Substituting Biofuel for Coal: Determining the Optimal Perennial Grass Species and Nitrogen Fertilization Level for Bioenergy Production in Eastern Ontario
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Renewable energy production has become increasingly important in recent years due to climate change and energy security issues, and bioenergy crops may be able to supply a large amount of the world’s energy needs. Bioenergy is a carbon-neutral energy source, and perennial grasses are an ideal bioenergy crop due to their high growth rates and ability to grow under a range of conditions. To enhance grass productivity, nitrogen fertilization is often applied to these crops, but this can lead to increased emissions of nitrous oxide (N2O), a potent greenhouse gas (GHG), from the soil. In collaboration with Lafarge Cement in Bath, Ontario, three perennial grass species (Panicum virgatum, Schizachyrium scoparium and Andropogon gerardii) were grown in conjunction with three fertilization treatments (0, 50 and 150 lbs/acre of nitrogen as urea) to explore the tradeoffs associated with using nitrogen fertilizer in these bioenergy systems. Soil N2O emissions were measured weekly during the growing season, following fertilizer application in May 2013. At the same time, various soil properties known to influence N2O emissions (pH, soil temperature and soil moisture) were measured. Crop productivity was measured at the end of the growing season to determine the species and fertilization level at which GHG emission benefits are maximized. N2O fluxes were significantly higher in the 150 lbs./acre treatment, with no significant difference between the 0 and 50 lbs./acre treatments. Grass species had no effect on N2O fluxes from the different fertilization treatments. Total GHG fluxes, which incorporate CO2 and CH4 in addition to N2O, exhibited similar results among the fertilization treatments, and were also shown to be higher in the control treatment than the other three species treatments due largely to differences in soil CO2 production. Nitrogen fertilizer, however, did not significantly increase grass aboveground biomass. My results indicate that these perennial grass species are viable bioenergy crops in Eastern Ontario, and that the addition of nitrogen fertilizer at this site would reduce the benefits of the bioenergy crop to the climate system.