## 3 Results and Discussion
### Establishment of Collision Impact Force Model and Regression Analysis
#### 3.3.3 Relationship between the Contact Stress Distribution of the Seedlings and Pot Damage  
The relationship between the pot damage and the collision impact force between the oil sunflower plug seedlings and different materials is shown in Table 5. The collision impact force of different materials and the matrix loss rate of seedlings were linearly correlated, and  
Figure 11: The relationship between average contact stress and drop height of different contact materials. Figure 10: The relationship between contact area and drop height of different contact materials. the determination coefficients (\(R^{2}\)) were all greater than 0.90. This shows that the contact stress and contact area of the plug seedlings with different materials measured by the flexible film network tactile pressure sensor could more accurately represent the pot damage. Analysis of Collision Contact Stress Distribution between Oil Sunflower Plug Seedlings and Plug Specifications  
4.1 Distribution Characteristics of the Collision Contact Stress between the Steel Plate and the Plug Seedlings with Different Plug Specifications  
The seedling age is 30 days, and steel was selected as the contact material. The drop impact test of oil sunflower plug seedlings of different plug specifications was carried out. During the test, the contact stress distribution of the seedlings was obtained through the flexible film network tactile pressure sensor. The test results are shown in Figure 12. When the drop height was constant, the contact area of the oil sunflower plug seedlings of different plug specifications and the steel plate was, from small to large, 105 plug, 72 plug, and 50 plug. With the increase in the drop height, the low-stress-distribution area decreased significantly, the high-stress area showed a gradually increasing trend, and the pot damage was larger. 4.2 Average Contact Stress and Contact Area between the Steel Plate and the Plug Seedlings with Plug Specifications  
As shown in Figure 13, the contact areas of drop impact of different plug specifications were linearly correlated, and the coefficients of determination (\(R^{2}\)) were all greater than 0.90. When the oil sunflower plug seedlings dropped at the same height, the contact area of the oilseed sunflower seedlings of different plug specifications from large to small was as follows: 50 plug, 72 plug, and 105 plug. The main reason for this was that the plastic deformation of the steel plate was small, and the deformation was mainly concentrated on the pot. With increasing drop height, the contact area of the oil sunflower plug seedlings and the pot damage gradually increased. The changing mechanisms of the contact area  
Figure 12: Typical stress distribution of oil sunflower seedlings of different plug specifications under different drop heights. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Contact Material** & **Regression Equation** & \(R^{2}\) \\ \hline Steel & \(K=1.81\times P\times A\times 10^{-3}-8.13\) & 0.976 \\ Soil & \(K=1.22\times P\times A\times 10^{-3}-5.98\) & 0.965 \\ ABS Plastic & \(K=2.11\times P\times A\times 10^{-3}-9.43\) & 0.940 \\ \hline \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 5: Relationship between matrix loss and collision impact force of plug seedlings with different contact materials. between the oil sunflower plug seedlings of different plug specifications and the steel plate collision were different, resulting in completely different damage degrees of the pot. As shown in Figure 14, the average contact stress of oil sunflower plug seedlings with different plug specifications and the steel plate was, from large to small, 105 plug, 72 plug, and 50 plug. The average contact stress between the 105 plug seedlings and the steel plate was significantly impact, and the average stress ranged from 18.1 to 21.9 kPa.