1. Handbook of Soil Analysis, Mineralogical, Organic and Inorganic Methods;Pansu,2006
2. Soil Organic Matter, Its Nature, Its Role in Soil Formation and in Soil Fertility;Kononova,1966
3. Humic Substances in the Environment;Schnitzer,1972
4. Soil Components;Flaig,1975
5. Soil Organic Matter;Schnitzer,1978