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.”
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.”
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
Skyphos
Fancy leaf types
Black Hawk
Cavernet
New Red Fire
Outredgeous
Red Sails
Ruby Sky
Oak leaf types
Oscarde
Romaine types
Green Forest
Ridgeline
Salvius
Truchas
David Kuack is a freelance technical writer in Fort
Worth, Texas: dkuack@gmail.com.
Visit our corporate website at http://www.hortamericas.com
No comments:
Post a Comment