Theses and Dissertations from UMD
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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.Item THE USE OF ORGANIC WASTE PRODUCTS AS SOIL AMENDMENTS FOR TURFGRASS ESTABLISHMENT: EFFECTS AND REGULATORY INFLUENCES(2024) Morash, Jennifer Dawn; Lea-Cox, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of organic waste products as soil amendments in highly disturbed urban soil is poised to grow due to rising fertilizer costs, waste-management issues, and greater emphasis on creating sustainable circular economies. Despite the advantages of using waste products as organic amendments to enhance fertility, their incorrect use may result in short-term unintended consequences such as nutrient losses or the immobilization of plant-essential nutrients, which could diminish efforts to establish vegetation on disturbed soil. To avoid these consequences, transportation authorities – cited as the largest users of compost in some states – have implemented measures to improve product specifications. This research details the efforts of one such organization, the Maryland Department of Transportation State Highway Administration (MDOT SHA), and the results of an initiative to increase the quality of manufactured topsoil and compost use through agency topsoil specifications. After determining which products were most likely to be incorporated into manufactured topsoil (finely shredded wood mulch and composted leaf yard waste), two greenhouse microcosm experiments were conducted to evaluate plant growth responses and the efficiency of nutrient uptake compared to leachate losses when those amendments were used in accordance with MDOT SHA specifications. Composted yard waste provided excellent results while wood mulch suppressed growth in the short-term studies. A biosolids treatment was included in the experiments due to widespread availability and growing interest. Biosolids improved soil fertility and plant growth. However, the difference between nitrogen (N) uptake and leachate mass losses required a second set of experiments, to quantify the effects of four biosolids amendments on plant growth, nutrient uptake, and leachate losses. Treatments were applied at the rate recommended by UMD for turfgrass establishment (2.54 cm, incorporated) and included fresh biosolids, biosolids that were stockpiled for two years, two blended products made from either the fresh or aged biosolids and fine wood mulch, an inorganic fertilizer, and a control. Aging and wood fines reduced N leaching losses but at the expense of N inputs to soil. The cumulative N leachate mass loss from the new biosolids treatment was 63 times greater than the cumulative fertilizer total. Aging did not reduce phosphorus (P) leaching losses but wood fines did by diluting the concentration of P in blends. However, biosolids mostly retained P in the soil and cumulative fertilizer losses were 2 times higher. Overall, growth measurements showed that biosolids enhanced growth during the first and second growing seasons. However, based on the results of this research, 2.54 cm of pure biosolids is not required to enhance turfgrass establishment. An application of 1.27 cm of pure biosolids or 2.54 cm of a biosolid/wood fine blend should provide comparable enhanced turfgrass growth results while reducing overall nutrient leachate losses.Item Quantifying the impacts of climate-smart farming practices for improved management and long-term carbon storage(2023) Boniface, Helen S; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Within agricultural production there is tension between feeding a rapidly growing population and conserving the finite resources at the foundation of our agroecosystems. Fortunately, in recent decades there has been a growing focus on farming practices that promote long-term soil health, land productivity, and resilience to climate change. The term ‘conservation agriculture’ encompasses practices that 1) promote minimum soil disturbance, 2) maintain permanent soil cover, and 3) diversify plant species. This research evaluated several conservation agriculture practices for their ability to deliver desired agroecosystem services across the Northeastern US. In the first study, a cover crop mixture field experiment was implemented in seven states to evaluate how climatic, edaphic, and management conditions affected the performance of cover crop bicultures that included species with varying functional traits. Seeding rate recommendations for mixtures are typically developed at the regional level, thus cover crop performance is highly variable due to site-level conditions and competition among species. Our results indicated that expected spring growing degree days and baseline soil fertility (i.e., inorganic N) are the most significant variables to consider when designing site-specific cover crop mixtures. The second study assessed the effects of long-term management on soil organic carbon (SOC) dynamics in mid-Atlantic grain cropping systems. At the time of sampling, five unique systems (two conventional, three organic) had been continuously managed for 25 years, representing a range of tillage and fertility practices and rotational complexities. Results showed SOC loss in all systems over time regardless of management, likely because of high baseline SOC stocks from long-term perennial forage production prior to research plot establishment. However, cropping systems that best maintained SOC over time included management with minimal soil disturbance, frequent manure inputs, and/or greater rotational diversity through perennial cropping or cover cropping. Both studies increase our understanding of the ability of specific conservation practices to support agroecosystem biodiversity, long term soil health, and potential carbon sequestration.Item Multispectral satellite remote sensing approaches for estimating cover crop performance in Maryland and Delaware(2022) THIEME, ALISON; Justice, Chris; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Winter cover crops encompass a range of species planted in late summer and fall for a variety of reasons relating to soil health, nutrient retention, soil compaction, biotic diversity, and erosion prevention. As agricultural intensification continues, the practice of winter cover cropping remains a crucial practice to reduce leaching from agricultural fields. Maryland and Delaware both incentivize cover cropping to meet water quality objectives in the Chesapeake Bay Watershed. These large-scale programs necessitate methods to evaluate cover crop performance over the landscape. Cover crop quantity and quality was measured at 2,700 locations between 2006-2021 with a focus on fields planted to four cereal species: wheat, rye, barley, and triticale. Samples were GPS located and timed with satellite remote sensing observations from SPOT 4, SPOT 5, Landsat 5, Landsat 7, Landsat 8, or Sentinel-2. When paired imagery at 10-30 m spatial resolution , there is a strong relationship between the normalized difference vegetation index (NDVI) and percent ground cover (R2=0.72) as well as NDVI and biomass (as high as R2=0.77). There is also a strong relationship between Δ Red Edge (a combination of 740 nm and 783 nm bands) and nitrogen content (R2=0.75). These equations were applied to Harmonized Landsat Sentinel-2 products and used to estimate cover crop aboveground biomass in ~300,000 ha of Maryland Department of Agricultures and ~60,000 ha of Delaware Association of Conservation Districts enrolled fields from 2019-2021 and grouped by agronomic method. Wintertime and springtime cover crop biomass varied based on planting date, planting method, species, termination date, and termination method. Early planted fields had higher wintertime biomass while fields that delayed termination had higher springtime biomass. Triticale had consistently higher biomass while wheat had the lowest biomass. Fields planted using a drill followed by light tillage or no-till drill had higher biomass, likely due to the better seed-to-soil contact. Fields that were taken to harvest or terminated for on farm use (roller crimped, green chopped) also had higher springtime biomass than other termination methods. Incentives can be used to encourage specific agronomic methods and these findings can be used to inform adaptive management in the Mid-Atlantic Region.Item Epidemiology and Fungicide Sensitivity of Grape Late Season Bunch Rots in the Mid-Atlantic(2022) Cosseboom, Scott David; Hu, Mengjun; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This project aims to improve the management of late season bunch rots of grape (LSBR) whichcan be caused by a wide range of fungal pathogens. LSBR collectively have been an increasing issue in Mid-Atlantic vineyards, severely affecting grape yield and quality. Despite intensive fungicide spray programs and cultural practices, severe LSBR epidemics threaten the budding Mid-Atlantic wine industry. The basic plant pathological variables of host, pathogen, and environment were investigated to improve knowledge of the diseases involved, and therefore improve management strategies. The most common causal agents of LSBR in the Mid-Atlantic were found to be Botrytis cinerea and Colletotrichum spp. and the species identity of less common fungi was also investigated. The next most prevalent fungi associated with LSBR, Alternaria alternata, Aspergillus uvarum, and Neopestalotiopsis rosae were evaluated for pathogenicity in field experiments through the artificial inoculation of grape clusters. Second, the sensitivity of A. uvarum, B. cinerea, and N. rosae to commonly used chemical classes of fungicides was tested. Lastly, the optimal infection conditions and timing for Colletotrichum spp. were evaluated in laboratory, field, and greenhouse experiments, resulting in a quantitative inoculum tracking technique and a disease prediction model. These experiments were focused on solving practical and important disease management issues experienced by local grape growers, while conducting novel research that was applicable to the broader science community. Beyond the increased knowledge of the etiology and epidemiology of LSBR, the conclusions of this research could lead to reformed LSBR management strategies with the elimination of unnecessary and ineffective fungicide applications, increased accuracy and timing of management efforts, and increased marketable grape yield.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 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 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 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 ADDRESSING THE IMPACT ON SOIL DEGRADATION OF CHANGE FROM GRASSLAND TO CROPLAND: A CASE STUDY IN THE URUGUAYAN GRASSLANDS(2017) Castano-Sanchez, Jose P; Prince, Stephen D; Izaurralde, Roberto C; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Globally, there has been large-scale conversion of natural grassland to cropland ecosystems which this has led to land degradation that could reduce future food security, other ecosystem services and even climate. Currently, there is a dearth of quantitative information assessing the severity, distribution, and causes of this land degradation. For practical purposes, this information is needed to develop improved methods of land use (LU) conversion. Uruguay, in contrast with many other regions, still has a high proportion of unimproved grasslands but, during the last 15 years, there has been extensive conversion to grow grain crops. The fundamental goal of this dissertation was to quantify soil degradation resulting from this LU change. Two aspects of soil degradation were studied, soil organic carbon (SOC) and erosion by water. The Environmental Policy Integrated Climate biophysical simulation model (EPIC) was used to model the grassland and cropping systems. The study consisted of three steps: (1) calibration and validation of the model for the Uruguayan agroecosystems, and development of a spatial version, (2) identification of the LU change areas, and (3) quantification of soil degradation as a result of the LU changes. The EPIC model adequately reproduced the field-scale SOC dynamics and erosion in field validation sites. Further, the spatial version of the model was found to simulate spatial and temporal performance adequately. LU change areas during 2000-2013 were mapped and found to cover an area of 410,000 ha, about 13% of potential area for commercial agriculture. LU greatly affected soil degradation. It was greatest for continuous Soybean cultivation with no crop rotation, and lowest for grassland (no conversion to cropping). In addition to LU, slope and initial SOC had significant effects on degradation. The main conclusions were that the recent and continuing conversion from grassland to cropland has caused significant soil degradation, but that some modifications of LU can reduce the risk of degradation.