Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2007
Publication Date: 4/1/2008
Citation: Sanderson, M.A. 2008. Upland switchgrass yield, nutritive value, and soil carbon changes under grazing and clipping. Agronomy Journal. 100(3):510-516. Interpretive Summary: Warm-season perennial grasses, such as switchgrass, can provide valuable forage during the summer and complement cool-season grass pastures. Growing warm-season perennial grasses as forage or biomass feedstock has been recommended as an atmospheric carbon dioxide mitigation practice. There have been few evaluations of switchgrass cultivars under grazing in the northeastern USA, and information is needed on how management of these grasses affects soil carbon changes. The objective was to determine forage yield and nutritive value of switchgrass cultivars along with soil carbon changes under clipping and grazing management. Three switchgrass varieties were compared under two clipping treatments (two or three cuts per year) in a field plot study and under grazing in replicated one-acre pastures. Annual variation in weather and harvest management had larger effects on yield and nutritive value of switchgrass than did genetics of the switchgrass cultivars. The three-cut treatment distributed some forage in each season, resulted in an 11 to 23% greater yield, and produced slightly higher forage quality than the two-cut treatment. Soil carbon levels to a 12-inch depth did not change after five years of grazing; however soil carbon in the 0 to 2-inch layer was 33% greater after seven years under clipping management. The Trailblazer variety is not adapted to the northeastern USA. The Cave-in-Rock and Shawnee varieties of switchgrass are equally suited for hay and grazing in the northeastern USA. Producers must consider the tradeoff between slightly greater forage yields and quality and stand decline with more frequent harvests.
Technical Abstract: There have been few evaluations of switchgrass (Panicum virgatum L.) cultivars under multiple harvest managements. The objective was to determine the performance and nutritive value of switchgrass cultivars under grazing and clipping management. In 1999, ‘Cave-in-Rock’, ‘Trailblazer’, and ‘Shawnee’ switchgrass were established in replicated field plots at Rock Springs, PA and in replicated pastures in southeastern PA. In 2000 and 2001, two-cut and three-cut clipping treatments were imposed at Rock Springs. At the southeast PA site, switchgrass pastures were grazed three or four times per year during 2000 to 2004. Forage dry matter yield, crude protein (CP), neutral detergent fiber (NDF), and digestible neutral detergent fiber (NDFD) were determined at each harvest. Soil samples for C, N, and stable carbon isotope analysis were taken at three depths (0 to 5, 5 to 15, and 15 to 30 cm) before planting in 1999 and at the end of the experiments. Cultivars differed slightly in yield and nutritive value; however, variation 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 for changes in soil C or N. 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 for hay and grazing in Pennsylvania and similar areas in the northeast.