Upland switchgrass yield, nutritive value, and soil carbon changes under grazing and clipping
There have been few evaluations of switchgrass (Panicum virgatum L.) cultivars under multiple harvest managements in the northeastern United States. The objective of this study was to determine the yield, nutritive value, and soil C changes of switchgrass cultivars under grazing and clipping. In 1999, ‘Cave-in-Rock’, ‘Trailblazer’, and ‘Shawnee’ switchgrass were established in field plots at Rock Springs, PA, and in pastures in southeastern Pennsylvania. In 2000 and 2001, two- and three-cut treatments were imposed at Rock Springs. At the southeastern Pennsylvania site, pastures were grazed three or four times per year during 2000 to 2004. Forage yield, crude protein (CP), neutral detergent fiber (NDF), and neutral detergent fiber digestibility (NDFD) were determined at each harvest. Soil was analyzed for C and stable C isotopes before planting in 1999 and at the end of the experiments. Cultivars differed slightly in yield and nutritive value. Variation in forage yield was greater among years and management treatments (3300 to 8200 kg ha–1) than among cultivars (5900 to 9400 kg ha–1). Trailblazer suffered from leaf diseases and lodging during wet years. There were no differences among cultivars in soil C. Soil C accumulated in the surface 5 cm of soil after 7 yr at Rock Springs, but soil C did not change after 5 yr of grazing. By the end of the experiments, about 20% of soil C in the surface 5 cm was derived from switchgrass. Cave-in-Rock and Shawnee are equally suited and superior to Trailblazer for hay and grazing in Pennsylvania and similar areas in the northeast.