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. / Doctor of Philosophy / Nitrogen (N) fertilizer is a crucial mineral nutrient input to produce container crops, however excessive application can have detrimental effects on the environment including gaseous N emissions and N leaching leading to water pollution. Therefore, three studies were conducted to investigate N losses during production and potential mitigation strategies using common management practices in the production of container crops. During the first study investigating how N fertilizer is lost from production, results showed that a significant portion of the N added to the containers is either emitted from the containers into the atmosphere or leached from the container. Only a small fraction of the applied N was utilized by the plants for growth and development. The second study investigated the reactions and transformations of different N fertilizers sources. When applying single N sources urea (CH4N2O), ammonium (NH4+), or nitrate (NO3-) result in a set of sequential reactions that occur based on the applied N source. Urea is hydrolyzed via CH4N2O hydrolysis leading to the formation of NH4+ which is nitrified via nitrification to NO3- which is denitrified via denitrification leading to the production of N2 gas. In the final study two pine bark substrate classes were compared when using either a water-soluble fertilizer (WSF) or a controlled-release fertilizer (CRF). Surprisingly there were only a few differences between the two substrate treatments in either the WSF or CRF studies. This body of work show the importance of investigating N fertilizer usage in container crop production. Collaboration between researchers and growers is crucial to develop management practices that maximize the associated economic input of N fertilizers and minimize losses of N that are detrimental to the environment.

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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. / Master of Science / Since the 1950's soilless substrates have been an important resource for growing a variety of fruits, vegetables, flowers, and ornamental plants. Soilless growing media have become more popular choices for containerized plant production compared to natural soils due to improved air exchange, increased disease resistance, and more plants per acre. They are also favored because they help conserve resources, reduce agricultural waste, and minimize transportation requirements as compared to traditional cropping methods. The most popular types of soilless media include peat, coir, compost, and pine bark. In the U.S., pine bark is the main substrate used, as it is renewable and widely available. Growers still face many issues when using containerized crop production. For example, pine bark is susceptible to water runoff which can cause environmental problems and increase costs from this loss of water and fertilizer. Further characterizing of water and gas dynamics in of pine bark growing media is important for conserving water and fertilizer resources while optimizing plant growth in this container cropping industry. Pore characteristics, aeration, and water movement are key factors of substrates to be described to solve these challenges. This project aimed to apply soil physics strategies to soilless media, focusing on describing pore sizes, water movement, water holding capacity, and air movement in pine bark substrates. We utilized three methods throughout this study. For the first method, we took infiltration measurements to examine how water moved into the media, while the second utilized controlled drainage experiments to observe how water moved out of the media. The final method was characterizing gas movement through the substrates at different water contents and particle sizes. The results found showed that the smaller particle sizes and pine bark mixed with peat and coir had increased ability to retain water and allow water movement as compared to the larger particle sizes and unamended pine bark. In contrast, the larger particles had less water retention but improved gas movement. These results could be applied by stacking different particle sizes or mixes over one another could optimize water retention in the top of the container and drainage and gas movement in the bottom of the container. Overall, the application of this work is to create best management practices for growers to be able to balance water retention and gas movement in order to optimize plant growth.

One of the motivating reasons for the development of hydroponics was avoidance of root pathogens. Hydroponics involves growing crops in relatively sterile media, isolated from the underlying soil which may have disease pressure. However, even when hydroponics is coupled with controlled environments such as high tunnels and climate-controlled greenhouses, soil-borne pathogens can enter the growing area and proliferate due to optimal environmental conditions for pathogen growth. Control of root pathogens is difficult and usually achieved through synthetic fungicides since few biocontrol options are available. Compost water extracts (CWE) have recently been gaining the attention of greenhouse growers because they may be a low-cost, environmentally friendly approach to control root disease. CWE are mixtures of compost and water incubated for a defined period of time, either with or without aeration, and with or without additives intended to increase microbial populations, which in turn suppress disease. Much anecdotal, but very little scientific, evidence exists describing CWE effect on suppressing soil-borne pathogens. The present study 1) examined the effect of an aerated CWE on disease suppression at the laboratory scale and in container studies using different soilless substrates, 2) investigated a phenotypic change at the root level caused by CWE that may be associated with disease suppression, and 3) isolated some factors in the production of CWE that affect the ability of a CWE to suppress disease. The common model pathogen-host system of Fusarium solani f.sp. pisi and pea was used to examine CWE-induced disease suppression, with information then being translatable to similar patho-systems involved in greenhouse crop production. In the first study, laboratory-based root growth and infection assays resulted in 100% suppression of F. solani when roots were drenched in CWE. These protected seedlings were then taken to a greenhouse and transplanted into fine coconut coir, watered with hydroponic nutrient solution, and grown for five weeks. At the end of the experiment, 23% of the shoots of the pathogen-inoculated, CWE-drenched seedlings remained healthy while only 2% of the inoculated seedlings without CWE drench remained healthy. All of the roots of the inoculated seedlings developed lesions, even those drenched in CWE. However, 29% of the CWE drenched roots were able to recover from disease, growing white healthy roots past the lesion, while only 2% recovered naturally. A shorter-term container study was conducted in the laboratory to determine the effects of CWE-induced suppression when peas were grown in different substrates and to determine if the hydroponic nutrient solution had an effect on the suppression. Peas were grown in sterilized fine and coarse coconut coir fiber and sand irrigated with water, with a second set of fine coir irrigated with hydroponic nutrient solution. Pea seeds with 20-25mm radicles were inoculated with pathogen and sown directly into CWE-drenched substrate and grown for three weeks. At the end of the experiment, 80%, 60%, 90%, and 50% of the shoots of the inoculated, CWE-drenched seedlings remained healthy when grown in fine coir, coarse coir, sand, and fine coir irrigated with hydroponic nutrient solution, respectively. Nearly 100% of the roots grown in coconut coir substrates again developed necrotic lesions but 83%, 87%, 100%, and 87% grew healthy roots beyond the disease region. The hydroponic nutrient solution had a negative effect on suppression, with a reduction of at least 30 percentage points. Sand demonstrated a natural ability to suppress F. solani. Only 23% of inoculated seedlings had dead or dying shoots by the end of the experiment (compared to 77-80% in coir substrates) and although all but one of the roots developed lesions, all were able to recover on their own with CWE. CWE further increased shoot health and also prevented 57% of the roots from developing lesions. In a second study, two different CWE were used to examine the effect on root border cell dispersion and dynamics in pea, maize, cotton, and cucumber and its relation to disease suppression. Dispersal of border cells after immersion of roots into water or CWE was measured by direct observation over time using a compound microscope and stereoscope. Pictures were taken and the number of border cells released into suspension were enumerated by counting the total number of cells in aliquots taken from the suspension. Border cells formed a mass surrounding root tips within seconds after exposure to water, and most cells dispersed into suspension spontaneously. In CWE, >90% of the border cell population instead remained appressed to the root surface, even after vigorous agitation. This altered border cell phenomena was consistent for pea, maize, and cotton and for both CWE tested. For most cucumber roots (n=86/95), inhibition of border cell dispersal in both CWE was similar to that observed in pea, maize, and cotton. However, some individual cucumber roots (8±5%) exhibited a distinct phenotype. For example, border cells of one root immersed into CWE remained tightly adhered to the root tip even after 30 minutes while border cells of another root immersed at the same time in the same sample of CWE expanded significantly within 5 minutes and continued to expand over time. In a previous study, sheath development over time in growth pouches also was distinct in cucumber compared with pea, with detachment of the sheaths over time, and root infection was reduced by only 38% in cucumber compared with 100% protection in pea (Curlango-Rivera et al. 2013). Further research is needed to evaluate whether this difference in retention of border cell sheaths plays a role in the observed difference in inhibition of root infection. In the third study, a series of investigations were conducted to isolate different factors that contribute to the suppression ability of a CWE by changing incrementally changing some aspect of the CWE production process. The basic aerated CWE recipe (with molasses, kelp, humic acid, rock phosphate, and silica) provided 100% protection of pea from root disease while the non-aerated basic recipe CWE provided 72% protection. Aerated CWE made of only compost and water resulted in 58% protection. It was found that molasses did not contribute to the suppression ability of the ACWE, while kelp contributed strongly. When soluble kelp was added by itself to the compost and water, the CWE provided 80% suppression. However, when all additives were included except molasses and kelp, suppression remained high (93%) indicating that humic acids, rock phosphate, and/or silica were also major contributors toward the suppression effect. Optimal fermentation time for ACWE was 24 hr to achieve 100% suppression, with increased time resulting in inconsistent suppression results. Optimal fermentation time for NCWE was 3 days or 8 days. These studies are important contributions to understanding the differences that might be expected in CWE suppression when growing in different substrates, some of the factors in the production of CWE that affects the ability of a CWE to suppress disease, and the phenotypic effect CWE has on the root zone of plants and the possible relationship between that effect and disease suppression.