Wilujeng, E D I, W Ningtyas, and Y Nuraini. 2015. “Combined Applications of Biochar and Legume Residues to Improve Growth and Yield of Sweet Potato in a Dry Land Area of East Java”. Journal of Degraded and Mining Lands Management 2 (4). Malang, Indonesia:377-82. https://doi.org/10.15243/jdmlm.2015.024.377.