**1. Introduction**

Cotton precision sowing is the key to realize mechanized cotton planting. Sowing quality directly affects crop growth and yield. Among them, missed sowing is an important factor affecting sowing quality [1,2]. Therefore, breaking through the sowing quality monitoring technology is a research hotspot in the current sowing field. It can provide key support for technical development, such as for real-time adjustment of sowing amount, real-time reseeding of missed sowing, and machine operation management systems. This has important practical significance for improving the informatization of cotton precision sowing operations and promoting the quality development of mechanized sowing operations [3,4].

**Citation:** Bai, S.; Yuan, Y.; Niu, K.; Shi, Z.; Zhou, L.; Zhao, B.; Wei, L.; Liu, L.; Zheng, Y.; An, S.; et al. Design and Experiment of a Sowing Quality Monitoring System of Cotton Precision Hill-Drop Planters. *Agriculture* **2022**, *12*, 1117. https://doi.org/10.3390/ agriculture12081117

Academic Editors: Jin Yuan, Wei Ji and Qingchun Feng

Received: 19 June 2022 Accepted: 11 July 2022 Published: 29 July 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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At present, it is in a closed state during the sowing process. The sowing quality cannot be directly monitored by human senses alone [5–7]. Therefore, it is particularly important to develop a seeding quality monitoring system. The research and application of precision seeder monitoring systems abroad began in the 1940s. Nowadays, the research on sowing quality monitoring technology is mature. The monitoring devices matching with seeders are widely used [2]. Precision Planting of the United States developed a 20/20 SeedSense monitoring system using WaveVision particle sensors. It could monitor the seeding quality in real time, and had the function of automatically correcting the seeding performance [8]. The Sistema Full Semina precision seeding system developed by MC electronic in Italy could realize the sowing monitoring of large and medium-sized seeds [9]. The John Deere Precision Planter was equipped with a Seed Star monitor. Statistics and analysis were carried out in various graphics, so that the operator could grasp the seeding quality information in real time. It uploaded data to the information center to provide data support for subsequent operations [10]. For different crop seeds, based on photoelectric method, image recognition method, piezoelectric method, capacitive method, etc. [11–14], different forms of monitoring systems have been developed abroad to monitor the seeding process in real time. Foreign seeding monitoring equipment has been commercialized and has good performance. However, it is expensive and not suitable for domestic general seeding tools and working environment conditions.

The domestic research on sowing monitoring system started relatively late. However, scholars were also actively exploring and developing a planting monitoring system suitable for the actual situation in our country. Che Yu et al. [2] designed an infrared monitoring system for seeding quality. It could monitor the sowing count, missed sowing, and outage of sowing, and the monitoring accuracy rate could reach more than 95%. Sun et al. [15] adopted the non-blind area anti-dust monitoring technology of non-point source, which improved the adaptability and monitoring accuracy of the no-tillage planter monitoring system to the dusty environment. Zhou et al. [16,17] developed a series of seed metering performance monitoring systems based on the dielectric properties of seeds and using capacitance detection technology; it realized the seeding detection of corn, rice, and cottonseed. Ding et al. [18–22] realized real-time monitoring of seeding frequency and total amount of seeding based on the characteristic analysis of the collision signal between seeds and piezoelectric films. Based on machine vision and BP neural network technology, Tan et al. [23,24] realized the precise monitoring of the seeding amount in the holes, with an average accuracy rate of 94.4%. To sum up, the existing monitoring methods of sowing parameters mainly included photoelectric monitoring, capacitive monitoring, and highspeed camera monitoring. Among them, the photoelectric monitoring method was the most widely used, with the advantages of low cost, reliable performance, and easy maintenance [25]. The machine vision method could solve the problems of low measurement accuracy and low degree of automation. However, the system was relatively complex and the cost was high, which was not suitable for field production applications [26–28]. The capacitive type was simple and economical, easy to maintain, and capable of non-contact real-time measurement. However, it had weak anti-interference and unstable performance, so it was difficult to apply it to field agricultural production activities [29].

At present, the cotton precision seeders generally adopt the method of hole seeding. Different from the common seed metering device structure and seed metering method, it belongs to "zero-speed seeding" (the instantaneous speed of the seeds falling into the seedbed is close to zero relative to the ground) [30,31]. The above monitoring technology is difficult to use directly. Therefore, to realize real-time monitoring of the sowing quality of cotton precision planters, a method for monitoring sowing parameters based on a colorcoded electric eye color fiber optic sensor is proposed. Labview is used to build and develop a seeding quality monitoring system, and bench tests and field performance tests are conducted. This method is expected to improve the quality of cotton precision sowing operations and meet the actual production needs of cotton.

#### **2. Materials and Methods**

#### *2.1. Research Carrier*

The double-storage rotary disc type cotton vertical disc hole seed metering device is used as the research carrier of the sowing quality monitoring system. It is mainly composed of a moving plate, a seed-taking plate, a seed-casting bin assembly, a seed spacer, and a core plate. The structure is shown in Figure 1. The working area is divided into 5 areas: a seed filling area, seed clearing area, transfer area, seed transfer area, and seed casting area. The specific working principle can be found in reference [32]. In the transit area, the installation position of the color-coded electric eye color fiber optic sensor is determined based on the structure of the seed spacer. It is necessary for it to face the hole of the seed tray.

**Figure 1.** Structural diagram of double-bin rotary disc type cotton vertical disc hole seeding and metering device: (1) moving plate, (2) seed hopper assembly, (3) seed Spacer, (4) seed tray, and (5) core plate.

When the seed-taking tray enters this area, the seeds in the socket will slide along the inner wall of the socket into the seeding cavity composed of the seed-taking tray and the seed spacer. The color-coded electric eye color fiber optic sensor collects the RGB color of the cotton species, compares the RGB value of the reference color, and identifies the color. It obtains the seeding amount by calculating the change in the number of pulses; the seeding distance is obtained by multiplying the time interval between the two adjacent pulses identified by the forward speed of the implement. Missing seeding is obtained by comparing the actual seeding grain spacing with the expected grain spacing, and an alarm is given. After the seeds in the socket hole pass through the color-coded electric eye color fiber optic sensor, they slide along the inner wall of the socket hole into the seed rowing cavity composed of the seed taking plate and the seed spacer. After entering the seeding area again, the seeds in the warehouse slide into the duckbill along the spacer sleeve. After the mouthpiece is opened, the cotton seeds fall into the seed hole to complete the seeding operation. This provides the basis for the design of the subsequent seeding quality monitoring system.

#### *2.2. Monitoring System Design*

The seeding quality monitoring system mainly includes two modules: a missed seeding monitoring module and a visualization module. Among them, the missing-seeding monitoring module mainly realizes the real-time monitoring of the seeding amount and the missing-seeding situation, while the visualization module mainly realizes the visualization of the monitoring results of seeding quality. The system structure diagram is shown in Figure 2.

**Figure 2.** Structural diagram of monitoring system.
