Basil is a popular fresh culinary herb commonly produced outdoors (Jensen, 2002; Simon et al., 1999). With the demand for fresh basil, year-round production in temperate climates is only possible in controlled environments (Succop, 1998; Wolf et al., 2005). In controlled environments such as greenhouses, hydroponic systems are commonly used to produce basil (Hochmuth and Cantliffe, 2012; Walters and Currey, 2015).
Nutrient solutions can influence growth, appearance, nutritional value, and shelf life of basil (De Pascale et al., 2006). For example, research on outdoor field or containerized greenhouse production of basil has demonstrated that increasing N fertilization increases shoot mass (Biesiada and Kuś, 2010; Golcz et al., 2006; Nurzynska-Wierdak et al., 2012; Sifola and Barbieri, 2006). However, commercial hydroponic producers commonly adjust nutrient solutions based on nutrient solution EC, which reflects the total concentration of fertilizer salts in solution, rather than specific nutrients such as N (Resh, 2013). We have found few reports on the effect of recirculating hydroponic nutrient solution EC and growth of basil species. Researchers found growth of different basil types grown over a 4- to 5-month period is influenced by EC (Suh and Park 1997); however, this exceeds the 5-week production time common commercially.
In addition to mineral nutrients, photosynthetically active radiation affects growth and development of crops grown in greenhouses and controlled environments. For basil and in many other culinary herbs, fresh and dry weight increases as DLI increases to a certain point (Beaman et al., 2009; Currey et al., 2017; Litvin and Currey, 2017). The ambient DLI varies over the course of the year and is at seasonally low levels during the fall, winter, and spring (Korczynski et al., 2002). Supplemental lighting may be used in greenhouses when the ambient DLI is low to increase herb growth and reduce production times (Currey et al., 2017; Fisher et al., 2017).
Some hydroponic producers adjust their nutrient solution between winter and summer, using a lower EC during the summer when both light intensity and air temperatures in the greenhouse are greater compared with the winter (Morgan, 2005). It is unclear how increasing light alone affects nutrient solution EC requirements, as would be the case for a producer using supplemental light during the fall, winter, and spring, when air temperatures in the greenhouse are more easily controlled. We have found no peer-reviewed research quantifying the effect of nutrient solution used in hydroponic basil production on plant growth and tissue nutrient concentrations under different DLIs. Therefore, the objectives of our research were to quantify the effect of nutrient solution concentration on growth and tissue nutrient concentrations of three basil species grown under low and high DLIs.
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