Tag: Roberto Lopez

LEDs found to have multiple uses on multiple crops

Researchers at Purdue University are finding LEDs can
have positive effects on both ornamentals and leafy vegetables.

By David Kuack

As more research is done with light emitting diodes
(LEDs), scientists are discovering new ways to use the lights on ornamental and edible
plants. Researchers at Purdue University have done extensive studies on annual
bedding plants, comparing the growth of seedling plugs and vegetative cutting liners
under LEDs.
“My goal is to continue to do research with LEDs because
we are finding new and exciting results, especially with the indoor production
of young plants and microgreens,” said associate horticulture professor Roberto
Lopez. “Some of the work that we have been doing has shown the benefits of
LEDs.
“If you would have asked me two years ago if I would ever
try to produce plugs indoors and not in a greenhouse, I would have said no. If
you would have asked me five years ago if I would be working on greens or
vegetables, I would have said no. Now I am doing both of those things with
LEDs.”

Purdue University graduate student Joshua Craven
(left)
and associate horticulture professor Roberto Lopez are
studying the effects LED
lights have on ornamental
plants and leafy vegetables.
Photo by Tom Campbell, Purdue University

No need for
sunlight

Lopez and former graduate student Wesley Randall found
that greenhouse-grown seedling plugs of impatiens, marigold, petunia, vinca and
zonal geranium did as well or better when supplemented with LEDs compared to
plugs supplemented with light from high pressure sodium lamps. What Lopez found
surprising was the quality of the plugs produced in a growth room with LEDs as
the only light source.

“LEDs produce better plugs when they’re grown indoors
than when they are grown in a greenhouse with sunlight supplemented with light
from LEDs or high pressure sodium lamps,” Lopez said. “It is amazing how good
the plugs look grown in an indoor multilayer production system with LEDs. The
plugs are compact, sturdier and greener with a similar root and shoot dry mass
to greenhouse-grown plants supplemented with light from LEDs or high pressure
sodium lamps.”
One crop that Lopez said they are still “tweaking” with
LEDs is petunias.
“Petunias, which are long day plants, when moved from an
indoor grow room equipped with red and blue LEDs, encountered a slight delay in
flowering in the greenhouse,” he said. “We are going to see if exposing the
plants to far-red LED light prior to moving them into the greenhouse will
induce them to flower.”
Using LEDs to
intensify leaf, flower color

Lopez said many of the annual spring bedding plants grown
in greenhouses in northern climates are produced under low light levels. The
result is that some plants don’t produce the same intense foliage colors that
they would if they were grown outdoors.

“Plants grown in glass greenhouses are not exposed to the
sun’s ultraviolet light because it is blocked by the glass,” he said. “The
result is that crops like zonal geraniums and purple fountain grass (Pennisetum setaceum ‘Rubrum’) don’t
“color up” like they would outdoors. One of the things we noticed with zonal
geraniums was the dark patterns on the leaves stood out much more when the
amount of blue light was increased. We hypothesized and found it was a result
of an increase in anthocyanin production. We have also looked at geraniums that
have very dark foliage and found not only does leaf color darken, but flower
color can be made darker by exposing market-ready plants to red:blue LEDs.”
Lopez said the change in leaf color due to anthocyanin
production was also dramatic for purple fountain grass.
“Purple fountain grass is a very popular ornamental
species produced by many growers,” Lopez said. “Grown in the greenhouse, the
leaves appear to be dull green and not very purple. We found that putting the
plants under a combination of red and blue LEDs for one to two weeks of what we
are calling “end-of-production lighting” resulted in an attractive purple
color. UV light is what stimulates anthocyanin synthesis.”
He said in the case of purple fountain grass, only the
leaves exposed to the LED lights change color. Those leaves not exposed to the
LED light remain green.
Expanding studies
to vegetable crops

Seeing the positive results that occurred with LEDs and
purple fountain grass, Lopez and PhD student W. Garrett Owen expanded the
research to red leaf lettuce to see if they could produce a similar response.

“Trying to produce red leaf lettuce can be difficult for
greenhouse growers if they are producing crops under low daily light integrals
(DLIs),” Lopez said. “Growers producing red leaf lettuce under low DLIs are
essentially producing green lettuce.
“We placed red leaf lettuce under the same LED treatments
used for purple fountain grass and the plants colored up in three to five days.
Based on our research, red leaf lettuce and purple fountain grass can be placed
under a 50-50 red and blue LED combination prior to harvesting or shipping
triggering anthocyanin formation.”
Based
on Purdue University research,
red leaf lettuce can be placed under a
50-50 red
and blue LED combination prior
to harvesting triggering anthocyanin formation
intensifying
the lettuce‘s red color.
Photo courtesy of Roberto Lopez,
Purdue University
Based on the results related to LEDs and anthocyanin
formation, Lopez said the studies may be expanded to look at the impact of LED
light on ornamental cabbage and kale. “Growers, especially those in the South,
have a hard time coloring up ornamental cabbage and kale,” he said. “It is
primarily a temperature response, as the night temperatures get cooler the
plants start to color up.”
Lopez and Owen did a small study placing ornamental cabbage
and kale under LEDs that resulted in a minimal color change. When
greenhouse-grown plants were grown under cool night temperatures and exposed to
LEDs, they exhibited the most intense color.
“What we are proposing is for growers in warmer climates
who have access to coolers, is to use a cool temperature/LED treatment,” he
said. “We will be conducting this study next fall. Smaller container sizes like
4-inch pots, could be rolled on carts into a cooler and exposed to cool
temperatures and LED lights for three to four days prior to shipping enabling
the plants to color up.”
Customized
microgreens

Another study conducted by graduate students Joshua
Gerovac and Joshua Craver looked at the effect of LEDs on the growth of three
different microgreen species (kohlrabi, mustard and mizuna) in an indoor
multilayer production system. The study included three different light
qualities and three different DLIs (light quantity).

“Overall what we have seen is as the DLI increases, this
is for three microgreen species we trialed, the length of the hypocotyl,
basically the height of the microgreen, decreases,” Lopez said. “The more light
the plants are provided, the more compact they are. If the plants received 6
moles of light, they were much taller than if they received 18 moles of light.
Depending on the growers’ market, some customers might want microgreens that
are a little leggier or they might want plants that are more compact. That will
depend on market preference.”
The ideal LEDs

Lopez said the ideal vertical LED light module would
contain all of the wavelength colors.

“The vertical LED light with all the different colors
would enable growers to turn them on when they need them and off when they
don’t, depending on the stage of plant growth,” he said. “Once flowering begins
a grower doesn’t want stem elongation. Far-red light works for flowering so the
far-red would be turned on for the minimum amount of time required for
flowering. If the grower wants to increase the amount of anthocyanin in the
leaves or flowers, he can turn on the red and blue light near the end of the
crop. To be able to turn on specific colors when a growers needs them, that is
something I envision happening with LEDs.”

For more:
Roberto Lopez, Purdue University, Department of Horticulture and Landscape
Architecture; (765) 496-3425; rglopez@purdue.edu;
https://ag.purdue.edu/hla/lopezlab/Pages/default.aspx.

David Kuack is a freelance technical writer in Fort
Worth, Texas; dkuack@gmail.com.

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Improving Greenhouse Production with LED Lights

U.S. researchers are looking at the potential benefits to
the propagation and production of greenhouse ornamental and vegetable crops
using LED lights.

By David Kuack
Although U.S. researchers have started studying the
effects of LED lights on the production of greenhouse ornamental and vegetable
crops, much of the data being used by American growers comes from studies done
in Europe. Purdue University horticulture professor Cary Mitchell said that studies
currently being done in the United States will provide growers with information
that is relevant to their production and climatic conditions.
Mitchell is leading a team of university researchers who
have received a $4.9 million grant, including $2.4 million from USDA, to study
LED lighting for greenhouse applications. Mitchell along with Purdue
horticulture professor Roberto Lopez is working with scientists and engineers at
the University of Arizona, Michigan State University, Rutgers University and
Orbital Technologies Corp. Mitchell is working with graduate student Celina
Gomez to study the impact of LED lights on the propagation and production of
high-wire tomatoes. Lopez and graduate students Christopher
Currey and Michael Ortiz are studying the use of LED lights on bedding plant
cuttings and plugs.
Propagation trials
Due to limited greenhouse research space, Gomez is using
one bench to compare the effect of providing supplemental light from a high
intensity discharge lamp or from LED lights with control plants that receive
only natural daylight. During the first year of the propagation study, Gomez is
conducting an experiment every month. The experiment includes a control group
of tomato seedlings that receive no supplemental light, an overhead HID lamp
that provides the industry standard and overhead LED arrays that provide three
different ratios of red to blue light.
“The propagation experiment is repeated for three weeks
every month,” Mitchell said. “We are measuring the differences in plant growth
from one month to the next. As we enter spring, the ambient light levels are
increasing. Gomez will measure the daily light integral (DLI) that is occurring
and the different red/blue ratios and what the plants prefer and determine what
they need. In addition to the plant metrics being collected, we are also
measuring the amount of electricity used for supplemental lighting.”
After the tomato seedlings reach the stage at which they
would be grafted onto the rootstock, data is being collected including plant
dry weight, height, stem diameter, leaf span and leaf area.
Mitchell said the propagation area that is equipped with
the lights receives 5 moles per square meter per day of supplemental light in
addition to the natural solar daily light integral that varies throughout the
year.
“Since we have only done the experiment a couple of times
so far this year, we’ve yet to see what kind of plant response pattern emerges,”
he said. The supplemental light we are providing now might not be enough light
during the dead of winter. Any benefits of supplemental light that occur during
the winter should disappear as the trials move later into spring. Once we have
obtained a full year profile of seedling response, we will be able to determine
the optimum amount of supplemental light to apply each month.
“One of the best management practices that we hope comes
of this long term study is to determine at what point it is important to use
supplemental lighting, as well as when it is no longer useful to do so.”
For the propagation study the tomato seedlings are
receiving supplemental light for 23 hours a day in order to achieve a daily
light integral of 5 moles per square meter per day.
Tomato seeds are being germinated in a substrate called
steadyGROWpro plugs. Six different tomato varieties are being tested: ‘Success’,
‘Komeett’, ‘Maxifort’, ‘Sheva-sheva’, ‘Liberty’ and ‘Felicity’. Seedlings of ‘Success’
and ‘Komeett’ are used for the production study after being grafted onto ‘Maxifort’.
These varieties were recommended by Marco de Bruin at Bushel Boy Farms in Owatonna, Minn., because they have
different growth habits.

Production trials
In the production experiments the grafted seedlings are
being transplanted into Coco Agro coir slabs.
“The lighting treatments containing both test cultivars
are blocked into separate half rows in order to determine if there are position
effects within the greenhouse that could affect yields,” Mitchell said.
The plants are being provided with supplemental light
twice a day. He said they are applying a daily light integral of 9 moles per
square meter per day.
“In early March we were lighting for 12 hours per day,”
Mitchell said. “Lighting usually starts well before sunrise and begins again
before the sun goes down.”
The first production study in 2012 began at the end of
January. Mitchell said the tomato plants that had received supplemental light
treatments were already setting fruit in early March.
“The control plants that didn’t receive any supplemental
light were way behind,” he said. “They were barely setting fruit. That’s what
you would expect in a cloudy region like Indiana.”
The first production experiment of 2012 will be
terminated after six months and a second will begin immediately. Mitchell said
the second experiment will be the exact opposite of the first in terms of solar
daily light integral changes.
“We want to see what challenges there are both with the
propagation and the production starting in the summer and going into the winter,”
he said. “If production is started in the greenhouse in July, the plants are
going to be receiving a lot of sunlight. As the photoperiod starts to shorten going
into fall that is when supplemental lighting will be more valuable.
“We are hoping to come up with recommendations for
growers in this region or in any other northern region that has cloudy weather regarding
when is the best time to start lighting their crops. We are also looking at
timing the production so that growers are not competing with home-grown or
field-grown tomatoes. That way the greenhouse growers are not competing with
availability and price for what’s being grown in backyards or in the field.”

Priming the ornamentals
propagation pump
Purdue horticulture professor
Roberto Lopez and graduate students Christopher Currey and Michael Ortiz are
studying the effect of supplemental light on the propagation of ornamental
vegetative cuttings and plugs.
“We’re looking at the top three
flowering crops that are produced from vegetative cuttings, which are
geraniums, petunias and New Guinea impatiens,” Lopez said. Currey and Ortiz are
comparing rooting, dry mass accumulation and other quality parameters under red
and blue LED lights to high pressure sodium lamps. Initial trials with cuttings
have shown that there are not a lot differences in terms of rooting time and
quality between the two light sources. Additionally, preliminary data is
showing no differences in the time to flower or quality of cuttings propagated
under the various LED lights and high pressure sodium lamps for the three
annual crops.
“Initially, the results
are very similar for
both rooted cuttings and finished plants,” Lopez said. “But this is very
preliminary. There were really no differences seen for these three crops. What
we were mainly trying to achieve was a certain daily light integral with both
the high pressure sodium and red and blue LEDs. With the additional trials that
we will be doing we will also be looking to quantify the amount of electricity
used by the high pressure sodium lights and the LEDs.”
Best timing,
amount of light
Lopez said none of the vegetative cuttings received
supplemental light during the first seven days of propagation because that is
when the cuttings are forming callus.
“A grower typically wouldn’t use lights during this
period unless the light level was really low,” he said. “During that period the
grower is trying to baby the cuttings to get them to form callus. If the light
level is too high during this period the cuttings could be stressed. After a
week the cuttings begin to form roots and start to photosynthesize. A grower
can maximize photosynthesis during rooting by increasing the daily light integral.”
Currey’s research and studies
Lopez performed at Michigan State University indicate growers should
provide a daily light integral of between 8-10 moles per square meter
per day to be able to increase rooting and the overall quality of the cutting.
Lopez and Ortiz are also
testing LED lights during plug propagation of celosia, cosmos, impatiens,
geranium, marigold, pansy and petunia.
“One of the biggest challenges with
plug production of annual bedding plants is keeping the plugs compact,” Ortiz
said. “Compact plugs ease transport in boxes and allow for a higher volume of
plugs to be transported at one time. This is definitely something to consider
as fuel prices continue to rise.
“Plugs are often grown in dense
288- or 504-cell trays that promote rapid stem elongation. We are using red and
far red LEDs in end-of-day treatments in an attempt to manipulate the
phytochrome-mediated genes that are responsible for stem elongation under dense
planting conditions. If LEDs can be used to control seedling height, the
industry can decrease its reliance on plant growth regulators.”
Lopez and Ortiz are also
investigating red and blue LEDs as a supplemental lighting source during winter
bedding plant plug production.
“The goal behind this
experiment is to quantify root development under different ratios of red and
blue LED light and high pressure sodium light,” Ortiz said. “We also are also
trying to determine if supplemental light from LEDs can offer more rapid root
development than light from high pressure sodium lamps. This can make a big
impact on energy use in the industry.”
Lopez said producing cuttings is much different than producing
plugs.
“With plugs a grower is starting out with plants that
have roots,” Lopez said. “A grower may end up being able to delay the sowing of
the plugs if he is using lights. We may find that the LEDs might prove to be
even more beneficial with plugs than with cuttings.”
For more: Cary Mitchell, Purdue
University, Department: Horticulture and Landscape Architecture, (765) 494-1347;
cmitchel@purdue.edu.
Roberto Lopez, Purdue University, Department of Horticulture
and Landscape Architecture, (765) 496-3425; rglopez@purdue.edu;
https://sharepoint.agriculture.purdue.edu/agriculture/flowers/default.aspx

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