Determining effects of nutrient solution electrical conductivity and daily light integral on the growth of specialty leafy greens
Controlled environment agriculture (CEA) operations are expanding the ways food is being grown and the food crops that are grown in the US. Hydroponic production of nutrient-dense leafy greens is becoming increasingly popular for bringing food production closer to consumers in metropolitan areas. There is a need for empirical data regarding the production of these specialty leaf greens in CEA. In the experiments outlined in this thesis, we sought to determine the effects of electrical conductivity (EC) of nutrient solution and daily light integral (DLI) on the growth and development of arugula, swiss chard, pac choi, and kale. In our first experiment, we explored the effects of nutrient solution EC on the growth and tissue nutrient content of these specialty leafy greens grown in deep flow technique hydroponic systems. We exposed arugula, swiss chard, pac choi, and kale to ECs of 0.5, 1.0, 2.0, 3.0, 4.0, or 5.0 dS∙m–1. Our results show growth response due to EC differs among species, but the growth of all species was not promoted at an EC over 2.5 dS∙m–1. Arugula and pac choi can be grown at lower ECs of 1.0 to 2.0 dS∙m–1 whereas swiss chard does best at 2.5 dS∙m–1. Growth of kale was unaffected by EC, but we recommend kale be grown at any EC between 1.0 and 5.0 dS∙m–1 to mitigate S deficiency. In our second experiment, our goal was to quantify the growth response of arugula, swiss chard, pac choi, and kale as DLI increases from 2 to 22 mol∙m–2∙d–1. For all species, growth increases with DLI. We found that arugula reaches its maximum yield at a DLI of 18 mol∙m–2∙d–1. Although we did not reach growth maxima for any of the other crops tested, we did observe occurrence of tipburn on pac choi when the DLI exceeded 15 mol∙m–2∙d–1.