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Beneficial effects of using a 3-d led interlighting system for organic greenhouse tomato grown in Canada under low natural light conditions

Pepin, S., Fortier, E., Bechard-Dube, S. A., Dorais, M., Menard, C., Bacon, R.
Acta horticulturae 2014 no.1041 pp. 239-246
Solanum lycopersicum, canopy, consumer demand, containers, fruit quality, fruit yield, greenhouses, harvesting, lamps, latitude, leaves, light intensity, organic foods, organic soils, photosynthesis, plant growth, profitability, seedlings, solar radiation, tomatoes, wavelengths, Canada
Supplemental lighting is required during the October-March period in northern latitudes to harvest vegetables on a year-round basis and meet the consumer demand for healthy organic food produced locally. Hence, inter lighting with light emitting diode (LED) modules is a promising approach to improve greenhouse crop productivity and profitability. A randomized complete block (n=3) experiment was performed in a greenhouse to determine the effects of using supplemental 3-D LED interlighting on photosynthesis, plant growth, yield and fruit quality. Tomato seedlings (Solanum lycopersicum 'Trust' grafted on 'Beaufort') were transplanted in 28 L containers filled with organic soil (2 plants/container; 12 containers/plot) and grown under natural light supplemented with 16-h LED lighting per day. Five m long LED lighting modules, which provided a photon flux density (PFD) of ~80 ┬Ámol m-2 s-1 at a 30 cm distance, were installed at mid-canopy. Measurements of PFD near leaves located i) 30 cm above, ii) 30 cm below, and iii) at the height of the LED modules showed higher light levels over three specific wavelength spectra (345-500, 400-700 and 700-800 nm) than in control plots. Light-saturated rates of photosynthesis were ~50% higher in leaves sampled close to the LED lamps and 30 cm below compared with leaves in the control treatment, but were similar between treatments at 30 cm above the LED fixtures. Total fruit yield per plant was higher (~24%; P= 0.091) in plots with supplementary LED lighting (5.2 kg plant-1) than in control plots (4.2 kg plant-1) after three months of LED interlighting. There was no difference in the number of fruit per plant between treatments, but tomatoes were significantly larger in the LED treatment (181 g) compared with controls (161 g). Growth parameters did not differ significantly between treatments. Under northern low light conditions, higher leaf photosynthesis and crop yield may be achieved by providing supplementary LED lighting within the plant canopy.