DEM–MBD Modeling and Experimental Validation of Straw–Soil Particle Migration and Separation During Straw Pickup and Feeding

The migration and separation behavior of heterogeneous straw–soil mixtures during agricultural processing involves complex particle interactions that are difficult to characterize experimentally. A coupled discrete element method–multibody dynamics (DEM–MBD) framework was developed to investigate soil entrainment and redistribution during spring-tine pickup, screw conveying, and screening. A tine–ground geometric interference model was integrated with functional-zone partitioning and particle-ID tracking to quantify cross-stage soil transfer. Macroscopic field validation was conducted using six operating treatments arranged in a randomized complete block design with five independent field replicates per treatment. Across six validation treatments, the MAE and RMSE between the simulated responses and the field-measured treatment means were 0.025 and 0.026 percentage points for feed-inlet soil content, respectively, and 0.082 and 0.084 kg for surface-deposited soil mass, respectively. Particle tracking in the simulations indicated that soil disturbance preceded entrainment, and that entrained soil mass was associated with effectively disturbed soil mass through a power-law fit (R2 = 0.9615). The field-evaluated operating combination comprised a pickup height of 30 mm, a pickup-drum speed of 86 r/min, a forward speed of 1.20 m/s, and a screw conveyor speed of 210 r/min. Under field conditions, this combination reduced feed-inlet and bale soil contents by 35.9% and 37.5%, respectively, while straw pickup efficiency reached 96.70%. These results provide a process-modeling framework for understanding particle migration, separation behavior, and operating-parameter optimization in biomass processing systems.