This study sought to construct and empirically validate a discrete element method (DEM) particle model representing post-tillage soil blocks. This model was developed to facilitate a detailed examination of granular movement and contact mechanics during the shaping process of planting chambers for rape plants. The research specifically targeted the sticky, cohesive soil prevalent in rice paddy fields of the middle and lower Yangtze River region. Simulations were conducted using EDEM software to improve the accuracy with which soil-tool interactions are predicted for the design and optimization of mechanical transplanters. The physical and bonding parameters of the sticky soil were calibrated using the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model and Hertz-Mindlin with Bonding contact model. A particle replacement method was adopted to create a discrete element model of cohesive soil aggregates with different shapes and sizes after rotary tillage. The accumulation angle of soil aggregates was used as the evaluation index in both the simulation and physical experiments. Design-Expert software was used to design a four-factor, three-level simulation experiment to identify the optimal parameter combinations for the physical and mechanical properties of the sticky soil and the JKR contact model, which comprised a soil-soil static friction coefficient of 0.32, soil-soil rolling friction coefficient of 0.10, soil-steel static friction coefficient of 0.51, and surface energy of soil for the JKR model of 5.50 J/m². Next, the steepest climbing test and Box-Behnken orthogonal combination test were then used to narrow down the range of values for the significant factors and identify the optimal parameter combinations for the bonding contact model parameters, which included a bonding bond normal contact stiffness of 2.1×10⁶ N/m, a bonding bond tangential contact stiffness of 2.2×10⁶ N/m, a normal ultimate stress of 0.55 MPa, a tangential ultimate stress of 0.55 MPa, and a bonding radius of 12 mm. Field experiments were conducted using a flat box device to measure the soil evenness and firmness after ridge formation and compaction by a rotary tiller. The results of these experiments were compared with the discrete element simulation optimization results. The relative errors between the field test results and the simulation test results for soil flatness and compaction were 10.7% and 9.8%, respectively, which indicated good accuracy of the parameters calibrated and optimized by EDEM discrete element simulation software. Overall, this research can provide a reference for understanding the working mechanism and optimizing the parameters of soil touching components in rape transplanting equipment.

Lily bulb is an underground tuber crop, which is mainly grown in southern China. At present, lily bulb harvesting mainly adopts manual excavation, resulting in low labor efficiency. Coupled with the high soil viscosity in lily bulb planting area, there are some problems in lily bulb mechanized harvesting, such as difficulty in fruit-soil separation and high damage rate of lily bulb. In order to solve the problems of poor separation effect, high rate of buried fruit and high crushing rate during lily bulb harvest in sticky soil, a kind of throwing roller lily bulb harvester suitable for operation in sticky soil was designed. The throwing roller lily bulb harvester is composed of vibration conveying device, throwing roller set, excavating shovel and other parts. It has the functions of vibrating crushing soil, throwing crushing soil and material conveying. It can effectively realize the secondary crushing of clay soil, and the separation effect of fruit-soil is good and does not hurt lily bulb, which is very suitable for the mechanical harvesting of lily bulb under the condition of clay soil. Combined with the growth condition of lily bulb and the requirements of planting agriculture, the motion process and separation mechanism of fruit and soil mixture on the vibration conveying device and the throwing roller set were analyzed, the dynamic model of throwing and colliding crushed soil on the throwing roller was established, and the relationship between the structure size of the throwing roller and the crushing of the clay-heavy soil block was established. Through the analysis, the structure and maximum swing Angle of the vibration conveying device, the series of throwing roll sets, the number of throwing roll teeth, the diameter of throwing roll and the contour size and other parameters were obtained. Through theoretical analysis and calculation, the structural parameters of vibration conveying device and throwing roller set of key components were determined. The length of vibration grating rod of vibration conveying device was 150mm, the distance between vibration grating rod was 50 mm, and the swing Angle of vibration grating rod was 59.12°. The number of teeth of the throwing roller wheel was 4 teeth. The radius of the throwing roller wheel was 250 mm. The spacing of the throwing roller wheel was 50 mm. According to the designed structural parameters, a prototype was built and the multi-factor test of operation parameters was carried out. The forward speed of the fruit-soil separation mechanism, the rotation speed of the throwing roller and the digging depth were taken as the test factors, and the embedding rate and crushing rate of lily bulb were taken as the test indicators. Box-Benhnken test method was used to establish the regression equation of factors and test indicators and the influence law of factors on lily bulb harvest index was obtained. When the optimum parameter combination was 0.6 m/s, 90 r/min and 170 mm, the field test values of the rate of buried fruit and the rate of broken lily bulb were 6.3% and 7.1%, respectively. The performance of the machine met the design requirements. The research results can provide reference for the research of mechanization harvesting technology and equipment of lily bulb.