ABSTRACT
The notion of soil organic matter (SOM) or soil organic carbon (SOC) functional pool is often quoted in literature (Tiessen et al., 1984; Duxburry et al., 1989; Theng et al., 1989; TSBF, 1989; Bonde et al., 1992; Christensen, 1992; Cambardella and Elliott, 1993, 1994; Feller, 1993; Woomer, 1993; Herrick and Wander, 1997;Monrealetal., 1997; Sternberg, 1998), but this notion is generally poorly defined, never quantified and is more generally restricted to the dynamics of SOM than applied to the different and numerous functions that SOM plays in the soils or in the soil-plant-atmosphere system. In fact, total SOM (expressed as total carbon Ct) exerts essential and different functions in soil:
• biological functions, such as easily mineralizable carbon or nitrogen (Cm, Nm), microbial nitrogen immobilization, enzymatic activities,
• exchange and sorption functions such as cation exchange capacity or sorption of pesticides, • function of aggregation, • functions of medium-to long-term storage (“sequestration”) of elements and/or nutrients for
plants and soil organisms, such as total organic carbon, nitrogen, phosphorus, sulfur, non exchangeable bases associated to SOM.
