Switchgrass biomass production in the Midwest USA: Harvest and nitrogen management

Information on optimal harvest periods and N fertilization rates for switchgrass (Panicum virgatum L.) grown as a biomass or bioenergy crop in the Midwest USA is limited. Our objectives were to determine optimum harvest periods and N rates for biomass production in the region. Established stands of 'Cave-in-Rock' switchgrass at Ames, IA, and Mead, NE, were fertilized 0, 60, 120, 180, 240, or 300 kg N ha(-1). Harvest treatments were two- or one-cut treatments per year, with initial harvest starting in late June or early July (Harvest 1) and continuing at approximately 7-d intervals until the latter part of August (Harvest 7). A final eighth harvest was completed after a killing frost. Regrowth was harvested on previously harvested plots at that time. Soil samples were taken before fertilizer was applied in the spring of 1994 and again in the spring of 1996. Averaged over years, optimum biomass yields were obtained when switchgrass was harvested at the maturity stages R3 to R5 (panicle fully emerged from boot to postanthesis) and fertilized with 120 kg N ha(-1). Biomass yields with these treatments averaged 10.5 to 11.2 Mg ha(-1) at Mead and 11.6 to 12.6 Mg ha(-1) at Ames. At this fertility level, the amount of N removed was approximately the same as the amount applied. At rates above this level, soil NO3-N concentrations increased.