Sorghum and Switchgrass as Biofuel Feedstocks on Marginal Lands in Northern China

Abstract

To avoid food versus fuel conflicts in China, the production of bioenergy crops requires the evaluation of marginal lands under arid and semiarid conditions. We conducted field experiments with sorghum (Sorghum bicolor (L.) Moench) and switchgrass (Panicum virgatum L.) in Northern China. The biomass yield and nutrient (N, P, and K) accumulation of sorghum (leaves and stalks) and switchgrass (aboveground portion) were examined in 2012 and 2013. The soil organic carbon (SOC) content at depths of 0–30 cm was quantified at sorghum, switchgrass, and native grassland sites. The aboveground biomass yield of sorghum averaged 13.9 t ha−1 (14.2 and 13.6 t ha−1 in 2012 and 2013, respectively), while the switchgrass yield had a higher variability (14.8 versus 8.1 t ha−1 in 2012 and 2013, respectively) and averaged 11.5 t ha−1. The removals of N, P, and K averaged 56, 10, and 160 kg ha−1, respectively, for sorghum and 41, 11, and 89 kg ha−1, respectively, for switchgrass. To attain maximum biomass yield with minimum nutrient removal and the lowest transportation costs (due to the moisture content), the switchgrass harvest should be delayed until approximately 160 days after regrowth (DAR) in this region, whereas sorghum, which matures earlier, can be harvested as early as 120 days after sowing (DAS). Earlier harvests would increase the flexibility for large-scale ethanol production facilities. The SOC content within the 0–15-cm layer averaged 15.8 and 11.6 g C kg−1 before and 3 years after the establishment of the switchgrass culture, respectively, although the SOC increased with the culture age. In contrast, the SOC content of the 15–30-cm layer did not differ between the adjacent native grassland and the switchgrass planting. Under sorghum, the SOC content was reduced although it did not differ significantly from that of the native grassland at a significance level of p < 0.05. We conclude that high biomass yields can be obtained from the two crops under natural rainfall in the arid and semiarid conditions of Northern China. To address nutrient removal and SOC reduction, the leaves of sorghum should be returned to the field to increase the input of organic materials into the soil and reduce nutrient removal, which enhances soil fertility and sustainable production.