“Biochar Based Soil Amendment Formulation for Improvement Upland Acidic Soil in East Lampung: Soil Properties and Maize (Zea Mays) Yield”. JOURNAL OF TROPICAL SOILS, vol. 24, no. 1, Jan. 2019, pp. 33-41, https://doi.org/10.5400/jts.2019.v24i1.33-41.