growing lettuce in indoor farms - ag.purdue.edu...indoor farming: benefits • on an average,...
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Growing Lettuce in Indoor Farms
Krishna NemaliEmail: knemali@purdue.eduTel: (765) 494 8179
Courtesy: Aerofarms
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More is produced in less space
Positive impact on environment• Low water use (~80 to 90% reduction)• Less pollution from reduced pesticides and fertilizers runoff• Reduced soil erosion
Human welfare• Focus is on nutritious and high value crops like vegetables, greens and herbs• Increase in locally produced vegetables leading to increased access and consumption•
Impacts large population• Urban farms provide employment in local communities• Small business model, opportunities for unemployed youth
Indoor Farming: Benefits
• On an average, artificial lighting is used for 16 h/day in indoor agriculture
• Electrical energy costs for lighting can be 25 to 30% of operational costs
Electrical energy use in indoor agriculture
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Price per KWh is continuously increasing in the US
Full spectrum Red : BlueFluorescent
Light fixtures for indoor agriculture
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How to determine which lighting option is best for you?
Electrical Energy‐use Efficiency (EUE)
𝐸𝑈𝐸𝑝𝑜𝑢𝑛𝑑𝑠 𝑜𝑓 𝑓𝑟𝑒𝑠ℎ 𝑙𝑒𝑡𝑡𝑢𝑐𝑒
𝑢𝑛𝑖𝑡 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦𝑙𝑏
𝐾𝑊ℎ
Fixtures with highest EEE are the best
Electrical energy consumption: KWh
Kilo Watt hour (KWh): A measure of electrical energy consumption; equivalent to 1000 W of electrical power consumed in an hour.
Electrical companies charge based on number of KWh ($11 to 13 cents/KWh)
Example: HPS lamps: 1000 W or 1 KWh
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Cost‐benefit analysis of fixtures
Red : Blue
Full spectrum
T8
Three commercial LED light fixtures (~130 W power each) were used as treatments:
SR6 , Red : Blue, Full spectrum
Green leaf, Red leaf, Romaine and Boston lettuce varieties were grown under each light
Plants were grown for 23 days under 24 h lighting, 22 to 27 o C and supplied a recycling nutrient solution with an EC of 1.8 dS∙m‐1
12 replications × 3 light treatments × 4 lettuce varieties × 4 plants/variety (split‐split plot design)
Light fixture Cost Power Energy consumption
($.m‐2) (W.m‐2) (KWh∙m‐2∙day‐1)
Fluence_FS 406 136 3.26
Fluence_RB 423 130 3.12
SR6 160 135 3.24
Light fixture characteristics
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Waveband Fluence_FS Fluence_RB SR6
Blue % (400‐499 nm) 20 13 25
Green % (500‐599 nm) 44 19 46
Red % (600‐699 nm) 36 68 29
Light intensity and composition
DLI (mol∙m‐2∙day‐1) 25 21 37
Plant growth differences among light treatmentsFull spectrum Red : Blue SR6
Butterhead
Romaine
Red leaf
Green leaf
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Fluence_FS Fluence_RB SR6
Butterhead62.2 b 71.7 a 55.0 b
Romaine44.8 a 51.4 a 41.6 a
Red leaf65.9 b 82.4 a 52.7 b
Green leaf85.7 b 112.0 a 77.6 b
Least square means for shoot fresh weight∙plant‐1
Mean separation within a variety by Tukey‐Kramer method, p<0.05 considered significant
Light FW Crop value1 Energy cost2
(g∙m‐2) ($∙m‐2) ($∙m‐2)Fluence_FS 2328 b 15.39 7.50Fluence_RB 2858 a 18.90 7.18
SR6 2042 b 13.51 7.45
Cost vs. Benefit
1 $2.50 per pound of lettuce2 $0.10 per KW.h
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Waveband Fluence_FS Fluence_RB SR6
Blue (400‐499 nm) 20 13 25
Green (500‐599 nm) 44 19 46
Red (600‐699 nm) 36 68 29
Percentage of blue, green and red wavebands emitted by light fixtures
Conclusions
Lower blue% in Fluence_RB increased leaf growth, thereby enabling plants to intercept more light early, leading to faster growth rate and biomass production and higher LUE; for higher EUE, it is important to increase LUE than merely increasing PPE. LUE appears to contribute more to energy use efficiency than PPE
Questions?
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