March 2020 - 9

looking at the differences between
the light treatments. Greenhouse
strawberry growers would want to
increase the light intensity. For most
strawberry cultivars the recommended
DLI is 20-25 moles. More light almost
always means higher yields for most
crops. This is something that needs
further study for strawberries. "
highest Brix at 9.4 degrees.
Cabrillo had slightly lower sugar
content than Albion. For Cabrillo,
grown with ambient light the Brix value
was 5.9 degrees. Under LEDs, the Brix
value was 6.7 degrees. As with Albion,
Cabrillo grown with HPS lamps had the
highest Brix at 7.3 degrees.
Impact of life
Throughout the five-month trial,
the plants were maintained as much
as possible at three crowns per plant.
Within that requirement, under the
ambient light treatment, there was
almost always one to two crowns per
plant. The plants under ambient light
never developed as many crowns as
the supplemental light treatments. The
vegetative growth on the ambient light
plants was also much slower.
Under ambient light the plants had
very little energy so the total strawberry
yield was much smaller. The ambient
light plants produced fewer berries and
each berry was larger. LEDs produced
more berries so the yields were larger
and had a larger berry size.
In all cases for the five-month trial,
the light treatments outperformed
the ambient light treatment for total
yield. Under ambient light, the yield
for Albion was 1.77 kilograms per
square meter. Under HPS lights, the
yield was 2.72 kilograms per square
meter. Albion had its highest yield
under LEDs at 3.68 kilograms per
Future strawberry research
Allred plans to run an identical trial
with Albion and Cabrillo at the same
time of year. Other experiments will
be conducted using a range of different
DLIs, including 15, 20 and 25 moles per
The sweetness of the strawberries (Brix value) was highest for both Albion (9.4°Bx) and
Cabrillo (7.3°Bx) plants grown under high pressure sodium (HPS) lamps.
square meter, which was 100% over
ambient light.
Cabrillo under ambient conditions
had a yield of 3.03 kilograms per
square meter. Cabrillo had a 72%
higher yield than Albion under
ambient light. Under HPS, the yield for
Cabrillo was 4.9 kilograms per square
meter. Under LEDs, the yield for
Cabrillo was 5.67 kilograms.
Under ambient and LED light, the
average berry size for Albion was 16
grams per berry. Under HPS light, Albion
berry size was 14 grams per berry.
Cabrillo followed the same berry size
trend as Albion. Under ambient and
LED light, the berry size for Cabrillo
was 18 grams. Under HPS light the
berry size was 15 grams.
Under HPS lights, both cultivars
produced the smallest berries, but
plants had more berry clusters. Allred
said the radiant heat provided by HPS
lamps wasn't necessarily beneficial
because the berries were smaller and
yields were lower than LEDs. He
couldn't say whether the differences
in yield and berry size were due to the
temperature difference or if the light
quality may have played a role.
The sweetness of the fruit (Brix
value, °Bx) was also measured for
the strawberries produced under the
three different light treatments. Under
ambient light, Albion had the lowest
Brix value at 7.4 degrees. Under LEDs,
Albion had a Brix of 8.5 degrees. Albion
strawberries grown under HPS had the
square meter per day.
" We are also going to be doing
some other experiments with light
and carbon dioxide, looking at the
interaction between DLI and carbon
dioxide, " he says. " One of the things
that can be done with greenhouse
lettuce is a higher level of carbon
dioxide can be used to achieve the
same yields as higher light levels. For
example, 1,000-ppm carbon dioxide
can offset the need for additional light
by a couple moles of light. We want to
look at the impact of higher carbon
dioxide levels on strawberries. It may be
possible to use higher carbon dioxide
levels to substitute for higher light levels
in respect to fruit yields. "
For more information: Contact
Jonathan Allred at jaa337@cornell.
edu, or visit www.cornellcea.com,
www.greenhouse.cornell.edu or
www.glase.org. VGN
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VGN | MARCH 2020 | 7
http://www.cornellcea.com http://www.greenhouse.cornell.edu http://www.glase.org http://www.growspan.com
March 2020

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