Ji, Pengtao, Yongwei Cui, Xiangling Li, Kai Xiao, Peijun Tao, and Yuechen Zhang. 2020. “Responses of Photosynthetic Characteristics and Enzyme Activity of Nitrogen Metabolism to Low Nitrogen in Maize With Different Nitrogen Tolerance”. International Journal of Agricultural and Biological Engineering 13 (6):133-43. https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/5891.