[Concepts and relative analytical techniques of soil organic matter]

The research of soil organic matter (SOM) has been highlighted in soil science. In the past 50 years, new perspectives in the relationship between SOM and sustainability of atmosphere and biomosphere, and strong motivation to find a vivid index for soil quality variation induced the transformation in concepts and analytical techniques of SOM: the curiousness to humic substances faded off since they were dull to anthropogenic activities, and interests were focused on the light fraction of organic matter (LFOM), organic carbon associated with different mineral particles in size, particulate and intra-particulate organic matter (POM and iPOM), water soluble organic matter (WSOM), and microbial biomass carbon (MB-C). The relative fractionation procedures have been developed, and the main research activities on SOM are transformed from the products of microorganisms (humus) to the organic matter comprised in plant residues at their various decomposition stages and the organic carbon in microorganisms, since they are biologically active and immediately respond to soil cultivation and tillage, crop rotation, and fertilizer application, etc.