Abstract

Maize plant detection was conducted in this study with the goals of target fertilization and reduction of fertilization waste in weed spots and gaps between maize plants. The methods used included two types of color featuring and deep learning (DL). The four color indices used were excess green (ExG), excess red (ExR), ExG minus ExR, and the hue value from the HSV (hue, saturation, and value) color space, while the DL methods used were YOLOv3 and YOLOv3_tiny. For practical application, this study focused on performance comparison in detection accuracy, robustness to complex field conditions, and detection speed. Detection accuracy was evaluated by the resulting images, which were divided into three categories: true positive, false positive, and false negative. The robustness evaluation was performed by comparing the average intersection over union of each detection method across different sub–datasets—namely original subset, blur processing subset, increased brightness subset, and reduced brightness subset. The detection speed was evaluated by the indicator of frames per second. Results demonstrated that the DL methods outperformed the color index–based methods in detection accuracy and robustness to complex conditions, while they were inferior to color feature–based methods in detection speed. This research shows the application potential of deep learning technology in maize plant detection. Future efforts are needed to improve the detection speed for practical applications.

Highlights

  • Site–specific fertilization (SSF), which is proposed within the framework of precision agriculture [1], aims to accurately apply fertilizer according to the spatial variability of crop and soil

  • The image data used were extracted from videos taken using a GoPro5 Black camera in a maize field located at Kyoto Farm of Kyoto University, Kyoto, Japan

  • The vertical resolution was set to 1080 pixels and the frame rate was set to 120 fps

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Summary

Introduction

Site–specific fertilization (SSF), which is proposed within the framework of precision agriculture [1], aims to accurately apply fertilizer according to the spatial variability of crop and soil. This study proposes a reliable method for maize plant detection, providing support for practical TF application. As a single–stage detector, YOLOv3 transforms the input image into a vector of scores and performs detection operations using a single CNN; detection is generally faster than that of two–stage detectors, such as Faster–RCNN [42] It has significant potential in agricultural detection tasks [43,44]. The color indices used in this study included ExG, ExR, and ExGR, which have been widely used by researchers as benchmarks for performance evaluation in their proposed methods [27,30,31]. The subsequent thresholds were determined by Otsu’s method, which is a widely applied method [13]

Color Index–Based Methods
Color Index Computation
Maize Plant Discrimination
Loss Function Definitions
Network Training
Performance Evaluation
Image Data Collection
Image Data Augmentation
Data Augmentation
Image Data Annotation
Robustness Analysis
Discussion
Conclusions
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