1. L. N. Aleksandrova, Soil Organic Matter and the Processes of Its Transformation, (Nauka, Leningrad, 1980) [in Russian].
2. O. S. Bezuglova, Humus Status of Soils in the South of Russia (Izd. SKNTsVSh, Rostov-on-Don, 2001) [in Russian].
3. L. A. Vorob’eva, Theory and Practice of the Chemical Analysis of Soils (GEOS, Moscow, 2006) [in Russian].
4. N. F. Ganzhara, “Conditions of Humification and Humus Status of Zonal Soil Types,” Izv. Timiryaz. S-Kh. Akad., No. 5, 84–89 (1986).
5. M. A. Glazovskaya, Soils of the World (Izd. Mosk. Gos. Univ., Moscow, 1973), Vol. 2 [in Russian].