Monitoring Rice Growth over a Production Region Using an Unmanned Aerial Vehicle: Preliminary Trial for Establishing a Regional Rice Strain

We monitored rice plant growth over a region in order to define a cropping system that could produce higher-quality paddy rice. Plant growth information is more useful when collected for a large area. Information on a production region can aid in realizing uniform, high-quality rice production with the competitive ability of a regional strain. We used an unmanned aerial vehicle (UAV) to monitor plant growth in paddies. The UAV was considered more effective than an unmanned helicopter for monitoring a wide area, and easier and more flexible to use than a piloted airplane or satellite. The vehicle carried a commercial digital camera for true-color images and a plant cover ratio camera for to acquire near-infrared images. Two paddy field sites (composed of 33 and 55 individual fields) were monitored near Myoko, Japan, when rice plants were at the panicle-forming stage. The ground area captured in each image measured about 410 m x 280 m. Both red-green-blue (RGB) and near-infrared images were analyzed using commercial image processing software. Several indices were calculated for each field, including the degree of greenness and the normalized difference vegetation index. Growth variability between fields was quantified, and suggestions for how to improve cropping systems were presented at meeting with local farmers. On the basis of our results, fertilizer use will be decreased with the intended benefit of producing a higher-quality rice crop. The monitoring method using a UAV was easier and cheaper than other remote sensing methods, and the acquired information was useful to local farmers. Further study is needed to optimize the monitoring period and image-analysis methods. Effects of the new cropping system implemented by farmers must also be investigated in a controlled trial.