August 2020 - 23

CONTROLLED ENVIRONMENT AGRICULTURE
0.5
Electrical conductivity (mS/cm)
1.0
2.0
3.0
4.0
5.0
more nutrients to plants for uptake. While Ca and S declined with
increasing fertilizer concentration in the seedling experiment, we
found that Ca and Mg decreased with increasing EC in the current
experiment. Again, we attribute some of this to the dilution effect.
However, we may have also seen decreasing Ca and Mg due to
competition from K. Since we used potassium hydroxide (KOH)
to raise pH to keep it at our target (5.8), the increasing K from
these additions may have competed with Ca and Mg for uptake.
Regardless, no Ca or Mg deficiencies were observed on any species
regardless of tissue concentrations. The only nutrient deficiency
symptom observed in our study was a S deficiency on kale grown
at 0.5 mS·cm-1
. The new growth of kale had chlorotic leaves that
were very brittle; however, this was the only apparent at the lowest
nutrient concentration, and was not present when kale was grown at
higher ECs.
Figure 2. Finished arugula (top row), pac choi (middle row), and kale (bottom
row) plants grown in recirculating deep-flow hydroponic system with nutrient
solutions maintained at 0.5 to 5.0 mS/cm throughout production.
diminish yields. Alternatively, swiss chard should be grown in solutions
maintained around 2.0 mS·cm-1
or higher (3.0 to 5.0 mS·cm-1
for kale should be at least 1.0 mS·cm-1
; if the EC is lower (0.5 or 1.0 mS·cm-1
) yield decreases. Finally, nutrient solutions
, as yields are lower if EC is
)
<1.0 mS·cm-1; however, yield did not increase as EC increased above
1.0 mS·cm-1. While these recommendations are species-specific, specialty
greens are frequently grown in a poly-culture, with multiple species
provided with the same nutrient solution.
The increasing tissue nutrient concentrations in response to increasing
EC makes sense, given that increasing nutrient solution EC provides
TAKE HOME
Specialty greens are an increasingly popular crop, and this work
aimed to improve nutrient management from propagation through
finishing. Healthy seedlings can be grown at a range of tissue
concentrations, and growth is promoted up to 200-ppm nitrogen.
While arugula and pac choi have low EC requirements during
finishing, kale and Swiss chard should be provided with nutrient
maintained at >1.0 mS·cm-1
or ~2.0 mS·cm-1 to maximize yield
and quality.
Christopher Currey (ccurrey@iastate.edu) is an associate professor,
Jean Yost is a graduate research assistant, and Rachel Sporer was an
undergraduate research assistant, all in the Department of Horticulture
at Iowa State University.
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August 2020

Table of Contents for the Digital Edition of August 2020
