Effect of Spectral Filters and Different Sources of Light on the Growth and Nitrate Concentration of Lettuce under Hydroponics Conditions

Document Type : Research Paper

Authors

Assistant professor, The University of Tabriz, Tabriz, Iran; Professor of Soil Sciences, The University of Tarbiat Modrres, Tehran, Iran., Rresearcher of the East Azarbyjan Agricultural Research Center. Tabriz, Iran, respectively.

Abstract

Lettuce (Lactuca sativa L.) is one of the important salad vegetables, which is consumed daily as contributing to nitrate intakes by humans. The lettuce nitrate contents depend on the plants growing conditions. For example the biochemical reactions within the plant are affected by light intensity and wavelength frequency to the extent that nitrate production and concentrations in the leaves are affected. Two separate experiments were carried out during the spring of 2003 to evaluate the effects of light spectra on the growth rate and nitrate concentrations of the lettuce plant. In the first experiment color filters (bright, blue, green and red) were used to create different light spectra, and in the second experiment different color light sources were used to grow the lettuce plant. The plants were grown under hydroponics conditions in both experiments with completely randomized designs and four replications. The results indicated no significant effects of light sources or filters on the yield of lettuce plant. The fresh weights of the stalks of the mature lettuce plants were significantly reduced by green light so that the ratio of lettuce leaf to stalk was 40 percent greater as compared with the control. The chlorophyll index for lettuce leaf improved in the blue light, however, other light sources had no significant effect on the leaf chlorophyll index as compared with the control. The concentrations of nitrate in lettuce were highest under green light or green filter, which were significantly different from those concentrations of the control samples. The lowest nitrate concentrations of 670 mg/kg were measured with red light and 800 mg/kg with bright filter, 1000 mg/kg for red filter, and 1300 mg/kg of fresh lettuce leaf with bright filter. It appears that the level of nitrate concentrations can not be controlled by color filters but more research in this area is recommended.

Keywords

References

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Iranian Journal of Soil Research
Volume 20, Issue 1
May 2006
Pages 25-32

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