He, Fen, et al. “Investigation of a Root Zone Heating System for Greenhouse Seedling and Its Effects on Micro-Environment”. International Journal of Agricultural and Biological Engineering, vol. 13, no. 6, Dec. 2020, pp. 47-52, https://ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/5905.