Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Now showing 1 - 4 of 4
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    Extending the Cover Crop Growing Season to Reduce Nitrogen Pollution
    (2021) Sedghi, Nathan; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Maryland currently has the highest rate of cover crop use in the United States. The Cover Crop Program, started as an initiative to clean nutrients from the Chesapeake Bay, has made it a common practice to plant a cereal cover crop after cash crop harvest in fall, and kill it several weeks before cash crop planting in spring. In Maryland, this practice does not allow enough growing time with warm conditions for optimal cover crop growth. Planting earlier in fall and killing a cover crop later in spring could improve soil N cycling. We hypothesized that interseeding into a cash crop in early fall, and delaying spring cover crop termination could increase cover crop biomass, carbon accumulation, and nitrogen uptake and decrease nitrate leached. We tested these hypotheses over four years with five field experiments, consistently using a brassica-legume-cereal cover crop mix. We evaluated the relationships between cover crop planting date and fall cover crop N uptake and reduction in nitrate leaching. In spring, we tested termination timing effects on cover biomass C and N, soil mineral N concentration, soil moisture, and corn yield. We tested multiple dates for broadcast interseeding cover crops into standing soybean cash crops. We partnered with farmers on Maryland’s Eastern Shore to test if our methods are feasible at a realistic scale. We measured nitrous oxide emissions to test if our recommended cover crop practice has the negative drawback of increasing emissions of nitrous oxide, a powerful greenhouse gas. The nitrate leached under late drilled and early interseeded methods were comparable under conditions which favored late drilling, but interseeding outperformed drilling when there was adequate rainfall for seed germination. The result was lower nitrate porewater concentrations under early planted cover crops. Nitrous oxide emissions increased slightly with cover crops relative to no cover crop, but the increase was negligible when compared to the nitrous oxide produced from applying N fertilizer. Our research showed that extending the cover crop growing season of a brassica-legume-cereal mix has multiple environmental benefits and few drawbacks.
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    Controlling ammonia emissions from concentrated feeding operations
    (2011) Satam, Chinmay Charuhas; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ammonia is an essential component in the formation of particulate matter which has been a growing concern for areas along the Mid-Atlantic region. Also, animal husbandry operations have been isolated as the single largest sources of ammonia. Hale III (2005) suggests a strategy to reduce ammonia emissions from chicken manure using a dietary gypsum-zeolite infusion and slight crude protein reductions. A follow up study conducted by Wu-Haan et al. (2007) places the ammonia reduction values at 39 %. Simulations of this strategy for the MANEVU region find PM2.5 reductions of up to 37.5% for the Delmarva Peninsula. Additionally, 6 hours of improved compliance (15 μg/m3 standard) is seen in this region, during moderate PM2.5 episodes. It was also observed that regions near the source, and down wind, with high available nitric to sulfuric acid ratios are benefited by this strategy which primarily targets ammonium nitrates.
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    USING "SMALL" MOLECULES AS TRANSMEMBRANE ANION TRANSPORTERS
    (2009) Okunola, Oluyomi Adeola; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Functional, "small" molecule anion transporters have been identified and developed from natural products and synthetic organic compounds. The major discoveries include the design of a transmembrane Cl- transporter whose activity is pH-tunable, a NO3- transporter that displays unique selectivity for NO3- over Cl- anions, and a series of small molecules that efficiently transport HCO3- across liposomal membranes via a HCO3-/Cl- exchange mechanism. An assay for detecting transmembrane HCO3- transport using paramagnetic Mn2+ and 13C NMR is also described. Modulated Cl- transport was achieved by lipophilic calix[4]arene amides 2.2-2.4, all in the cone conformation. Modulation was achieved through functional group modification to one of the four side-chains. The cone conformation was confirmed by both 1H NMR and X-ray crystallography. Significantly, Cl- transport was gated by pH in the presence of triamido calixarene TAC-OH 2.3, which possesses a phenolic hydroxyl group. Using fluorescence assays, the rate of Cl- transport by TAC-OH 2.3 across liposomal membranes decreased with increasing pH, while transport rate by cone-H 2.2a, lacking an OH group, was not affected by pH. Nitrate was selectively transported over Cl- in the presence of nitro tripod 3.1, a small molecule receptor for both anions. The selective transport of NO3- by 3.1 is a significant discovery as most known synthetic Cl- transporters also transport NO3- ions and vice versa. Nitrate transport across liposomal membranes was confirmed by enzyme-coupled and fluorescence assays. Tripod 3.1 induced an increase in the intravesicular pH of liposomes that were not experiencing a pH gradient, while no pH changes occurred in the presence of calixarene 2.1 a known Cl- and NO3- transporter. This result suggests that 3.1 is an H+/NO3- symporter. Transmembrane HCO3- transport was achieved using the natural product, prodigiosin, 4.1, and synthetic isophthalamides 4.2-4.4. The Cl-/HCO3- exchange mechanism by which compounds 4.1-4.4 transport HCO3- was elucidated by ISE and NMR assays. The 13C NMR assay provided direct evidence for HCO3- transport in the presence of paramagnetic Mn2+ ions, and was adaptable to various assay conditions.
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    Brassica Cover Crops for Nitrogen Retention in the Maryland Coastal Plain
    (2006-07-27) Dean, Jill Elise; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Brassica cover crops, forage radish (Raphanus sativus L. cv 'Daichon'), oilseed radish (Raphanus sativus L. cv 'Adagio'), rape (Brassica napus L. cv 'Dwarf Essex'), and cereal rye (Secale cereale L. cv 'Wheeler') were examined for ability to decrease mineral N losses and influence organic N cycling at two Maryland Coastal Plain agricultural sites. Brassicas were similar or superior to rye regarding N uptake and soil profile NOsub3-N depletions (105-180 cm depth). Rape and rye maintained soil porewater NOsub3-N below 3 mg L to the minus 1 throughout spring while radish performed similarly on fine-textured soil, but caused porewater NOsub3-N > 10 mg L to the minus 1 on coarse-textured soil. Dissolved organic N averaged 51% of total N in porewater, but was unaffected by cover crops. Brassicas were as effective as rye in minimizing mineral N losses, but the role of cover crops in managing organic N was unclear.