Relationships between soil organic carbon and soil quality in cropped and rangeland soils: The importance of distribution, composition, and soil biological activity

The often-cited positive relationship between soil organic carbon (SOC) content and soil quality (Arshad and Coen, 1992; National Research Council, 1993; Doran and Parkin, 1994; Manley et al., 1995; Pikul and Aase, 1995; Karlen and Cambardella, 1996) is consistent with the results of over one hundred years of modern agricultural research (Bauer and Black, 1994) and with thousands of years of on-farm observation and experimentation (Magdoff, 1992). This relationship is based on contributions which SOC makes as a constituent of soil organic matter (SOM) to critical soil properties, processes and functions. The term “SOM” will be used in the remainder of this chapter except where carbon per se is of interest. “SOM” is preferred here because it reflects the reality that impacts of SOC on soil quality are determined by its chemical, physical, and biological configuration within SOM.