UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

2018 - 201912020 - 20232

Settings

Subject: search.filters.subject.Cover crops

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Evaluating the Potential Benefits and Sustainability of a Novel Living and Dead Cover Crop Mixture in Mid-Atlantic Crop Production
    (2023) Johnson, Veronica; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Modern vegetable production systems are often characterized by monoculture fields andthe intensive use of tillage and/or synthetic agrochemicals for managing weeds and insect pests. A growing public interest in more sustainable and eco-friendly production practices has resulted in increased demand that crops be produced with lower inputs. Incorporating flowering living mulches and cover crop residues within crop fields can create an environment more hospitable to beneficial organisms and less conducive to pest outbreaks. My dissertation research aims to advance our knowledge in this area by evaluating the impacts of a novel cover cropping tactic which involves combining a perennial flowering living mulch with cover crop residue on insects and/or weeds. Further, it is often suggested that weed management requires a holistic approach; and that cover cropping will not be successful as a sole weed management tactic. As such, another research aim is to investigate whether combining a cover cropping tactic with herbicide sprays would result in better weed suppression and increased yield in sweet corn compared to using cover crops alone. An economic assessment was also performed to further evaluate the practicality of sweet corn producers adopting the management practices being investigated. Cost of seeds, labor and other expenses can be a primary limitation to cover crop usage. To this point, I also evaluated the feasibility of using a single cover crop planting to suppress weeds over multiple cropping systems and field seasons. If a single cover crop planting can be used over multiple seasons, this could reduce the cost of cover crop use. Agricultural intensification and conversion of natural landscapes to crop production fields have contributed to declines in insect biodiversity including natural enemies and pollinators. Advancing our understanding of how increasing vegetational diversity within crop fields influences weed pressure and populations of herbivores and beneficial arthropods, as well as production costs, can facilitate the adoption of practices in annual cropping systems that favor beneficial organisms and conserves insect biodiversity.
  • Thumbnail Image
    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.
  • Thumbnail Image
    Item
    DEEP SOIL NITROGEN CAPTURE AND RECYCLING BY EARLY-PLANTED, DEEP-ROOTED COVER CROPS
    (2018) Hirsh, Sarah Marie; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The overall purpose of this study was to improve the efficiency of nitrogen (N) cycling in Mid-Atlantic cropping systems through the use of cover crops. Our focus was on describing soil inorganic N pools (0-210 cm deep) and investigating the potential for cover crops to scavenge and recycle deep soil N. Few agronomic studies consider soil properties and processes deeper than the upper 20 to 30 cm, as the majority of roots, amendments, and practices such as fertilizer application or tillage occur on the soil surface or in the topsoil. We 1) assessed amounts of deep soil N on 29 farms in the Mid-Atlantic region, 2) used 15N tracer to investigate the capacity of various cover crops with early- or late-planting dates to capture and recycle deep soil N, and 3) investigated early-planted cover crop systems on 19 farm trials to assess their performance on farms with various soils with diverse management practices. We found that on average 253 kg N ha-1 of inorganic N remained in the soil following summer crops, 55% from 90-210 cm deep. Soil following soybean had the same amount or more of inorganic N than soil following corn throughout the soil profile. Using 15N isotopic tracer, we determined that radish, rye, and radish/rye mixes with and without crimson clover all could capture N from deep soil (60+ cm), but in order for cover crops to capture agronomically meaningful amounts of nitrate-nitrogen (NO3-N) from deep soil, they had to be planted by early-September. Cover crop trials on 19 farms indicated that, while variable site-by-site, early-planted cover crops tended to accumulate substantial N in the fall and reduce residual soil NO3-N levels substantially in the fall and spring. Cover crops also impacted subsequent corn growth and yield, with winter cereal tending to cause lower yields or increased corn N fertilizer needs compared to a no cover crop control, and forage radish sometimes leading to higher yields compared to the control. Overall, cover crops are effective at scavenging deep soil N in the fall, before winter leaching occurs, and under certain conditions, can release N for subsequent crops.