To produce high-quality crops, not only excellent cultivation techniques but also accurate nutrient management techniques are important. In recent years, many nondestructive tools such as the chlorophyll meter "SPAD" and the leaf nitrogen meter "Agri Expert CCN" have been developed for measuring crop leaf chlorophyll and nitrogen contents. However, such devices are still relatively expensive for individual farmers. In this research, we developed a low-cost and small-size camera with built-in LEDs of several specific wavelengths for evaluating the nutrient status of fruit trees. A total of 2 camera prototypes were developed by integrating 3 independent LEDs of specific wavelengths (Camera 1: 950 nm, 660 nm and 560 nm; Camera 2: 950 nm, 660 nm and 727 nm) into the device. In addition, a simple software tool was developed to enable the camera to capture leaf images under different LED lighting conditions. Using the prototypes, we acquired images of apple leaves and investigated the possibility of using the images to estimate the leaf nutrient status indicator SPAD (chlorophyll) and CCN (nitrogen) values obtained using the above-mentioned standard tools. The results indicate that the Camera 1 prototype is superior to the Camera 2 prototype and can potentially be applied to the evaluation of nutrient status in apple leaves.
Keywords: built-in LED; fruit trees; low-cost and small-size camera; nutrient status evaluation; specific wavelengths.