1. Asio, V. B. (1996): Characteristics, Weathering, Formation and Degradation of Soils from Volcanic Rocks in Leyte, Philippines. Hohenheimer Bodenkundliche Hefte 33, Stuttgart, 209 pp.
2. Bremner, J. M. (1965): Inorganic forms of nitrogen, in C. A. Black: Methods of Soil Analysis. Part II. Chemical and Microbiological Properties. Agron. Soc. Amer., Madison, Wisconsin, p. 1179 – 1232
3. Dale, V. H., R. A. Houghton, A. Grainger, A. Lugo and S. Brown (1993): Emissions of greenhouse gases from tropical deforestation and subsequent uses of the land, in National Research Council: Sustainable Agriculture and the Environment in the Humid Tropics, National Academy Press, Washington, D.C., 702 pp.
4. Department of Environment and Natural Resources (1990): The Philippine Environment in the Eighties. EMB, Diliman, Q. C., Philippines.
5. Djegui, N., P. de Boissezon and E. Gavinelli (1992): Statut organique d’un sol ferrallitique du Sud-Benin sous foret et differents systemes de cultures. Cah. Orstom. ser. Pedol. XXVII: 5 – 22