The high value and relatively short production schedules of bedding plants demand intensive production methods such as frequent fertigation (Roude et al., 1991). Historically, commercial greenhouse growers in the United States have applied relatively high nutrient concentrations (e.g., 250–350 ppm N) to maximize growth and reduce the production time of crops, such as petunia (Petunia ×hybrida), that are considered to be “heavy feeders” (Dole et al., 2002; Zhang et al., 2012). Additionally, fertilizer is relatively inexpensive; therefore, growers have tended to err by applying excess fertilizer to avoid nonoptimal growth and nutritional deficiencies. However, excessive fertilizer application results in nutrient runoff, which has become an increasingly important environmental concern because of the potential nitrate and phosphate contamination of groundwater (Klock-Moore and Broschat, 1999). Moreover, the amount of N applied to greenhouse crops is typically greater than those used for field crops on an area basis (Martín et al., 2007).
Growers have been motivated to reduce the amount of fertilizer applied to their crops because excess nutrients do not necessarily translate to higher profits for ornamental production (Cardarelli et al., 2010). Nutrient concentrations of 100 to 150 ppm N are now quite common in commercial bedding plant production. An additional benefit of reduced fertilization rates is the reduction in plant growth rates, which means that the amount of plant growth regulator applied to bedding plants can be reduced. Although these trends in greenhouse production are typically viewed as positive, one recent observation is that consumer performance has been negatively impacted (M. Kramer, personal communication). For example, plant growth after retail purchase is often limited because consumers frequently fail to fertilize their plants. Lower fertilization rates during production reduce consumer performance because of the lack of nutrients in the plant and the growing substrate at the point of sale.
In this study, we propose solutions that growers have the ability to control and implement because changing consumer practices and knowledge is a daunting task. Petunia was chosen as the subject of the experiment because it is one of the most popular bedding plants. Approximately 25 million pots of petunias were sold in 2015 in the United States; petunia ranks fourth among bedding/garden plants, followed by geranium, pansy, and impatiens (U.S. Department of Agriculture, 2016). Three fertilizer delivery strategies were assessed for their potential to maintain adequate growth of petunia during greenhouse production while improving plant growth during the postproduction environment. The fertilizer delivery strategies used included CLF, CRF, and PF treatments. Constant liquid fertilization is the standard industry practice for greenhouse production, whereas CRF and PF provide alternative approaches. Controlled-release fertilizer refers to a fertilizer designed to gradually release nutrients to the growing substrate over time and is most often used for production outdoors, where CLF is not practical because of the lack of control over water supplied during rainfall events (Medina et al., 2008; Tian and Saigusa, 2002). Pulse fertilization refers to a one-time fertigation application performed before placing the plants in a postproduction environment and at a higher rate than the CLF rates applied during production. Both the CRF and PF methods have the potential advantage of providing nutrients to the plant after the greenhouse production phase, thus improving postproduction performance compared with the conventional CLF method. The objective of this research was to evaluate the effects of CLF, CRF, and PF on petunia growth and flowering in the production and subsequent postproduction environments.
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