Assessment of the water status of mandarin and peach canopies using visible multispectral imagery

The production of high-quality mandarin or peach fruits depends on the ability to maintain an optimal level of water stress in the plant during the sugar accumulation period. This study investigates the use of visible imaging for monitoring water stress. Experiments were conducted on satsuma mandarin (Citrus unshiu Marc. var. Satsuma) and peach (Persica vulgaris Mill.) in south-western Japan. Water stress was induced using plastic mulching at the field scale. Images of crop leaves as well as orchard canopy were taken in near-infrared (760–900 nm), red (580–680 nm) and green (490–580 nm) spectral channels for 6 days. Neutral Grey Card was used as the reflectance standard and leaf water potential was the monitored crop parameter. A reflectance difference was found between water-stressed and non-water-stressed mandarin and peach plants in red and green spectral channels both at the individual leaf level and at the field-scale canopy level. A moderately good correlation was found between red reflectance and leaf water potential as well as between green reflectance and leaf water potential. Future research should aim at developing visible imaging into a precision irrigation tool applicable to mandarin and peach crops.