Under Control - 2019 - 13

7
6
5
4
3
2
1
provided to the plants in each 24hour
period.
Daily light integral (DLI), measured
d
c
c
e
d
c
b
a
a
Collards
Daily Light Integral
6 mol·m-2
d-1
Lettuce
12 mol·m-2
d-1
18 mol·m-2
Mizuna
d-1
b
c
d
e
a
a
Pac choi
24 mol·m-2
d-1
30 mol·m-2
d-1
Figure 2. Images of vegetable species utilized in this experiment where A, B, C and D represent
collards, lettuce, mizuna and pac choi.
STUDY PARAMETERS
In this study, four leafy vegetable
species; collards (Brassica oleracea
7
6
5
4
3
2
1
b
b
a
a
a
c
b
a
a
a
a
a
a
a
a
b
b
c
c
c
L. 'Flash'), lettuce (Lactuca sativa L.
'Sulu'), mizuna (Brassica rapa L. var.
japonica) and pac choi (Brassica rapa
L. var. chinensis 'Red Pac') were studied
(Figure 1). These species were chosen for
their presence in baby leaf salad mixes,
similarity in germination rate and hours
to germination (as determined in a
preliminary experiment), and for their
diversity in color, texture and leaf shape.
Plants were grown in a growth
Collards
Daily Light Integral
6 mol·m-2
d-1
Lettuce
12 mol·m-2
d-1
18 mol·m-2
Mizuna
d-1
·d-1
Pac choi
24 mol·m-2
d-1
30 mol·m-2
Figure 3. Average fresh weight per plant at Day 12 of collards, lettuce, mizuna and pac choi
under five DLI treatments of 6, 12, 18, 24 and 30 mol·m-2
.
with high, predictable yields and short
growth cycles.
As the popularity of baby leaf
vegetables grows, so does the need
for research into their growth
and development in controlled
environments. Decades of research
has gone into developing detailed
strategies for the optimal production of
mature lettuce and other leafy greens;
however far less research has gone
into developing these optimization
standards for plants grown specifically
as baby leaf vegetables.
THE IMPACT OF DLI
The intention of this article is to
share some thoughts on using daily
light integral (DLI) to improve the
growth and development of baby leaf
vegetables. Ultimately, this could help
growers to make supplemental lighting
decisions to increase yields, shorten
growth cycles and enhance the ability to
produce year-round.
Our study aimed to look at the effects
of increasing light quantity, an important
lighting characteristic, on the growth
and development of hydroponically
grown baby leaf vegetables. Light
quantity is a product of instantaneous
light intensity, or the number of photons
of photosynthetically active radiation
(PAR) delivered to the plant surface at
any given moment, and photoperiod
which is the number of hours of light
d-1
chamber under T5 fluorescent lamps and
the photoperiod was fixed at 20 hours.
The experiment was conducted over time,
with the growth chamber set to one of
five DLI treatments for each of the crop
cycles. The DLI treatments were 6, 12, 18,
24 and 30 mol·m-2
·d-1
at plant level. Plants
of each species were randomly assigned
different mini hydroponic ponds within
the chamber.
At experiment initiation, seeds were
single seeded by hand into individual
cells of the 40 cell polystyrene flats
filled with a commercial peat-lite
germination mix (LM-1, Lambert Peat
Moss) resulting in a density of 144 plants
per square foot. Flats were individually
wrapped in one-gallon plastic bags to
maintain moisture during germination
and then placed on benches inside of the
growth chamber and covered by light
restrictive flats.
Preliminary experiments were
conducted to determine hours to
germination for each species which
yielded germination times of 47 hours
for mizuna and pac choi and 54 hours
UNDER CONTROL: TIPS FOR CONTROLLED ENVIRONMENT GROWING * 2019 13
b
b
c
d
e
in mol·m-2
·d-1
, is the metric most
commonly used to measure light
quantity. The optimal DLI varies by
species, for example, for head lettuce
up to 17 mol·m-2
·d-1
·d-1
is used and for
tomatoes a minimum of 20 and ideally
30+ mol·m-2
is common. In general,
within bounds, increasing DLI usually
leads to an increase in photosynthesis
and crop biomass, but this has not been
well studied for baby leaf vegetables.
Leaf Height (g/plant)
Fresh Weight (g/plant)

Under Control - 2019

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