Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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 BIRD COMMUNITY RESPONSE TO CONSERVATION RESERVE PROGRAM HABITAT IN MARYLAND(2010) Blank, Peter Joshua; Dively, Galen P.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The populations of many bird species in the United States that use early-successional habitats have been substantially declining over the last 40 years. The main reason for these declines is habitat loss. Land enrolled in the U.S. Department of Agriculture's Conservation Reserve Program (CRP) often represents the only uncultivated herbaceous areas on farmland in the mid-Atlantic and therefore may be important habitat for early-successional bird species. CRP filter strips are strips of herbaceous vegetation that are planted along agricultural field margins and are usually planted with native warm-season grasses or introduced cool-season grasses. We studied the breeding and wintering bird use of CRP filter strips adjacent to wooded edges in Maryland from 2004-2007. We conducted bird and vegetation surveys in filter strips and measured landscape attributes around CRP plantings. We used 5 bird community metrics (total bird density, species richness, scrub-shrub bird density, grassland bird density, and total avian conservation value), species-specific densities and abundances, nest densities, and nest survival estimates to assess the habitat value of filter strips for birds. Bird community metrics were greater in filter strips than in field margins without filter strips, but did not differ between cool-season and warm-season grass filter strips. Most breeding bird community metrics were negatively related to the percent cover of orchardgrass (Dactylis glomerata). Several grassland birds were more common in wide filter strips (>60 m) compared to narrower filter strips (<30 m). The density of early-successional bird species was greater in filter strips with higher plant species richness and shorter and less dense grasses. Wintering bird use was significantly less in filter strips mowed in the fall than in unmowed filter strips. The abundance of northern bobwhite (Colinus virginianus), an important game bird and species of conservation concern, was positively associated with the percent cover of CRP land in the surrounding landscape. These results suggest that the CRP has created additional habitat for many early-successional bird species, but changes in the planning and management of CRP plantings may improve their habitat value for breeding and wintering birds.Item Assessing the Potential for Doormats to Reduce Pesticide Residues in the Home(2006-05-04) Ganser, Leanne Marie; Brown, Amy E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the recommended practice of using doormats at entryways into the home to reduce indirect pesticide exposure. Using doormats to reduce track-in of pesticides is commonly recommended to pesticide applicators, but no studies of the usefulness of this recommendation appear in the literature. The effectiveness of doormats was evaluated by determining the soil levels dislodged from doormats and by determining the ability for laundering to remove pesticide residues embedded into the mats. The performance of three doormat types was assessed. High levels of soil were dislodged from all doormat types. Results from laundering mats showed large variability in the level of residues detected. The results from both studies were influenced by the methods used to test the dislodgeability and effectiveness of laundering. The results of the study suggest further studies are needed to determine the effectiveness of doormats to reduce the potential for pesticide contamination inside the home.Item Vegetation and Nutrient Dynamics of Forested Riparian Wetlands in Agricultural Settings(2005-05-03) Herbert, Rachel; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Exported agricultural nutrients have been a major supply of excess nutrients into the environment. Riparian wetlands may play an important part in mitigating these nutrients and thus preventing them from migrating downstream in high concentrations. Two riparian wetland systems, one was influenced by agriculture (agricultural site) and one was not (reference site), were studied in Maryland. Both the plant community structure and abiotic factors were studied. The agricultural site had lower overall species richness and tree diversity than the reference site. Also the tree leaf litter and herbaceous leaves at the agricultural site had higher nitrogen and phosphorus concentrations and higher productivity based on fixed carbon than the reference site. Two nutrient enrichment experiments were conducted at the reference site to determine the nature of nutrient limitation. The results from these studies indicate that both plant communities are nitrogen limited. Furthermore, individual species showed a response to increased nutrients.