Zhang, Jicheng, Shouyin Hou, Runtao Wang, Wenyi Ji, Ping Zheng, and Shi Wei. 2018. “Design of Variable-Rate Liquid Fertilization Control System and Its Stability Analysis”. International Journal of Agricultural and Biological Engineering 11 (1):109-14. https://ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/2583.