Phenotypic Analysis of Fruit Crops Water Stress Using Infrared Thermal Imaging

This study sought to develop and evaluate infrared thermal imaging technology capable of analyzing the water status of crops in a noncontact and nondestructive manner. An infrared thermal imaging device was employed to obtain thermal images from crops. Additionally, to obtain accurate leaf temperatures, we implemented an infrared thermal imaging process capable of precisely extracting the leaf temperature from a peach tree. Furthermore, leaf temperatures were corrected with regard to experimentally obtained leaf emissivity of the peach tree. Leaf temperature and environmental information were then utilized for the analysis of crop water stress index (CWSI). The CWSI was used to compare and evaluate the water stress levels among four different types of peach trees in soils that were subjected to different irrigation conditions. Leaf temperature and environmental information are utilized in the analysis of CWSI, which successfully indicates the quantitative water status of the subject trees. For the crop subjected to the highest water stress (− 80 kPa), CWSI reached a value of 0.76 before irrigation. After irrigation in the morning of the fourth day, CWSI is notably lower; however, it increases the next day when water stress resumes. For crops exposed to lower water stress (control and − 30 kPa), the CWSI values drop immediately to almost zero upon irrigation; however, their CWSI values also resume increasing on the fifth day. We demonstrate that crop water stress, which happens under conditions of water deficiency, causes an increase in leaf temperature that can be detected via the proposed thermal imaging technique. These results show that time-resolved thermal images of leaf temperatures are meaningfully related to the physiological characteristics of crops that are exposed to water deficits.