Rapid population growth continues to generate non-point source (e.g., runoff, leaching, and volatilization) pollution, including plant nutrients (Tang et al., 2005). This non-point source nutrient pollution is in part attributed to homeowners who may over apply fertilizers in an attempt to attain aesthetically pleasing landscapes (Israel and Knox, 2001). Targeted fertilization of urban landscape plants based on plant nitrogen requirements could reduce the likelihood of over fertilization and reduce the potential for nutrient losses from urban landscapes.
Most of the research on fertilization of landscape annuals has focused on nutrient requirements of containerized plants during production in greenhouses and nurseries. For example, van Iersel et al. (1998a, 1998b, 1999) reported that growth of impatiens (Impatiens walleriana), salvia (Salvia splendens), vinca (Catharanthus roseus), and petunia (Petunia ×hybrida) in the nursery generally increased with increasing N fertilizer rate (8–32 mm or 50–150 mg·L−1), but that optimal N rates varied with species and plant growth stage (pretransplant plugs vs. posttransplant seedlings). However, the results of N fertilizer requirement studies conducted with containerized annual bedding plant species do not translate well into a landscape setting, where plant roots are no longer confined to a container and environmental conditions are more variable. Few studies have evaluated plant response of annual bedding species to N fertilizer when grown in the landscape. Wright et al. (2009) determined the growth response and quality of annual bedding plants [‘Cocktail Vodka’ begonia (Begonia ×semperflorens-cultorum), ‘Red Hot Sally’ salvia, ‘Bonanza Yellow’ marigold (Tagetes erecta), and ‘Cooler Pink’ vinca] grown in the landscape that received N at 0, 1, or 2 lb/1000 ft2 per year. The authors reported a significant increase in dry weight and plant growth (plant size) for all species as fertilizer rates increased, but N rate did not affect the aesthetic quality of plants.
Despite the limited amount of research on annual bedding plant response to N fertilization in the landscape, general N rate recommendations for field-grown ornamentals exist in the literature. For example, Rose (1999) reported that various states (based on published extension bulletins) recommended N rates for field-grown woody landscape ornamentals ranging from 44 to 261 lb/acre; however, there were few guidelines for selecting a rate within the range for a particular species. Tjia and Black (2003) recommended a biweekly application of fertilizer containing 10% N at a rate of 1 lb/100 ft2 for begonia planted in a landscape in Florida. Currently, the Florida Friendly™ Landscaping (FFL) program, under the auspices of the University of Florida—Institute of Food and Agricultural Sciences (UF-IFAS), provides fertilizer recommendations for ornamentals growing in the landscape. Annual FFL N fertilizer recommendations are divided into low maintenance (0–2 lb/1000 ft2), medium maintenance (2–4 lb/1000 ft2), and high maintenance (4–6 lb/1000 ft2) categories (Florida Department of Environmental Protection, 2010). However, the basis for the FFL N fertilizer recommendations for landscape-grown ornamentals is unclear.
Because of the limited amount of research related to fertilizer N response of landscape-grown annual bedding species, there is a need to validate existing N rate recommendations for these types of plants. The objective of this research was to evaluate plant response of selected warm- and cool-season annuals to N fertilizer applied at five rates in the landscape. The overall goal was to validate or, if necessary, update current N fertilizer recommendations for annual plants grown in the landscape. Nitrogen fertilizer rate information will be used to provide recommendations for N fertilization that will provide acceptable quality plants while minimizing the potential for excessive fertilizer inputs that could be subject to leaching and runoff losses.
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