Forage Yield, Quality, and Persistence of Switchgrass and Caucasian Bluestem1

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Abstract
Switchgrass (Panicum virgatum L.) and Caucasian bluestem [Bothriochloa caucasica (Trin.) C.E. Hubbard] provide forage during summer when cool‐season grasses in the southern Corn Belt are unproductive. Information is limited on the response of these grasses to defoliation, especially the effect of harvest management on regrowth. Field studies on a Creldon silt loam soil (fine, mixed, mesic Mollic Fragiudalf) were conducted to determine forage yield and quality trends and persistence of Switchgrass and Caucasian bluestem as influenced by date of first harvest and stubble height. Five dates of first harvest and two cutting heights (8 and 23 cm) were imposed factorially on established stands of Switchgrass and Caucasian bluestem for 3 years. The first harvests were taken consecutively at 1 week intervals with the initial first harvest made when plants were in a vegetative to early jointing growth stage. When cut at an 8 cm stubble height, first harvest yields of Switchgrass and Caucasian bluestem averaged over 3 years increased 763 and 1,010 kg/ha per week, respectively, with each week delay of first harvest. However, corresponding total regrowth yields/ha declined 424 kg for Switchgrass and 632 kg for Caucasian bluestem. Trends were similar for cutting at a stubble height of 23 cm, but yields were usually less than at 8 cm. Forage in vitro dry matter disappearance declined 2.0 percentage units per week for both Switchgrass and Caucasian bluestem while crude protein declined 1.6 and 1.0 percentage units per week, respectively, with each week delay in first harvest. Neutral detergent fiber (NDF) increased 1.4 percentage units per week for Caucasian bluestem at both stubble heights and for Switchgrass at 8 cm; the NDF of Switchgrass at 23 cm increased 0.4 percentage units per week. Our results indicated that Switchgrass and Caucasian bluestem should be harvested when plants begin to joint. Early harvest results in forage of higher quality and regrowth potential than harvest at later growth stages.