UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Characterizing nutrient budgets on and beyond farms for sustainable nutrient management(2023) Zou, Tan; Zhang, Xin; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The production and security of food are heavily reliant on adequate nitrogen (N) and phosphorus (P) inputs in agriculture. However, ineffective management of N and P from the farm to the table can result in nutrient pollution, triggering both environmental and social issues. Moreover, another important challenge for P management is limited and unevenly distributed P resources, leading to P scarcity in many parts of the world. Inefficient use of nutrients in agriculture-food systems is the root cause of both nutrient pollution and scarcity. To improve nutrient use efficiency and reduce nutrient loss, it is crucial to address key knowledge gaps in nutrient management research, which include inadequate quantification of nutrient budgets, as well as identifying and addressing nutrient management challenges across various systems and spatial scales. This dissertation tackles the knowledge gaps in two studies, including a global-scale study and a case study of the Chesapeake Bay watershed. In the global-scale study, I establish and utilize a unique P budget database to assess historical P budget and usage patterns at the national and crop type level from 1961 to 2019. This analysis reveals the impacts of various agricultural and socioeconomic drivers on cropland P use efficiency (PUE), including N use efficiency (NUE), fertilizer-to-crop-price ratio, farm size, crop mix, and agricultural machinery. The findings indicate that P management challenges vary by country and spatial scale, necessitating tailored country-level strategies. The regional-scale study applies a framework adapted from N studies to the Chesapeake Bay watershed, analyzing nutrient (N and P) management across systems and spatial scales. This approach uncovers that nutrient loss potential beyond crop farms is larger than that at crop farms. This highlights the need to enhance nutrient management and curb nutrient loss in animal production, food processing and retail, and human consumption. This study also identifies a large potential for meeting cropland nutrient demand by increasing the recycling of nutrients in manure, food waste, and human waste. To tackle the challenges surrounding nutrient management in the watershed, it is imperative to target factors significantly related to nutrient management, such as agricultural practices, soil properties, climate change, and socioeconomic conditions. This dissertation contributes to a deeper understanding of N and P management challenges, gaps, priorities, hidden drivers, and potential solutions at various scales, from regional to national and global levels. The analytical procedures and statistical tools developed in this dissertation are generalizable, allowing for their adaptation to similar nutrient management studies in different regions and for diverse research purposes.Item The long-term change of Chesapeake Bay hypoxia: impacts of eutrophication, nutrient management and climate change(2019) Ni, Wenfei; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication-induced coastal hypoxia can result in stressful habitat for marine living resources and cause great economic losses. Nutrient management strategies have been implemented in many coastal systems to improve water quality. However, the outcomes to mitigate hypoxia have been mixed and usually small when only modest nutrient load reduction was achieved. Meanwhile, there has been increasing recognition of climate change impacts on estuarine hypoxia, given estuaries are especially vulnerable to climate change with multiple influences from river, ocean and the atmosphere. Due to the limitation of observational studies and the lack of continuous historical data, long-term oxygen dynamics in response to the changes of external forces are still not well understood. This study utilized a numerical model to quantitatively investigate a century of change of Chesapeake Bay hypoxia in response to varying external forces in nutrient inputs and climate. With intensifying eutrophication since 1950, model results suggest an abrupt increase in volume and duration of hypoxia from 1950s-1960s to 1970s-1980s. This turning point of hypoxia might be related with Tropical Storm Agnes and consecutive wet years with relatively small summer wind speed. During 1985-2016 when the riverine nutrient inputs were modestly decreased, the simulated bottom dissolved oxygen exhibited a statistically significant declining trend of ~0.01 mgL-1yr-1 which mostly occurred in winter and spring. Warming was found to be the dominant driver of the long-term oxygen decline whereas sea level rise had a minor effect. Warming has overcome the benefit of nutrient reduction in Chesapeake Bay to diminish hypoxia over the past three decades. By the mid-21st century, the hypoxic and anoxic volumes are projected to increase by 10-30% in Chesapeake Bay if the riverine nutrient inputs are maintained at high level as in 1990s. Sea level rise and larger winter-spring runoff will generate stronger stratification and large reductions in the vertical oxygen supply to the bottom water. The future warming will lead to earlier initiation of hypoxia, accompanied by weaker summer respiration and more rapid termination of hypoxia. The findings of this study can help guide climate adaptation strategies and nutrient load abatement in Chesapeake Bay and other hypoxic estuaries.Item Evaluating Soil Phosphorus Dynamics over Time(2017) Lucas, Emileigh Rosso; Coale, Frank J; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agricultural nutrient management became mandatory in Maryland (MD) due to water quality concerns. Phosphorus (P) management is complex due to the stability of P in the soil, nutrient mass imbalance, and “legacy” P. To explore how potential P application bans impact historically manured fields, agronomic and environmental soil tests were conducted on plots treated with five manure-P rates, then no P applications, spanning 15 years. Mehlich-3 extractable P (M3P) declined slowly and then generally did not change during the last six years. Phosphorus saturation declined slowly or not significantly. Excessive P soils had sufficient P for crop growth in solution. Phosphorus saturation and M3P were compared in fifty sites across MD pre- and post- nutrient management planning. Results showed an increase in P concentration of Maryland agricultural fields. This response was logical, as better management would increase below-optimum P concentrations, and the regulations were not designed to draw down P.Item On-Farm Dry Matter Analysis to Improve Feed Delivery Precision on Dairy Farms(2011) French, Karin R.; Kohn, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Uncertainty in dairy ration content impacts feed efficiency, milk production, expenses, and environmental losses. When measuring silage by weight, unknown changes in dry matter (DM) may change the total mixed ration. The objective of this study was to measure variation in silage DM on selected farms and evaluate an electronic method of on-farm DM analysis. Of 31 Maryland farms surveyed, 63% reported DM analysis by an on-farm method, 83% by any method including laboratory measurement. Eight producers performed DM analysis daily for 21 days using a Farmex 1210 Electronic Silage Tester (on-farm) and they recorded precipitation; matching samples were analyzed for DM in a laboratory after oven drying ("standard" method, 55°C followed by 100°C) and by using a Farmex 1210 (laboratory). The standard deviation of mean silage DM varied from 0.72% to 3.33% DM, depending on farm. The electronic method compared poorly to standard DM analysis for most farms.