The NASS CDL product is a crop-specific land cover classification
map developed from satellite observations, USDA-collected
ground reference data, and other ancillary data (e.g., the National
Land Cover Database) (Boryan et al., 2011). Based on the accuracy
assessments of the 2008–2011CDL maps, the state-level accuracies
at the pixel level for the individual tilled crop type categories are in
the range 70–95% (Johnson, 2013). Switchgrass land cover type has
been available in the NASS CDL map for the conterminous United
States since 2008 and the switchgrass pixels have been mapped in
the GP region since 2010. In this study, we generated the 2010–
2012 switchgrass land cover maps for the GP based on the
following procedures: