Characterization of Soil Organic Carbon Relative to Its Stability and Turnover

A wide variety of techniques have been applied to the measurement and characterization of soil organic matter (SOM) in relation to its dynamics under various management conditions. Organic matter associated with different primary particles has been shown to have varying rates of turnover. One of the greatest problems with the use of sonication in SOM studies is the potential for redistribution of organic matter among size/density fractions. The physical fractionation of soil is generally accomplished using dry or wet sieving, sedimentation, and/or density separations. If labile substrates are released from physical protection, mineralization may be rapid, whereas mineralization may be slow where recalcitrant SOM is released from the disruption of aggregates. The energy flux through the microbial biomass drives decomposition of residues and detritus and indicates whether the system is building or depleting the SOM pool. The Chloroform Fumigation-Extraction method is based upon the fumigation technique but microbial constituents released by fumigation are extracted directly.