1. L. N. Aleksandrova, Soil Organic Matter and the Processes of Its Transformation (Nauka, Leningrad, 1980) [in Russian].
2. Analytical Support of the Monitoring of Soil Humus Status: Methodological Recommendations, Compiled by B. M. Kogut, Ed. by V.A. Bol’shakov (Izd. Rossel’khozakad., Moscow, 1993) [in Russian].
3. The Great Russian Encyclopedia, Vol. 8 (Moscow, 2007), p. 157 [in Russian].
4. Tentative Recommendations on Soil Sampling for Determining Soil Humus upon Agrochemical Survey of Arable Lands in the Russian Federation, Compiled by I. P. Stokozov, A. A. Zenin, et. al. (Izd. MSKh RSFSR, VNIPTIKhIM, Moscow, 1985) [in Russian].
5. L. A. Grishina and D. S. Orlov, “A System of Indices of the Soil Humus State,” in Problems of Soil Science (Nauka, Moscow, 1978), pp. 42–47 [in Russian].