Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2010
Publication Date: 1/7/2011
Citation: Garten, C.T., Brice, D.J., Castro, H.F., Graham, R.L., Mayes, M.A., Phillips, J.R., Post, W.M., Schadt, C.W., Wullschleger, S.D., Tyler, D.D., Jardine, P.M., Jastrow, J.D., Matamala, R., Miller, R.M., Moran, K.K., Vugteveen, T., Izaurralde, R.C., Thomson, A.M., West, T.O., Amonette, J.E., Bailey, V.L., Metting, F.B., Smith, J.L. 2011. Response of Alamo switchgrass tissue chemistry and biomass to nitrogen fertilization in West Tennessee, USA. Agriculture, Ecosystems and Environment. 140:289-297. doi:10.1016/j.agee.2010.12.016. Interpretive Summary: Switchgrass is a perennial, warm-season grass that has been identified as a potential biofuel feedstock throughout a large part of North America. The purpose of this research was to examine above- and belowground responses to nitrogen fertilization in 5-year old “Alamo” switchgrass. Nitrogen fertilization impacted both above- and belowground biomass and tissue chemistry in a way that potentially affects soil carbon cycle processes; high fertilization could accelerate root decomposition and reduce soil carbon. The data from these experiments will be especially useful for scientists and producers of switchgrass to determine the nitrogen needed for high yield production of switchgrass for biofuel feedstock.
Technical Abstract: The purpose of this research was to examine above- and belowground responses to nitrogen fertilization in 5-year old “Alamo” switchgrass (Panicum virgatum). A fertilizer experiment included spring and fall sampling of switchgrass grown under annual applications of 0, 67, and 202 kg N ha-1. Nitrogen fertilization impacted both above- and belowground biomass and tissue chemistry in a way that potentially affects soil carbon cycle processes. Our first hypothesis, that nitrogen fertilization would significantly alter plant biomass or carbon allocation, was only partly supported because even though end-of-growing season mean (±SE) root:shoot ratios declined significantly (P =0.05) with fertilization (2.16 ±0.08, 2.02 ±0.18, and 0.88 ±0.14, respectively, at 0, 67, and 202 kg N ha-1) both above- and belowground biomass tended to increase in response to nitrogen fertilization. Results supported a second hypothesis that nitrogen fertilization would decrease root C:N ratios, primarily as a consequence of increasing tissue nitrogen concentrations. Nitrogen supply through fertilization appeared to most closely matched by plant nitrogen demand at the lowest fertilizer treatment where calculated annual nitrogen uptake was 6.6 g N m-2. Because of changes in root C:N ratios, high rates of nitrogen fertilization (>67 kg N ha-1) could accelerate root decomposition and result in reduced soil carbon inputs beneath switchgrass; however, this response depends on the interplay between processes leading to protection of soil carbon inputs and changing root decomposition rates as a function of changes in tissue chemistry.