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Determination of Canopys Average SPAD Readings Based on the Analysis ofDigital Images

Li Jinwen

Chlorophyll meter SPAD (Soil Plant Analysis Development) is one of the most popular tools used to monitor the N Status of rice (Oryza Sativa L.) but its high price limits it from being widely adopted. Digital imaging analysis used to detect nitrogen offers a promising, inexpensive substitute at canopy level. And the present study evaluated rice canopy SPAD readings by analyzing digital images captured with a domestic digital camera. A field experiment was conducted in 2011 using a completely randomized split-plot design, with main-plot treatments of six N fertilizer application rates and subplot treatments of different plant densities. To remove the image backgrounds, the images were segmented and a dark green color index (DGCI). The index, which is derived from values of hue, saturation, and brightness (HSB), was used to assess the greenness of the rice canopy. The DGCI was significantly correlated with average SPAD readings rice canopy at each growth stage, but the regression lines were different from each other. This might be caused by different lighting conditions, which lead us to conclude a calibration is indispensable when using a digital camera for the diagnosis of a plant’s nitrogen status.