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dc.contributor.advisor Masiello, Caroline A.
dc.creatorGallagher, Morgan Elizabeth
dc.date.accessioned 2013-03-08T00:33:50Z
dc.date.available 2013-03-08T00:33:50Z
dc.date.issued 2011
dc.identifier.citation Gallagher, 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. https://hdl.handle.net/1911/70243.
dc.identifier.urihttps://hdl.handle.net/1911/70243
dc.description.abstract Agriculture 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.extent 482 p.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subjectApplied sciences
Earth sciences
Biological sciences
Carbon cycles
Nitrogen cycles
Corn
Oxidative ratio
Cellulosic ethanol
Fertilization
Biofuels
Feedstock quality
Alternative energy
Biochemistry
Agriculture
dc.title The Coupling of the Carbon and Nitrogen Cycles in Agriculture: Crop Ecosystem Oxidative Ratio and the Effects of Fertilization on Biofuel Feedstock Quality
dc.type Thesis
dc.identifier.digital GallagherM
dc.type.material Text
thesis.degree.department Earth Science
thesis.degree.discipline Natural Sciences
thesis.degree.grantor Rice University
thesis.degree.level Doctoral
thesis.degree.name Doctor of Philosophy


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