The Effects of N Fertilization and Harvest Frequency On Switchgrass Feedstock Quality for Biofuel Production.

Although nitrogen (N) fertilization increases the grain mass yield of food crops (e.g. corn), it does not always increase the yield of individual biochemicals (Mg ha^-1), such as carbohydrates, in the same way.  Biochemicals relevant for biofuel production (e.g. carbohydrates and lignin) respond differently to N fertilization depending on the crop type and crop fraction (grain versus crop residue).  This suggests that it might not be necessary to fertilize crops intended for biofuel production (e.g. switchgrass) to the same extent as food crops, and that N management may be one way to optimize crop biochemistry to meet specific biofuel feedstock needs.

Here we measure the impact of N fertilization rate and harvest frequency on aboveground biochemical inventories of switchgrass crops (Mg ha^-1 yields of lignin, carbohydrate, protein, and lipid) using solid-state ¹³C Nuclear Magnetic Resonance Spectroscopy (NMR).  We analyze samples collected from the 2011 harvests at the Kellogg Biological Station-Great Lakes Bioenergy Research Center (KBS-GLBRC; Michigan, USA) Switchgrass Nitrogen/Harvest Frequency Experiment (Cave-In-Rock variety) as well as the University of Tennessee Research and Education Center (UT-REC; Milan, TN) N Rate Trial on switchgrass (Alamo variety).  At the KBS-GLBRC site, N fertilization rate is varied at 8 levels ranging from 0 to 196 kg ha^-1 and harvest frequency is either a two-harvest system (summer and fall harvest) or one-harvest system (fall harvest only).  At the UT-REC site, N fertilization rate is varied at 4 levels ranging from 0 to 201 kg N ha^-1.  Our goal is to determine the least amount of N fertilization needed to reach maximum yields for individual biochemical relevant to biofuel production.