Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2001
Publication Date: 3/1/2002
Citation: Vogel, K.P., Brejda, J.J., Walters, D.T., Buxton, D.R. 2002. Switchgrass biomass production in the midwest: harvest and nitrogen management. Agronomy Journal. Agronomy J. 94:413-420. Interpretive Summary: The U.S. Department of Energy has identified switchgrass as a potential biomass fuel crop for the USA. Information on optimal harvest periods and N fertilization rates for switchgrass grown as a biomass or bioenergy crop in the Midwest is limited. Results of this study indicate that in the Midwest, the optimal time to harvest switchgrass for biomass yields is when nit is at the 3.3 (R3) to 3.5 (R5) stage of maturity (panicles fully emerge to post-anthesis). Maximum first cut yields were obtained at these growth stages. In some years, sufficient regrowth may be obtained for a second harvest after a killing frost. These morphological stages usually occur the first three weeks of August for adapted cultivars. In terms of time management, this would be a good time for most Midwest farmers because corn and soybeans are not ready for harvest and other field work has often been completed by this time. Approximately 20 lbs N per acre needs to be applied for each ton of switchgrass biomass produced when harvested at the R3 to R5 maturity stages to obtain optimal yields. Yields for harvests at these maturity stages averaged between 5 and 6 tons dry matter per acre. At these fertility levels the amount of N removed in the biomass was approximately the same as the amount applied.
Technical Abstract: Information on optimal harvest periods and N fertilization rates for switchgrass (Panicum virgatum L.) grown as a biomass or bioenergy crop in the Midwest 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 with six rates of N equivalent to 0, 60, 120, 180, 240 or 300 kg N ha-1. Harvest treatments per year were two or one cut treatments and based on initial harvest dates starting in late June or early July (Harvest 1) and continuing at approximately weekly intervals until the latter part of August (Harvest 7) with a final 8th harvest after a killing frost at which time regrowth was also harvested on previously harvested plots.Soil samples were taken before initiation of the fertilizer treatments in the spring of 1994 and again in the spring of 1996.Maximum first harvest yields and total lyields occurred at harvests made after the plants were at maturity stages R3 to R5 (panicle fully emerged from boot to post-anthesis) at both locations. Results indicate 10 to 12 kg ha-1 of N needs to be applied for each Mg ha-1 of switchgrass biomass yield when harvested at the R3 to R5 maturity stages. Yields for harvests at these maturity stages averaged 10.5 to 11.2 Mg ha-1 at Mead and 11.6 to 12.6 Mg ha-1 at Ames.At these fertility levels the amount of N removed was approximately the same as the amount applied. At rates above these levels, soil NO3-N concentrations increased. Nitrogen removed in the biomass harvest after a killing frost and the N concentration of the biomass from that harvest were significantly lower than for other treatments.