Thesis (Ph. D.)--University of Florida, 2004. / Title from title page of source document. Document formatted into pages; contains 343 pages. Includes vita. Includes bibliographical references.

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Excessive delivery of fine sediment from agricultural river catchments to aquatic ecosystems can degrade chemical water quality and ecological habitats. Management of accelerated soil losses and the transmission of sediment-associated agricultural pollutants, such as phosphorus, is required to mitigate the drive towards sustainable intensification to increase global food security. Quantifying soil erosion and the pathways and fate of fine-grained sediment is presently under-researched worldwide, and particularly in Ireland. This thesis established a sediment monitoring network upon an existing catchment study programme (Agricultural Catchments Programme) in five instrumented catchments (~10 km2) across Ireland. The research used novel, high quality measurement and analysis techniques to quantify sediment export, determine controls on soil erosion and sediment transport, and identify sediment contributions from multiple sources in different agricultural systems over time to evaluate approaches to fine sediment management. Results showed suspended sediment measurement using a novel ex situ methodology was valid in two of the study catchments against in situ and direct depth-integrated cross-section methodologies. Suspended sediment yields in the five intensive agricultural catchments were relatively low compared to European catchments in the same climatic zone, attributed to regionally-specific land use patterns and land management practices expressed in terms of ‘landscape complexity’ (irregular, small field sizes partitioned by abundant hedgerows and high drainage ditch densities) resulting in low field-to-channel connectivity. Variations in suspended sediment yield between catchments were explained primarily by soil permeability and ground cover, whereby arable land use on poorly-drained soils were associated with the largest sediment yields. Storm-event sediment export and sediment fingerprinting data demonstrated that sediment connectivity fluctuations resulted from rainfall seasonality, which in turn regulated the contrasting spatial and temporal extent of surface hydrological pathways. Increased transport occurred when and where sediment sources were available as a result of hillslope land use (low groundcover) or channel characteristics. Field topsoils were most vulnerable when low groundcover coincided with surface hydrological pathways; frequently on poorly-drained soils and following extreme rainfall events on well-drained soils as storage decreased. Although well-drained soils currently demonstrate low water erosion risk, past sugar beet crops exposed freshly drilled soils during periods of greater rainfall risk and soil removal during crop harvesting. Sediment loss from grassland catchments dominated by poorly-drained soils and extensive land drainage (sub-surface and surface) primarily derived from channel banks due to the delivery of high velocity flows from up-catchment drained hillslopes. Catchment specific soil erosion and sediment loss mitigation measures are imperative to cost-effectively preserve or improve soil and freshwater ecosystem quality worldwide.

Thesis (M.A.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 21, 2009) Includes bibliographical references.

Over the last 50 years populations of certain farmland birds have undergone severe declines over the same timescale that agriculture has intensified. The larvae of grassland sawflies (Hymenoptera, Symphyta) are a key component of the fledgling diet and it is thought that agri-intensification has reduced the numbers of these insects to such an extent that the populations of bird species dependent on them are limited. Sawfly populations may be more than usually susceptible to disturbance because firstly, their adult stages are poor dispersers and secondly, some species possess Complementary Sex Determination (CSD), a mechanism which can produce sterile males under inbreeding conditions. This study has produced a sawfly transcriptomic library through the use of 454 pyrosequencing, the first genetic resource for any farmland sawfly. From this library, a set of 13 polymorphic microsatellite markers were isolated for use in the common farmland sawfly Dolerus aeneus. Using these markers, three Scottish populations of D. aeneus, a species common to all six UK sites sampled in this study, exhibited similar levels of genetic diversity and low levels of genetic differentiation. However, evidence of inbreeding was detected in each of the three populations. In addition, potential diploid males were detected in D. aeneus using microsatellite markers, a primary indication that CSD may be operating in this species. The population genetic analysis in the current study suggests that fragmentation of suitable sawfly habitat as a result of agricultural intensification has not yet acted to isolate D. aeneus populations, although some genetic effects (inbreeding and low diversity compared with non-threatened hymenopterans) are apparent. In addition, diploid males have been detected which may have compromised fertility. This study will be of interest to research groups working on the genetics of the Hymenoptera and on the conservation and management of sawflies and the bird species dependent on them.

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It has been argued that organic farming sustains a higher biodiversity than conventional farming. This might promote the ecosystem services that exist in agricultural landscapes such as pollination and pest control. Here, I examined the effect of farming system (organic vs. conventional) with respect to the time since farming system transition, landscape heterogeneity and plant richness on pollinating and predatory insects. In total, data from 30 farms were used, of which 20 were organic and 10 were conventional. The data were analyzed using general linear models and model averaging. The results show that insect groups responded differently to various factors. Pollinators were more sensitive to landscape complexity, showing an increase of abundance and species richness with an increased heterogeneity. Predators on the other hand reacted to farming system, where there was an increase in abundance and species richness on organic farms.

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The Midwestern United States is a nationally and globally important producer of agricultural products and uses intensive practices to achieve high grain yields. However, intensive agriculture is a major contributor of nitrogen and phosphorus export to the Mississippi River and the hypoxic zone in the Gulf of Mexico. Cover cropping is a recommended conservation practice for providing soil cover throughout the winter and taking up nutrients that may otherwise be lost in bare fallow systems, but the associated costs limit widespread adoption of this practice. Double cropping, which involves growing two crops in one year, is functionally similar to cover cropping and can be harvested for an additional income, but the water quality impacts of applying fertilizer to maximize yields and the systemic impacts of intensification with another crop on corn-soybean rotations are not well understood. This two-year, plot scale study in Carbondale, Illinois was designed to assess nutrient leaching, referring to nitrate-N, ammonium-N, and dissolved reactive phosphorus (DRP), nutrient availability, and crop yields when using bare fallow, cereal rye (Secale cereale) cover crops, or winter wheat (Triticum aestivum) double crops with varying nitrogen fertilizer rates and timings in the winter seasons of corn-soybean rotations. Four blocks with randomly assigned treatments comprised of two treatment factors were used. These treatment factors included rotations with either bare fallow or cover crops in alternate winters and winter wheat fertilizer management intensity with a high fertilizer treatment level, grower recommended rates applied at planting, tillering, and jointing, a medium fertilizer treatment level, grower recommended rates applied at tillering and jointing, a low fertilizer treatment level, with reduced nitrogen rates applied at tillering and jointing, and a no fertilizer treatment level, which was used as either corn-soybean or corn-cover crop-soybean-cover crop control. Additional nutrient inputs from fertilizers in the winter wheat seasons did not significantly increase nitrate-N, ammonium-N, or DRP leaching in the 2021-2022 winter wheat sampling season and nitrate-N and ammonium-N leaching was significantly less in some or all the winter wheat plots compared to the control plots. Winter wheat yields and nitrogen uptake in 2022 were significantly greater in medium fertilizer plots while yield-based nitrogen leaching and partial nitrogen balances were significantly greater in high fertilizer treatments, indicating that delayed fertilization in winter wheat can improve nitrogen use efficiency and yields. Soybean yields were significantly greater in plots without winter wheat due to a longer growing season, but plant available ammonium-N concentrations, which were greater in winter wheat plots, also had a significant negative relationship with soybean yields, indicating that this may have impeded biological nitrogen fixation. Using cover crops in alternate winters reduced nitrate-N leaching by 106% and plant available nitrate-N concentrations by 107% in the season as well as the subsequent corn season by 66% and 90%, respectively, compared to the bare fallow plots, and the decreased plant available nitrate-N concentrations in cover crop plots caused a 6% yield penalty in the corn harvest. Despite yield penalties to cash crops from winter crops, the use of double crops was the only factor that significantly impacted total crop yields. The use of cover crops in alternate winters was the most significant factor in nutrient leaching, demonstrating that these practices can be used to increase total crop yields without contributing significantly to nutrient export. For farmers concerned with the costs of cover cropping, double cropping is a practice that can provide some of the same ecosystem services while also providing an additional financial incentive.