# Current Status and Future Directions for Combined Tillage and Sowing Technology and Equipment
## 4 Research on Precision Sowing Technology
### Mechanical Precision Seed Metering Device
The seed scraper wheel scrapes off the excess seed and the remaining seed is discharged by gravity or by the seed pusher. & Simple structure, low seeding height, and can be replaced by different types of holes and aperture eyelet wheels sowing different crops. It is easy to reseed and hurt seeds, and this should not be used for high-speed operation. & \\ \hline Spicker finger & & Simple structure, low seeding height, and enhance of their weight. The seed scraper wheel scrapes off the excess seed and the remaining seed is discharged by gravity or by the seed pusher. & \\ \hline Spicker finger & & The scends rotate with the disk to the seed scraper to complete the seed cleaning, and the rest of the seeds fall into the seedbed via gravity or by the action of the seed pusher. & Seed disks can be changed to suit different crops, the operating speed needs to be less than 6 km/h, otherwise the quality of seed discharging will be significantly reduced, and the shape and size of the seed is more demanding. & Seed disks can be changed to suit different crops, the operating speed needs to be less than 6 km/h. It is susceptible to field vibration and tilt angle. & Seed disks can be changed to suit different crops, the operating speed needs to be less than 8 km/h. generalization of high, relatively stable operation and other characteristics, it is still applied often in many combined tillage and sowing machine. The socket-roller-type seed metering device also has a relatively simple structure. Moreover, the seed-filling holes can be designed according to the external dimensions of crop seeds, so it has good universality. However, when operating at high speeds, that is, when the working speed is above 6 km/h, the phenomenon of seed duplication is likely to occur, and the seeds may be damaged, which will affect the operation effect. In the research of a socket-roller seed metering device, [PERSON] improved the structure of components such as the locking paw, seed search frame, and socket eye wheel in the existing socket-roller seed metering device, effectively solving problems such as the high leakage rate and uneven plant spacing distribution [78]. [PERSON] et al. designed a Coperus esculentus Cell-wheel seed metering device with low-position seeding and cavitation function. A low-level seeding device was added under the seeding wheel to reduce the seeding height and improve the hole formation effect. The diameter, hole, and V-shaped groove of the seed discharge wheel are also designed to improve the effect of fine separation and seed filling, and to solve the problems of poor seed mobility and poor seed filling performance [79]. [PERSON] et al. developed a hook-hole-type seed metering device (Figure 10) in combination with wheat precision seed discharge technology, and explored the effects of the horizontal distance of the seed layer thickness adjustment plate, the form of the nesting arrangement, and the number of nesting eyes on the seed filling performance to solve the scattered distribution of seeds in the seedling belt, and its performance was better than that of the fluted-wheel type [80]. The socket-roller-type seed metering device currently has high rates of seed duplication and missing sowing, with an average seed-filling rate and poor uniformity of seed spacing. It is not suitable for high-speed operations. In the future, it is still necessary to improve its seed-metering performance according to its structural characteristics through means such as mechanism analysis and structural innovation, so that it can be applicable to high-speed operations and can be better applied in complex environments and multi-process operations. Disk seed metering devices are mainly divided into horizontal and inclined types, with the seed rotating through the seed disk toward the seed scraper to complete seed clearing, and the seed disk can be swapped to adapt to different crops; but when the operating speed is too fast, the quality of the seed discharged will significantly decline as the shape and size requirements of the seeds increase.