Browsing by Author "Owen, James Stetter"
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- Characterizing the physical and hydraulic properties of pine bark soilless substratesWolcott, Caroline Courtney (Virginia Tech, 2023-11-06)Soilless substrates, such as peat, pine bark, and coir, are widely used as growing media in containerized crops for their favorable characteristics, including low bulk density, balanced air exchange and water retention, disease resistance, and low pH and salinity. However, improper irrigation of these media can have negative outcomes such as root asphyxia, pathogen development, and reduced plant growth. Understanding pore size distributions, water dynamics, and gas diffusivity of these substrates is essential to promote plant growth. The effects of different particle sizes of soilless media on processes such as infiltration, hydraulic conductivity, and gas diffusivity are also not well understood. The characterization of these effects is important for the overall improvement of container crop production. This thesis presents three studies that aimed to characterize the physical and hydraulic properties of pine bark substrates, both unamended and amended with peat or coir. The first study looked at three substrate types: unamended, unscreened pine bark, peat-amended pine bark, and coir amended pine bark. Three methods were employed to quantify pore distributions: non-equilibrium infiltration measurements, equilibrium water retention characterization, and scanning electron microscopy. We characterized pore distributions during wetting and drainage for the three substrates. Coir-amended bark had the largest water-conducting porosity, highest hydraulic conductivity, and most water retention. Unamended pine bark had the highest microporosity, and the addition of peat and coir lowered macroporosity, with peat having the greater effect. The total porosity inferred from the infiltration method was significantly smaller than that inferred from drainage experiments due to assumptions related to pore shape. The second study focused on defining hydraulic conductivity and water retention for pine bark substrates of five different particle sizes, <1 mm, 1-2 mm, 2-4 mm, 4-6 mm, and an unscreened fraction. We utilized the same methods from the first study. The resulting data showed that the smallest particle sizes (i.e., <1 mm and 1-2 mm) had the highest hydraulic conductivity and greatest water retention. The three larger sizes had lower hydraulic conductivity and poor water retention, including the unscreened fraction, which more closely followed the results of the 2-4 mm size. The final study examined gas diffusivity of the five pine bark particle sizes at different moisture levels: 60% moisture content (initial conditions), saturated at the bottom of the sample, near-saturated at the sample bottom, and drained from saturation to container capacity. We used a one-chamber gas diffusion setup to find gas diffusion coefficients (Ds). The results displayed an inverse relationship between Ds values and substrate water content. In addition, the larger particle sizes were less sensitive to changes in water content due to their well-draining large pores. Proper balance of aeration and water retention is necessary for the success of soilless growing media. Overall, the smaller particle size fractions had the best water retention and hydraulic conductivity rates while the larger fractions had the largest Ds coefficients. This work contributes valuable knowledge on the physical and hydraulic properties of different size fractions of pine bark substrates, which can assist nursery growers in optimizing water usage for sustainable container crop production.
- Economic Analysis of Recapturing and Recycling Irrigation Techniques on Horticulture NurseriesFerraro, Nathaniel Klug (Virginia Tech, 2015-09-22)The horticulture industry is facing limited water resources and public pressure to reduce non-point source pollution. In some circumstances, recapturing and recycling of irrigation water in horticultural nurseries can generate significant savings relative to the costs of alternative water sources and potentially reduce non-point source pollution. However, obtaining these savings may also incur substantial risk and capital cost outlays. Disease risk may increase in nurseries that implement recapturing and recycling if recycled water is not properly treated. These added costs must be compared with costs of alternative sources of water, such as municipal or well water. This study employed partial budgeting to compare irrigation water being extended or supplemented through recapturing and recycling against the most feasible alternative. On-site visits were conducted to obtain information for partial budgets and to clarify the reasoning of nurseries choosing to recycle irrigation water. The partial budgets were supplemented with sensitivity analysis with regard to the extraction cost of water and opportunity cost of land used for recapture of water. Six of eight nurseries obtained water from recapturing and recycling at a lower cost compared to a feasible alternative source. The regrading of land for maximum recapture, opportunity cost of land dedicated to a recapture pond, and the cost of municipal water were parameters that were critical to the irrigation choice. Sensitivity analysis indicated that water price and land cost had little effect on the least cost option. Irrigation recycling could be incentivized to motivate further water conservation within the horticulture industry.
- Hops Production in Virginia: Nutrition, Fungal Pathogens, and Cultivar TrialsJudd, Barslund Duane (Virginia Tech, 2018-11-29)In the United States, hops (Humulus lupulus L.) are grown mainly in the Pacific Northwest (PNW). For this reason, most cultural information is based on the growing conditions of the PNW. Growing conditions in Virginia differ drastically and present unique disease and production challenges. Three studies were conducted with the intent of increasing hop cultivation knowledge for Virginia growers. For the first study, 13 cultivars of hops grown at the Virginia Tech hop yard were compared for growth, yield, and quality. Mean cone fresh weight per plant ranged from 12.00 g for Mt. Hood to 1002.87 g for Crystal in 2016 and from 97.98 g for Mt. Hood to 900.33 g for Cascade in 2017. In 2016, only Alpharoma, Cascade, Mt. Rainier, and Southern Cross had alpha acid levels, an indicator of cone quality, within the accepted range. In 2017, Alpharoma, Centennial, Mt. Rainier, and Nugget had alpha acid levels within the expected range. Three cultivars (Cascade, Crystal, and Ultra) were above the expected alpha acid range, which indicates more bittering potential for beer brewers. In a nutrient deficiency study, hop plants were grown in hydroponic solutions, and deficiencies were induced for nitrogen (N), phosphorus (P), and potassium (K). After visual deficiency symptoms had been induced, leaf tissue samples were taken and analyzed for nutrient content. Images were taken at each deficiency stage. For N, incipient deficiency symptoms were observed at a mean of 3.18% dry weight in leaf tissue samples. Visual symptoms included a chlorotic appearance, undersized leaves, and red petioles. Incipient symptoms for P were observed at a mean of 0.307% dry weight in leaf tissue samples. Necrotic spots, leaf cupping, and undersized leaves were apparent with this deficiency. Incipient symptoms for K were observed at a mean of 1.21% dry weight in leaf tissue samples. Symptoms included rounded leaf tips, blue veins, and marginal scorch. In the third study, a whole leaf powdery mildew (Podosphaera macularis) assay was developed and tested using five hop cultivars, Alpharoma, Cascade, Comet, Sorachi Ace, and Tahoma. Leaves were inoculated with powdery mildew (PM) using a settling tower. This method was used to rapidly assess the resistance of cultivars. Leaves were successfully inoculated and PM colonies were allowed to grow for two weeks. Images of the PM colony development on inoculated leaves were compared using ImageJ to determine percentage of coverage. Tahoma was the only cultivar found to produce a significantly different mean percent coverage (19.5%) compared with the resistant cultivars Cascade and Comet (<1%).
- Nitrogen Fate and Transformations in the Production of Containerized Specialty CropsBrown, Forrest Jackson (Virginia Tech, 2024-05-07)Nitrogen (N) fertilizer is a required mineral nutrient in containerized crop production that is necessary for crop growth and development. Due to production aspects, the N added to crops far exceeds the amount that the plant uses and such inefficiency results in adverse environmental impacts related to N gaseous and aqueous emissions from containers on the production site. Growers are responsible for optimizing nutrient usage in crop production. Three studies were conducted to investigate and better understand the fate of applied N fertilizers, the transformations associated with individual N sources, and the influence of substrate texture on losses of aqueous and gaseous N species. The first study conducted a mass balance looking at the four major avenues of N fate in an open-air container production setting (plant uptake, immobilized or bound N in a pine bark substrate, leached aqueous N, and gaseous emissions of N), the mass balance was speciated to measure applied and intermediary forms of N fertilizer species to provide insight into the overall fate of applied N. Show Off® Forsythia ×intermedia' Mindor' were grown using two control-release fertilizer (CRF) treatments [AN (ammonium-nitrate based) or UAN (urea ammonium-nitrate)] products. This study determined that 97% of the released N from the CRF treatments was lost via aqueous or gaseous pathways. The aqueous losses were inferred to be predominately composed of NO3-N, while the gaseous emissions were inferred to be predominately lost as inert nitrogen gas (N2). During a second experiment, individual N sources treatments [urea (CH4N2O), ammonium (NH4+), and nitrate (NO3-)] were applied to established containers of At LastⓇ Rosa x 'HORCOGJIL' grown in a pine bark substrate in either open wall high tunnel or a glass greenhouse to determine subsequent reaction sequence and fate based on applied N source. By applying an individual form of N it was determined that based on the N source applied, a sequential set of reactions occurs based on the N source. This study determined that the reactive N gaseous species occurred from the hydrolysis of CH4N2O-N to NH4+ and the nitrification of NH4+ to NO3- and then the denitrification of NO3- to N2. Hibiscus moscheutos' Vintage wine' was grown in either a coarse or fine texture substrate utilizing either a water-soluble fertilizer or a CRF to compare the influence of pine bark texture on N leachate losses and RN gaseous emissions. There were few differences between the two substrate texture treatments related to aqueous or gaseous N losses. In both experiments, the Hibiscus grown in the fine texture substrate resulted in higher above and below-ground biomass at experimental termination. Working with growers to develop best management practices will help to improve the use of N fertilizers and impact growers economically, while simultaneously reducing losses leading to less environmental impact on the areas surrounding production sites.
- Phosphorus Requirement and Chemical Fate in Containerized Nursery Crop ProductionShreckhise, Jacob Hamilton (Virginia Tech, 2018-07-09)Environmental contamination issues related to phosphorus (P) in surface waters substantiates the need to identify minimally-sufficient P fertilization amounts for production of containerized nursery crops and better understand the effect of routine amendments (i.e., dolomite [DL] and micronutrient fertilizer [MF]) added to pine bark substrates on chemical fate of P fertilizer. Four studies were conducted to accomplish two overarching objectives: 1) determine the minimum P fertilization amount and corresponding pore-water P concentration needed to achieve maximal growth of common containerized nursery crops and 2) determine the effect of DL and MF amendments in pine bark on P retention during irrigation and P fractions in substrate pore-water. In a fertigation, greenhouse study, calculated lowest P-fertilizer concentration that sustained maximal growth in Hydrangea paniculata ‘Limelight’ (panicle hydrangea) and Rhododendron ‘Karen’ (azalea) was 4.7 and 2.9 mg·L⁻¹ , respectively, and shoot growth Ilex crenata ‘Helleri’ (holly) was the same when fertilized with 0.5 to 6.0 mg·L⁻¹ P. Porewater P concentrations corresponding with treatments that sustained maximal growth of panicle hydrangea, azalea and holly were as low as 0.6, 2.2 and 0.08 mg·L⁻¹ P, respectively. In a separate study, utilizing low-P controlled-release fertilizers (CRFs), shoot growth of Hydrangea macrophylla ‘P11HM-11’ (bigleaf hydrangea) produced in two ecoregions was maximal when fertilized with as little as 0.3 g CRF-P per 3.8-L container, a 50% P reduction from the industrystandard CRF. Holly required 0.2 or 0.4 g CRF-P depending on ecoregion. Mean pore-water P concentrations that corresponded with highest SDW were 0.8 and 1.2 mg·L⁻¹ for hydrangea and holly, respectively. When irrigating fallow pine bark columns containing CRF for 48 d, amending pine bark with DL and MF reduced orthophosphate-P (OP-P) leachate concentrations by ≈ 70%, most of which was retained within the substrate. In a greenhouse study, containerized Lagerstroemia ‘Natchez’ (crape myrtle) were grown for 91 d in pine bark containing CRF. In pine bark amended with DL and MF, pore-water OP-P and total P concentrations, measured approximately weekly, were reduced by, on average, 64% and 58%, respectively. Total dry weight values of plants grown with DL plus MF or MF-only were 40% higher than those grown with no amendments; however, tissue P amounts and relative P uptake efficiency were the same among plants in these three treatments. Therefore, sorption of OP-P by DL and MF reduced water-extractable OP-P but did not limit P uptake by plants.
- Soilless Substrate Hydrology and Subsequent Impacts on Plant-Water Relations of Containerized CropsFields, Jeb Stuart (Virginia Tech, 2017-02-03)Freshwater is a finite resource that is rapidly becoming more scrutinized in agricultural consumption. Specialty crop producers, especially ornamental crop producers, must continually improve production sustainability, with regards to water resource management, in order to continue to stay economically viable. Soilless substrates were initially developed to have increased porosity and relatively low water holding capacity to ensure container crops would not remain overhydrated after irrigations or rain events. As a result, substrates were selected that are now considered to be in efficient in regards to water resource management. Therefore, to provide growers with additional means to improve production sustainability, soilless substrate hydrology needs be innovated to provide increased water availability while continuing to provide ample air filled porosity to ensure productive and efficient water interactions. Historically, soilless substrates have been characterized using "static" physical properties (i.e. maximum water holding capacity and minimum air-filled porosity). The research herein involves integrating dynamic soilless substrate hydraulic properties to understand how substrate hydrology can be manipulated to design sustainable substrates. This task involved adapting new technologies to analyze hydrological properties of peat and pine bark substrates by employing evaporative moisture characteristic measurements, which were originally designed for mineral soils, for soilless substrate analyses. Utilizing these evaporative measurements provide more accurate measures of substrate water potentials between -10 and -800 hPa than traditional pressure plate measurements. Soilless substrates were engineered, utilizing only three common substrate components [stabilized pine bark (Pinus taedea L.), Sphagnum peatmoss, and coconut coir fiber], via particle fractionation and fibrous additions. The engineering process yielded substrates with increased unsaturated hydraulic conductivity, pore connectivity, and more uniform pore size distributions. These substrates were tested in a greenhouse with irrigation systems designed to hold substrates at (-100 to -300 hPa) or approaching (-50 to -100 hPa) water potentials associated with drought stress. Substrate-water dynamics were monitored, as were plant morphology and drought stress indicators. It was determined that increased substrate unsaturated hydraulic conductivity within the production water potentials, allowed for increased crop growth, reduction in drought stress indicators, while producing marketable plants. Furthermore, individual plants were produced using as low as 5.3 L per plant. Increased production range substrate hydraulic conductivity was able to maintain necessary levels of air-filled porosity due to reduced irrigation volumes, while providing water for plants when needed. The substrates were able to conduct water from throughout the container volume to the plant roots for uptake when roots reduced substrate water potential. Furthermore, increased substrate hydraulic conductivity allowed plants within the substrate to continue absorbing water at much lower water potentials than those in unaltered (control) pine bark. Finally, HYDRUS models were utilized to simulate water flux through containerized substrates. These models allowed for better understanding of how individual hydraulic properties influence substrate water flux, and provided insight towards proportions of inaccessible pores, which do not maintain sufficient levels of available water. With the models, researchers will be able to simulate new substrates, and utilize model predictions to provide insight toward new substrates prior to implementing production tests. It has been determined, that increasing substrate hydraulic conductivity, which can be done with just commonly used components, water requirements for production can be reduced, to produce crops with minimal wasted water resources. Concluding, that re-engineering substrate hydrology can ameliorate production sustainability and decrease environmental impact.
- Water and nutrient transport dynamics during the irrigation of containerized nursery cropsHoskins, Tyler Courtney (Virginia Tech, 2014-05-28)Increased water- and fertilizer-use-efficiency in containerized crop production, via reduced water loss, enhances crop-available nutrients while reducing non-point source agrichemical contributions in accordance with regulatory standards. Previous studies detailed nutrient leaching patterns throughout crop production seasons, leaving little known about water and dissolved nutrient (solute) movement through soilless substrates during irrigation. The following experiments evaluated fundamental water and solute transport principles through pine-bark based substrates. 1) Ilex crenata Thunb. 'Bennett's Compactum' were grown in 2.7 L containers. Tensiometers detected wetting front (WF) movement throughout the substrate during irrigation. 2) Tracer solution (containing NO3-, PO43- and K+) and deionized water (DI) were applied to substrate-filled columns to characterize tracer breakthrough under saturated and unsaturated conditions. 3) Controlled-release fertilizer (CRF) was topdressed (surface-applied), incorporated (throughout substrate), dibbled (center of substrate) or not applied to fallow substrate, irrigated with DI and leachate analyzed to determine nutrient concentrations throughout irrigation. Tensiometers revealed that seasonal root growth affected substrate pre-irrigation moisture distribution. Wetting fronts channeled through the substrate before becoming thoroughly wetted. Tracer breakthrough occurred with less effluent volume under unsaturated conditions. Breakthrough of NO3- and PO43- was relatively conservative, though 37% of K+ was retained by the substrate. Leachate concentrations for topdressed and incorporated CRF peaked early (first 50mL effluent) before diminishing with continued leaching. Leachate concentrations for dibbled CRF initially increased (first 150mL leachate), plateaued and then diminished. These results show the relative rapidity which water and solutes move through pine-bark during irrigation and demonstrate methods for future research on within-irrigation solute transport.