The compatibility between the morphological characteristics (MCs) of rapeseed bare-root seedlings and transplanters directly affects planting quality. To improve the adaptability of transplanters to the MCs of different rapeseed cultivars, this study focused on six winter rapeseed cultivars (A1: Huyou 17, A2: Huayouza 9, A3: Fengyou 520, A4: Zhongyou 108, A5: Zheyou 50, and A6: Huayouza 62). Five MCs—root length (RL), seedling height (SH), root diameter (RD), stem thickness (ST), and seedling width (SW)—were measured during the seedling ages (25-40 d). Multiple comparisons were conducted to identify cultivars with no significant differences (NSD, α=0.05) in MCs, while skewness and kurtosis were analyzed to assess temporal variations in MC distributions. Quadratic polynomial regression was employed to model the growth trends of MCs for each cultivar. The results showed that the skewness and kurtosis ranges of MCs were –0.65 to 1.16 and 1.62 to 6.28, respectively, indicating significant variability in growth symmetry and concentration both within and among cultivars. As seedling age increased, the number of cultivars with NSD in MCs progressively decreased (25 d: 5; 30 d: 4; 35 d: 3; 40 d: 2), but A3, A5, and A6 maintained consistent stability before 35 d. Based on MC statistical analysis, the key design parameters for the transplanter were determined as follows: flat belt width was 180 mm, positioning bar spacing was 70 mm, flexible belt width was 150 mm, clamping distance was 8 mm, seedling drop height was 180 mm, and planting depth was 40 mm. Field tests demonstrated that the transplanter exhibited superior compatibility with cultivars A3, A5, and A6, achieving seedling delivery success rates of 93.75% (A3), 93.23% (A5), and 92.71% (A6), along with significantly higher planting success rates compared to the control group (A1, A2, A4). This study provides a theoretical basis for optimizing the compatibility between transplanters and rapeseed bare-root seedlings, as well as guiding the structural design of transplanting machinery.

Existing micro-ridge seedbed preparation devices can often be equipped with conventional rotary tillage. However, the shallow tillage depth has been confined to the suboptimal operational efficiency. Particularly, the rapeseed cannot resist extremely adverse climates during optimal sowing and seedling in the current cultivation. In this study, a shallow plow was proposed with the high-speed micro-ridge direct seeding for rapeseed. Three sequential functions were integrated: 1) high-speed strip shallow tillage. A "lift-first and throw-later" mechanism was utilized to rapidly form the ridges using directional soil throwing; 2) micro-ridge seedbed shaping. The geometric configuration of the ridges was optimized to enhance the soil structure, and 3) sowing on ridge tops and furrows. The moisture was regulated to improve the stress resilience and yield stability of the rapeseed in the micro-ridge system. According to the operational requirements of the high-speed strip shallow tillage, a directional soil-throwing shallow plow was developed for the soil displacement at high speed. The micro-ridge morphology was analyzed for the curved surface of a variable-pitch twisted spiral plow body. The plowshare parameters were then determined: a cutting-edge angle of 120°, an entry angle of 30°, and a plowshare width of 120 mm. A mathematical model was established for the shallow plow guide curve. A kinematic analysis was also conducted on the soil lifting and throwing. Single-factor experiments were performed using EDEM software. A systematic investigation was also made on the effects of the shallow plow height, shallow plow opening, and end helix angle on the directional soil-throwing performance. A central composite design (CCD) with two factors (shallow plow opening and end helix angle) and five levels was implemented to determine their interactions on the directional soil-throwing performance. The optimal combination of the parameters was identified after iterative simulation and optimization: the shallow plow height of 375 mm, shallow plow opening of 200 mm, and end helix angle of 40°. Field experiments were conducted on the sandy clay loam and loam soil. The shallow plow achieved better soil-throwing performance at the high speed (12 km/h), compared with the conventional speed (4 km/h). Furthermore, the directional soil throwing was enhanced under the high-speed operation. There were well-defined furrows and strip-shaped soil accumulation in ridging zones. Key metrics included a soil flow back ridge-furrow ratio of 26.18%, a soil-directed migration ratio of 57.42%, and a soil throw accumulation height of 160.60 mm. The better operational passage of the machined to the stable ridge with a ridge height of 148.64 mm and a ridge width of 349.6 mm. The coefficients of variation were less than 5% for the ridge height and width. The high stability was also achieved in the directional soil throwing position, soil quantity, and throwing accumulation height, thus fully meeting the micro-ridge requirements. Furthermore, directional soil-throwing with the shallow plow can be expected for optimal operational passage in the high-speed micro-ridge seedbed preparation. Seedling emergence validated that the micro-ridge seedbed configuration fully met the agronomic requirements for the rapeseed direct-seeding. These findings can provide a viable technical pathway to develop high-quality rapeseed seedbeds for micro-ridge direct seeding.

Rice-rape rotation is often planted in the mid-lower reaches of the Yangtze River as the main winter rapeseed production area in China. But there is also the previous crop of rice straw residue and high stubble in the period of rapeseed planting. Rapeseed direct seeding machines are prone to straw entanglement, congestion, and clogging in the rotary tillage and deep fertilization, particularly for the humid and rainy climate, while the sticky and heavy plate soil. The quality of the seedbed can depend mainly on the buried cover rate of rice straw and the surface of compartments during rapeseed planting. In this study, a combined stubble burying and anti-blocking device was designed in the rapeseed direct seeding machine suitable for the high stubble, sticky, and heavy field. Two kinds of blades were included in the cylinder blade shaft in the herringbone row, including a burying stubble curved blade and a double-edged rotary blade. The burying stubble curved blade was installed in front to directly realize the deep fertilizing shovel. The soil stubble was buried at the same time. The scraping deep fertilizing shovel in front of the region also prevented the soil and straw adherence to the front surface of the fertilizing shovel. The adjacent deep fertilizing shovels were installed between the double-edged rotary blade. Both broken stubble and scraping adjacent deep fertilizing shovels were realized in the middle of the region. The soil and straw mixture clogging accumulation was reduced in the adjacent deep fertilizing shovels in the middle of the region, in order to improve the performance of deep fertilizing shovels. The counter-rotating mode was adopted to increase the operating time between the blade and the soil, in order to realize the fine crushing of the sticky soil, the burying of the high stubble, and the leveling of the compartment surface. Archimedean spiral was selected as the blade curve of the side-cutting edge on the stubble-burying curved blade. The eccentric circular arc curve was the anti-blocking straight blade. EDEM simulation was performed on the structural and working parameters of the burying stubble curved blade and double-edged rotary blade. An optimal combination was achieved, where the rotary radius of the burying stubble curved blade was 245 mm, the angle of the tangent bending line was 27°, the angle of the bending line was 125°, the width of the working width was 75 mm, the rotary radius of the anti-blocking straight blade was 275 mm, and the angle of the sharpening blade was 15°. The experiments under two working conditions showed that the rapeseed direct seeder equipped with a combined stubble burying anti-blocking device performed the higher pass rate in the high stubble and sticky surface; There was no straw winding and clay blocking, where the levelness of the compartment surface was 19.19-22.14 mm, and the straw burying rate reached more than 90%. Compared with the rapeseed direct seeding machine installed with an ordinary rotary tillage device, the levelness of the compartment surface was improved by more than 12.01 mm, and the straw mulching rate increased by more than 27.19 percentage points. The combined stubble-burying anti-blocking device shared the better performance of stubble burying and anti-blocking. The quality of the seedbed fully met the agronomic requirements for the direct seeding of rapeseed. This finding can provide a strong reference for developing seedbed preparation devices under high stubble and sticky working conditions.