Study of Soil Organic Matter

As seen in Chapter 1, Section 1.1.2, soil organic matter is an undefined system, consisting of many components. So, the determination of soil organic content and the study of humic substances are challenging. For practical purposes, the humus content or, more correctly, soil organic matter content, is determined by standard procedures however, the results cannot be considered as absolutely real values, and can only be compared to each other. 

Soil organic matter can be measured with or without their separation from the mineral phases. In the case of there being no separation, the usual procedure is the oxidation of soil organic matter, for example, by potassium dichromate in acidic medium. In this way, the carbon content is determined, from which soil organic matter content is calculated using the average elementary composition of humic substances (Kononova 1972). 

Elemental analysis and the detailed characterization require the extraction and purification of soil organic matter. International Humic Substances Society (2008) 

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Wolf DC, Legg JO, Boutton TW. Isotopic methods for the study of soil organic matter dynamics. In Hickelson SH (ed.), Methods of Soil Analysis Part 2 Microbiological and Biochemical Properties. Madison, WI Soil Science Society of America 1994, pp. 865-906. 

Bremner, J. M., and Lees, H. (1949). Studies of soil organic matter II.The extraction of organic matter from soil by neutral reagents. /. Agric. Sci. 39,274-279. 

Tiessen, H., and Stewart, J. W. B. (1983). Particle-size fractions and their use in studies of soil organic matter. II. Cultivation effects on organic matter composition in size fractions. 

Smernik, R. J. (2005). Solid-state C-13 NMR spectroscopic studies of soil organic matter at two magnetic field strengths. Geoderma 125, 249-271. 

Khalaf, K.Y., MacCarthy, P., and Gilbert, T.W, Application of thermometric titrations to the study of soil organic matter-II. Humic acids. Geoderma 14, 331-340 (1975). 

Balesdent J., Mariotti A., and Guillet B. (1987) Natural carbon-13 abundance as a tracer for studies of soil organic matter dynamics. Soil Biol. Biochem. 19(1), 25—30. 

Sinclair, A. H. and Tinsley, J. (1981). Studies of soil organic matter using formic acid solvents Factors affecting composition and degree of formylation of organic isolates. J. Soil Sci. 32, 103-117. 

Randall, E.W., Mahieu, N. and Ivanova, G.l. (1997) NMR studies of soil, organic matter and nutrients spectroscopy and imaging. Geoderma 80, 307-325. 

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