Soil Organic Matter
Research pertaining to the organic fraction of soils can be traced back in excess of 200 years. Achard (1786) isolated a dark amorphous precipitate upon acidication of an alkaline extract from peat. ¤e e¦ect of organic matter on soil N fertility (von Liebig, 1840), studies on the use of animal manures for maintaining soil fertility (Lawes, 1861), and the in¥uence of soil and tree species on the development of humus form (Muller, 1887) all demonstrated the importance of organic matter in soil processes. ¤e advancement of organic chemical methodologies and conrmation of the presence of various chemical structures in soil organic matter (SOM) lead to the development of theories that SOM was composed of a heterogeneous mixture of dominantly colloidal organic substances containing acidic functional groups and N. More recently, the polyphenol theory was proposed in which quinone structures of lignin and microbial origin polymerize in the presence of N-containing groups (amino acids, peptides, and proteins) to produce nitrogenous polymers (Flaig et al., 1975).