The Coupling of the Carbon and Nitrogen Cycles in Agriculture: Crop Ecosystem Oxidative Ratio and the Effects of Fertilization on Biofuel Feedstock Quality

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dc.contributor.advisorMasiello, Caroline A.
dc.creatorGallagher, Morgan Elizabeth
dc.date.accessioned2013-03-08T00:33:50Z
dc.date.available2013-03-08T00:33:50Z
dc.date.issued2011
dc.description.abstractAgriculture significantly impacts the global carbon (C) and nitrogen (N) cycles through land use change, soil C loss, greenhouse gas emissions, and increased fixed-N availability. Agriculture occupies a third of the terrestrial biosphere, making understanding its impacts on the C and N cycles critical. I used a novel analytical tool (solid-state 13 C nuclear magnetic resonance spectroscopy) to characterize properties of the C and N cycles in agriculture, including biochemical responses to N fertilizer and agriculture gas fluxes. A central component of the C cycle is the rapid exchange of carbon dioxide (CO 2 ) and oxygen (O 2 ) between the terrestrial biosphere and the atmosphere. Gas flux O 2 /CO 2 ratios (oxidative ratio-OR) vary depending on ecosystem type, plant species, and nutrient status. It is necessary to constrain OR to assess the uptake of anthropogenic CO 2 by the terrestrial biosphere and ocean. I measured the OR of the top three crops in the United States (soybean, corn, and wheat) and found significant variability. I additionally tested the effect of N fertilizer application on corn ecosystem OR and on the difference between respiration and photosynthesis OR and observed no detectable changes. Conversely, soil organic matter OR is different from gas flux OR values, likely due to the influence of past land use and fractionation of OR during decomposition. I also analyzed how anthropogenic inputs to the N cycle (N fertilizer) and sustainable agriculture practices (cover crop) change plant biochemistry. This work has immediate implications for the biofuel industry. A central challenge to cropping for cellulosic ethanol feedstocks is the potential environmental damage from increased fertilizer use. I showed that yield increases in response to fertilization are not uniform across biochemical classes (carbohydrate, protein, lipid, lignin) or tissues (leaf and stem, grain, reproductive support). Heavy fertilizer application yields minimal grain benefits and almost no benefits in residue carbohydrates, while degrading the cellulosic ethanol feedstock quality and soil C sequestration capacity. Further cost analysis of these results showed that it is not cost-effective for farmers to apply high levels of N fertilizer, whether the crop is intended for food or fuel.
dc.format.extent482 p.en_US
dc.format.mimetypeapplication/pdf
dc.identifier.callnoTHESIS GEOL. 2011 GALLAGHER
dc.identifier.citationGallagher, Morgan Elizabeth. "The Coupling of the Carbon and Nitrogen Cycles in Agriculture: Crop Ecosystem Oxidative Ratio and the Effects of Fertilization on Biofuel Feedstock Quality." (2011) Diss., Rice University. <a href="https://hdl.handle.net/1911/70243">https://hdl.handle.net/1911/70243</a>.
dc.identifier.digitalGallagherMen_US
dc.identifier.urihttps://hdl.handle.net/1911/70243
dc.language.isoeng
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.
dc.subjectApplied sciences
dc.subjectEarth sciences
dc.subjectBiological sciences
dc.subjectCarbon cycles
dc.subjectNitrogen cycles
dc.subjectCorn
dc.subjectOxidative ratio
dc.subjectCellulosic ethanol
dc.subjectFertilization
dc.subjectBiofuels
dc.subjectFeedstock quality
dc.subjectAlternative energy
dc.subjectBiochemistry
dc.subjectAgriculture
dc.titleThe Coupling of the Carbon and Nitrogen Cycles in Agriculture: Crop Ecosystem Oxidative Ratio and the Effects of Fertilization on Biofuel Feedstock Quality
dc.typeThesis
dc.type.materialText
thesis.degree.departmentEarth Science
thesis.degree.disciplineNatural Sciences
thesis.degree.grantorRice University
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
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