## 4 Conclusions  
In this paper, the mole rat's digits are taken as the biomimetic prototype to design a biomimetic potato digging shovel (YS), and finite element analysis, soil bin experiments as well as field experiments for the planar digging shovel (DZ) and YS are conducted to compare its performance with that of DZ. Results confirm the feasibility and effectiveness of the biomimetic macroscopic surface modification method to reduce the draught force of potato digging shovels, and the following conclusions can be drawn.  
(1) The finite element soil-shovel interaction model predicts the draught force well, but slightly higher errors are seen for the soil rupture distance ratio. Hence, more efforts should be made to improve the soil preparation technics and further calibrate the parameters used in the soil-shovel interaction model. All factors have a great influence on the draught force of DZ and YS, and the order of the contribution is as follows: digging depth > cutting speed > mounting angle. For DZ, the increase in cutting speed, digging depth and mounting angle all result in the increase in the draught force; however, for YS, the draught force increases as the cutting speed and digging depth increase, but decreases as the mounting angle increases.  
(2) YS, compared with DZ, illustrates brilliant draught force reduction performance. For single shovels, YS increases the draught force at low mounting angle but decreases the draught force significantly by more than 8.41% when the mounting angle is higher than 30\({}^{\circ}\). For grouped shovels, YS decreases the draught force and fuel consumption by more than 13.33% and 9.18%, respectively.  
(3) The draught force reduction reasons of YS are that the biomimetic spatial surface of YS leads the soil mass to move upward and changes the soil's stress state with the motion state continually, which reduces the friction and adhesion between soil-shovel interfaces, improving soil mobility, and finally reducing soil compaction and making soil easier to be broken.  
This paper provides a reference for the application of finite element method in soil tillage and draught force reduction design for tillage tools. Considering the limitation of this study, further work will be conducted to explore the effect of the soil types and conditions (e.g., soil moisture, and soil cone index) as well as other constitutive model parameters on the interaction between soil and single shovels; in addition, different operation conditions on the interaction between soil and grouped shovels will also be further studied.  
Conceptualization, J.Y., Y.M., H.W. and J.Z.; methodology, J.Y. and H.W.; software, J.Y., S.W., Z.X. and L.H.; validation, J.Z. and H.Q.; formal analysis, J.Y. and X.L.; investigation, J.Y., S.W., Z.X. and X.L.; resources, Y.M.; data curation, J.Y. and S.W.; writing--original draft preparation, J.Y., Z.X. and H.Q.; writing--review and editing, H.W., Y.M. and J.Z.; visualization, J.Y., S.W. and H.W.; supervision, Y.M. and J.Z.; project administration, Y.M. and H.W.; funding acquisition, Y.M. and H.W. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Key Research and Development Program of China (Grant No. 2016 YED0701601), the National Natural Science Foundation of China (Grant No. 51875242), the Scientific Research Planning Program of the Education Department of Jilin Province during the \"13 th Five-Year Plan\" (Grant No. JJKH20201008 KJ) and the Foundation for Development of Science and Technology of Jilin Province (Grant No. 2021020202 NC).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.