Submitted to: Soil Science Society of America Special Publication Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 12/1/2003
Publication Date: 3/1/2005
Citation: Clapp, C.E., Hayes, M., Simpson, A.J., Kingery, W.L. 2005. Chemistry of soil organic matter. In: Tabatabai, A., Sparks, D.L., editors. Chemical Processes in Soils. Soil Science Society of America Special Publication Book Chapter. Book Series 8, Madison, WI. p. 1-150.
Technical Abstract: The term 'soil organic matter' (SOM), according to Stevenson (1994), refers to 'the whole of the organic matter in soils, including the litter, the light fraction, the microbial biomass, the water-soluble organics, and the stabilized organic matter (humus).' The term natural organic matter (NOM) is now widely used to describe the natural organic compounds in soils, sediments, and waters. Hayes and Swift (1978) considered the complete soil organic fraction to be made up of live organisms, and their partly undecomposed, partly decomposed and completely transformed remains, as well as those of plants. However, they regarded SOM to be a more specific term for the non-living components that may be described as 'a heterogeneous mixture composed largely of products resulting from microbial and chemical transformations of organic debris.' The major components are considered to be recalcitrant remains of plants and algae, including materials derived from lignins, tannins, sporopollenins, and large aliphatic molecules such as algaenans, cutans, and suberans (Derenne & Largeau, 2001). There is increasing interest in the presence of black carbon (arising from the incomplete combustion of organic materials) in SOM. The major components of SOM can be considered to consist of humic substances, saccharides and peptides, and products derived from recalcitrant materials such as those listed above. More recently, the importance of SOM to considerations of environmental quality has been considered in relation to global warming, or the greenhouse effect. It is now accepted that human activity, both agricultural and industrial, has created an imbalance between global sinks and sources of C, giving rise to increases in atmospheric gases. Soil management is important in relation to the role of soils as sources and sinks of C in the environment, and hence it is important in terms of global warming issues (Lal et al., 1995).