**4. Conclusions**

In this study, spraying precision control technology was evaluated for use in a traction liquid manure variable spraying control system, and a control system model was built. Simulation analysis and tests were carried out for liquid manure flow control under the classical PID, fuzzy PID, BPNN–PID, and GA–BPNN–PID control modes. The following conclusions were drawn:

(1) The GA–BPNN–PID optimized the dominant fertilizer system. This family has a variable-rate fertilizer-spraying control system model. GA–BPNN was used to optimize PID parameters, which enhanced the stability of the control system.


Taken together, the results presented in this study provide a reference for the fertilization control of maize in the field.

**Author Contributions:** This study was conceptualized by P.W. and M.C. Test setup was completed by P.W., B.X., A.W. and B.M. The software was designed by P.W. and A.W. B.X. and J.F. provided resources and P.W. curated the data. The original draft of the manuscript was prepared by P.W. and Y.C., B.M. reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the basic scientific research business expenses of CAAS, No. S202106-03, the Jiangsu Modern Agricultural Machinery Equipment and Technology Demonstration and Promotion Project (NJ2021-23), and the Jiangsu Modern Agricultural Machinery Equipment and Technology Demonstration and Promotion Project (NJ2022-26).

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** All relevant data presented in the article are stored according to institutional requirements and, as such, are not available on-line. However, all data used in this manuscript can be made available upon request to the authors.

**Acknowledgments:** We are grateful to Wei Zhao for his help in project management. We also thank Taian Yimeite Company for providing the experimental conditions for us to successfully complete this experiment.

**Conflicts of Interest:** The authors declare no conflict of interest.
