## 2 Materials and Methods
### Test Equipment and Methods  
#### 2.5.1 Experimental Arrangement  
To test the effect of the sowing depth control of the system at different vehicle speeds and to compare the profiling performance of the mechanical adjustment and electro-hydraulic adjustment. The field test was conducted on November 10, 2022, in Huijazhuang Township, Laishui County, Baoding City, Hebei Province, China. As shown in Figure 12, the test plot was no-till land, divided into an operating area of 150 m long and 25 m wide. The soil temperature of 5 cm below the surface of the test area was 10 \({}^{\circ}\)C and the relative humidity was 18.0% using the five-point sampling method (measured by RS-ECH-I20 temperature and humidity meter, Shandong Renke Measurement and Control Technology Co., Ltd., Jinan, China). The resolution of the measurement was 2.5 cm and 35 kPa (TJSD-750-IV soil compactness measuring instrument, Zhejiang Topunnong Technology Co., Hangzhou, China), as shown in Figure 13a. The test device was a 2 BJ-470B corn no-till precision seeder (Hyundai Agricultural Equipment Technology Co., Ltd.) equipped with this paper's sowing depth control system, with an overall mass of 1700 kg, a supporting power of 66.15 kW, an operating width of 2.8-3.2 m and a tractor traction connection, with a working row number of 4 and a row spacing of 0.7 m.  
According to the agronomic requirements of the area, the sowing depth of all the row units was uniformly set to 50 mm by the sowing depth adjustment handle before the test, and the test plot was divided into three blocks in order to compare and test the sowing depth effect of different vehicle speeds. Three different speeds of 5-6 km\(\cdot\)h\({}^{-1}\), 7-8 km\(\cdot\)h\({}^{-1}\) and 9-10 km\(\cdot\)h\({}^{-1}\) were used for the test. In order to compare the effect of the sowing depth with different adjustment methods, No.1 and No.2 were set as the mechanical spring adjustment in two pretightened, No.3 as the self-weight adjustment and No.4 as the electro-hydraulic adjustment. Before the test, the target compressive force range was set to  
Figure 12: Field tests.  
Figure 13: Field tests. (**a**) Soil compaction measurement; (**b**) sowing depth measurement.  
[200, 500] N through the display. A total of 4 \(\times\) 1500 kg counterweights were added to the seed drill to ensure that the downforce can be applied properly.  
In order to facilitate visual measurement data, the closing wheel assembly at the end of the row unit was removed, the furrow closing operation of the seeder was cancelled and only the furrowing opening test was conducted. In order to reduce the influence of tractor acceleration and deceleration on the test results when turning around the ground, points were selected in the middle area 25 m away from the ground edge, and one measurement point was selected every four theoretical seed distances. The sowing depth was measured as the vertical distance from the surface plane to the bare seed skin (Figure 13b). Each vehicle speed was divided into 3 areas of the front, middle and back, and each area measured 10 sowing depth data as a group to carry out 3 sets of sowing performance tests under different vehicle speeds. The soil compaction of the seed groove after sowing was also measured using a soil compactness measuring instrument. The compaction measurement method is measure and record the soil compaction data of 2.5 cm, 5 cm, 7.5 cm and 10 cm depth below the ground surface on both sides of the seeds.