Browsing by Subject "agroecology"
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Item Agroecological approaches to warm-season cover cropping in northern climate vegetable systems and building collaborations with farmers(2020-07) Wauters, VivianSummer cover crops are a management tool that vegetable farmers can use to counteract the negative effects of soil degradation by physically protecting soil, contributing biomass to soil organic matter (SOM), suppressing weed growth, and enhancing nutrient cycling, but their use may be limited in the short growing season of northern climates. Evaluating the effects of cover crops on soil nutrient cycling and SOM in northern climates is an opportunity to collaborate with farmers, which is important because such collaboration improves the quality of knowledge gained from research by recognizing the incompleteness of any single perspective. Collaborative and participatory research is also a means to address the unequal power dynamics in agriculture that have systemically disadvantaged immigrant and minority farmers through interlocking challenges accessing capital, land, and information. In this dissertation, summer cover crops were evaluated in collaborative on-farm trials in northern climates for their ability to accumulate biomass, suppress weeds, affect soil C and N pools, and contribute to fall cash crop yield. Additionally, this dissertation includes a qualitative analysis of existing collaborative relationships between members of a local immigrant farmer cooperative and representatives from Extension, the Department of Agriculture, and a local agricultural non-profit. The summer cover crop trial consisted of four cover crop species treatments, grown for 30 (SD) or 50 days (LD) alongside bare fertilized and unfertilized control treatments: buckwheat (Fagopyrum esculentum) and sunn hemp (Crotalaria juncea) monocultures, and biculture of chickling vetch (Lathyrus sativus) or cowpea (Vigna unguiculata) with sorghum-sudangrass (sudax) (Sorghum bicolor x S. bicolor var. Sudanese). To quantify cover crop quantity, quality, and weed growth and seed set suppression capability, we measured cover crop and weed biomass and biomass C:N. To quantify effects on cash crops, we measured fall broccoli yield and biomass. Soil N and C cycling were quantified at cover crop peak growth (directly before termination) and one week after cover crop termination for mineral N, PMN, organic N, POX-C, extractable organic C, as well as fluorescein diacetate hydrolysis (FDA) as a proxy for microbial activity to contextualize the other measurements. Cover crops produced biomass consistent with that of more southern climates but legumes did not grow well and did not overcome weed pressure. All cover crops contribute to nutrient retention but not fertility benefits and negatively impacted fall cash crop yield. Collaborative relationships with farmers were dependent on external institutional support, and food systems professionals differed in whether they adopted an equity or equality lens.Item Arthropod Predation in Brassica Agroecosystems: Effects of Latitude, Community Composition, and Diet Breadth(2020-04) Gray, HannahArthropod predators provide crucial pest management services by consuming herbivore prey in agroecosystems. Yet, variation in arthropod predation strength among cropping systems and regions can prevent farmers from taking advantage of this alternative pest management strategy. This research examines underexplored potential causes of variation in arthropod predation in agroecosystems. Arthropod predation increases at lower latitudes. However, it is unknown whether this gradient extends to agroecosystems. Diet breadth of an arthropod predator can influence whether a predator can adequately control resident herbivore populations and can impact predation in a community context by determining whether predatory taxa will compete over shared prey, attack each other as intraguild prey, or partition herbivore taxa into distinct prey niches. To assess the effect of latitude, I first compared predation rates on live and artificial sentinel prey in Brassica agroecosystems between the tropical Federal District, Brazil and temperate Minnesota, United States. Contrary to expectations, I found that predation rates on all bait types were similar between the two localities and that reduced predation rates in the Federal District may be related to higher prey densities. Next, to further explore latitudinal effects, I assessed predation rates in Brassica agroecosystems across 15 degrees of latitude in the United States and 21 degrees of latitude in Brazil. Surprisingly, my results revealed a reverse predation gradient whereby arthropod predation increased with latitude in both countries. To examine the role of diet breadth, I first tested methods to improve molecular gut content analysis of arthropod predators by verifying broad metabarcoding results with species-specific melting curve analysis. This study documented common false positive and false negative taxonomic results and suggested that a species-specific verification step is necessary to ensure accurate depictions of arthropod trophic interactions. Lastly, I use the results of the gut content analysis to characterize the diet breadth of three coccinellid predator species (Coleomegilla maculata, Hippodamia convergens, and Harmonia axyridis) collected from a Brassica agroecosystem in Minnesota. I found that both herbivore and intraguild prey consumption were common among coccinellid species, but that C. maculata was least likely to engage in intraguild predation of fellow coccinellids.Item Examining propolis use, social immunity, and food systems transformation to support colony health in honey bees and stingless bees(2023-05) Shanahan, MaggieAs the industrialization of agriculture and other environmental stressors threaten honey bees, stingless bees, and beekeeper livelihoods throughout the world, beekeepers and researchers seek solutions to support bee health. Although many beekeeping practices are designed to support colony health, some inadvertently constrain the natural defenses (or mechanisms of social immunity) that help bees thrive in an unmanaged context. In addition, although most honey bee research seeks to counteract the multiple interacting stressors that cause colony loss, researchers often fail to mention industrial agriculture – the root cause of those stressors – and thus further normalize a major source of bee decline. This dissertation seeks to understand and bolster the natural defenses bees use to support colony health, and to identify ways in which honey bee researchers can reframe their research to contribute to food systems transformation. In Chapter 1, I unpack the relationship between honey bee health and industrial agriculture. I propose steps researchers can take to account for the impacts of this destructive system in our research narratives, and I discuss the uncomfortable questions that surface when we engage in this process. In Chapter 2, I review the use of antimicrobial resin by honey bees and stingless bees for nest construction and defense, and I discuss the ways in which this material contributes, or may contribute, to social immunity in different species. In Chapter 3, I test strategies to stimulate the construction of a robust propolis envelope – a resin-rich structure that wild honey bee colonies build when they nest in hollow tree cavities – in multiple beekeeping contexts. I collaborated with researchers from the United States Department of Agriculture- Agricultural Research Service to assess different surface texture treatments (rough wood boxes, boxes outfitted with propolis traps, and standard, smooth wood boxes) in terms of their ability to stimulate propolis collection, and examined the effect of propolis on colony health, pathogen loads, immune gene expression, bacterial gene expression, survivorship, and honey production. We found that rough wood boxes are the most effective box type for stimulating propolis deposition. The use of rough boxes led to decreased pathogen loads, modulated immune function, and increased colony size. In Chapter 4, I review resin use by stingless bees, specifically. Like honey bees, stingless bees – social, honey-producing bees native to tropical regions – integrate antimicrobial resins in the form of propolis into their colonies. However, the impact of smooth wood box hives on resin collection and the role of propolis in stingless bee colony social immunity have not been examined. In Chapter 5, in collaboration with researchers from the Bee Team at El Colegio de la Frontera Sur, I monitored resin collection and colony development over the course of one year in smooth wood boxes, rough wood boxes modified to mimic hollow tree cavity textures, and thin boxes designed to test the hypothesis that bees use propolis to insulate against temperature change. I also added or removed propolis stores from a second set of colonies and monitored the effect of propolis manipulation on resin foraging and colony development over the course of one year. I found that the use of rough wood boxes leads to increased resin collection, but I did not detect an effect of increased resin collection on colony development. Propolis manipulation in general – and propolis removal specifically – led to increased resin collection, a finding that could have important implications for beekeepers looking to sustainably harvest propolis for medicinal or commercial use.