Drying studies of sorghum for forage and biomass production

Test plots of sorghum were planted and cut at maturity. Natural drying of the cut material was monitored in the field. Laboratory drying tests were conducted to determine the drying kinetics of the stalks under four different configurations at 50 °C and 0.5 m/s air velocity. These included: 20 cm long sections with sealed ends to duplicate stalks of infinite length and remove “end effects”; 20 cm long sections with open ends to account for “end effects”; and 20 cm sections with longitudinal splitting to remove the effects of the outer layer of the stalks. In addition, short sections (5 cm) were dried to determine the impact of enhanced “end effects” on drying. Mathematical models were derived from replicate laboratory trials and were used to predict the times required to reach a final moisture content of 10% (wet basis). These times ranged from over 200 hours with the sealed ends to 15 hours with splitting of the stalks to expose the interior fully to the drying medium. Field drying of cut sorghum was found to be insufficient to adequately dry these materials for storage or use in energy production, especially under wet-weather conditions. Laboratory tests showed the need for substantial disruption of the stalk surface to promote drying. This can be achieved through mechanical maceration of the stalks. Simply cutting the stalks at ground level and relying upon open-air drying did not reduce the moisture content to acceptable levels for animal feed or energy production.