Southavong, Sisomphone, et al. “Biochar and Biodigester Effluent Increase the Yield of Yardlong Bean (Vigna Unguiculata) and Improve Soil Properties”. Champasack University Scientific Journal, vol. 1, no. 1, May 2015, pp. 11-22, https://cu-journal.com/index.php/files/article/view/5.