## 4 Discussion  
Combined with networking technology and wireless serial port transceiver technology, a ground pressure measurement system was designed. It includes a ground pressure measurement module, an Internet of things wireless data transmission module, a data display and storage module, and so on. Its hardware mainly includes a Mega2560 Arduino controller, JHBS-1-5 KG foil pressure sensor, and JHBM- H3 column pressure sensor. It is calibrated by combination, and the experimental results show that the ground pressure measurement system can meet the requirements set by the measurement experiment for forward resistance and ground pressure of the sliding seeder of the rice direct seeding machine. It has the characteristics of Internet of things remote wireless measurement, high precision, sensitive response, stable performance, simple operation, wide practicability, and so on.  
An experimental field study on the ground pressure measuring system was carried out. The single-factor multi-horizontal experiment of ground pressure was carried out by taking the seeding skateboard of the rice direct seeding machine as the research object and taking the traveling speed, v, and vertical load, G, as the influencing factors. The experimental results show that with the increase of vertical load, G, and traveling speed, v, the forward tilting angle of the skateboard, the ground pressure of the skateboard, and the forward resistance all showed an upward trend. The ground pressure measurement system can work continuously and stably in the paddy field. In addition, the measured data can be wirelessly transmitted to the computer and mobile phone stably at a high speed.  
By observing the distribution law of the stagnant mud generated by the skateboard, it was found that a large amount of stagnant mud is generated in the middle of the skateboard, which increases the forward resistance and ground pressure of the skateboard, and reduces the working efficiency of the rice direct seeding machine. In order to reduce the mud generated by the seeding slide of the rice direct seeding machine and improve the work efficiency of the rice transplanter, the surface of the slide can be treated to reduce the sliding resistance, for example, by adding a water retention support plate to the bottom of the slide to form a muddy channel under the skateboard. It is also possible to use a slide material with a small friction coefficient and to design a separate skateboard so that the mud in the middle of the skateboard can be quickly discharged.  
Conceptualization, Y.G. and G.Z.; methodology, G.Z.; software, Y.G.; validation, Y.G., A.S. and J.F.; formal analysis, Y.G.; investigation, Y.Z.; resources, Y.Z.; data curation, Y.G.; writing--original draft preparation, Y.G.; writing--review and editing, H.W.; visualization, G.Z.; supervision, G.Z.; project administration, Y.Z.; funding acquisition, G.Z. All authors have read and agreed to the published version of the manuscript.  
The APC was funded by Innovative Research Group Project of the National Natural Science Foundation of China (No. 51775220).  
Not applicable.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflict of interest.