2015 Volume 84 Issue 4 Pages 432-438
Paddy rice chlorophyll meters can measure leaf color values in real time. Because of that accumulation of test data, it is becoming increasingly popular in research on paddy rice cultivation, as well as in extension services and education organizations. However, the meter only measure one section of each leaf. To obtain representative values, we need to measure of several points on each leaf, and thus it is time consuming. In recent years, photographs taken by common household digital cameras have been used to evaluate canopy color in paddy rice. In this study we assessed the efficiency and accuracy of this method. We separated color images of paddy rice canopies into RGB images, using commonly available image analysis software, and binarized these images. We then compared the synthetic image with the original color image. We copied the paddy rice leaf color chart onto the lower part of the screen when taking photographs, to act as color standards, and created calibration curves. For each of the three relevant growth stages (maximum-tiller-number, panicle formation, and nine days before heading), the correlation coefficient between the leaf color chart value and the measured leaf color value (chromaticity) was r=0.80 or above, and the relationship was significant. This method allows more efficient evaluation of rice paddy nutrition than the use of chlorophyll meters. Furthermore, it give valuable information for making decisions about topdressing, which is done to prevent the degradation of rice that can occur during ear ripening at high temperatures.
