Establishing sustainable sweet sorghum-based cropping systems for forage and bioenergy feedstock in North China Plain

Sweet sorghum [Sorghum bicolor (L.) Moench] offers a sustainable and renewable bioenergy resource for feed and biomass production. Two separate field experiments were conducted on arable land at Shangzhuang Station and on saline-alkali land at Quzhou Station in the North China Plain. Three cultivars of sweet sorghum including early- (ZS1) (114 days), medium- (CT2) (138 days), and late-maturity (LN3) (160 days), were sole cropped on arable land in 2006-2007. Using the same cultivars, sweet sorghum based - double cropping systems with winter wheat rotation were analyzed on saline-alkali land in 2009-2011. This study aims to determine the planting potential of three sweet sorghum cultivars and develop an optimized sweet sorghum - based double cropping system on saline-alkali land to maximize the production outputs. The aboveground biomass yield, energy output, theoretical ethanol yield (TEY), and chemical composition of three sweet sorghum cultivars - based cropping systems were assessed. Results indicate that: (1) the annual average dry biomass yield and dry matter content of the three sweet sorghum cultivars showed an overall uptrend with the increasing crop growth length. The average dry biomass yield of three sorghum maturity groups on arable land were 48.9% higher than that on saline-alkali land. (2) Sweet sorghum cultivars of late- (LN3) and medium- maturity (CT2) displayed better chemical composition for both bioenergy utilization (higher starch, soluble sugar, cellulose and hemicellulose and lower ash) and forage quality (better relative feed value (RFV) and lower acid detergent fiber (ADF) and neutral detergent fiber (NDF)). (3) The double cropping system of medium-maturity sweet sorghum (CT2) and winter wheat presented the best total dry biomass yield (24.9 t ha(-1)), energy output (394.6 GJ ha(-1)), and theoretical ethanol yield (6857 L ha(-1)). Therefore, this double cropping system can be recommended for extensive planting in the North China Plain for bioenergy or forage production.