Abstract: This study focused on the design and testing of a rotary seedling tray conveying device to resolve critical challenges in oilseed rape transplanting, such as high pot damage rates and difficulties in separating seedling plugs from their trays. The research proposed an innovative rotary feeding mechanism aimed at reducing the adhesive forces between seedling plugs and tray walls, thereby improving the efficiency and reliability of the transplanting process. The device was specifically designed to minimize damage to the seedling structure while maintaining high retrieval success rates. The mechanical behavior of seedling plugs was investigated to understand the forces influencing their integrity during the separation process. Internal forces, including cohesion between substrate particles and root-soil binding, were analyzed alongside external forces such as friction and adhesion between the seedling plug and tray walls. A rotary bending approach was introduced, wherein the trays were bent along specific trajectories to expand the openings at the top while compressing the bottom. This deformation reduced the contact area and adhesion forces, enabling easy separation of the plugs without structural failure. The theoretical model provided the basis for optimizing the bending radius, angle, and other critical parameters. The rotary seedling tray conveying device comprised key components, including a seedling tray frame, a chain conveyor system, transmission mechanisms, and seedling protection rails. The conveyor system used a servo motor to provide intermittent motion, driving the trays along a curved path. As the trays moved through predefined bending segments, controlled deformation was applied at specific angles and radii, significantly reducing adhesive forces. Extensive experiments were conducted to evaluate and optimize the device’s performance. The tests focused on three critical factors: substrate moisture content, rotary radius, and bending angle. These parameters were systematically varied to determine their effects on pot damage rates and detachment force reduction. Orthogonal experiments were performed using 40-day-old oilseed rape seedlings with substrate moisture contents of (50±1)%, (55±1)%, and (60±1)%; rotational radius of 58, 113, and 168 mm; and bending angles of 35°, 55°, and 75°. The results indicated that a substrate moisture content of (50±1)%, a rotary radius of 113 mm, and a bending angle of 55° provided the optimal configuration, achieving a pot damage rate of 2.01% and a detachment force reduction rate of 21.08%. Field trials validated the device’s effectiveness under real-world conditions. These trials measured critical metrics such as seedling retrieval success rates during operation at a working speed of 0.4 m/s. The results showed an average retrieval success rate of 96.75%, compared to 3.70 to 6.01% improvement compared to existing transplanters. However, field trials also identified potential improvements, such as mitigating vibration-induced errors and addressing occasional interference caused by overlapping seedling stems. The rotary seedling tray conveying device demonstrated significant advancements in addressing the limitations of traditional seedling transplanting machines. By employing rotary bending to reduce adhesion forces, the device ensured precise and efficient plug separation without compromising structural integrity. This design enhances the reliability and efficiency of automated transplanting systems, reducing labor dependency and improving agricultural productivity. Furthermore, the research provides valuable guidelines for developing transplanting technologies for other crops with similar requirements for plug separation.