Switchgrass (Panicum virgatum L.) is considered a valuable perennial biofeedstock with significant potential to sequester soil organic carbon (SOC).  A study was conducted to document SOC change under switchgrass at 10 sites along a transect from Nebraska to North Dakota (Figure 1).  The sites, located on farmer-managed fields, were sampled prior to planting switchgrass in 2000 and 2001, and again in 2005 and 2006 to determine change in SOC over time.  Sites in Nebraska were sampled to a depth of 1.2 m, while sites in North and South Dakota were sampled to 0.3 m.  Soil organic carbon increased over time (P≤0.1) in at least one sampled depth at seven sites (Streeter, ND; Highmore and Ethan, SD; Atkinson, Crofton, Douglas, and Lawrence, NE).  Soil organic carbon increased most consistently across sites at 0 to 0.05 m and below 0.2 m.  Cumulative depth assessments indicated significant increases in SOC at Streeter, ND (P=0.08), Highmore, SD (P=0.09), and Atkinson and Lawrence, NE (P=0.10 and 0.09, respectively) for the 0 to 0.3 m depth, and at Lawrence, NE (P=0.01) for the 0 to 1.2 m depth.  Rates of SOC accrual for the 0 to 0.3 m depth at responsive sites ranged from 0.9 to 1.4 Mg C ha^-1 yr^-1, while the SOC accrual rate at the Lawrence, NE site for the 0 to 1.2 m depth averaged 3.8 Mg C ha^-1 yr^-1.  On-farm documentation of increased SOC over time underscores the capacity of switchgrass to effectively sequester atmospheric C in soil.

Figure 1.  Sampling sites for on-farm evaluation of SOC change under switchgrass.