ABSTRACT
Soil organic matter (SOM) is one of the most important components in soil because it affects many soil functions such as nutrient cycles, water movement, thermal properties, and the fate of chemical use for soil management (Carter, 2002). The assessment of changes in SOM is a key issue for soil quality. Soil organic carbon consists of humic and non-humic substances, which are formed by the decomposition of natural organic matter. Humic substances are powerful complexing and chelating entities whose sorption characteristics depend on their chemical composition. They contribute significantly to the chemical, physical, and biological properties of soil (Garcia et al., 1992; Chefetz et al., 1998; Varanini and Pinton, 1995). Due to the relatively slow biodegradation rate of some components of SOM, their influence on soil properties and performance lasts over a long time.
