## 4 Conclusions  
In this paper, we analyzed the process of sowing depth control of a 470B row unit, optimized the profiling mechanism with the IPRC, developed the feedforward adjustment sowing depth control algorithm under the CODESYS environment and designed an integrated electro-hydraulic-driven sowing depth measurement and control system. It solves the problems of the complex structure of the profiling mechanism, improves the stability of the sowing depth and reduces the compaction of the sidewall of the seed groove. The main research conclusions are as follows.  
1. The step response test results show that when the target compressive force is in the range of 0-280 N, the steady-state error of the system response is less than 10. When the target compressive force is 280 N, the adjustment time and rise time are at a maximum, 6.1 s and 0.64 s, respectively. The overshoot range of the four tests is 18.7%-26.6%, and the average value is 21.8%. The range of the steady-state error is 6.2-10.7, the average value is 8.63 and the error is within 10% when the system is stable.
2. The field performance test results show that under the condition that the sowing depth is set at 50 mm and the vehicle speed is 9-10 km\(\cdot\)h\({}^{-1}\), the sowing depth qualification rates of the three adjustment methods of self-weight, mechanical and electro-hydraulic adjustment are 89.2%, 96.7% and 98.6%, respectively. The corresponding maximum sowing depth coefficients of variation are 16.7%, 12.9% and 6.4%, respectively. The SFEQ was further analyzed in combination with soil compaction, and the average pass rates under the three adjustment methods are 88.3%, 91.6% and 98.2%, respectively. The test confirms that suitable downforce can effectively reduce the effect of vehicle speed on sowing depth and soil compaction, while electro-hydraulic regulation can avoid over-compaction of seed groove soil while ensuring the sowing depth. It further shows the superiority of electro-hydraulic regulation in high-speed no-till operation and reflects the importance of seeding row unit downforce regulation in building a qualified seed groove environment.
3. Seed depth and soil compaction are an opposite problem; when we guarantee 100% seed depth, we necessarily give up some compaction issues. This paper for soil compaction tests only in the same plot, and the soil hardness variation range is small. The compaction effect of the seeder under different degrees of soil hardness was not examined. In the follow-up study, we will test the consistency of seedling emergence in a changing environment, such as different soil types and conditions, tillage practices, etc. In addition, the generally high pass rate of the sowing depth measured in this paper's experiment is due to the good uniformity of the plots and the lack of a large sample size, and the need to define the criteria more strictly in subsequent experiments. Based on future test data, we aim to optimize the sowing depth measurement and control algorithm and gradually improve the performance of the multi-row seeder.  
**Author Contributions:** Conceptualization, L.Z.; methodology, L.Z. and Y.M.; software, Y.M. and H.Z.; validation, H.Z. and K.N.; formal analysis, K.N. and B.Z.; investigation, B.Z.; resources, L.W.; data curation, L.W; writing--original draft preparation, S.B.; writing--review and editing, S.B.; visualization, Y.Z.; supervision, Y.Z.; project administration, W.Z.; funding acquisition, W.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was mainly supported by the National Program on Key Basic Research Project of China (Grant No. 2022 YFD2001502).  
**Data Availability Statement:** Data are contained within the article. The data presented in this study can be requested from the authors.  
**Conflicts of Interest:** The authors declare no conflict of interest.