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.en_US
dc.creatorGallagher, Morgan Elizabethen_US
dc.date.accessioned2013-03-08T00:33:50Zen_US
dc.date.available2013-03-08T00:33:50Zen_US
dc.date.issued2011en_US
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.en_US
dc.format.extent482 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS GEOL. 2011 GALLAGHERen_US
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>.en_US
dc.identifier.digitalGallagherMen_US
dc.identifier.urihttps://hdl.handle.net/1911/70243en_US
dc.language.isoengen_US
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.en_US
dc.subjectApplied sciencesen_US
dc.subjectEarth sciencesen_US
dc.subjectBiological sciencesen_US
dc.subjectCarbon cyclesen_US
dc.subjectNitrogen cyclesen_US
dc.subjectCornen_US
dc.subjectOxidative ratioen_US
dc.subjectCellulosic ethanolen_US
dc.subjectFertilizationen_US
dc.subjectBiofuelsen_US
dc.subjectFeedstock qualityen_US
dc.subjectAlternative energyen_US
dc.subjectBiochemistryen_US
dc.subjectAgricultureen_US
dc.titleThe Coupling of the Carbon and Nitrogen Cycles in Agriculture: Crop Ecosystem Oxidative Ratio and the Effects of Fertilization on Biofuel Feedstock Qualityen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentEarth Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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