Plant Science & Landscape Architecture Theses and Dissertations
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Browsing Plant Science & Landscape Architecture Theses and Dissertations by Subject "Agriculture"
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Item Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation(2016) Allard, Sarah Michelle; Micallef, Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.Item Bt GENETICS EFFECT ON CORN HYBRID PERFORMANCE: A COMPARISON OF TWO NEAR ISOLINE CORN HYBRIDS(2018) Thorne, Louis; Kratochvil, Robert J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most corn (Zea mays L.) hybrids planted in the U.S. are the result of genetic modification that gives them a Bt gene or genes obtained from the bacterium, Bacillus thuringiensis (Berliner) (Bt), that express insecticidal proteins and enables these hybrids to be resistant to several insects. European corn borer (ECB) (Ostrinia nubilalis, Hübner) is the main Lepidopteran pest targeted by the Bt corn technology. All Bt events used in current corn hybrids provide 100% control of ECB. This has led to widespread use of Bt hybrids and has resulted in a drastic decrease in the ECB population. This raises the question whether it is still economically feasible to plant Bt hybrids that have higher seed costs in environments where the ECB pest level is low. The objectives of this study were: 1) compare the yield and agronomic performance of a pair of corn near-isoline hybrids with and without the ¬Bt traits; and 2) evaluate the agronomic and economic optimums for yield and nitrogen (N) rate for each near-isoline hybrids. A two-year study at three University of Maryland research farms in 2013-2014 examined each hybrid type for stalk damage due to ECB, yield performance, the optimum N rate for maximizing yield, and the economic returns the two hybrids provided. This study found minimal ECB stalk damage and no consistent agronomic or economic yield difference between the Bt and non-Bt hybrids. Neither hybrid type was determined to have a consistent nitrogen use efficiency (NUE) advantage. The results of this study indicate that producers should not have concerns over hybrid type choice, now that there is significant regional suppression of ECB below economic levels.Item CUCURBIT DISEASE MANAGEMENT WITH REDUCED CHLOROTHALONIL AND IMPROVED UNDERSTANDING OF PSEUDOPERONOSPORA CUBENSIS POPULATION DYNAMICS(2020) Jones, Jake Gardner; Everts, Kathryne L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research has linked chlorothalonil exposure to declines in pollinator health due to an increased likelihood of Nosema ceranae infection, altered gut microbial community, and a reduction in colony fitness and survival of honey bees (Apis mellifera). Therefore, a reduction in use of chlorothalonil, a large component of cucurbit disease management, may be needed. Without chlorothalonil, a widely used, broad-spectrum fungicide, the fungal and oomycete pathogens in cucurbit cropping systems can more quickly evolve resistance to targeted fungicides due to a limited number of efficacious modes of action and frequent sprays. Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, for example, has a short life cycle, experiences repeated applications of fungicides, and has a wide host range making it a high risk for fungicide resistance development. Our research focused on the development of an alternative fungicide spray program in melons to reduce the use of chlorothalonil, identifying the fungicide insensitivities of local P. cubensis populations and determining the efficacy of fungicides used to manage cucurbit downy mildew, and investigating the clade-host relationship and formation of oospores in regional P. cubensis samples. Efficacy on two important diseases in melon, powdery mildew and gummy stem blight, can be largely maintained without chlorothalonil but anthracnose control was not adequate without the inclusion of chlorothalonil. Currently, there are a number of highly effective targeted fungicides available to growers for management of cucurbit downy mildew including oxathiapiprolin, zoxamide + chlorothalonil, chlorothalonil, and cyazofamid. Our research shows evidence of P. cubensis clade-host associations, with clade 1 preferentially infecting acorn and summer squash (Cucurbita pepo), butternut squash (Cucurbita moschata), and watermelon (Citrullus lanatus), while clade 2 preferentially infects cucumber (Cucumis sativus). Melons (Cucumis melo) and pumpkin (Cucurbita maxima) are hosts to both clade 1 and clade 2 P. cubensis. Using these findings, producers can choose the fungicide that most appropriately targets the more virulent clade 2 or less virulent clade 1 infections.Item DESIGNING AN ACCESSIBLE AGRICULTURAL GARDEN: CONNECTING SOLIDARITY & AGROECOLOGY(2024) Boyle, Patrick Robert; Ruggeri, Deni; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis explores the potential of agroecology as a transformative framework for guiding the transition of Bergamo's agricultural landscape toward sustainability, resilience, and community well-being. Grounded in the evolution of agroecology from farm-scale design to regional planning, the research investigates how this approach can integrate ecological methodologies and participatory action research in design to implement sustainable farming practices, rehabilitate landscapes, and cultivate solidarity-driven producer-consumer relationships. By emphasizing the interconnectedness of ecology, economy, and society, the study addresses whether agroecology can shape a district into a resilient landscape that enhances people's lives and promotes health and well-being.Through an interdisciplinary lens, the thesis also delves into the broader concept of landscape, highlighting its role in social well-being and advocating for the protection and responsible management of landscapes as a fundamental human right. It explores the principles of landscape democracy and solidarity, aiming to empower communities to reconnect with their environments and promote ecological restoration through collective action and ethical practices. Ultimately, the research strives to contribute to the discourse on agroecology and landscape planning, offering proposals and strategies for actionable change in regenerative and organic agricultural systems that prioritize the needs and values of local communities.Item Dual water quality responses after more than 30 years of agricultural management practices in the rural headwaters of the Choptank River basin in the Chesapeake Bay watershed(2023) Silaphone, Keota; Fisher, Thomas R; Natural Resource Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication is the water quality response to over-enrichment by nitrogen (N) and phosphorus (P) in fresh, estuarine, and coastal waters globally. Agricultural best management practices (BMPs) are the primary tool for controlling eutrophication in rural areas, particularly in the Chesapeake Bay watershed, where BMPs are vital to achieving TMDL goals. However, despite the application of BMPs, local water quality in the headwaters of the Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula, has not improved. Thus, further investigation of agricultural BMP impacts on water quality in the Greensboro watershed is needed. My overarching research question is, “Why have N and P concentrations increased at the USGS Greensboro gauge if agricultural Best Management Practices (BMPs) have been implemented?” I applied statistical approaches to three linked, testable hypotheses to systematically evaluate agricultural BMPs and their impacts on nutrient (N and P) export from the Greensboro watershed. My first hypothesis was that agricultural BMPs have increased significantly in the Greensboro watershed. To test this hypothesis, I obtained publicly available modeling data via the Chesapeake Assessment Scenario Tool (CAST) and estimated the subsequent edge-of-stream N and P export. My findings indicated that the number of BMPs in the agricultural sector increased significantly between 1985 and 2021, supporting the hypothesis. Overall, modeled agricultural N and P export significantly decreased between 2010 and 2021 (p < 0.001). However, the modeled edge-of-stream agricultural nutrient export resulted in no significant change in N export and an increase of 3% in agricultural P export resulting from BMP implementation levels in 2021 compared to 2010. This study demonstrated the use of CAST to acquire reported BMP implementation levels and increased nutrient inputs into the Greensboro watershed between 1985 and 2021. The watershed nutrient inputs mirror the upward trends in N and P export captured by the USGS long-term monitoring station at Greensboro. With this improved access to BMP implementation and nutrient data, decision-makers can consider adaptive management measures to decrease nutrient export downstream. My second hypothesis was that agricultural BMPs have an adequate basis for estimating their capacity to reduce N export. To test this hypothesis, I conducted a meta-analysis on 689 cover crop N efficiencies reported in 18 empirical and modeling studies. The cover crop N efficiency was calculated as the ratio of an N interception by cover crop biomass or a reduction in soil or groundwater N divided by an N input, e.g., previous spring fertilizer or a previous soil or groundwater N concentration or flux. These variable approaches resulted in wide ranges in mean cover crop N efficiency (10-80%) due to empirical and modeling experimental approaches, varying methods, and parameters used to calculate efficiency. The modeling approach generally resulted in N efficiency values significantly higher than the empirical approach, as did the parallel control-treatment experiments compared to the sequential before-and-after implementation method. Because of these variables, there appears to be no standard methodology to report the effects of cover crops or standardized metadata describing the variables used in the N efficiency calculations. I suggest a standard methodology and metadata that should accompany future reports of cover crop N efficiencies to improve the modeled effects of BMPs on nutrient export. My third hypothesis was that three methods of estimating N and P concentrations and yields are in agreement and show a relationship to BMP implementation in the Greensboro watershed. To test this hypothesis, I compiled annual nutrient (N and P) datasets based on (1) USGS field measurements of concentrations and discharge, (2) USGS flow-normalized weighted regression based on time, discharge, and season (WRTDS) of concentrations and yields, and (3) CAST-modeled nutrient yields. Statistical analyses revealed time, discharge, agricultural BMPs, and animal waste management practice trends of the three methods. Results indicated that the USGS field measurements and WRTDS flow-normalization methods consistently showed an increase in N and P concentrations and yields. In contrast, all CAST-modeled regressions showed significantly decreasing nutrient concentrations and yields (p ≤ 0.05), which did not support the hypothesis that all three methods are in agreement. Despite CAST-modeled results decreasing with increasing BMPs, which supports the hypothesis that N and P concentrations and yields show a relationship with BMP implementation, USGS methods resulted in increasing nutrient concentrations and trends. These results indicated significant underestimates of modeled N and P export by CAST. I recommend using adjusted BMP efficiencies during cultural and structural BMP lifespans to improve model outputs. I also suggest two approaches to reflect the role of annual poultry manure applications: (1) model nutrient transport via artificial drainage ditches that interfere with natural nutrient flow pathways and exacerbate N and P transport, and (2) model the accumulation of soil-P and saturated soil-P, resulting in increases in dissolved P and particulate P in downstream surface waters. Agronomic recommendations include developing efficient manure recycling approaches within the local agricultural systems via nutrient management practices and concurrent research and development to support alternative uses of animal waste, including composting, bioenergy generation, granulating/pelletizing, and establishing a marketplace to support the sale of these products and to offset the costs of transporting manure from areas of manure surplus to manure deficit areas. This dissertation revealed that modeling studies overestimate cover crop N efficiencies in the United States Coastal Plain province and that CAST modeling is not in agreement with the USGS field measurements. CAST-modeled nutrient concentrations and yields decrease over time, indicating improvements in water quality. In contrast, USGS methods consistently show that nutrient concentrations and yields increase, indicating that BMPs are insufficient, inadequate, overwhelmed by nutrient inputs, or efficiencies are overestimated. Indeed, nutrient-reducing BMPs have increased between 1985 and 2021. With over 35 years of BMP implementation, measurable water quality response is expected. However, BMPs that relocate and apply higher amounts of manure annually have also increased with nutrient-reducing BMPs. Rising manure application rates combined with higher fertilizer application rates due to economic pressures on farmers to increase crop yields appeared to have overwhelmed implemented BMPs. Continued manure applications onto croplands in the Greensboro watershed suggest nutrient export will continue to rise; thus, reaching water quality goals is unlikely.Item EFFECT OF COMPOST ON THE MICROCLOVER ESTABLISHMENT AND USE OF COMPOST AND MICROCLOVER TO REDUCE LAWN NUTRIENT RUNOFF(2016) Xiao, Xiayun; Carroll, Mark; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High volume compost incorporation can reduce runoff from compacted soils but its use also associated with elevated N and P concentrations in runoff making it difficult to assess if this practice will reduce nutrient loading of surface waters. Additionally, little is known about how this practice will effect leguminous species establishment in lawns as means to reduce long term fertilizer use. When 5 cm of compost was incorporated into soil a reduction in runoff of 40 and 59% was needed for N and P losses from a tall fescue + microclover lawn to be equivalent to a non-compost amended soil supporting a well fertilized tall fescue lawn. Use of compost as a soil amendment resulted in quicker lawn establishment and darker color, when compared to non-amended soil receiving a mineral fertilizer. Biosolid composts containing high amounts ammonium severely reduce the establishment of clover in tall fescue + micrclover seed mixture.Item Effects of a Simulated Dicamba Misapplication on Non-tolerant Soybeans (Glycine max)(2015) Morris, Matthew; Ritter, Ronald L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Approval is pending for the registration of dicamba tolerant (DT) soybeans [Glycine max (L.) Merr.]. The use of dicamba on DT soybeans and other DT crops will increase. Risks associated with dicamba applications include off-target movement to sensitive crops. The objective of this study was to evaluate misapplication of dicamba on non-DT soybeans. Greenhouse and field studies examined a rate titration (0.004 to 0.5 lb ai a-1) of dicamba on non-DT soybeans (V3 stage - three trifoliates). Field studies also examined dicamba application to various growth stages (PRE- preemergence to R5- early pod fill) of non-DT soybeans. Results from the greenhouse and field studies showed that as the rate of dicamba increased, the level of injury to vegetative and yield components also increased. Soybean growth stage at time of application influenced the amount of injury. Less injury was observed when dicamba was applied at the PRE growth stage.Item EVALUATION OF COMPOST TOPDRESSING, COMPOST TEA AND CULTIVATION ON TALL FESCUE QUALITY, SOIL PHYSICAL PROPERTIES AND SOIL MICROBIAL ACTIVITY(2015) Chen, Siqi; Carroll, Mark J.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Compost topdressing, compost tea, and hollow tine cultivation are common cultural practices employed in organic lawn care programs. Restrictions on the amount of bagged fertilizer nitrogen and phosphorus applied to turf have raised questions about the need to place similar restrictions on compost turfgrass applications. In a three-year study the effect of reduced and common practitioner use rates of compost topdressing, the use of compost tea and of hollow tine cultivation on soil physical and biological properties and turfgrass quality were evaluated. Cultivation, monthly compost tea application and compost topdressing applied at rates consistent with annual bagged fertilizer nitrogen restrictions had little effect on soil organic matter, microbial activity, bulk density and infiltration. The use of a synthetic fertilizer resulted in higher turf quality than the use of compost on most evaluation dates. Nutrient fertilizer restrictions if applied to compost will likely result in a decline in turf quality.Item Genetic Control of Flowering Time in a Soft Red Winter Wheat Doubled Haploid Population(2015) Miller, Daniela Michelle; Costa, Jose M; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flowering time in wheat is regulated mainly by response to seasonal environmental cues and controlled by the photoperiod and vernalization pathways. Allelic diversity in genes controlling these pathways is used by breeders to adapt wheat for optimal yield in a broad range of environments. This study characterized genetic loci influencing heading date in a soft red winter wheat doubled haploid population. Two photoperiod insensitivity alleles, Ppd-A1a and Ppd-D1a, were found to have major effects in eight field locations. The Ppd-A1 locus explained up to 16.8% of variation in heading date, whereas the Ppd-D1 locus explained up to 39.7%. In reduced vernalization greenhouse experiments, a QTL in the same region as the VRN-A1 gene explained up to 42.4% of variation in heading date, suggesting that the population differed in this region. Assays for previously-described allelic diversity in the VRN-A1 gene, however, did not detect any polymorphism between parents of the population.Item Getting Legume Cover Crops to Work in Mid-Atlantic Crop Rotations(2020) Peterson, Cara; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the mid-Atlantic United States, legume cover crop adoption is limited by the shortened establishment window after double-crop soybean (Glycine max (L.) Merr.) harvest. Interseeding legume cover crops into wide-row (76 cm) double-crop soybean presents an opportunity to supplement inorganic nitrogen (N) fertilizer in the subsequent corn (Zea mays L.) crop. We conducted field trials in Maryland and Delaware in which mixtures of cereal rye (Secale cereale L.) + hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), red clover (Trifolium pratense L.), or winter pea (Pisum sativum var. arvense (L.) Poir) were interseeded into double-crop soybean. We then examined the N contributions of the cover crop mixtures in combination with sidedress applications of inorganic N fertilizer on corn yields in Maryland in 2018 and 2019. This research demonstrated that interseeding cover crops into double-crop soybean is a potential strategy for increasing regional adoption of legume cover crops.Item MAKING APPLES BLUSH: UNDERSTANDING HOW THE COMBINED USE OF REFLECTIVE GROUNDCOVERS AND PLANT GROWTH REGULATORS IMPACT RED SKIN COLORATION AND QUALITY OF ‘HONEYCRISP’ APPLES IN THE MID-ATLANTIC US(2024) Miah, Md Shipon; Farcuh, Macarena; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Apples are among the most valuable fruits globally, with 'Honeycrisp' ranking as the top sales-producing cultivar in the US. However, challenges such as insufficient red skin coloration and increased preharvest fruit drop significantly diminish their market value. Reflective groundcovers have been reported to enhance apple skin coloration, while the application of the plant growth regulator AVG reduces fruit drop but may negatively impact skin coloration. Research on the impacts of these practices in mid-Atlantic US-grown apples remains limited. In this two years study, our aims were 1) to evaluate the effect of reflective groundcovers on solar radiation (PPFD, UV) distribution; 2) to assess the combined effect of reflective groundcovers and ethylene inhibitor (AVG) on preharvest fruit drop, ethylene production, red blush percentage, and overall fruit quality; 3) to investigate the combined effect of reflective groundcovers and ethylene inhibitor (AVG) on expression level of key anthocyanin and ethylene biosynthesis related genes; 4) to determine the combined effect of reflective groundcovers and ethylene inhibitors (AVG) in the accumulation of total anthocyanin. Apples underwent four treatment combinations of reflective groundcover (Extenday) and AVG (130 mg L−1). Our findings revealed that Extenday significantly enhanced skin coloration (>75% blush) through increased reflectance of PPFD and UV radiation, along with increased IEC, while also accelerating fruit maturity, i.e., overripening. In fact, Extenday-only treated fruit exhibited the highest upregulation of ethylene and anthocyanin biosynthetic-related genes, as well as total anthocyanins. Conversely, AVG notably reduced fruit drop and decreased IEC, delaying fruit maturity while significantly diminishing red coloration (30–48% blush). AVG treated fruit significantly suppressed the expression of key ethylene and anthocyanin biosynthetic structural and regulatory genes, as well as total anthocyanins. The combined application of Extenday and AVG synergistically decreased fruit drop while enhancing skin coloration (>50% blush), but without inducing overripening. This combination fine-tuned the transcript accumulation of ethylene and anthocyanin biosynthetic-related genes, as well as total anthocyanins, enabling 'Honeycrisp' fruit to exceed 50% blush, while moderately increasing IEC (compared to Extenday-only and control fruit), thus enhancing fruit economic value. Therefore, combining Extenday and AVG can boost the market value for 'Honeycrisp' apples in the mid-Atlantic US.Item MANAGEMENT OPTIONS FOR FARMERS FACING SALTWATER INTRUSION ON THE EASTERN SHORE OF THE CHESAPEAKE BAY(2023) Schulenburg, Alison Nicole; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising sea levels, storms, and perigean spring tides push saltwater into coastal agricultural fields. This phenomenon, known as saltwater intrusion, alters nutrient cycling and damages crop yields. As sea levels continue to rise, saltwater intrusion will only worsen, with devastating consequences to agroecosystems along the coast of the Chesapeake Bay. Researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion. Landowners may respond by altering their management practices. Farmers may 1) adapt by planting a salt-tolerant crop, 2) attempt to remediate soils with trap crops, 3) restore native marsh grasses, or 4) abandon fields altogether. My project investigates the survival of different crops and plant treatments under saltwater-intruded conditions and the potential for these plants to survive and to remove excess nutrients (e.g. sodium and phosphorus) from the soil, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. Results from this study will help inform new management practices to increase soil health and maintain crop yields. Finally, the goal of this work is to guide local best management practices and potential easement opportunities for landowners facing saltwater intrusion, and ultimately determine optimal strategies for climate resilience.Item MANAGING WATER, NITROGEN, AND ALLELOPATHY WITH A CEREAL RYE COVER CROP(2018) Otte, Briana; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A cereal rye (Secale cereale) cover crop is a multi-functional tool in a no-till corn agroecosystem. The objectives of this study were to (1) quantify soil phenolic acid concentration under cereal rye shoots and roots, and how tillage impacts their release (2) evaluate the effects of cereal rye termination date on soil water, nitrogen, and corn performance compared to no cover crop. Soil phenolic acids have known allelopathic effects, inhibiting some weed seed germination or growth. Results suggest that cereal rye roots release more phenolic acids into the soil than cereal rye shoots, a novel finding. Results also suggest that corn grain yield following a late-terminated cereal rye cover crop is mediated by precipitation pattern and N release from cereal rye residues. During years of above average summer precipitation a late-terminated cereal rye cover crop does not affect corn grain yields and decreases residual inorganic soil N in the agroecosystem.Item MECHANISMS OF DISEASE SUPPRESSION BY A HAIRY VETCH (VICIA VILLOSA) COVER CROP ON FUSARIUM WILT OF WATERMELON AND THE EFFICACY OF THE BIOCONTROL ACTINOVATE.(2013) Himmelstein, Jennifer Carol; Everts, Kathryne; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The cover crop Vicia villosa suppresses Fusarium wilt of watermelon but the mechanisms of disease suppression are unknown. Possible mechanisms were examined in field, greenhouse, and in vitro experiments. The effects of cover crop treatments (V. villosa, Trifolium incarnatum, Secale cereale, Brassica juncea) and the biocontrol treatment Actinovate (Streptomyces lydicus WYEC 108) on Fusarium wilt of watermelon and its causal pathogen, Fusarium oxysporum f. sp. niveum (FON) were evaluated. In four of five field experiments there were significant elevations in soil microbial respiration. Arbuscular mycorrhizal colonization of watermelon roots following cover crop amendments of V. villosa and T. incarnatum, were significantly higher compared to bare ground. The elevation in respiration was significantly positively correlated with disease suppression of Fusarium wilt induced by V. villosa and T. incarnatum (both cover crops reduced Fusarium wilt as much as 21%). In greenhouse experiments using infested field soil, Fusarium wilt suppression was observed in pots amended with V. villosa and T. incarnatum. However, there was an increase in Fusarium wilt of watermelon in pots that were amended with V. villosa and T. incarnatum which were also inoculated with FON when compared to plants in nonamended, inoculated pots. These leguminous cover crops may have served as a nutrient source for the pathogen. In addition, in vitro growth experiments showed that media amended with V. villosa leachate significantly stimulated the in vitro growth rates of FON and Trichoderma harzianum compared to nonamended plates. It was hypothesized that V. villosa stimulation of nonpathogenic F. oxysporum spp., which provides cross protection against FON, may have contributed to the wilt suppression. Cover crop leachate amendments did not significantly influence colony forming units of S. lydicus. In both field and greenhouse trials Actinovate applications either had little or no effect on Fusarium wilt of watermelon. However, S. lydicus significantly inhibited in vitro growth of FON. These studies demonstrate that both general and specific disease suppression play a role in V. villosa suppression of Fusarium wilt of watermelon and that T. incarnatum is a viable alternative biocontrol.Item MODELLING DECOMPOSITION AND NITROGEN RELEASE FROM SURAFCE COVER CROP RESIDUES IN NO-TILL SYSTEMS IN THE MID-ATLANTIC AND SOUTHEASTERN US(2020) Thapa, Resham; Tully, Katherine L.; Mirsky, Steven B.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the mid-Atlantic and Southeastern US regions, cover crops (CCs) are planted during the winter fallow periods or between cash crops to provide living roots and to cover soil for extended time periods. Cover crops can provide a suite of agroecosystem services to cropping systems including soil and water conservation, weed suppression, and nitrogen (N) cycling. After CCs are terminated, the rate of residue decomposition determines both N availability and the longevity of residue cover in conservation tillage (reduced- and no-till) systems. Accurate predictions of plant-available N from decomposing CCs are needed to improve N fertilizer recommendations in order to reduce environmental losses of N while meeting cash crop N needs. The objective of this work is to improve our understanding of the factors controlling CC residue decomposition in conservation tillage systems at varying temporal (diurnal to seasonal) and spatial (laboratory to regional) scales. At a diurnal scale, the moisture (θg)/water potential (ψresidue) and temperature in the surface CC residue layers fluctuated more dramatically and dynamically than the underlying soils. Decomposition of surface CC residues also showed distinct diurnal patterns that were closely related to diurnal variations in residue θg or ψresidue. In a controlled microcosm experiment, the effect of residue location on C and N mineralization during repeated dry-wet cycles were also primarily explained by differences in residue water dynamics than by differences in soil-residue contact between the surface and incorporated residues. At a regional scale, the combination of residue quality and climatic variables explained the majority of the variations in residue decomposition rates, i.e. k-values. I found faster decomposition of surface CC residues in humid environments and in site-years with more frequent rain events. The k-values decreased with increasing biomass, C:N, residue holo-cellulose concentrations, and lignin:N, but increased with increasing residue carbohydrate concentrations. Mathematical equations were developed and integrated into the existing CERES-N sub-model to adjust k-values based on residue environment. Once such models are well-calibrated and well-validated, they will be used to make evidence-based management recommendations to farmers. Thus, this research helps to optimize provisioning of agroecosystem services in CC-based conservation tillage crop production systems.Item MODIFYING GREEN ROOF SUBSTRATE FOR NUTRIENT RETENTION IN URBAN FARMING SYSTEMS(2020) Howard, Ian Nathaniel; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interest in urban agriculture is steadily increasing in the Mid-Atlantic region. The conversion of extensive green roofs to food production is particularly appealing due to space availability. The modification of a relatively unfertile shale-based substrate for increased water and nutrient availability was investigated, adding mushroom and yard-waste composts, but potentially contributing to nutrient runoff from rainfall and irrigation events. Alumina and biochar were therefore tested as substrate amendments to determine their effect nutrient availability and retention. Fifteen substrate mixes were screened by column leaching tests, and four were further studied over nine-months, with crop and leachate studies. Basil, lettuce and peppers were grown and harvested in succession in replicated 50-liter tubs, with leachate collection systems. Biochar did not reduce nitrogen or phosphorus leaching and did not have an effect on plant growth. Alumina significantly reduced the amount of phosphorus leached from substrates with little to no effect on plant growth.Item MOWING TO GROWING: TRANSFORMING A MUNICIPAL GOLF COURSE TO URBAN AGRICULTURE IN BALTIMORE CITY(2016) Allen, Nathan; Kweon, Dr. Byoung-Suk; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis demonstrates how landscape architects can transform underused golf course facilities located within cities for urban agriculture (UA). In the last decade more than 1000 golf courses have closed in the United States. Municipal golf courses represent some of the largest pieces of open space in cities and because of their inherent infrastructure they can provide the ideal location to support large-scale UA. In Southwest Baltimore large food deserts are a serious health concern and represent a lack of access to healthy food options for residents. Carroll Urban Agriculture Park is a design response resulting from a detailed analysis of the existing Carroll Park Golf Course and the surrounding community of Southwest Baltimore. The design will create an urban farm in a park-like setting to provide readily accessible healthy food options and various educational opportunities, and to support current and future urban agriculture related businesses in Baltimore.Item Nitrogen cycling by grass-brassica mixtures in the Mid-Atlantic(2019) Gaimaro, Joshua Ruben; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mixtures of cover crop species may be more effective than monocultures at internal nutrient cycling due to their ability to occupy different niches. Our study investigates nitrogen (N) cycling of radish (Raphanus sativus L.) and rye (Secale cereal L.) in monocultures and mixtures compared to a no cover crop control. The study was established on fine-textured soils near Laurel, MD where we estimated N leaching losses, quantified mineral soil N (to 60 cm), and cover crop biomass N for two years. Forage radish suppressed estimated N leaching in the fall, while cereal rye suppressed estimated N leaching in the spring. In this study, growing radish in a mixture with rye decreased the risk of N leaching losses and enhanced N cycling due to the difference in timing of N uptake and release. Our research indicates that grass-brassica mixtures are a flexible management tool for mitigating N leaching in the Mid-Atlantic.Item Nitrogen Management in Corn: Influences of Urea Ammonium Nitrate (UAN) Applications With and Without Nitrogen Stabilizer Products.(2013) Watkins, Patrick Howard; Kratochvil, Robert J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Corn (Zea mays, L.) is a major crop produced in the nutrient sensitive Mid-Atlantic region. Nitrogen use efficiency (NUE) for corn is considered sub-optimal and farmers in the region use a number of best management practices (BMPs) to improve corn NUE. Two sidedress application methods (surface banding and sub-surface injection) and four commercially available nitrogen stabilizer products (`Agrotain', `Agrotain Plus', `Instinct', `Nutrisphere-N') were investigated during 2009-2011 over three N fertilizer rates at nine total locations. Headspace ammonia accumulation (post-sidedress) was indexed to the surface applied UAN treatment and resulted in application method and stabilizer products having a significant effect for headspace ammonia accumulations. Post-harvest inorganic soil nitrogen was not affected by application method or stabilizer products. Yield was not significantly affected by application method or stabilizer products but was affected by N rate. Total plant N concentration was not significantly affected by application method or stabilizer products.Item PRODUCTION RECOMMENDATIONS FOR INDUSTRIAL HEMP (CANNABIS SATIVA) FOR FIBER PRODUCTION IN MARYLAND: OPTIMIZING PLANTING DATE FOR FIBER YIELD, QUALITY, AND WEED MANAGEMENT(2024) Myers, Erin; Fiorellino, Nicole; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Management recommendations, namely timing of planting and harvest, are well established for a wide range of agronomic crops, but this data is lacking for industrial fiber hemp (Cannabis sativa L.), especially in the Mid-Atlantic region. With the re-introduction of legal hemp production in the US in 2014, farmers faced many challenges to growing this crop, both policy and production challenges alike. As hemp production was illegal since World War II, there was virtually no applied agronomic research performed on hemp in that time. Moreover, there are no pre-emergence herbicides approved for weed management in industrial hemp production, and research is needed to determine which cultural practices can be utilized to manage weeds in this crop. This void of applied research performed on fiber hemp has left many Land-Grant universities and Extension personnel unable to provide basic production recommendations to farmers interested in growing this novel crop. To begin providing such recommendations to Maryland farmers interested in incorporating fiber hemp into their crop rotation, the objectives of this research were to 1) determine the effect of planting and harvest date on fiber hemp yield, plant characteristics, and fiber quality and 2) observe weed populations under a competition or germination prevention scenario in fiber hemp across the planting date spectrum. Based on this research, we believe fiber hemp can be successfully incorporated into Maryland crop rotations, as early planting and harvest of fiber hemp will result in quality fiber hemp, management of weeds through available cultural practices, and minimal disruption to other agronomic crops.