1. Lyubarskaya, L.S., Effect of Long-Term Use of Fertilizers on Soil Fertility and Productivity of Crop Rotations, Tr VIUA, Moscow: Kolos, 1964, issue 2.
2. Cooke, G. W., The Control of Soil Fertility, London: Crosby Lockwood & Son Ltd, 1967.
3. Gamzikov, G.P. and Kulagina, M.N., Izmenenie soderzhaniya gumusa v pochvakh v rezultate sel℉skokhozyaistvennogo ispol℉zovaniya. Obzornaya informatsiya (Change in Humus Content in Soils as a Result of Agricultural Use. Review Information), Moscow: VNIITEIagroprom, 1992.
4. Mineev, V.G. and Gomonova, N.F., Agrokhimiya, 2005, no. 1.
5. Chagina, E.G., Berkhin, Yu.I., and Khatsevich, N.V., Izmenenie plodorodiya pochv pri intensivnom zemledelii (Change in Soil Fertility during Intensive Agriculture), Novosibirsk: Nauka. Sib. Otd., 1986.