Soil carbon under switchgrass stands and cultivated cropland

Switchgrass (Panicum virgatum L.) is considered to be a valuable bioenergy crop with significant potential to sequester soil organic carbon (SOC). A study was conducted to evaluate soil carbon stocks within established switchgrass stands and nearby cultivated cropland on farms throughout the northern Great Plains and northern Cornbelt. Soil from 42 paired switchgrass/cropland sites throughout MN, ND, and SD was sampled to a depth of 120 cm and analyzed for soil carbon in depth increments of 0-5, 5-10, 10-20, 20-30, 30-60, 60-90, and 90-120 cm. SOC was greater (P<0.1) in switchgrass stands than cultivated cropland at 0-5, 30-60, and 60-90 cm. Differences in SOC between switchgrass stands and cultivated cropland were especially pronounced at deeper soil depths, where treatment differences were 7.74 and 4.35 Mg ha−1 for the 30-60 and 60-90 cm depths, respectively. Greater root biomass below 30 cm in switchgrass likely contributed to trends in SOC between switchgrass stands and cultivated cropland. Switchgrass appears to be effective at storing SOC not just near the soil surface, but also at depths below 30 cm where carbon is less susceptible to mineralization and loss.