## 2 Overall Structure of Fertilization and Spraying System
### Fertilizer Unit Design  
The fertilizer unit is a crucial component of the vehicle, designed to facilitate hole-planting fertilizer operations. It plays a significant role in determining the volume of fertilizer applied, the application speed, and overall efficiency. The operational vehicle was equipped with four fertilizer units, and to enhance the fertilizer application rate, a disc hole-pricking fertilizer applicator was utilized, as depicted in Figure 6. This fertilization device significantly improves efficiency by 150% to 200% compared to traditional manual methods and increases fertilizer utilization from 40% to 70%, effectively reducing waste. The principle of operation is as follows: during the vehicle's movement, the fertilization disc is driven to rotate the entire fertilizer applicator by the friction force of the ground. At this time, the duckbill on the disc contacts the ground during rotation and punches out fertilization holes. Subsequently, the fertilizer falls into the holes through the fertilization pipe by its own gravity, thus realizing fertilization. The disc hole-punching fertilization device can well adapt to different soil conditions. The Huanghuai region is dominated by loam soil, and in this soil environment, the device can achieve efficient and stable fertilization operations. In clay soil, the specially designed anti-slip grooves on the disc  
Figure 5: Schematic diagram of mechanism frame. 1—Connecting frame. 2—Searchlight. 3—Emergency stop button. 4—Steering wheel. 5—Control panel. 6—Seat. 7—Pesticle box. 8—Wheelbase adjustment mechanism. 9—Frame lifting mechanism. 10—Travelling drive motor. 11—Transformer. 12—Control electric box. 13—Detect plant limit switch. (**a**) Side front view of structure and partial enlargement. (**b**) Rear structural drawings and partial enlargement. can effectively enhance the friction with the soil, thereby ensuring the effectiveness of punching and fertilization. In addition, the vehicle speed can be adjusted according to the soil hardness to optimize performance. As illustrated in Figure 6, the entire fertilizer unit is securely connected to the frame and comprises several key components including the upper and lower arms of the fertilizer unit bracket, electric cylinder, fertilizer tanks, maize plant detection limit switches, and the disc hole-punching device. The lifting push rod's primary function is to elevate the fertilizer monobloc to a specified height during non-operational periods, thereby protecting the hole-punching device from structural deformation. The fertilizer box is fixed within the fertilizer monobloc bracket and is connected to the lower hole-punching device via a corrugated pipe. As shown in Figure 7, the upper arm is a square tube machined into a fork shape, which can be installed with two sets of disc hole punchers. The upper arm has two round holes and a long hole slot, the upper round hole limit spring, the middle round hole for the spring mounting holes, and the upper round hole with the long hole slot and the lower arm limit bolts with the lower arm to limit the distance of movement. Upper arm parts and lower arm and so on form a whole, so that the fertilizer applicator can use adaptive height adjustment with the ground undulation. The lower arm is divided into two parts, one part of the linkage with the upper arm connection nested therein, and the other part of the fork arm structure connected to the disc fertilizer applicator. There are scales and limit confinement screws can be shifted left and right to adapt to the spacing of the corn rows. The corn plant detector is fixed at both ends of the lower arm; after triggering the metal contact of the limit switch, the control system drives the rear-wheel spacing adjustment system to work, adjusting the wheel spacing so that the fertilizer applicator reaches the right position. Field tests have shown that the rear-wheel spacing adjustment precision can reach \(\pm\)5 mm, enabling it to accurately adapt to the row spacing of corn plants.