Using 13c Nuclear Magnetic Resonance Spectroscopy to Estimate Biochemical Stocks and Biofuel Feedstock Quality.

Increasing concern over rising oil prices and greenhouse gas emissions has led to a growing demand for alternative energy sources, particularly biofuels.  Ethanol has been the major biofuel in production to date, and increasing food prices and malnourishment have led to an increased focus on cellulosic ethanol, since this fuel uses non-food feedstocks.  Understanding how feedstock quality can vary with feedstock and agricultural management (i.e. N management) is critical to sustainably advancing the biofuels industry.  Estimating feedstock biochemical (lignin, carbohydrate, lipid, and protein in Mg/ha) stocks using ¹³C nuclear magnetic resonance (NMR) spectroscopy can help us understand how feedstock quality can vary with species and agricultural management. 

NMR spectra qualitatively and quantitatively assess the bonding environment of carbon in a sample.  The relative proportions of major classes of biochemicals can be directly calculated from ¹³C NMR peak areas using a mixing model developed by Baldock et al. (2004).  C-13 NMR is an improvement over wet chemistry techniques, since it is nondestructive, relatively cheap and fast, and can detect all types of C present in a sample in one measurement, while wet chemistry techniques are typically compound-specific and only detect between 20-80% of the C present (Baldock et al. 2004; Harmon and Lajtha 1999).  

Here we show ¹³C NMR biochemical stocks results for biofuel feedstocks (crop residues, grasses, switchgrass, etc.), focusing on how they differ from each other and corn grain.  We discuss how measuring biochemical stocks can be used to monitor, compare, and improve feedstock quality (e.g. more carbohydrate, less lignin) and biochemical quantity.  Different feedstock species (e.g. corn/switchgrass) and organ fractions (e.g. grain/residue) respond differently to agricultural management, specifically nitrogen fertilization.  Our results imply that nitrogen fertilization may be one way crop quality can be altered for an intended purpose (food or fuel).