**4. Conclusions**

The compression molding behavior of peat substrate blocks was evaluated by the combination of a physical experiment and simulation. The simulation parameters of peat particles were calibrated first by the discrete element and response surface methodology. Then, the calibrated parameters were brought into the contact model of the compression system–particles, and the effect of the loading speed on the compression behavior of the substate blocks was investigated. The following conclusions were drawn:

(1) In the proposed calibration method of the DEM parameters of peat particles, the shear modulus of the particles, the static friction coefficient of the particle–particle interactions, the rolling friction coefficient of the particle-particle interactions, and surface energy were found have significant effects on the stacking angle of peat through the Plackett–Burman test. After the range was narrowed by the steepest climbing

test, the significant parameters were optimized by the second-order regression model established in the Box–Behnken test. The result of the validation test of the stacking angle of peat under optimal parameters showed the average relative error between the simulated (50.89◦) and the physical stacking angle (51.15◦) was 0.51%, indicating the good reliability and accuracy of the DEM model and the simulated parameters of the peat particles.


In summary, this study established a DEM model that could better simulate the compression molding of peat particles to prepare substrate blocks, which will contribute to the performance improvements of substrate blocks. The finding of this work could provide a reference for the design of the forming machine of substrate blocks suitable for mechanical transplanting.

**Author Contributions:** Conceptualization, J.F., Y.C. and M.C.; methodology, J.F., Z.C., C.G. and B.M.; software, J.F.; validation, J.F., M.C. and B.M.; formal analysis, J.F.; investigation, J.F., Z.C. and C.G.; data curation, J.F.; writing—original draft preparation, J.F.; writing—review and editing, J.F., M.C. and B.M.; visualization, J.F.; supervision, Y.C. and M.C.; funding acquisition, C.G., Z.C. and Y.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Nanjing Modern Agricultural Machinery Equipment and Technology Innovation Demonstration Project (Grant No. NJ [2022] 03), Jiangsu Agricultural Science and Technology Innovation Fund (Grant No. CX (22) 3092), and Innovative research group of Agricultural Production Waste Resource Utilization Equipment.

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the article.

**Acknowledgments:** The authors thank the editor and anonymous reviewers for providing helpful suggestions for improving the quality of this manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
