Under Control - 2019 - 14

Species
6
Collards
Lettuce
Mizuna
Pac choi
0.22a
0.12a
0.31a
0.17a
FRESH WEIGHT (LBS PER FT2
Daily Light Integral (mol·m-2
12
d-1
18
0.35b
0.22b
0.64b
0.37b
0.53c
0.28c
1.09c
0.49c
)
24
0.71d
0.39d
1.27c
0.58d
30
0.80e
0.43e
1.75d
0.82e
*Yield calculations assume 100% germination which is not representative for commercial
production.
Table 1. Fresh weight at Day 12 in pounds per square foot of collards, lettuce, mizuna and pac
choi under five DLI treatments of 6, 12, 18, 24 and 30 mol·m-2
·d-1. Assuming a plant spacing of
144 plants per square foot (one plant per square inch).
increases in fresh weight and dry weight
in each of the four species of baby leaf
vegetables studied.
Figure 3 shows the average fresh
weight per plant at Day 12 for each
of the four species at each of the five
DLI levels. It is also very easy to see in
Figure 3 that there are large differences
in yields between the four species.
This variation in average yields is an
important takeaway as it highlights
the importance of species and cultivar
selection for optimizing baby leaf
vegetable yields.
In Table 1, these fresh weight yield
Species
Collards
Lettuce
Mizuna
Red Pac
6
14.8a
15.6a
11.9a
19.0a
DAYS TO 4-INCH LEAF HEIGHT
Daily Light Integral (mol·m-2
12
d-1
18
14.2a
15.1a
11.2a
14.8b
d-1
13.0b
15.9a
10.4a
16.0b
)
24
12.2c
15.8a
9.7b
13.3c
30
12.0c
15.6a
9.6b
13.0c
Table 2. Days to 4-inch tallest leaf height for collards, lettuce, mizuna and pac choi under five
DLI treatments of 6, 12, 18, 24 and 30 mol·-2
.
for lettuce and collards. For each
experiment, all flats were seeded at the
same time and then the mizuna and pac
choi flats were floated 47 hours after
seeding, whereas the lettuce and collard
flats were floated after an additional
seven hours (54 hours after seeding).
The day that the plants were floated was
considered Day 0.
Flats were then floated on mini
hydroponic ponds each filled with 28 L
of reverse osmosis water and 0.28 L each
of 1:100 concentration Jack's Hydroponic
5-12-26 (JR Peters Inc.) and calcium
nitrate resulting in 150 mg L-1
nitrogen.
The ponds were topped off with nutrient
solution to maintain this volume
14
throughout the experiment.
During each of the three harvests, one
randomly assigned float from each pond
was removed from the nutrient solution
and the non-germinated cells were
noted. The plants around the edges were
removed to account for edge-effects.
Plants from the inner 18 cells were
then individually cut and weighed. Five
representative plants from the inner cells
were randomly selected and measured
for tallest leaf height, widest leaf width,
total leaf number, and total leaf area.
RESULTS
This experiment showed that
incremental increases in DLI between 6
UNDER CONTROL: TIPS FOR CONTROLLED ENVIRONMENT GROWING * 2019
results were translated into terms of
pounds per square foot to estimate
potential commercial yields of larger
crop stands. Both Figure 3 and Table 1
show that for each of the four species
there continued to be an increase in
yield up to the mol·m-2
·d-1
treatment,
however, for lettuce and collards a
relatively small yield increase was noted
between the 24 and 30 mol·m-2
·d-1
treatments, suggesting there may not be
an economic benefit of lighting beyond
24 mol·m-2
·d-1
for these species.
This experiment also revealed that
incremental increases in DLI have some
significant impacts on leaf height, as
well as leaf width, leaf area, and leaf
number. Leaf height in particular is
often used to characterize baby leaf
vegetables - along with number of
true leaves and days to maturity -
with the typical harvestable leaf height
usually being described as ~4 inches
(or ~10 cm). Figure 4 shows the tallest
leaf height per plant at Day 12 for each
of the four species under each DLI
treatment; it can be seen from this
graph that leaf height response to DLI
varies greatly by species - with almost
no impact being shown for lettuce.
Additionally, the leaf height growth
curves between Day 0 and Day 12 were
used to create Table 2 to show the days
to reach 4 inches in leaf height for each
of the four species under the different
DLI treatments. Table 2 indicates
that for some species, increasing the
DLI could shorten the days to reach
harvestable height, thus allowing for
more harvests per year.
)
and 30 mol·m-2
·d-1
resulted in significant

Under Control - 2019

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