Tag: leafy greens

Plant factories continue to evolve

As technology improves, plant factories have the
potential to operate in the U.S. and Canada to produce crops that are difficult
to grow using current conventional methods.

By David Kuack
When you hear the term “plant factory” what picture comes
to mind? University of Florida professor and mechanical engineer John Schueller
said the traditional definition of a plant factory is a place in which there is
no natural light and artificial light is used to produce plants.
“I’m more of a traditionalist in that I feel a plant
factory is a place that has mainly or only artificial lights in order to grow
plants,” Schueller said. “But a greenhouse with multiple levels of plants in
which natural light is the dominant source and is supplemented with artificial
light, I would also consider that to be a plant factory.
“People involved in protected plant agriculture,
including greenhouses and indoor plant factories, are displaying a lot of
creativity. There are a lot of different systems being tried out. It’s
difficult to make a hard and fast definition of a plant factory. A traditional
greenhouse with plants on raised benches or growing on the floor is not usually
recognized as a plant factory.”
Plant factory
automation

Schueller, who spoke at the Plant Factory Conference in
Kyoto, Japan, in Nov. 2014, said the most important automation that occurs in a
plant factory is during the growth stage.

“The application of light and fertilizer is when the main
automation occurs,” he said. “There is automation during planting when a grower
is trying to establish the plants. And there is also automation during
harvesting.”

University of Florida mechanical engineer John
Schueller
said the technology of plant factories
is improving with the main improvement
occurring with LED lighting.

Photos
courtesy of John Schueller, Univ. of Fla.

Schueller said during the Plant Factory Conference there
was a lot of discussion about which lights are the best for using in plant
factories.
“There are questions that still need to be answered about
what are the best wavelengths and what are the best cycles for different
crops,” he said “Even though there are a considerable number of plant
factories, we still don’t know what the optimal conditions are for growing
plants. There is a lot of variation and experimentation occurring.”
Schueller said automation in the plant factories will
probably occur with the planting practices before it happens with harvesting.
“In Japanese plant factories the finished plants are
brought to the harvesters,” he said. “There is automation to transfer the
plants. People are doing the harvesting of leafy greens, but they are brought
to the workers at an appropriate height and position so that they can be very
efficient and very productive. Obviously, if there are 14 layers of plants
under lights the plants are moved to the harvesters. But there is still some
human involvement in harvesting the plants.”
Schueller said an advantage to a plant factory is the
ability to precisely control the environment. “The technology is improving,” he
said. “The main improvement is with LED lighting. As LEDs become less expensive
and better that will help in the development of plant factories. Also, less
expensive sensors for measuring nutrient solutions are becoming available. As
growers gain more experience with this technology they get better at
controlling the production environment.”
Plant factory
economics

Schueller said economics play a big role in what will be
feasible in how these factories operate.

“The Japanese market for fresh fruits and vegetables is
much different than in the U.S. and Canada,” he said. “In the U.S. and Canada,
vegetables are cheaper. The market will not bear some of the costs that will be
accepted in Japan. In Japan consumers are willing to pay $40 for a watermelon.
“From an agricultural economic standpoint, it seems to me
the big advantage of a plant factory is that a grower can control the
production situation very well. The disadvantages are the energy costs for
running the artificial lights and the capital equipment costs. The best
opportunity is to produce a product that has certain characteristics, that has
no pesticides applied, that has no bacterial contamination, so that a grower
can demand a premium price for it.”

John
Schueller said one area of plant factory production
that shows great potential
is being able to develop
techniques that allow high end vegetables to have
nutritional characteristics that can be easily manipulated.

Schueller said one area of plant factory production that
shows great potential is being able to develop techniques that allow high end
vegetables to have nutritional characteristics that can be easily manipulated
more so than in other production environments.
“One of the Japanese plant factories that was built by
Fujitsu is growing lettuce which has a low potassium content,”
he said. “This lettuce is being produced for kidney dialysis patients and
people with chronic kidney disease. This type of crop has a lot of potential
for U.S. and Canadian markets. Developing vegetables that have nutritional
characteristics so that the markets will be able to tolerate higher production
costs that are associated with plant factories.”
Schueller said the plant factories in Japan can produce
leafy green vegetables in about 15 days.
“The production cycle needs to be as short as possible,”
he said. “If a plant factory is controlled properly and maintains sanitary
conditions, it is possible to produce leafy green vegetables with specific
nutrient characteristics without pesticides. For those types of crops a grower
can demand a premium price to pay for the equipment and energy to produce
them.”
Fast, precise
production

Schueller said the plant factories in Asia are producing
primarily leafy green vegetables.

“I expect these crops would have the greatest potential
in the U.S. as well,” he said. “As more consumers move away from iceberg
lettuce and romaine lettuce, they tend to look for other types of lettuce and
leafy greens and microgreens. There might be real potential with these crops
because they can usually be turned much more quickly.”

Japan
has over 200 plant factories. One of the reasons that
the country has experienced
a proliferation of these facilities
 is food security. Sixty percent of the country’s
food is imported.

Schueller said some of the issues pushing plant factories
in Asia are related to domestic food production and land availability.
“Japan imports almost 60 percent of its food,” he said.
“For the Japanese it’s an issue of food security. Singapore has increased its
vegetable consumption from 7 percent to 8 percent. In Singapore there is a
limited amount of land. They are looking for ways to maximize food production
and plant factories offer them a solution. With plant factories that have
vertical farming they can push the production to maximize the space. In the
U.S. that isn’t a big concern. The plant factories in the U.S. that will be
successful are the ones that grow products that are difficult to produce using
conventional methods.”

For more: John
Schueller, University of Florida, Departments of Mechanical and Aerospace and Agricultural
and Biological Engineering; (352) 392-0822; schuejk@ufl.edu.

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

Visit our corporate website at https://hortamericas.com

Using Grodan for Lettuce and Herbs

Using Grodan for Lettuce and Herbs 

In recent years there has been
a worldwide increase
in the consumption
of lettuce and fresh herbs. Naturally this has led to an increase in production.  More and more growers are now opting to use GRODAN
as their substrate.
The benefits of
using GRODAN in the production process are:
  • It is an
    inert and hygienic substrate
  • The speed and
    uniformity of germination and growth.
  • There is
    sufficient substrate volume to propagate to the
    desired plant size.
  • Once it is
    placed in the gutter or raft system the
    propagation blocks provide further stability.
Inert and clean
GRODAN stone wool
is an inert and hygienic
substrate, so it provides your crop with a clean,
disease free start. Furthermore, stone wool retains its structure throughout the cultivation
cycle. Filters remain clean and free from blockages, cleaning between crops is
easier and more importantly, faster, allowing less downtime between crops. The
fact that it is also inert means that all applied nutrients and
water are directly available for the growing crop. The combination of faster turnaround
and faster growth adds to the possibility of extra cultivation cycles during
the year.
Uniformity and speed of germination and growth
One of the most critical
stages of cultivation is germination. Seed holes cut into the stone wool plugs provide
the perfect air/water ratio around the seed which facilitates a high
germination percentage. More importantly, as the stone wool substrate is
uniformly saturated, each seed has the same germination environment, which provides uniformity in
emergence and initial growth. The speed and uniformity of growth which
follows results in a higher quality end product. It also provides a crucial opportunity
for additional cultivation cycles during the year.
Substrate volume to propagate the desired plant size
There are two distinguishable
stages in the production process; propagation and final production.
With the propagation of lettuce, a favorable microclimate is required. This is partly achieved
by retaining a high plant density. 
In GRODAN trials, we have seen that when the propagation period
is extended (21-24 days), the microclimate created results in more speed in
final production. Also, as larger plants are used, the production cycle is shortened,
once again providing an opportunity for additional cultivation cycles during
the year.
In order to extend the propagation
period you also require a larger substrate volume (i.e. AO
36/40 or MM40/40). This larger volume allows more root growth and
more stability.  Crucially, it also
allows irrigation to be managed. Often in propagation, too much water is given.
This results in weaker plants with greater susceptibility to disease.
Having the right irrigation strategy with the right substrate volume will give
you the possibility to be critical to the moment of irrigation. Having a precise irrigation
strategy will also retain the roots within the plug and therefore result in less
damage during transplanting.
To improve the irrigation strategy, we would suggest that you weigh
the blocks or AO sheets to decide if irrigation is needed (table 1).
Table 1. Indicative weights to irrigate the
blocks or AO sheets.
Grodan product
Approximate substrate volume
Indicative weight to base irrigation on (±60% WC)
MM 40/40
64 ml per block
40 gram per block
AO 36/40
40 ml per plug
3926ml per sheet
24 gram per plug
2.4 kg per sheet

Stability during use in gutter or raft system

Depending on the production system
which is used, the
GRODAN propagation component provides a certain degree of stability. For plants in
gutter systems, suitable products are MM blocks or the AX
plugs (figure 1). For plants in a raft system an AO plug is recommended, as its tapered
base makes planting
into the raft faster.
Figure 1. Left picture showing Grodan AX  plugs with basil seedlings, middle Grodan MM
blocks with lettuce during propagation stage, right picture showing Grodan AO
plug.
Conclusion
GRODAN stone wool
will give you an inert, clean substrate which provides fast, uniform
germination and growth. Whether you have a raft or gutter system, we have a plug or block that
will fit your needs.

For more information
contact Hort Americas at 469-532-2383 or customerservice@hortamericas.com 

Visit our corporate website at https://hortamericas.com

Update on trialing supplemental lights in Hawaii

By David Kuack

On Dec. 14, 2014, a Hort Americas blog update was posted about University of Hawaii graduate student Robert Saito, who is
comparing the growth of pak choi (Chinese cabbage) under T5 fluorescent lamps
and Philips GreenPower LED Production Module Deep Red/Blue 120 fixtures. Saito
has conducted seven trials. The first four trials were preliminary to determine
the best growing medium and which plants should be used to measure light effect
differences. Initially Saito was planning to grow mizuna, but he ran into
issues with micronutrient deficiencies and switched to pak choi instead. Both
of these leafy greens are in the Brassica family.

University of Hawaii graduate student Robert Saito is studying
the differences in growth of pak choi under fluorescent (top)
and LED lights (bottom).
Photos courtesy of Robert Saito


Preliminary results
Saito has measured fresh weight, height and chlorophyll
content of the plants grown under the two light sources.
“I also took SPAD readings to measure the relative chlorophyll
and there were differences among the treatments,” Saito said. “I am now going
to run the data statistically to see if there was a significant difference.”
Plant samples are also being analyzed for nutrient
content to see what kind of nutritional value they can offer to consumers.
“I am doing a tissue analysis to measure some of the
secondary metabolites,” he said. “I am looking at total phenolics, carotenoids
and glucosinolates. A mineral nutrient analyses will measure such things as
total nitrogen, phosphorus and potassium. Once the mineral and tissue analyses
are done then I hope to publish the results.”
For more:
Robert Saito, University of Hawaii, College of Tropical Agriculture and Human
Resources, Manoa, Hawaii; rjnsaiot@hawaii.edu.
David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com. 
Visit our corporate website at https://hortamericas.com

LED Grow Lights used in Leafy Green Trials

Philips GreenPower Production Module LED Experiment with
Specialty Greens in Lafayette, CA

Lights: Philips GreenPower Production Modules Deep
Red/Blue 120cm

Objectives: 1.) Can a variety of greens (gourmet
lettuces, high nutrient greens and herbs) be grown under production LED lights
well enough and quickly enough to be commercially viable. The target is a 30
day cycle from seed to harvest.

2.) Would two lights per hydroponic unit (ez clone
cloner) achieve this goal or are three necessary?

Seeded: 9/15/13

Experiment under lights began: 9/26/13
Initial recommendation to hang lights 16-18” above plants produced
leggy and weak seedlings.  Lights
remounted above plants 7-8” Philips GreenPower Production Modules are being run
14 hours/day.  Ambient room temperature
ranges from 70 degrees during the night to 85 degrees during the day. The
nutrient used is DynaGrow at a dilution of 1/2 teaspoon per gallon so about 5-6
teaspoons per cloner. ProTect, an auxiliary nutrient, was used at the same
dilution. An ArtDne recycling timer is being used 24 hours per day at a rate of
1 minute on for every 5 minutes off. There will be one nutrient change during
the experiment after approximately two weeks to refresh the set up and new
nutrient will be applied at the dilution described above.
Specialty Greens is providing growers interested in hydroponics all the they need to grow hydroponically in a 2 ft sq. space!
To
find out more about Specialty Greens Check them out here or like them on Facebook
Here are some photos taken of the Experiment on 9/26/13

Experiment information provided by Patty Phaneuf from Specialty Greens, and Posted by Maria Luitjohan from Hort Americas.
Visit our corporate website at https://hortamericas.com

Using organic fertilizers for hydroponic lettuce production


Research at Kansas State University shows comparable size
and quality lettuce plants can be grown hydroponically with organic or
inorganic fertilizers.
 
By David Kuack

According to the Organic Trade Association’s “2013 U.S. Families’ Organic Attitudes and Beliefs Study,”
81 percent of U.S. families report they purchase organic products at least sometimes.
The study found that the majority of those buying organic foods are purchasing
more items than a year earlier. Those households that are new to buying organic
products represent 41 percent of all families.

The study showed that produce continues to be the leading
category of organic purchases. Ninety-seven percent of organic consumers
indicated they had purchased organic fruits or vegetables in the past six
months. Breads and grains, dairy and packaged foods all scored above 85 percent
among those who buy organic products.
 
A 2013 study done by the Organic Trade Association showed
that 97% of consumers indicated they had purchased
organic fruits or vegetables in the past six months. 
Retailers should be particularly interested in the
results of the study. Organic buyers reported spending more per shopping trip
and shopping more frequently than those who never purchase organic food.

This month national retailer Target
announced its plans to begin offering a new line of organic products called
Simply Balanced. The line is an outgrowth of similar products within its existing
Archer Farms store brand. The Minneapolis-based company plans to boost its
organic food selection by 25 percent by 2017.

Comparing organic,
inorganic fertilizers

With the increased interest in organic produce by growers,
retailers and consumers, researchers at Kansas State University looked at the
production of hydroponically-grown lettuce using organic fertilizers. Jason
Nelson, who received his Master’s degree this year, said the purpose of the
research was to study overall plant performance with organic and inorganic
fertilizers. Another aspect of the research was to study the effects of
commercial microbial inoculants that are marketed to promote plant growth.

Lettuce plants were grown hydroponically comparing organic
and inorganic fertilizer solutions to which were incorporated
microbial inoculants.

‘Rex’ butterhead lettuce was grown in nutrient film
technique troughs. The nitrogen sources of the complete inorganic fertilizer were
ammonium nitrate and ammonium phosphate. The organic fertilizers consisted of four
Kimitec products for hydroponic production,
including Bombardier (8-0-0), Caos (10.5 percent calcium), Espartan
(2.7-3.0-2.6) and Tundamix NOP (micronutrients), plus KMS (potassium magnesium
sulfate) from a different supplier. The microbial inoculants included
SubCulture-B bacterial root inoculant and SubCulture-M mycorrhizal root
inoculant.

“Nitrogen in organic fertilizers is primarily found in proteins
and other complex molecules that break down to ammonium,” Nelson said. “The
ammonium levels could be considered comparable between the two types of
fertilizer systems, although the level was slightly higher with the inorganic
fertilizer. The biggest difference was in the nitrate nitrogen. Starting out,
the inorganic fertilizer contained 75 parts per million nitrate. With the
organic fertilizer there was no nitrate at all. For the other nutrients,
including phosphorus, potassium, calcium and sulfur, using all of Kimitec
products except Katon, which is a potassium source, those were all comparable
with the inorganic fertilizer.”

Nelson said the purpose of incorporating the microbial
inoculants was to learn if they had any impact on the plants grown with either
of the fertilizers.

“Growers have had some trouble getting the same amount of
growth using organic fertilizers compared to inorganic fertilizers,” he said.
“These microbial inoculants are advertised as being able to boost plant growth.
One purpose of the study was to determine if the inoculants would boost growth
in an organic hydroponic system so that it would be comparable to plant growth
with inorganic fertilizers.”

Differences in
growth

One of the things that Nelson noticed in his trials was
that the inorganic-fertilized lettuce plants were harvestable earlier than the
organic-fertilized plants. He said this was particularly evident during the
summer trial when the inorganic lettuce actually bolted.

“Comparing the amount of nutrients in the inorganic fertilizer
to the organic, it makes sense that this growth difference occurred,” he said. “There
was more nitrate in the inorganic fertilizer, so there was a better nitrogen
balance from the start and the plants grew and matured a little faster and were
probably about five days earlier to harvest in the summer and fall trials.

“The limiting factor with the organic fertilizer is the
nitrate. If a grower added some calcium nitrate to the organic nutrient
solution the plants would catch up to the inorganic plants. I expect it would
only take a small amount of nitrate, 30-50 ppm, for the organic plants to match
the growth rate of the inorganic plants.”

Lettuce grown with the four Kimitec products and
potassium magnesium sulfate were comparable to the inorganic plants in size and
fresh weight. However, the inorganic plants consistently had a higher dry
weight than the organic plants.

“The heads of lettuce looked comparable in size,” Nelson
said. “If a consumer was buying a fresh head of lettuce they wouldn’t be able
to tell the difference between the organic- and inorganic-fertilized plants.”

Heads of lettuce grown with inorganic or organic fertilizer
looked comparable in size. The growth rate of the inorganic
lettuce was slightly faster, finishing about five days earlier
than the organic lettuce. Microbial inoculants didn’t seem to
have an effect on this short-term crop.
One area where there was a noticeable difference was in
the taste of the lettuce. Nelson said that the inorganic-fertilized lettuce is
going take up nitrate nitrogen, which is going to be deposited in the leaves.

“There was definitely a flavor difference between the
inorganic and organic plants,” he said. “I attribute the flavor difference more
to the nitrate level than anything else since the other nutrient levels were very
similar between the inorganic and organic plants. The petiole nitrate level was
much higher in the inorganic plants. The flavor was much heavier. We did an
informal classroom taste-test with students and that was a common response. Many
of them preferred the taste of the organic lettuce over the inorganic lettuce.”

Nelson said the use of microbial inoculants with both the
inorganic and organic fertilizers didn’t appear to have any effect on the
growth of the lettuce plants.

“The plants that we were growing were under a relatively
stress-free, temperature-controlled environment,” he said. “I really didn’t see
any difference in the studies with the inoculants except in one circumstance.
That was when the solution nutrient levels were incredibly low. The inoculants
actually had some nitrogen bound up in kelp meal as part of their constituents.
I saw some growth differences in that instance.

“Mycorrhizal fungi take about eight to 10 weeks to become
established and colonize the plant roots. For crops like lettuce which finish
as quickly as four weeks, a mycorrhizal inoculant isn’t going to become active
within such a short production cycle.”

Managing fertilizer
solution pH

Nelson said one of the biggest challenges facing growers
who are trying to grow in an organic hydroponic system is pH management.

“The Kimitec line of products was able to provide an
adequate amount of nutrients for the plants to grow. But the nutrient solution
required more pH management,” Nelson said. “Managing the pH is the biggest
challenge with organic fertilizers because a grower can follow the recommended
rates so the proper amounts of nutrients are available, but the pH fluctuation
is so much more pronounced than it is with inorganic fertilizer treatments.

“It depended a little on plant size, but the nutrient
solution pH for the inorganic plants was adjusted on average maybe once a week.
For the organic plants, at minimum I was checking the solution pH and electrical
conductivity at least once a day whether I was making any changes or not. Some
days I would check the pH twice. If I checked the pH, adjusted it to what I
wanted, by the next day I would have to add acid to bring the pH back down
because it would increase overnight. Somebody might be able to stretch that to two
to three days. When the plants were young, I was checking every day and
adjusting the organic solution pH every day. That’s what the organic solution seemed
to require.”

For more:
Jason Nelson, jsn0331@k-state.edu. Kim Williams, Kansas State University, Department of Horticulture, Forestry and
Recreation Resources; kwilliam@ksu.edu. http://krex.k-state.edu/dspace/bitstream/handle/2097/15574/JasonNelson2013.pdf?sequence=5

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

Visit our corporate website at https://hortamericas.com

Choosing an organic fertilizer

By David Kuack
Growers looking to make the switch from traditional
inorganic fertilizers to organic fertilizers might feel a bit overwhelmed when
considering the number of options available. Kansas State University
horticulture professor Kim Williams said growers looking to use organic
fertilizers should start out trialing a small number of plants to avoid
sizeable losses. She also recommends that growers start with a commercially
blended organic fertilizer rather than a straight product like manure.
“It’s going to take some practice, some trialing, so
growers don’t burn their plants because that is another transitional change
compared to conventional starter nutrient charges,” Williams said. “Where a lot
of growers can get into trouble is incorporating manure or composted manure
into organic substrates as a starter nutrient charge. That is something that I
would not recommend doing for the novice organic grower. What sometimes happens
is high levels from the manure burn young seedlings. Fresh and incompletely
composted manure can also introduce disease problems and/or weed seeds into the
production system as well.”
Williams said that there can also be a lot of variability
in nutrient availability from products like bone and blood meal depending on
the source and their particle size.
“Different sources of bone meal for example are going to
have significantly different nutrient release rates,” she said. “This can
result in an excessive nutrient release too early in the production cycle. If
the grower is not expecting this, he can lose a lot of plants depending on
their stage of growth. Seedlings and plugs are much more sensitive than older
plants to high salts. It really does take some practice with a new nutrient
source.
“If a grower uses a commercially blended product as
opposed to manure from his neighbor’s horse farm, he is going to avoid
potential problems. I would recommend a commercially prepared organic product
like composted and processed turkey litter that is not going to contribute
disease problems.
Williams said growers should start with an organic
nutrient source that has a known N-P2O5-K2O
ratio and then trial it at a few different rates with a small number of plants
before using it extensively.
Supplying enough
nutrients
Williams said that growers who incorporate a preplant
organic fertilizer into their growing mix still need to provide additional
fertilizer to the production system.
“I have yet to use an organic nutrient source that didn’t
provide an initial nutrient release that was very significant,” she said.
“Nutrient release then tends to tail down quite a bit depending on the rate of
application, temperature and media moisture content, all of which influence
microbial breakdown of the organic material and thus nutrient release.
“This can be a challenge for growers. There is an initial
spike of nutrients released so growers have to protect against that by reducing
the rate of what they are adding as a preplant. But then their crops are going
to need supplemental nutrition later on when the soluble fraction of the
organic fertilizer is used up.”
Research conducted by Williams showed that organic
fertilizers bring a lot of microorganism populations with them into the
production system. It is these beneficial microbial populations that are then
contributing to the nutrient conversion.
“In our experience so far with organic fertilizers it has
not been necessary to do additional microbial inoculations when organic
fertilizers are used,” she said. “Growers who apply a preplant dry organic
fertilizer will start to get microbial activity even before applying a
supplemental liquid organic fertilizer. Growers who incorporate a preplant
fertilizer are providing microorganisms with a food source of carbon so that
the populations can really take off much more quickly than if they applied
conventional inorganic fertilizers. However, the disadvantage with the organic
fertilizers is that they are less predictable for growers. Managing nutrition
is more challenging since the growers are relying on microbial release of
nutrients from the organic sources.”
Williams said some growing media manufacturers are
producing organic potting mixes into which an organic fertilizer is
incorporated as a starter nutrient charge.
“Media manufacturers put in a preplant organic fertilizer
to provide a starter charge,” she said. “Then the growers can decide on a
schedule with supplemental soluble feed.”
Dry and liquid
formulations
Growers have the choice of both solid and liquid
formulations of organic fertilizers. Williams said many growers are applying a
dry preplant amendment to their potting mixes.
“Some growers have chosen to incorporate solid forms of
certain fertilizers such as bone meal that have a smaller nitrogen component or
something like feather meal that is going to take some time to break down.” she
said. “These growers then supplement with a liquid organic fertilizer.”
Williams said that organic fertilizer manufacturers are
making products that are more convenient to use and more consistent in their
nutrient formulations.
“There are some fertilizers that have more complete
nutrient formulations. These are the result of digested or fermented
combinations of a number of organic materials,” she said. “These types are
really the only way that a grower can get a somewhat balanced N-P2O5-K2O
ratio in a fertilizer.”
Williams said most of the commercial organic fertilizers
are very shelf stable. Because the formulations are so concentrated, microbial
populations cannot grow in them.
“When growers start to dilute these fertilizers in a
stock tank is when other micro-organisms can come in and start feeding on the
nutrients before the fertilizer solution is applied to the crops,” she said.
“When a fertilizer is taken out of the concentrated container and diluted down
in a stock tank is when organisms can grow in it. Growers have said that within
a couple of days organisms will be growing in the stock tank.”
Williams said to avoid problems with organic fertilizers
going bad, most growers mix up just enough tank solution to feed the plants
they want to fertilize that day.
“That’s also a disadvantage with organic fertilizers.
With inorganic fertilizers a grower can make up a month’s worth of stock
solution and let it sit there and not be concerned with it going bad,” she
said. “With organic fertilizers a grower has to mix up just enough to feed his
plants and if he has to do that every few days that’s a lot more work.”
Williams said another thing growers should consider when
choosing a soluble organic fertilizer is whether it can be used with their
current injector equipment.
“The grower needs to ask the question, “What fits into my
liquid fertilization system in terms of how I mix up liquid fertilizer and how
I apply it to my crop?” Some injectors will handle organic fertilizers better
than others. Some fertilizers can clog injector systems.”
Hydroponic
production
Williams said growers using conventional hydroponic
production systems generally tend to use fertilizers that contain very little
ammoniacal nitrogen compared to nitrate nitrogen. The reason is that the plants
can run into ammonium toxicity problems.
“A hydroponic system doesn’t have the buffering capacity
of a growing medium that has some cation exchange capacity,” she said. “The
substrate would hold some of the ammonium and not make it available for plant
uptake.
“If ammonium is in solution then it’s available for the
plant roots to take up. Ammonium can’t be stored in the plant cells like
nitrate can. If plants are absorbing too much nitrate, that’s not really a
problem because the excess can be stored in the vacuoles of the plants’ cells
and it’s not going to cause toxicity problems.
“When plants absorb ammonium they need to assimilate it
right away, their cells can’t store it. If the plants can’t use the ammonium
then it’s going to damage the cells and burn the plants.”
Williams is starting a hydroponic research project to
determine the differences in growing butterhead lettuce with organic and
inorganic fertilizers and different types of microbial inoculums.
For more: Kim
Williams, Kansas State University, Department of Horticulture, Forestry &
Recreation Resources, (785) 532-1434; kwilliam@ksu.edu.

David Kuack is a freelance technical writer in Fort
Worth, Texas; dkuack@gmail.com.Visit our corporate website at https://hortamericas.com

Hydroponic Lettuce Production in Phenolic Foam

By
David Kuack and Vijay Rapaka
Inorganic
growing substrate materials that have been used for hydroponic crop production
include rockwool, perlite, vermiculite, expanded clay and pea gravel. Phenolic
foam is a relatively new inorganic substrate that offers many desirable
production properties.
Phenolic foam
cubes
The
Oasis Horticube Growing Medium is a sterile phenolic foam. Like rockwool,
Horticubes have no cation exchange capacity, no
buffering capacity and no initial fertilizer charge.
Horticubes come in a variety of sizes, including: 1-inch Thin-Cut
(276 cubes/sheet), 1-inch (162 cubes/sheet), 1¼-inch (104 cubes/sheet) and 1½-inch
(50 cubes/sheet). All of the sheets measure 10- by 20-inches and fit into
standard 1020 trays. Each sheet is pre-scored on the bottom and top to allow
for easy separation of the cubes at transplant.
The 1-inch Thin-Cut Horticube was developed primarily for
hydroponic lettuce production. This high density configuration accommodates 276
seeds in a standard 1020 tray. Each cube is pre-punched with a dibble hole that
is uniform in depth and has center to center spacing. This allows for the use
of automated seed sowing equipment. Horticubes work equally well with both nutrient
film technique (NFT) and a raft (float) growing system.
Using the North Carolina State University porometer, the 1-inch
Thin-Cut Horticube has a water-holding capacity of 80 percent and air porosity
of 20 percent. A comparable rockwool product, which has grooves at the bottom
of the sheet, has a water-holding capacity of 60 percent and air porosity of 40
percent.
Sowing the seed
Horticubes can be seeded dry and do not need to be watered prior
to sowing the seed. Seed can be sown using a vacuum seeder or manually by
placing the seed in the dibble holes. The specially designed hole is tapered to
ensure the seed sets properly in each cube.
After the seed is sown irrigation can be done manually with a hose
and water breaker (i.e., wide fan nozzle) or automatically by passing the
Horticube sheets through a watering tunnel. The sheets should be thoroughly
saturated.
Water-holding
capacity
A single Horticube sheet holds about 4 liters (1 gallon) of water.
However, it takes more than 4 liters of water to ensure total saturation of the
foam because of water channeling through the dibble holes and grooves on the Horticube
sheet. To ensure thorough saturation about 10 liters (2.6 gallons) should be
applied so that the water pours through the bottom of the sheet. As rule of
thumb, water each sheet for 2 minutes at regular tap water pressure.
If the seedlings are going to be irrigated/fertigated by overhead
irrigation, place the Horticube sheets in solid bottom trays with drain holes. Never
use a solid bottom tray without drain holes. If sub-irrigation is going to be
used, place the Horticube sheets in trays that have solid sides and web bottoms.
Like rockwool, the Horticube sheets can be rewetted. Both of these
media should not be allowed to go completely dry between waterings.
Once the Horticubes are thoroughly saturated, the cubes should
stay moist during the course of germination.
Lettuce seed sown in Horticubes does not have to be topdressed
with vermiculite. The seed also does not require a dark treatment for germination.
The best germination usually occurs when the Horticube temperature is below
70°F. The seed usually germinates in two to three days.
Watering
and fertilizing seedlings
Generally lettuce seedlings in Horticubes do not require misting
or watering during germination. However, on bright hot summer days consider a
brief misting (5 seconds once a day) on Day 2 and Day 3. Apply clear tap water
with no fertilizer.
Once the lettuce seed has germinated the mist frequency needs to
be adjusted. A typical misting program consists of starting from Day 4 to Day
7, three times a day for 10 seconds. From Day 7 to finish, mist four times a
day for 10 seconds. If the seedlings are going to be either hand-watered or on
a sub-irrigation system, irrigate only once a day.
Start fertilizing the seedlings on Day 4. All of the different
nutrient formulations developed for lettuce production will work with
Horticubes. Growers should customize their specific formulations depending on
water supply, lettuce cultivars, production system, climate and season. The
nutrient solution pH should range from 5.5 to 6. The recommended electrical
conductivity during propagation is 1.0 mS/cm. The recommended electrical
conductivity during production is 1.2 to 2.2 mS/cm.
Transplanting
seedlings
Lettuce seedlings should be ready to transplant 10 to 14 days
after sowing depending on seasonal climate conditions. During summer months it
takes about 10 days from sowing to transplant and during winter months it takes
about14 days. The criteria for transplant are development of two true leaves
and root penetration through the bottom of the Horticubes.
At transplant the pre-scored sheets can be easily separated into
individual cubes. The easiest way is to break the individual cubes from the top
down along the scoring.
Production
and harvest
Lettuce seedlings in Horticubes transplanted into a NFT or raft
system perform equally well. During production the recommended electrical
conductivity of the nutrient solution should be 1.2 to 2.2 mS/cm. With a NFT
system the water flow rate should be 1 to 1.2 liters per minute. Analysis of
the nutrient solution should be done on a regular basis in order to make
formulation adjustments.
Hydroponically-grown lettuce produced in Horticubes can be harvested
with the root system intact. Leaving the root system intact can help to extend
the shelf life of the lettuce.
For more: Smithers-Oasis
North America; (800) 321-8286; www.oasisgrower.com or Hort Americas, LLC at +1 469 532 2383.
David
Kuack is a freelance technical writer in Fort Worth, Texas, dkuack@gmail.com.
Dr. Vijay Rapaka is Manager—Grower Research, Smithers-Oasis Co., Kent, Ohio, vrapaka@smithersoasis.com.

Visit our corporate website at https://hortamericas.com