Precise and continuous measurement of plant heights in an agricultural field using a time-lapse camera

Abstract

　Plant height is an important trait linked to yield potential and phenotyping; hence, a method for measuring plant height with sufficient temporal and spatial resolutions is required. Furthermore, a low-cost and easy-to-use method is desirable for practical application in agricultural fields. In previous studies, methods for measuring plant height have only fulfilled one or a few of these requirements, and there have been very few studies that have attempted to fulfill all the above requirements in one method. The current study proposes a low-cost plant height measurement system using a commercial time-lapse camera to capture seasonal and year-to-year variations in plant height that represent plant heights at the site scale. The system's performance was tested in a rice field in Japan for two growing seasons. Plant heights were determined to the nearest 1-cm in height from the camera images by referencing a scale bar that was erected next to the four target plants. The obtained plant heights were corrected for vertical distortion (referred to as the 'displacement effect' in the main text), and those were compared with the direct height measurements for each the target plant and site-scaled plant heights that were averaged from 10 samples. For both cases, good agreement between the captured and referenced plant heights was obtained. The system was able to reflect detailed seasonal variations in the plant heights including the maximum heights and the times at which they occurred as well as year-to-year differences. Consequently, the developed system appears to fulfill all the necessary requirements for practical measurement of plant height on-site in agricultural fields.