## 4 Conclusions  
In this paper, the kinetics equations of the plug seedlings were established in the process of dropping based on the generalized Hertz-theory. The drop impact test of the plug seedlings was carried out under different factors with the matrix loss rate as the test index. The Tekscan pressure distribution measurement system measured the collision impact force. The orthogonal tests were conducted under different factors. The influence degree of each factor on impact force was obtained. The regression equation between the contact stress distribution and the pot damage was obtained by analyzing the significant influence parameters. The main conclusions are as follows:  
(1) The influence laws of different factors on pot damage were obtained through a drop impact test. The Tekscan pressure distribution measurement system measured the collision impact force, and the orthogonal tests were conducted. The test showed that the influence of the collision impact force was on the order of plug specification > drop height > contact material.  
(2) The Tekscan pressure distribution measurement system measured the change law of contact stress distribution under significant influencing factors. The test results showed the collision contact area between the plug seedlings and different contact materials from large to small was soil, steel, and ABS plastic. The collision contact area between the plug seedlings and other plug specifications was 50 plug, 72 plug, and 105 plug from the largest to the smallest. When the plug seedlings collided with different contact materials, the average contact stress between the seedlings and the steel plate ranged from 19.4 kPa to 22.8 kPa. When the plug seedlings of various sizes collided with steel plates, the average contact stress was ordered as 105 plug, 72 plug, and 50 plug in descending order. A linear regression model between collision impact force and matrix loss rate under different factors was established based on the pressure data collected by the Tekscan pressure distribution testing system, and the determination coefficients (R2) were more significant than 0.90.  
Conceptualization, X.L. ([PERSON]); methodology, F.Z. and H.B.; software, F.Z. and J.C.; data curation, Y.Z. and X.L. ([PERSON]); formal analysis, writing--original draft preparation, writing review and editing, F.Z. All authors have read and agreed to the published version of the manuscript.  
This project was funded by National Natural Science Foundation of China (NSFC) (32160423) and the Natural Science Foundation of the Inner Mongolia Autonomous Region of China (2020 MS05055).  
Not applicable.  
The data presented in this study are available on demand from the first author at ([EMAIL_ADDRESS]).  
The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (NSFC) (32160423) and the Natural Science Foundation of the Inner Mongolia Autonomous Region of China (2020 MS05055). We also appreciate the work of the editors and the reviewers of the paper.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c} \hline
**Sizes** & **Regression Equation** & \(\mathbf{R^{2}}\) \\ \hline
50 plug & \(K=1.56\times P\times A\times 10^{-3}-8.57\) & 0.958 \\
72 plug & \(K=1.81\times P\times A\times 10^{-3}-8.13\) & 0.976 \\
105 plug & \(K=1.73\times P\times A\times 10^{-3}-6.99\) & 0.915 \\ \hline \end{tabular} Note: \(K\) is the matrix loss rate, %; \(P\) is the average contact stress, kPa; \(A\) is the contact area, mm\({}^{2}\).  
\end{table}
Table 6: The relationship between the matrix loss and the collision impact force of different specifications of oil sunflower plug seedlings.