Design and experiments of the key components for centralized pneumatic rice dry direct seeding machine

Modern rice drilling needs to meet the increasing requirements of different rice varieties, high speed operation and large seeding rate for direct seeding farmland in China. In this study, a kind of centralized pneumatic rice seeding machine with high precision was developed for dry land, including uniform distributing unit, seeds metering unit, pneumatic tube line conveying unit, synchronous transmission unit, large size integrated seed box, ditching, soil covering and compacting unit, supporting and suspension unit. The distributing mechanism and uniformity of the pneumatic centralized distributor were investigated according to the rice varieties, working speed, and seeding rate of seeding machine. The theory of airflow conveying was utilized to evaluate the movement trajectories of seeds in the distributor under continuous air flow in terms of physical characteristics of different rice varieties. A groove-wheel metering device was designed to adjust the seeding rate, in order to meet the requirement of large tailoring speed of seeding, where the groove shape was arc-shaped, and a dual ground wheels driving was used to ensure the synchronization between seeding rate of seed metering device. Variable speed transmission devices were utilized to increase adaptability of high-speed working for the seeds metering unit. A centralized-pneumatic rice seeding machine was trail-produced and tested, and the comparison study was conducted to explore the movement behavior and field seeding effects by using varieties of indica and japonica rice in the direct seeding process. The test results showed that the seeding rate of rice seeding machine was 75-375 kg/hm2, the maximum working speed was 14 km/h, the working width of the 10 rows was 2 m and 20 rows was 4 m, and the coefficients of variation of sowing quantity per row were 4.89% and 5.06%, respectively. The broken rate of rice seeding in paddy field was 0.46%. In 2017, the rice yield of japonica Fu Yuan No. 4 was 10 372.5 kg/hm2 in Ningxia, the rice yield of indica Yue Nong Si Miao was 7 074 kg/hm2 in Guangdong. The production results demonstrated that the developed centralized pneumatic rice seeding machine for dry land could reach the design goal and meet the working requirements for direct seeding farmland in China.