29.0 Mg ha⁻¹). Several plant carbohydrates were affected by seeding date in 2005, but not 2006. Theoretical ethanol yields averaged 10,616 and 11,408 L ha⁻¹ in 2005 and 2006, respectively, and were highest when sweet sorghum was planted earlier in the season and in narrow rows. In contrast, N fertilization and seeding rate had few impacts on sweet sorghum growth, biomass yield or ethanol potential. Based on these results, sweet sorghum in Iowa should be planted in May or June in 20 cm rows at a low to moderate seeding rate and a low N fertilization rate.