Quantification of Strawberry Plant Growth and Amount of Light Received Using a Depth Sensor

Abstract

In Miyagi Prefecture, Japan, the scale of strawberry cultivation facilities has recently increased and productivity has improved because of various environmental controls. For example, long-day treatment is conducted for promoting leaf growth (Vince-Prue and Guttridge, 1973). Control of atmospheric carbon dioxide, known to increase strawberry yield, is used widely in strawberry cultivation greenhouses (Lieten, 1997; Wada et al., 2010). Temperature management is also important for obtaining high yields of strawberries (Hidaka et al., 2016). On the basis of the environmental information in greenhouses, producers can continuously control the environment. Skilled producers base their cultivation management on a combination of environmental information and plant information obtained from growth surveys. Growth surveys are useful because they quantify and record the growth state of strawberries; however, as the work involved takes time, and the majority of producers judge growth state by plant appearance and they do not keep records. The vegetative and reproductive growth of strawberries both need to be properly controlled, yet experts currently carry out this task based on experience and plant growth data. In Miyagi Prefecture, the management target for strawberry is to obtain a plant height of >25 cm during the winter season by temperature control, fertilizer management, carbon dioxide control and long-day treatment. While plant height is regarded as an index of management because it is easy to measure, this parameter is not sufficient to quantify strawberry vigor. Skilled producers look at the appearance of strawberry plants to assess vigor, and plant height is only an auxiliary indicator. Plant height is usually measured once a week rather than daily. The optimal method for assessing strawberry growth has not yet been determined scientifically and management methods for strawberry plants vary among producers. In addition, inexperienced producers may struggle to perform adequate controls. There is a need for a management technique based on quantitative information. Although data on strawberry plant height is currently used, the amount of data obtained from visual inspection is limited. Therefore, it is necessary to develop a method that can easily evaluate the growth of strawberry plants at different times and can accurately quantify their appearance. A technique for acquiring plant data using a three-dimensional (3D) shape sensor has been