## 2 Precision Seeding Technology
### The Seed-Spacing Consistency-Regulation Technology
[PERSON] designed a pneumatic combination hole-type precision corn-seed metering device to realize the improvement in seed-filling performance of the seed metering device under high-speed operation; this improves seed mobility under positive pressure of the airflow, removes the seed-stirring mechanism of traditional machinery, has a simple structure and works stably in a high-speed operation [31]. [PERSON]. [PERSON] carried out a simulation and experimental research on an air-blown corn-seed metering device, mainly conveying seeds to the seed-drop port through the typed hole on the rowing wheel. During the operation,  
Figure 3: Pneumatic seed metering devices. (**a**) Pneumatic-suction type. (**b**) Pneumatic-pressure type. (**c**) Air-blown type. (**d**) Central set-row type. Figure 2: Mechanical seed-metering devices. (**a**) Tilting-disc type. (**b**) Spoon-wheel type. (**c**) Finger-clip type. the airflow at the mouthpiece can blow away the excess seeds to realize single seeding [32]. [PERSON] established a mathematical model of the distribution system of the central set-row seeder in the process of pneumatic conveying, and calculated and analyzed the parameters of air velocity and seed dynamic inertia in the conveying process, to provide a reference for the design and improvement of the set-row seeder [33]. Smooth seed-guiding technology, also known as zero-speed seed drop, means controlling the seed to achieve zero speed in the horizontal direction as it falls into the seed bed during the descent. A brush-belt seed-guide device developed by [PERSON], USA (Figure 4) effectively solves the problem of bouncing seeds falling into the seed bed under high-speed souring operation conditions [34]. To improve the quality of the high-speed souring operation, [PERSON] designed a toggle-finger synchronous belt-type seed precision delivery mechanism, which realizes the complete control of the seed transport trajectory from the seed metering device to the seed bed, in precision seeding [35]. The USA developed the conveyor-belt seed guide for the speed tube for a no-till seeding operation (Figure 5); each partition takes single seeds from the seed metering device. The speed of the partitioned seed delivery belt is adjusted with the operating speed to achieve zero-speed seed delivery [36]. Under high-speed seeding operations, the seed falling into the seed bed with precision is essential to ensure uniform seeding. Through research on seed-guide tubes for seed transportation, the restraint effect of seed-guide tubes on seeds can reduce the kinetic energy of seeds falling into the seed bed and reduce seed collision in the seed bed. The falling of the seed into the seed bed using precision technology mainly reduces the bounce of seeds when they fall into the seed bed. Because seeds are discharged from the seed discharging device of the precision seeder and fall into the seed bed through the seed-guide tube, the seeds have specific kinetic energy at this time. The seeds may bounce or roll when falling into the seed bed and touch the soil, resulting in uneven distribution of seed spacing in the seed bed [37]. Seed pressing devices are often used to press the seed falling into seed beds into position, in a timely way. The commonly used seed-pressing devices mainly include the seed-pressing tongue and the seed-pressing wheel, primarily used in pneumatic precision seeders. For example, [PERSON] et al. designed a seed-pressing device (Figure 6) applicable to a precision seeder with airflow-assisted high-speed seed delivery, which can effectively reduce the inconsistent grain spacing caused by the collision of seeds in the seed-guide tube [38]. Precision-seeding research in the USA has developed a plastic wear-resistant seed-pressing tongue (Figure 7) that enhances the seed contact with the soil in the seed bed and effectively positions the seed in the seed bed [22]. Figure 4: Brush-belt type seed-guide device. Figure 5: Conveyor-belt type seed-guide device.