## 5 Conclusions  
1. Based on EDEM 2020 software, the recovery coefficient, static friction coefficient, rolling friction coefficient, and JKR surface energy factor between soil particles and between soil and 65 Mn steel were selected as the test factors at 3, 6, 9, and 12%, the rest angle error rate of the physical and simulation tests was used as the evaluation index, and the Plackett-Burman test was used to screen the significant factors: JKR surface energy, interparticle recovery coefficient, and interparticle rolling friction factor of soil.
2. A single simulation of multiple Box-Behnken response surface analysis was performed to optimize the model. The JKR surface energy coefficients were obtained as 0.3558, 0.356, 0.363, and 0.371 for soil with moisture contents of 3, 6, 9, and 12%, respectively, and the interparticle rolling friction was 0.188, 0.15, 0.193, and 0.338, respectively. The simulation was carried out using the above parameters, and the simulation rest angle was obtained as 32.98\({}^{\circ}\), 35.26\({}^{\circ}\), 37.63\({}^{\circ}\), and 41.80\({}^{\circ}\), respectively, with a maximum error rate of 4.72%.
3. The parameters required for the bonding key of the EDEM simulation were obtained using direct shear and lateral limitless compression tests. The EDEM simulation approach combining direct shear and unconfined compression tests was proposed to obtain the force distribution images of bonds in the shear and compression processes. The error rates of the simulation and physical tests for the direct shear test were distributed in the range of 3.71-6.53%, and those of simulation and physical tests for the unconfined compression test were distributed in the range of 0.6-8.07%, which were within tolerable limits, and the overall trend was consistent.  
In this study, a model of sandy soil with different water content in potato growing areas was established, which provides reliable parameters for EDEM simulation of the process of separating potatoes from soil and has a catalyzing effect on the optimization of the potato harvester swing separation mechanism. At the same time, a parameter calibration method is proposed for slab soil with different water content, which has different textures in different areas. The method can calibrate the contact parameters of soil with different water content using a single test, which greatly reduces the workload and provides a new research idea for soil calibration.  
**Author Contributions:** Conceptualization, J.L.; methodology, J.L. and S.X.; software J.L. and X.Z.; validation, J.L. and S.X.; investigation, Y.G. and J.L.; resources, J.L.; data curation, C.L. and Z.S.; writing--original draft preparation, J.L.; writing--review and editing, S.X. and F.L.; visualization, J.L. and S.X.; supervision, F.L.; funding acquisition, S.X. and F.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Found of China (31901409), the Science and Technology Program of Inner Mongolia Autonomous Region of China (2020 GG0168), and the Natural Science Foundation of Inner Mongolia Autonomous Region of China (2019B805013).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article. All the code generated or used during the study are available from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.