Effects of Nitrogen Fertilizer On Soil Organic Matter Pools Under Switchgrass Agriculture.

The cropping of switchgrass (Panicum virgatum) for biomass shows potential for high yields in marginal lands with low fertilizer inputs, while the extensive root system can act to improve soil quality and sequester atmospheric carbon dioxide in the soil carbon pool. We are investigating the impact of nitrogen fertilizer inputs on soil organic matter quantity and quality in a biofuels cropping trial in Michigan. Here we test the hypothesis that fertilizer application rate can affect the partitioning of organic matter into different storage pools within the soil: roots, particulate organic matter (density <1.8 g/cm³), and protected organic matter (density > 1.8 g/cm³).  Additionally, we use ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy to study the bulk chemistry (carbohydrate, lignin, lipid, and protein) of the roots and particulate soil organic matter. The NMR data also allow us to estimate the relative decomposition of the soil organic matter using a standard decomposition index (alkyl/O-alkyl peak ratio). We use these data to infer the influence of fertilizer management on the mechanisms of soil C storage and decomposition in switchgrass agriculture.