1. Badan Pusat Statistik, Statistik Kakao Indonesia 2020, https://www.bps.go.id/publication/2021/11/30/a553dc1b3648d2f5cdad1789/statistik-kakao-indonesia-2020.html
2. Effect of rubber wood biochar on nutrition and growth of nursery plants of Hevea brasiliensis established in an Ultisol
3. M. M. Alley and B. Vanlauwe, The Role of Fertilizers in Integrated Plant Nutrient Management (Tropical Soil Biologi and Fertility Institute of The International Centre for Tropical Agriculture, Paris, 2009)
4. S. Asmiaty. Teknologi Mikroba: Actinomycetes dan Rhizobium untuk Perbaikan dan Produksi Tanaman Kedelai (Pers Ficus, Makassar, 2021).