Abstract:The high speed operation is the development trend of precision seeding. Air flow assisted seed delivery can reduce the variation of plant spacing caused by the collision of seeds with the pipe wall and meet the requirements of highspeed operation. However, the air flow also accelerates seeds during delivery. Seeds with high speed tend to bounce after landing, which resulting in uneven plant spacing. Aiming at the above problems, a seed pressing device suitable for precision seeder with air flow assisted seed delivery was designed. The seed pressing device was installed behind the seed delivery tube on the seeder unit. When the seed fell to the ground, it was pressed by the squeezing action between the pressing wheel and the soil to avoid the seed jump and realize the accurate plant spacing. The seed pressing device was installed on the soybean precision seeder for field test, and the theoretical plant spacing was set to be 10cm. The orthogonal test was carried out, and the factors were operating speed, horizontal distance between the end of the seed delivery tube and the pressing wheel, and projection angle of seed at the end of delivery tube. The test indexes were plant spacing qualification index and variation coefficient. The results showed that the operating speed, the horizontal distance between the end of the delivery tube and the pressing wheel had impact on the plant spacing qualification index and variation coefficient, while the projection angle had no significant impact on the plant spacing qualification index and significant impact on the plant spacing variation coefficient. At the same time, the comparison experiment was carried out under the conditions of seed pressing wheel, seed pressing tongue and no seed pressing. The results showed that the uniformity of plant spacing of seed pressing tongue and seed pressing wheel was better than that of no seed pressing operation, while the seed pressing wheel was better than the seed pressing tongue. This showed that the seed pressing wheel can significantly reduce seed bounce and had the ability to obtain the uniform plant spacing. For the seed pressing wheel, the plant spacing qualification index and coefficient of variation were significantly better than those under the conditions of seed pressing tongue and no pressing. The optimal working parameters of the seed pressing wheel were the working speed of 9.5km/h, the projection angle of 30°, and the horizontal distance between the end of the delivery tube and the pressing wheel of 75mm. Under these working conditions, the plant spacing qualification index and coefficient of variation were 95.68% and 10.32%, respectively. The research result can provide theoretical basis and technical support for solving the uneven planting space under the condition of air flow assisted seed delivery.
