Design of pneumatic single seed metering device for coated hybrid rice

Direct seeding of rice is widely expected as one of the most important technology in mechanized rice planting. At present, two ways were mainly divided into the transplanting and direct seeding. The direct seeding can reduce the input of procedures and costs, while the growth cycle. In the complex field environment, direct-seeded rice seeds are easily affected by diseases, pests, weeds, and flooding, leading to greatly reduce the emergence rate and the yield. Alternatively, the seed coating technology can be used to provide micro-fertilizers, growth regulators and pesticides for the germination of seeds and the growth of seedlings. Specifically, the film-forming agents, adhesives, and other ingredients are generally used to uniformly bond the active ingredients on the surface of seeds. Since its convenient application, low cost, as well as resistance to pests and diseases, the seed coating technology can greatly contribute to enhance the seedling rate in the field, and the growth potential of seedlings. Particularly, small environmental pollution can meet the harsh requirement of ecological agriculture. In recent years, the mechanical direct seeding technology of rice has been commonly used in a large area in China, one of which the precision hole direct seeding technology of rice has good ventilation and permeability in the paddy field. The rice seeds are distributed evenly in the field, according to the agronomic requirements of rice varieties. The main types of direct seeding rice are the conventional rice and hybrid rice. The sowing rate is normally 5-10 per hole of conventional rice, while the sowing rate is generally 2-4 grains per hole for the hybrid rice with strong tillering ability. With the emergence of super hybrid rice and some high-quality rice varieties, the single-grain sowing has become particularly important, due to it meets the requirements of agronomic planting. In this study, a single-grain pneumatic seed metering device was designed for the coated rice to meet the demand of single-grain sowing of super rice. The physical parameters of coated rice seeds were measured. A movement model was established between rice seed and diversion suction plate during adsorption, according to the movement process of rice seed under the action of suction tray. The optimal negative pressure was calculated under the ideal condition of seed suction disk. Taking the coated rice variety (Super Rice Wuyou 1179) as the experimental object, the three-factor and three-level all-factor test was used to analyze the seed absorption of rice varieties at the speed of suction tray, negative pressure of suction chamber, and structure of seed suction tray. The experimental results show that the seed suction effect was the best, when the rotating speed of diversion suction tray was 30 r/min, and the negative pressure of suction chamber was 1 400 Pa. The seed sucking effect was best in the seed sucker structure with diversion groove and auxiliary seed sucking device, where the maximum of single seed sucking rate was 81.58%, and the leakage rate was 2.89%. Therefore, the suction tray can effectively improve the seed absorption rate per grain, suitable for the needs of single-grain sowing of super rice. The finding can provide a theoretical basis for the rapid development of single-grain sowing of rice.