1. Orlov, D.S., Sadovnikova, L.K., and Sukhanova, N.I., Khimiya pochv (Soil Chemistry), Moscow: Vysshaya Shkola, 2005.
2. Orlov, D.S., Gumusovye kisloty pochv i obshchaya teoriya gumifikatsii (Humic Acids of Soils and the General Theory of Humification), Moscow: Mosk. Gos. Univ., 1990.
3. Stevenson, F.J., Humus Chemistry: Genesis, Composition, Reactions, New York: Wiley, 1994, 2nd ed.
4. Perminova, I.V., Doctoral (Chem.) Dissertation, Moscow: Moscoe State Univ., 2000.
5. Khimicheskaya entsiklopediya (Chemical Encyclopedia), Knunyants, I.L., Ed., Moscow: Sov. Entsiklopediya, 1988, Vol. 1.