Damage patterns and germination experiments of rice seeds using high-speed air-assisted centralized seed metering device

Multiple compression and impact of the air-assisted centralized seed metering device on rice seeds during high-speed sowing (≥12km/h) can easily lead to seed damage and adversely affects the emergence rate. This study aims to explore the damage of rice seeds under single and multiple mechanical compression in the air-assisted centralized seed metering device, according to the damage accumulation theory. The fitting equations of seed impact damage and compression were clarified to determine the matching range of stirring speed and the conveying airflow parameters during high-speed seeding. A systematic analysis was also implemented to explore where the seed was damaged under the repeated compression by the seed mixing device during high-speed seeding. The multiple impacts of airflow were evaluated during transportation and distribution in the air-assisted centralized seed metering device. The single compression test was carried out on the hybrid rice and conventional rice varieties. An elastic-plastic model was constructed suitable for rice seeds, in order to determine the critical value of elastic-plastic deformation. The multiple equal displacement compression tests were then carried out to determine the process of damage to rice seeds under multiple compressions. The critical deformation of rice seeds was determined and verified to combine with the seed germination rate test under multiple compressions. According to the conservation of energy, the critical speed was constructed at which the rice seeds were compressed and damaged by the stirring device. The fitting equation of impact damage and compression was combined to analyze the speed of seed airflow impact damage. The results showed that the crushing forces of conventional and hybrid rice seeds under single compression were (118.4±35.6) N and (113.2±39.9) N, respectively, the deformation during crushing was (0.59±0.07) mm and (0.63±0.11) mm, respectively, and the average critical deformation of elastic plasticity was 0.4 and 0.44 mm, respectively. In multiple compression tests, the maximum compression force of the seeds remained consistent, when the compression distance was less than the elastic-plastic average critical deformation; Once the compression distance was greater than the critical elastoplastic deformation, the maximum compressive force on the seed decreased gradually. Verification tests were also performed on the rice seeds germination rate. There was the a 0.44 mm critical deformation of hybrid rice seeds that caused damage. When the deformation of compressed seeds was less than 0.44 mm, there was no significant difference in the germination rate between compressed and uncompressed seeds after multiple compressions; When the compression deformation of the seeds was greater than 0.44 mm, the germination rate of rice seeds decreased after multiple cycles of compression. Therefore, the deformation of rice seeds after being loaded should be avoided to be greater than 0.44 mm. After that, the rotation speed range of the stirring device should be lower than 125 r/min and the seed transport speed should be lower than 8.5 m/s, in order to reduce the compression and impact damage of the air-assisted centralized seed metering device on rice seeds. This finding can provide a theoretical basis and parameter range to match the operating parameters during rice high-speed sowing.