supplemental led lighting increases winter tomato ... · winter tomato production in central north...
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Supplemental LED Lighting Increases Winter Tomato Production in Central North Carolina Greenhouse
Introduction We tested winter tomato production in a central North Caroli-na commercial greenhouse (34.5˚ latitude) to compare between non-lit and LED-lit bays. 2,100 plants were grown hydroponically in a 7,400 sq ft greenhouse divided into three bays: a non-lit bay; a center guard bay; and a LED-lit bay. Plants were illuminated with 42 lights for a density of 1 light/59 sq ft for 15 hours/day.
Seeds were planted mid-October 2014. After 8 weeks of propagation under sole-source LED lighting, seedings were transplanted to the greenhouse. Bias was given to the non-lit and guard bays by placing the “strongest seedlings” in these bays 4 days before placing the lesser seedlings in the LED-lit bay. However, by 3 weeks under LED-light, the initially-lesser seedlings were more vigorous than the non-lit plants as indicated by more compact growth and greater stem diameter.
The first harvest of the LED-lit bay was 9 days earlier than the non-lit control. At final harvest, the LED-bay had a yield increase of 30%. Final evaluation indicated the LED-lit vines were taller and heavier with greater stem diameter. This study confirmed that lighting in a geographic region where greenhouse lighting was not traditionally used improved time to harvest and yield.
James Byrtus and Dr. Melanie YeltonLumiGrow Inc., Emeryville, California, USA
©2017. LumiGrow, Inc. All right reserved.
(800) 514-0487 • [email protected] • www.lumigrow.com
MeasurementsInitialPlants were measured for height and stem diam-eter to determine relative plant vigor 3 weeks after transplanting
OngoingTomatoes were harvested 3 days per week begin-ning on February 28, 2015 for the LED-lit plants and March 9, 2015 for the non-lit plants. Supple-mental LED lighting was used December 19, 2015 to April 30, 2015; fruit harvest continued until May 15.
FinalOn June 15, 2015, 11 plants from both treatments were dissected and measured for vine length (m), vine weight (kg), and stem diameter (cm) 1” above the root zone.
Overview Solanum lycopersicum var. Heritage, was planted into grow cubes and grown under sole source LED at 100 µmol•m-2•s-1 for approximately eight weeks. Plants were transplanted into the greenhouse December 15-19, 2015, with the plants that appeared most vigorous being transplanted first in the non-lit bay and guard bays. LED-lit plants were transplanted 4 days later with lower quality plants. Plants were illuminated 15 hours per day from 1:00 am until 4:00 pm. (Lights were turned of at 4:00 pm to facilitate normal return to the hive behavior for the bees.) All plants were grown with under typical hydroponic-cococoir conditions in the greenhouse.
Stress FactorsWater stress was introduced to promote flowering by eliminating fertigation at 3 pm (one hour prior to the lights going off) until 2 am (one hour after the lights turning on).
Phosphorus stress was suggested in the LED-lit plants indicated by anthocyanin on the underside of the plant leaves. This stress response was observed to a lesser degree on the non-lit plants. We hypoth-esized that this stress was due to the lights being turned on prior to dawn (while plants roots were cold from reduced nighttime temperatures), re-ducing phosphorous uptake. Increasing the growth temperature in the greenhouse 2˚ C eliminated this stress within 1 week.
Non-Lit LED LED Difference
Transplant Date 12/15/2015 12/19/2015 (4 Days)
First Harvest 3/9/2015 2/28/2015 9 Days
Total Weight (Kg) 3606.06 4677.67 30%
1.25
0.93
1.59
0.85
0.000.200.400.600.801.001.201.401.601.80
Vigor (cm) Height (m)
Plant Vigor at Three WeeksAverage Stem Diameter (cm) and Height (m) 1/8/2015
Non-LitLED
22.00
39.44
15.03
30.66
45.81
22.36
0.005.00
10.0015.0020.0025.0030.0035.0040.0045.0050.00
March April Until May 15
Monthly Production Kg/m2
Non-LitLED
4.91
0.971.28
5.17
1.46 1.42
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Vine Length (m) Vine Weight (kg) Stem Diameter (cm)
Final Harvest Vine Analysis6/15/2015
Non-LitLED
©2017. LumiGrow, Inc. All right reserved.
(800) 514-0487 • [email protected] • www.lumigrow.com
ConclusionThis study suggests LED lighting can be beneficial for tomato production even in areas of the country where supplemental lighting is not typically used. As more growers choose to benefit from the economic advantages of supplemental LED greenhouse lighting, care must be taken to review and adapt management practices; particularly with regard to heat and fertigation.
Another grower in this area introduced lighting into a previously poor performing greenhouse without reviewing growth practices with mixed results. Compared to prior production results, plants were very vigorous, producing an increase in plant material but without an increase in fruit production. In conclusion, this grower achieved an increase in production of 29.72% for the LED-lit bay over the non-lit bay. Phenotypically the LED-lit plants had a slight (5%) increase in vine length, an 11% increase in stem diameter and a 50% increase in vine weight at the end of the study. Fruit harvest from the LED-lit plants began 9 days earlier than the non-lit plants. Based on these metrics it is clear that the LED-lit plants were superior in production and overall plant performance.
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