Direct seeding has been one of the most efficient cultivation modes for a wide range of plants, such as rapeseed. Among them, the existing ditching device cannot fully meet the practical direct seeding in recent years, due to the low stability of the furrow shape and the seedbeds on both sides of the furrow. In this study, a propeller-type ditching device was designed to actively open the furrows at high speed (≥10 km/h) and simultaneously distribute the soil in the middle and lower reaches of the Yangtze River. A quasi-propeller ditching blade was then proposed, according to the working mode of propellers. The blade arrangement was determined using kinematic and dynamic analysis. The critical parameters (the pitch and edge structures) were also determined to reduce the cutting resistance. A simulation experiment of the blade cutting was carried out using the discrete element model of the blade cutter-soil system. The simulation results indicated that the cutting resistance first decreased and then increased with the increase of the pitch angle, whereas, the rear grinding edge reduced the soil cutting resistance. The quasi-propeller blade group with the optimal combination of pitch angle and edge structure achieved a resistance torque of 176.6 N·m and a traction resistance reduction of 447.7 N, compared with the straight spoon-blade group with a travel speed of 12 km/h and rotation speed of 810 r/min. The dynamic analysis was implemented to determine the curved structure parameters of the soil homogenizing plate. Furthermore, a soil-distributing simulation experiment was carried out using the ditching cutter-soil distributing plate-soil interaction model. The better performance of soil distributing was achieved, when the camber of the left and right distributing plates was 0.19 and the down-inclination angle was 10° and 7°, respectively. The field experiment indicated that the work quality of the overall device fully met the requirements of direct rapeseed seeding when operating at a high speed of 9-12 km/h. An optimal combination was achieved: the furrow depth was 169.1-188.6 mm, the furrow depth stability coefficient was 92.5%-95.6%, the flatness of the furrow surface was 22.2-23.0 mm, the coefficient of variation of soil distributing on both sides was 14.3% and 17.2%, and the stubble burying rate was 81.96%-87.46%, the operating power consumption at the operating speed of 12 km/h was 66.84 kW. This finding can provide a strong reference for the high-speed no-tillage, ditching, and high-quality seedbed preparation for rapeseed in the rice-oil rotation areas of the mid-lower Yangtze River.

A ditching device has been widely used for rapeseed direct-seeding in the rice-oil rotation areas of the mid-lower reaches of the Yangtze River. However, the high-power consumption and unstable furrow shape cannot fully meet the large-scale production in recent years, when operating at the high speed (≥10 km/h). In this study, a quasi-propeller ditching device was developed with a blade-soil contact surface similar to that of a propeller suitable for high-speed no-tillage rapeseed direct seeder. The ditching blade group was also optimized. A quasi-propeller cutter group consisted of four sets of cutters. The blade layout structure was then determined using kinematics and dynamics. An optimal model of power consumption and soil throwing efficiency was established for the operation of the blade group using dynamic analysis. The key structural parameters and working factors were determined to improve the power saving and soil throwing efficiency in the ranges of parameters. Single-factor tests were conducted on the blade edge type, pitch angle, and bending angle using EDEM software. The results show that the smallest resistance was achieved in the back blade edge type; The blade resistance first decreased and then increased, as the pitch angle increased, whereas, the soil throwing performance decreased significantly; There was a decrease in the overall resistance of the blade group and the soil throwing performance, as the bending angle increased. Once the blade edge structure of the cutter-1, cutter-2, cutter-3, and cutter-4 was the back edge (BE) type, the pitch angles were 7°, 5°, 4°, and 3°, respectively, and the bending angles were 120°, 120°, 90°, and 90°, indicating the relatively small resistance of the cutter group and the better performance of soil throwing. A Box-Behnken simulation test was conducted on the pitch angle, working velocity, and cutter rotary speed, according to a single factor test. A genetic algorithm (GA) was also used for the multi-objective optimization in the power consumption and soil throwing performance. Box-Behnken results showed that the pitch angle, cutter rotary speed, and working velocity greatly contributed to the power consumption. The most significant impact was found on the working velocity, indicating the lower working velocity and the higher cutter rotary speed, while the higher efficiency of soil throwing. After optimization, the optimal pitch angles of cutter-1, cutter-2, cutter-3, and cutter-4 were 6.7°, 4.7°, 3.5°, and 2.5°, respectively; The optimal rotary speeds of the cutter were 540, 620, and 810 r/min, respectively, at the working velocity of 6, 9, and 12 km/h; The power consumption of the optimized blade group was lower than that of the control group and the international IS225 blade group; The total power consumption of the optimized cutter group was reduced by 5.51-28.99 kW, compared with the control group. The higher the working velocity was, the higher the resistance reduction rate was; The reduction rate of resistance was the highest at 12 km/h, about 41%. Field experiments showed that the total power consumption of the optimized ditching device was 15.1-41.8 kW when operating at a speed of 6-12 km/h, with a relative error of less than 10%, compared with the simulation. The width range of the furrow was 421.3-452.7 mm, the depth range was 163.7-178.7 mm, the stability coefficient range of the furrow width was 95.2%-98.6%, and the stability coefficient range of the furrow depth was 93.8%-97.5%. The working velocity also caused the furrow pattern to change from a circular arc to a V-shape. This research can provide a strong reference to improve the high-speed ditching device for the rapeseed direct-seeding in the rice-oil rotation cropping area of the mid-lower reaches of the Yangtze River.