Evaluating field-bred lettuce varieties for hydroponic greenhouse production

University of Arkansas researchers trialed 65 lettuce varieties to determine their potential for production in greenhouse hydroponic systems.

 

By David Kuack

 

An increasing number of greenhouse ornamental plant growers are looking to expand into edible crops. There are also field vegetable growers who would like to expand their production to include greenhouse crops.
Some of the easier and faster crops for growers to try to produce in a greenhouse are lettuce and other fresh greens.
One of the issues these growers are facing is what varieties of lettuce can be grown in a greenhouse environment. Much of the commercial lettuce breeding is focused on outdoor field production. Growers looking to expand their lettuce offerings beyond commonly produced greenhouse varieties usually have to do their own trials looking for field varieties that can be adapted to a greenhouse environment.

 

Need to expand greenhouse varieties
University of Arkansas horticulture professor Mike Evans said he is constantly receiving inquiries from growers about what lettuce varieties can be grown in greenhouses.
“At Cultivate’14 we surveyed growers who participated in one of the greenhouse vegetable seminars about their educational and research needs,” Evans said. “One of the growers’ responses was the need for variety information.
“If you look at seed catalogs, most of the information describing lettuce varieties is based on field production, not greenhouse. So if a grower wanted to grow lettuce hydroponically in a greenhouse during the winter there is little information available. If a grower wanted to use nutrient film technique or deep flow floating systems in a greenhouse, there’s basically very little information on how lettuce varieties would do in these production systems. Most of the production information is field-based.”
Evans said there is also a need for evaluating lettuce varieties for fall, winter and spring greenhouse production. He said these variety evaluations need to be done in different regions of the country to see how they perform under different climates.

 

Lettuce variety evaluations
University of Arkansas researchers selected 65 lettuce varieties for evaluation in greenhouse production systems. A nutrient film technique and deep flow floating system were used for the trials.
“Our goal with the variety trials was to generate better and more variety information and to determine which varieties would work best in climates similar to ours,” Evans said. “We especially wanted to be able to make variety recommendations across a production year. That is, varieties which work well in the fall, winter and spring.

“There are certain varieties that do well during winter. But as soon as the days start getting longer, the variety begins to bolt. Or a variety may do well in the fall and spring, but during the lowest light levels of winter, it has some type of production issue.”

Photo 1, IMG_1619, Mike Evans, Univ. of Ark.
University of Arkansas researchers selected 65
lettuce varieties for evaluation in greenhouse
production systems.
Photos courtesy of Mike Evans, Univ. of Ark.

 

Evans said the information that has been collected is for lettuce varieties that perform well in a glass greenhouse in Arkansas.
“These varieties may not respond the same way in Michigan, Arizona, Florida and Texas,” he said. “They also won’t respond the same way in locations where the light and humidity levels are different. These trials are probably good recommendations for growers in climates similar to ours.”
Lettuce varieties were planted from September through May. No crops were grown in June, July and August. Four crops were produced during the fall to spring cycle.
“Some growers try to grow during the summer months by chilling the nutrient solution,” Evans said. “We weren’t set up for summer production. Having trialed 65 varieties we will probably select 15 of the best performing varieties to evaluate for summer performance. For the summer evaluations we will have to use a different greenhouse set up in order to chill the nutrient solution.”

 

Measuring growth rate
Evans said one of major growth parameters measured was biomass production or growth rate.
“The quicker the plants grow, the shorter the production cycle,” Evans said. “Every day on the bench is cost to the grower. We looked at fresh weight and dry weight, two measures of growth.
“Some growers let lettuce grow for a specific amount of time. Other growers try to achieve a specific weight.”
Evans said the lettuce crops were grown on a 42-day production cycle in both the NFT and deep flow systems. At the end of the 42-day cycle the lettuce was harvested and measurements were taken.
“Sometimes if a variety is a fast grower, the lettuce might exceed the weight that a grower would want,” Evans said. “That tells us this variety could have been grown in a much shorter period of time. Or a variety that didn’t reach a minimum weight at the end of the 42-day cycle was considered a slow grower. Fresh and dry weights were used as a measure of how fast a variety can grow. How fast can a variety put on biomass? That is what growers are selling—biomass.”

 

Photo 2, IMG_1600, Mike Evans, Univ. of Ark. (1)
Lettuce varieties that did well in a nutrient film
technique system tended to do well in a deep
flow float system.

 

Evans said there were similarities in how varieties performed in the two production systems.
“If the varieties did poorly in NFT, they tended to perform similarly in deep flow too,” he said. “If a variety did well in NFT, odds were high that it did really well in deep flow.”

 

Identifying disorders
Evans said the two most common problems he hears about lettuce from growers are powdery mildew and tipburn.
“Ninety percent of the calls I receive are about these two problems,” he said. “We rated the lettuce varieties we trialed for tipburn and powdery mildew. Powdery mildew, in our region of the country, is the disease that can often give growers fits. It can really wallop a lettuce crop.  We also measured the incidence of tipburn, which can be a problem on a number of greens.”
Evans said semi-heading and heading (butterhead) types seem to be more prone to tipburn.

“What happens is that as these varieties start to form heads there is an area of high humidity,” he said. “There is this little microclimate of high humidity. If a grower is growing under real high humidity, has structures with poor air circulation or the nutrition levels aren’t right, a calcium deficiency can occur. These can create a tipburn problem. We saw much less tipburn on varieties that tend to be loose leaf types.

 

For more: Mike
Evans, University of Arkansas, Department of Horticulture, Fayetteville, AR
72701; (479) 575-3179 (voice); mrevans@uark.edu; http://hort.uark.edu/5459.php.

 

Top performing lettuce varieties
The following lettuce varieties did well in the four greenhouse production trials conducted at the University of Arkansas.

 

Butterhead types
Adriana
Deer Tongue
Nancy

Rex

Rex
Rex

 

 

Skyphos
Fancy leaf types
Black Hawk
Cavernet

Dark Red Lollo Rossa

Dark Red Lollo Rossa
Dark Red Lollo Rossa
New Red Fire
Outredgeous
Red Sails
Ruby Sky
Oak leaf types
Oscarde
Panissee
Rouxa

 

Panissee
Panissee

 

Romaine types
Green Forest
Red Rosie
Red Rosie
Red Rosie

 

Ridgeline
Salvius
Truchas

 

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

Greenhouse research shifting focus to food crops

To meet the interest and needs of students and a changing
greenhouse industry, the horticulture department at the University of Arkansas is
shifting its focus to the controlled environment production of new and
underused food crops.

By David Kuack

An increasing number of students majoring in horticulture
at the University of Arkansas are focused on food crop production. Horticulture
professor Mike Evans said there has been a shift in interest by the students
from greenhouse-grown floriculture crops to greenhouse-grown food crops. Evans
said that except for turf management, students interested in food crop
production make up the majority of students majoring in horticulture at the
university.

“More and more students who are interested in greenhouse
production want to learn about growing food crops. To accommodate this
interest, we are starting a new class in which we are teaching about the
production of tomatoes, cucumbers, greens and other food crops. We are putting
in different kinds of production systems including hydroponics. The students
will have a really well outfitted lab where they can go in and they will be
raising various food crops with different systems. It will be hands-on.”

Evans said the growing interest in greenhouse food crops
has rejuvenated him and his program.

University of Arkansas horticulture professor
Mike Evans (right) is working with other professors
to develop a program on greenhouse food production
for both students and commercial growers. 

“As the ornamental side of the greenhouse industry has
been undergoing consolidation with fewer but larger operations, we have seen an
increased interest from the industry in growing greenhouse food crops,” he said.
“The number of emails and phone calls related to greenhouse food crops have
greatly increased.

“There are a lot of people growing tomatoes, peppers and
cucumbers in greenhouses. So I started looking at greenhouse food production
and found the area of herbs and greens in many respects has been neglected.
There are people out there doing these crops, but if you look for referenced
research or talk to people, there is a lot less solid research on greens and
herbs.”

Evans has started working with fellow university
horticulture assistant professor and breeder Ainong Shi.

“We are interested in looking at new species of fresh greens
and the breeding of greens,” Evans said. “We are particularly interested in
developing crops that can take Southern hot climates. By converting our
facilities to focus on greenhouse food crops we are looking to become a central
institution to study new species of greens, developing new crops, breeding new
cultivars, and developing production protocols for these crops.”

Developing greenhouse
food crops

Evans said the agriculture industry in the United States
has been largely field-based, but there are signs that changes are occurring
when it comes to controlled environment food production.

“Much of Europe and many parts of Canada and Japan are
significantly ahead of the U.S. when it comes to the development of controlled
environment food production systems,” he said. “We are very much in a catch-up
mode.”

One of the crops that Evans will be looking at regarding
new species is fresh greens.

“Most of the greens research, including breeding, being
done in this country, by-and-large, is for field production,” he said. “Those
same varieties that were originally evaluated in the field are then taken and
grown in the greenhouse. We typically have not bred varieties for greenhouse
production.

“We want to find greens that have lower inputs, that
don’t need much water or fertilizer. They also shouldn’t have many pest
problems, have a rapid production cycle and can especially take heat.”

Evans said the issue with heat is a major obstacle for
greens grown in the southern United States.

“The problem that growers in the southern half of the
U.S. run into during the summer is what kind of greens can they produce? Greens
in the South are more of an early spring and late fall crop. The question is
can we develop greens that can be grown in the heat of summer?”

Mike Evans said he is looking for fresh greens that have lower
inputs, including water and fertilizer, few pest problems, a rapid
production cycle and can do well in hot temperatures.


One of the crops that University of Arkansas researchers
are working on is to develop a heat-resistant spinach.

“We had a breeder here, Teddy Morelock, who did a lot of
spinach breeding,” Evans said. “He passed away, but left us with hundreds
of spinach lines. We’re trying to figure out what we’ve got. Teddy never conducted
greenhouse trials or evaluated the germplasm for production in greenhouses. All
of his evaluations were done in the field. We might be sitting on the best
spinach variety to grow in a greenhouse.”

Another crop that Evans is excited about studying is
dandelion (Taraxacum officinale).

“Dandelion has a higher nutritional value than spinach,”
he said. “It is loaded with iron, vitamins A and C and beta-carotene. It was
considered a medicinal plant. The early immigrants to America brought
dandelions with them for food. A lot of people suffered vitamin deficiencies
and developed scurvy. So they brought the dandelions with them.”

Evans said dandelions can be grown quickly, don’t need a
lot of inputs and are very heat tolerant.

“They are short day plants so they might need some night
interruption lighting,” he said. “That’s not real a concern because the plants
would probably be harvested before they flower.

“There is a great deal of genetic diversity in dandelions
because they are spread worldwide and are segregated. There are a lot of flavors and
traits. We are going to be collecting germplasm from all over the world. We are
going to be breeding dandelions so that they develop into what we want them to
be.”

Setting up a strawberry
cam

As part of the National Strawberry Sustainability Initiative, Evans will be working with professor
Elena Garcia, who is the university’s fruit specialist. The research they will
be doing is part of a program funded by the Walmart Foundation, which is being
administered by the university’s Center for Agricultural and Rural
Sustainability.

“We want to demonstrate and teach growers about various
types of hydroponic systems for strawberry production,” Evans said. “Those
systems might include NFT troughs, gutters, Dutch buckets, etc. There are
various types of hydroponic systems that we feel bring some significant
advantages to the production of strawberries and help to promote a number of
sustainability goals in the program’s guidelines.”

Evans said the type of structures used to grow the
strawberries will also be discussed.

“If a grower considers using high tunnels, he can extend
the season,” Evans said. “Or a grower might consider using drop wall
greenhouses. There is the possibility of providing heat, which could result in
year-round production. There are a lot of possible benefits for our growers.”

Evans and Garcia have been traveling around the state and
meeting with growers talking to them about the different production systems and
explaining how they can be used for strawberry production. Evans said many of
the growers that he and Garcia have met with didn’t know about the differences
in the production systems and didn’t understand the differences.

University of Arkansas professors Mike Evans and Elena Garcia
will be teaching growers in their state about various types
of hydroponic systems for strawberry production.

Evans has renovated two of the university greenhouses in which various strawberry production
systems will be installed and used to produce crops. About 4,000 square feet
has been converted to hydroponic food production with about 1,600 square feet
devoted to strawberries and the remaining used for greens.

“Our
goal is to put in several different systems and to shoot video of what we are
doing from the beginning to end,” he said. “We will shoot video of the assembly
of the different systems as well as the production of the strawberries in each
system. We will film and document in detail everything we do. The videos will
walk the growers through all aspects of design, build, manage, maintain and
grow the strawberries using a specific system.”

Evans said the videos will be used as an educational tool
allowing growers to look at the different production systems and to see the
advantages and disadvantages of each system.
Evans has also been working with University of Arizona
horticulture professor Chieri Kubota and research specialist Mark Kroggel to
prepare videos on the strawberry production research they have been conducting
at the university’s Controlled Environment Agriculture Center.

“Not every system is perfect for everyone,” Evans said.
“Everyone has to look at what they are growing or planning to grow and what is
their market. We want to use the videos as a way to demonstrate these systems
to teach growers how to effectively select one and how to effectively use it.”

For more: Mike
Evans, University of Arkansas, Department of Horticulture; (479) 575-3179; mrevans@uark.edu.

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

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