Chittawanij, A., Marubodee, R., and Pornsuriya, P. “Study of biochar on growth and yield of Choy Sum (Brassica chinensis L.var parachinensis)”. International Journal of Agricultural Technology, vol. 18, no. 3, May 2022, pp. 965-74, https://li04.tci-thaijo.org/index.php/IJAT/article/view/7243.