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8 November 2005 Early detection of calcium deficiency in plants using red edge position
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Brassica chinensis var parachinensis was grown in a recirculating water culture system until the '6-leaf stage' when the plants were separated into two groups: a 'Control' group where plant growth was continued in complete nutrient solution and a '-Ca' group in which the plants were grown in calcium-deficient nutrient solution. Leaf reflectance data was collected daily for eight days, starting from the day before the two treatments were imposed. No visual difference was found between 'Control' and '-Ca' groups during the experimental period. Total calcium content in '-Ca' plants decreased significantly from about 20,000 ppm to steady-state levels at 5,000 ppm by Day 5 while leaf chlorophyll levels in both 'Control' and '-Ca' were relatively similar. However, as the plants matured in the two nutrient solutions, the position of the red edge inflection point (REIP defined as the maximum first derivative of the reflectance spectrum in the 680 nm to 750 nm region) in 'Control' plants shifted towards longer wavelengths, while that in the '-Ca' plants remained relatively unchanged. Good correlation was found between Δ[Ca] and Δ[REIP] of 'Control' and '-Ca' plants. Our results showed that monitoring REIP shifts can provide invaluable spectral cues for pre-visual diagnosis of calcium deficiency in plants.
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Bingqing Li, Oi Wah Liew, and Anand Krishna Asundi "Early detection of calcium deficiency in plants using red edge position", Proc. SPIE 5996, Optical Sensors and Sensing Systems for Natural Resources and Food Safety and Quality, 599609 (8 November 2005);

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