## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Plug** **Tray** & **Seedling** & \begin{tabular}{c} **No. of** \\ **Seedlings** **Fed** \\ \end{tabular} & \begin{tabular}{c} **No. of Pick-Up** \\ **Failures** \\ \end{tabular} & \begin{tabular}{c} **No. of Soil** \\ **Lump** **Breadage** \\ \end{tabular} & \begin{tabular}{c} **No. of Seedling** \\ **Damages** \\ \end{tabular} & \
\begin{tabular}{c} **No. of Discharge** \\ **Failure** \\ \end{tabular} &
\begin{tabular}{c} **Success** \\ **Ratio \%** \\ \end{tabular} \\ \hline \multirow{3}{*}{128-cell} & Tomato & 640 & 12 & 9 & 3 & 5 & 95.47 \\  & Cucumber & 640 & 11 & 6 & 16 & 7 & 93.75 \\  & Pepper & 640 & 8 & 7 & 13 & 3 & 95.16 \\ \hline \multirow{3}{*}{72-cell} & Tomato & 360 & 7 & 5 & 7 & 3 & 93.89 \\  & Cucumber & 360 & 4 & 7 & 12 & 4 & 92.50 \\ \cline{1-1}  & Pepper & 360 & 8 & 6 & 10 & 6 & 91.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of the automatic transplanting performance experiment. In automatic transplanting performance tests, the percentage analysis was made between the unsuccessful transplanting plants and the integral fed seedlings (Figure 11). The pick-up failures and the root-soil breakage were less than 5%, which showed that the designed transplanting system was satisfied with grasping seedlings from the tray cells and transferring them to the growth pots for planting (Figure 11a,b). For three common vegetable seedlings, pick-up failures sometimes occurred. Compared with tomato and pepper seedlings, there was less possibility of failure in picking cucumber seedlings. For the 128-cell and 72-cell trays of tomato seedlings, the pick-up failures and the root-soil breakage were similar. Transplanting failures easily occurred when pepper seedlings were grown in large trays. A plunger was used to push out of the unsuccessful plug seedlings. Since the root soils were not well developed, most transplanting failures often occurred with those weak seedlings [7; 18]. In general, plug seedlings should have a well-developed root system [33]. At the same time, the roots must be evenly distributed in the rhizosphere soil so that the growth media is not broken during transplantation [26; 27]. Once transplanted, they should tolerate mechanical challenges and continue growing to achieve optimum yield. This is consistent with previous findings that successful extraction of plug seedlings depends on the root coiling state [8; 14]. For the injuries of seedling plants, stem breakage was severe in the cucumber and pepper seedlings (Figure 11c). Since 72-cell trays of pepper seedlings were relatively upright, their plants were broken in the picking and discharging. The situation was mainly that the seedling's leaves would snag on the tips of the fingers as the gripper moved down toward the base of a seedling, which would cause the seedling to bend or buckle. In comparison, the tomato plug seedlings were so hard that no excessive injuries occurred during transplanting. As we all know, cucumber seedlings have wide branches and leaves, and pepper seedlings are tall and upright. Especially, those seedlings were grown in  
Figure 11: Failure analysis in automatic pick-up seedlings from the tray cells: (**a**) pick-up failure; (**b**) root-soil breakage; (**c**) seedling damage; (**d**) discharge failure. 72-cell trays, which were often tangled with the working gripper in transplanting. When the gripper discharged cucumber and pepper seedlings into the destination pots, it was difficult to discharge them with precision. The discharge failure possibility of cucumber and pepper was higher than that of tomato (Figure 11d). There was consequently a need for a vegetable-specific study on seedling qualities for compatibility with mechanized transplanting operations [33,34]. Short seedlings might reduce the problem of entanglement when the gripper moves along a straight-down approach path to the seedlings in the plug [28,34]. It was also necessary to further optimize the working parts in the direct contact and their motion trajectory.