Runoff generated from landscape nursery operations contains agrochemicals such as pesticides and fertilizers, which, if released off-site, may pollute the environment. Nursery producers are increasingly interested in alternatives to using freshwater for irrigation due to increased environmental awareness and reduced water availability. As a result, some progressive nursery growers are already adopting the Runoff generated from landscape nursery operations contains agrochemicals such as pesticides and fertilizers, which, if released off-site, may pollute the environment. Nursery producers are increasingly interested in alternatives to using freshwater for irrigation due to increased environmental awareness and reduced water availability. As a result, some progressive nursery growers are already adopting the practice of retaining and recycling nursery runoff water for irrigation. While retaining and recycling runoff may be a practical solution, growers' concerns about the potential negative impact of residual pesticides on crop growth and quality still impede its adoption. Therefore the objectives of my studies were to reduce the concentration of nutrients in runoff water and to evaluate the impact of irrigating with recycled runoff water on growth and physiology of nursery crops.The first study was to identify minimum phosphorus concentration required for the optimum morphological and physiological performance in three common woody ornamental taxa; Hydrangea quercifolia (Queen of hearts), Cornus obliqua (Redtwig dogwood) and Physocarpus opulifolius (Seward). The optimum phosphorus concentrations for growth and photosynthetic biochemistry ranged between 4 and 7 mg·L-1, depending on taxa. For the second study, I investigated the response of common landscape nursery plants to residual pesticide commonly found in nursery runoff. Hydrangea paniculata (Limelight), Cornus obliqua (Powell Gardens), Hosta (Gold Standard) were exposed to low residual concentrations of isoxaben, chlorpyrifos and oxyfluorfen, simulating irrigation with nursery runoff. Exposure to oxyfluorfen produced phytotoxicity symptoms (visual leaf damage), while chlorpyrifos and isoxaben did not produce phytotoxicity. Among the three taxa, H. paniculata was the most sensitive species, and C. obliqua was the most resistant. Therefore the effects of pesticides were pesticide-specific and taxa-specific. For the third study, I investigated whether phytotoxicity in response to residual herbicide exposure was dependent on the growth stage of plants. In this study, H. paniculata plants were exposed to a low residual concentration of oryzalin and oxyfluorfen at the various growth stages, starting shorty after bud-break. Residual herbicide exposure had more impact on growth and photosynthetic physiology at early growth stages; however, the recovery rate of those plants was also rapid. For my final study, I conducted three-year field research replicating an actual nursery grower practice of recycling nursery water. Six ornamental species were irrigated with recycled water obtained from a nursery bed receiving ten different pesticides. In addition, the efficacy of woodchip bioreactors to reduced pesticides in water was also tested. Results from this study established the possibility of using recycled water to irrigate ornamentals plants such as Hydrangea macrophylla (Let's dance blue jangles), Hydrangea paniculata (Limelight), Thuja occidentalis (American Pillar), Juniperus horizontalis (Blue rug), Hydrangea arborescens (Invincibelle Spirit II®) and Rosa sp. (Oso Easy Double Red®) without impacting the growth and physiology of those plants. Woodchips bioreactor was also found to be effective in remediating pesticides from water. The results of three greenhouse studies and a field study together provide new information on reducing the concentration of nutrients and pesticides in nursery runoff water and demonstrate the possibility of recycling nursery runoff. The findings of this dissertation are vital in solving the emerging problem of agrochemical pollution and water scarcity that is currently faced by nursery growers.
Read
