Rapeseed and wheat are sown in autumn after rice is harvested in the Yangtze River basin and their seeding processes are similar. Seeding uniformity is a key index to evaluate a planter's seeding performance. The air-assisted centralized seed-metering device which can be widely used in seeding is capable of handling a wide range of seeds with different sizes and shapes with high sowing speed and large width. The typical characteristics of air-assisted centralized seed-metering device were mechanical seed feeding and uniform air-seed flow distribution. The seeding performance was affected by many key parts, such as seed-feeding device, distribution head and seed tube. The long seed tube and airflow in seed tube were typical characteristics in air-assisted centralized seed-metering device. The longer seed tube and airflow affected seed migration trajectory and seeding performance. In order to improve the seeding performance of air-assisted centralized metering device for rapeseed and wheat, the structural parameters of seed tube and working parameters affecting the seeding performance were optimized by mechanics analysis. It revealed that the drag force and gravity promoted seeds' movement and the seed dropping process was affected by airflow. The seed velocity and accelerated velocity increased under the function of drag force. The collision between seed and seed tube was enhanced when the angle between the seed tube and horizontal plane decreased. Furthermore, the airflow uniformity among different seed tubes was the basis of apiece row consistency. The impact factors included seed tube material, structure, arrangement and working parameters of air-assisted centralized seed-metering device. The structure optimization and seeding performance experiments were performed in bench test. The effects of seed tube material, diameter, length combination, and angle, seed-feeding rotational speed and airflow pressure upon seeding performance were investigated. The seeding performance evaluation indices included variation coefficient of total seeding quantity, apiece row consistency variation coefficient of seeding quantity, variation coefficient of seeding uniformity, and seed damage rate. The seeding uniformity was tested on JPS-12 test bench to simulate seeding in the field. Moreover, the seeding field experiments were carried out to verify the sowing quality of air-assisted centralized seed-metering device using the Huayouza 62 and Zhengmai 9023 as materials. The results showed that: The seed tube material, diameter, the interaction between seed tube material and diameter, and seed tube length combination affected the average seeding quantity and apiece row consistency variation coefficient of seeding mass significantly. It suggested that the PVC (polyvinyl chloride) material and the diameter of 20 mm with the consistent seed tube length were the optimal. The seed-feeding rotation speed and airflow pressure affected the piece row consistency variation coefficient of seeding mass remarkably. When seed-feeding rotational speed was within the range of 20-40 r/min, with the airflow pressure of 1 200 Pa of rape and 1 600 Pa of wheat, respectively, variation coefficient of total seeding mass and apiece row consistency variation coefficient of seeding mass were less than 1.0% and 4.0% for rape and wheat, respectively. Moreover, variation coefficient of seeding uniformity was 19.0% and 12.5%, respectively, and the seed damage rate was less than 0.1%. Field experiments indicated that the plant density was 40-68 plants per square meter with the variation coefficient of stability less than 20% for rape; and when the plant density was 129 and 252 plants per square meter, the variation coefficient of stability was 8.34% and 8.12% for wheat, respectively. It showed that the plant density and growth characteristics could meet the agronomic requirements for both rape and wheat. The results provide the basis for the structure optimization of air-assisted centralized seed-metering system and improvement of seeding performance.%为提高油菜小麦兼用气送式集排器的排种性能,该文针对集排器具有较长导种管和气流扰动影响种子迁移轨迹的问题,通过构建导种过程力学模型确定了影响排种性能的主要因素,分析了导种管材料、直径、长度组合、角度布置、气流压强和供种转速对排种性能的影响.试验结果表明:导种管材料、直径、材料与直径的交互作用、长度组合对平均行排种量和各行排量一致性变异系数均有显著(P＜0.05)或极显著(P＜0.01)影响,角度布置影响不显著,导种管材料和直径分别为PVC钢丝软管和20 mm的排种性能较优,且应尽量布置导种管长度一致.气流压强和供种转速对各行排量一致性变异系数影响显著(P＜0.05);供种转速为20～40 r/min时,排种油菜、小麦时气流压强分别为1 200和1 600 Pa时具有较好的排种均匀性,总排量稳定性变异系数和各行排量一致性变异系数分别低于1.0%和4.00%;油菜、小麦的排种均匀性变异系数分别低于19.0%和12.5%,种子破损率低于0.1%.田间试验表明油菜种植密度为40～68株/m2时,稳定性变异系数低于20%;小麦单位面积植株数量为129和252株/m2时,稳定性变异系数分别为8.34%和8.12%,达到油菜、小麦的农艺种植要求.该研究为气送式集排器结构优化和排种性能提升提供了参考.
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