Meiqing, Li, Li Jinyang, Wei Xinhua, and Zhu Wenjing. 2017. “Early Diagnosis and Monitoring of Nitrogen Nutrition Stress in Tomato Leaves Using Electrical Impedance Spectroscopy”. International Journal of Agricultural and Biological Engineering 10 (3):194-205. https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/3188.