Switchgrass Biomass Production in the Midwest USA: Harvest and Nitrogen Management

quirement of switchgrass is N. Switchgrass usually grows in association with mycorrhizae and is a very efficient Information on optimal harvest periods and N fertilization rates user of many soil nutrients, including P (Brejda et al., for switchgrass (Panicum virgatum L.) grown as a biomass or bioen1998; Brejda, 2000; Muir et al., 2001). The N requireergy crop in the Midwest USA is limited. Our objectives were to determine optimum harvest periods and N rates for biomass producment of switchgrass used for hay or grazing largely detion in the region. Established stands of ‘Cave-in-Rock’ switchgrass pends on the yield potential of the site, productivity at Ames, IA, and Mead, NE, were fertilized 0, 60, 120, 180, 240, or of the switchgrass cultivar, and management practices 300 kg N ha 1. Harvest treatments were twoor one-cut treatments being used. In the central Great Plains and Midwest per year, with initial harvest starting in late June or early July (Harvest states, optimum N rates for switchgrass managed for 1) and continuing at approximately 7-d intervals until the latter part pasture or hay range from about 50 to 120 kg ha 1 of August (Harvest 7). A final eighth harvest was completed after a (Brejda, 2000). In Texas, the optimum N fertilization killing frost. Regrowth was harvested on previously harvested plots rate for ‘Alamo’ switchgrass managed for biomass proat that time. Soil samples were taken before fertilizer was applied in duction was 168 kg ha 1 (Muir et al., 2001). the spring of 1994 and again in the spring of 1996. Averaged over Limited research information is available on harvest years, optimum biomass yields were obtained when switchgrass was harvested at the maturity stages R3 to R5 (panicle fully emerged from schedules for switchgrass managed as a bioenergy crop. boot to postanthesis) and fertilized with 120 kg N ha 1. Biomass yields In a previous study in Iowa, the greatest total switchgrass with these treatments averaged 10.5 to 11.2 Mg ha 1 at Mead and yields were achieved when the first harvest was taken 11.6 to 12.6 Mg ha 1 at Ames. At this fertility level, the amount of at the stem elongation stage when the fourth and fifth N removed was approximately the same as the amount applied. At nodes were palpable and when the regrowth was harrates above this level, soil NO3–N concentrations increased. vested 6 wk later (George and Obermann, 1989). In Georgia, greater yields were achieved when plants were harvested once during the growing season when they S is a perennial warm-season C4 photosynreached either 61 or 91 cm in height and the regrowth thetic system grass that is native to the tallgrass harvested in the fall after a killing frost compared with prairie regions of North America (Moser and Vogel, a single harvest in the fall after a killing frost (Beaty 1995). Based on a series of evaluation trials, the U.S. and Powell, 1976). In Tennessee, Reynolds et al. (2000) Department of Energy has identified switchgrass as the evaluated two harvest treatments (early summer and most promising species for development into an herbalate autumn vs. late autumn) for switchgrass grown at ceous biomass fuel crop (Vogel, 1996). It has an array a constant N fertilization rate of 50 kg ha 1 yr 1 for 5 yr. of desirable attributes for use as a bioenergy crop, inTreatments with the highest biomass yields varied with cluding broad adaptation and high yields on marginal years. Total N concentration of switchgrass herbage was and erosive croplands, and it can be harvested with significantly lower in biomass in late autumn compared conventional hay-making equipment. Major costs assowith summer harvests. ciated with producing switchgrass biomass include N Information on the interaction of N rates and harvest fertilization, harvesting, and transportation (Keeney and regimes is not available for managing switchgrass for DeLuca, 1992). The number of harvests and the yields biomass production in the Midwest. The main objectives per harvest affect the economics of harvesting switchof this research were to determine optimum harvest grass biomass. periods and N fertilization rates for the production of Research has been conducted on fertilizer requireswitchgrass as a biomass crop in the Midwest. The treatments of native warm-season grasses, including switchments resulted in plots that differed significantly in soil grass when managed for hay or grazing. The results of NO3 concentrations, which provided us an opportunity these trials have recently been reviewed and summato determine the response of switchgrass biomass yields rized by Brejda (2000). In brief, the main fertilizer reto residual NO3 concentrations in the year following completion of the main study. Utility of soil tests depend on significant response of the crop to soil nutrient conK.P. Vogel and J.J. Brejda, USDA-ARS, 344 Keim Hall, Univ. of centrations. Nebraska, Lincoln, NE, 68583; D.T. Walters, Dep. of Agron., 279 Plant Sciences, Univ. of Nebraska, Lincoln, NE 68583; and D.R. Buxton, USDA-ARS, 5601 Sunnyside Ave., Beltsville, MD 20705-5139. This MATERIALS AND METHODS research was funded in part by the U.S. Dep. of Energy’s Biomass Fuels program via Oak Ridge Natl. Lab., USDA-ARS, and the Univ. Experiment Design and Establishment of Nebraska. Contract no. DE-A105-900R21954. Joint contrib. of the USDA-ARS and the Univ. of Nebraska Agric. Exp. Stn. as Journal This research was conducted at the University of Nebraska Article 13263. Received 1 Feb. 2001. *Corresponding author (kpv@ Agricultural Research and Development Center near Mead, unlserve.unl.edu). Abbreviations: NIRS, near-infrared reflectance spectrometer. Published in Agron. J. 94:413–420 (2002).